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Advances in two-dimensional organic–inorganic

hybrid perovskites
Cite this: Energy Environ. Sci.,
2020, 13, 1154
Fei Zhang, †a Haipeng Lu, †a Jinhui Tong, a
Joseph J. Berry, b

Matthew C. Beard a and Kai Zhu *a

Two-dimensional (2D) perovskites have attracted considerable interest for their promising applications
for solar cells and other optoelectronics, such as light-emitting diodes, spintronics, and photodetectors.
Here, we review the recent achievements of 2D perovskites for various optoelectronic applications. First,
Received 20th November 2019, we discuss the basic structure and optoelectronic properties of 2D perovskites, including band structure,
Accepted 17th February 2020 optical properties, and charge transport. We then highlight recent achievements using 2D perovskites in
DOI: 10.1039/c9ee03757h solar cells and beyond solar cells, including progress on various synthesis strategies and their impact on
structural and optoelectronic properties. Finally, we discuss current challenges and future opportunities
rsc.li/ees to further develop 2D perovskites for various applications.

Broader context
Perovskite solar cells (PSCs) have attracted attention from academia and industry due to its rapid performance advancement. However, the long-term
operational stability of PSCs remains an issue. One promising approach involving the use of two-dimensional (2D) or quasi-2D perovskite has shown potential
for improving the stability of PSCs. In addition to solar cell applications, 2D perovskites offer a great playground for chemists to investigate fundamental
structure–property relationships. The rich chemical tunability provides unique opportunities to control their structural distortion, quantum and dielectric
confinement, exciton–phonon coupling, and Rashba splitting, which, in turn, modulate their optical, electronic, and spin properties. For this reason, 2D
perovskites have also shown tremendous potential for photoemission, spintronic, and photodetector applications. Here, we review the recent achievements of
2D perovskites for various optoelectronic applications. First, we discuss the basic structure and optoelectronic properties of 2D perovskites, including band
structure, optical properties, and charge transport. We then highlight recent achievements using 2D perovskites in solar cells and beyond solar cells, including
progress on various synthesis strategies and their impact on structural and optoelectronic properties. Finally, we discuss current challenges and future
opportunities to further develop 2D perovskites for various applications.

1. Introduction properties were further developed by Mitzi et al.7,8 However, the

initial several reports on PSCs between 2009 and 20129–11 are what
Photovoltaics (PV) have witnessed the rapid rise of solution- caused these materials to begin to attract worldwide attention.
processable organic–inorganic halide perovskites, which will In the first report of PSCs, Miyasaka et al. used methyl-
likely become competitive in providing efficient and cheap ammonium lead triiodide (CH3NH3PbI3, or MAPbI3) as a light-
solar energy.1,2 Over the course of about a decade, the power absorbing material with a liquid electrolyte in dye-sensitized
conversion efficiency (PCE) of single-junction perovskite solar solar cells (DSSCs), yielding a PCE of 3.8% in 2009.9 Later, Park
cells (PSCs) has achieved a certified 25.2%,3 which is compar- et al. used the solid-state hole-transport material (HTM) of 2,20 ,7,70 -
able to that of other commercial PV technologies.4 As a result, tetrakis(N,N-di-p-methoxyphenylamine)-9,90 -spirobifluorene (spiro-
PSCs have attracted explosive attention from academia and OMeTAD) to replace the liquid electrolyte, and they obtained
industry. Weber et al. first established the unique structure and an efficiency of 9.7% in 2012.10 Around the same time, Snaith
properties of three-dimensional (3D) perovskites in 1978.5,6 Then, et al. demonstrated performance of 410% for the solid-state
in the 1990s, more findings of their unique optoelectronic PSCs.11 These breakthroughs have led to extensive research
interest in PSCs.12–25
During the past several years, the PSC field has focused
a
Chemistry and Nanoscience Center, National Renewable Energy Laboratory,
more on increasing the long-term operational stability of
Golden, Colorado 80401, USA. E-mail: kai.zhu@nrel.gov
b
Materials Science Center, National Renewable Energy Laboratory, Golden,
PSCs.26 A large number of studies have focused on optimizing
Colorado 80401, USA perovskite absorbers (e.g., composition,27,28 perovskite nano-
† These authors contributed equally to this paper. structures,29,30 tolerance factor,31,32 defect passivation,33,34

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additive control35,36), device structures (e.g., contact layer37–40 4.73% PCE,50 the reported PCE of 2D PSCs has reached B18%,51
and interface modification41,42), and device encapsulation.43,44 which is still much lower than that of 3D PSCs (B25%). Rather
One promising category involving the use of two-dimensional than directly using 2D perovskites as the solar cell absorbers, an
(2D) or quasi-2D perovskite has also shown great potential for alternative approach—using 2D perovskite structures to enhance
improving the stability of PSCs.45,46 the surface properties of 3D perovskite grains and films (normally
Unlike small cations in 3D perovskites (e.g., MA+, formamidi- referred to as 3D/2D mixed-dimensionality perovskites)—has
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nium (FA+), and Cs+), the bulky organic cations in 2D perovskites shown promise for improving both the stability and performance
provide a steric barrier for surface water adsorption.47,48 The large of perovskites across a wide range of compositions.21,22,52–55
hydrophobic cation in the 2D perovskite crystal lattice can effec- In addition to solar cell applications, 2D hybrid perovskites
tively suppress moisture intrusion.49 However, the 2D perovskites offer a much greater playground for chemists to investigate
are generally not a good choice as an absorber for solar cell fundamental structure–property relationships. In contrast to
application because of their wide optical bandgap and limited their 3D counterparts, where the choice of the organic moiety is
charge transport associated with the 2D structure. Since the first restricted by the Goldsmith tolerance factor, many paths of
report in 2014 of 2D perovskites as absorbers in solar cells having chemical engineering in 2D perovskites are possible because

Fei Zhang is currently a Post- Haipeng Lu is a Postdoctoral

doctoral Researcher in the Researcher at the National Renew-
Chemistry and Nanoscience Center able Energy Laboratory (NREL)
at the National Renewable Energy under Matthew C. Beard. He
Laboratory (NREL). He obtained his received his BSc in chemistry
BEng and PhD degree under the from Nanjing University in 2012,
supervision of Prof. Shirong Wang and completed his PhD in 2017
at Tianjin University in 2011 and in chemistry at the University
2017, respectively. He was a visiting of Southern California under
PhD student in Laboratory of Richard L. Brutchey. His current
Photonics and Interfaces (LPI) at research is focused on the mole-
Ecole Polytechnique Fédérale de cular design of low-dimensional
Fei Zhang Lausanne (EPFL) under the Haipeng Lu hybrid perovskites for optoelec-
guidance of Prof. Michael Grätzel tronic and spintronic applications.
and Dr Shaik Mohammed Zakeeruddin from 10/2015 to 04/2017. His
interests concentrate on synthesis of novel hole transporting materials,
low-dimensional perovskites and device engineering for perovskite
solar cells.

Jinhui Tong is currently a Joseph Berry is a senior scientist at

Postdoctoral Researcher in the the National Renewable Energy
Chemistry and Nanoscience Laboratory working on halide
Center at the National Renewable perovskite solar cells. His PhD for
Energy Laboratory (NREL). He work was on spin transport and
received his PhD degree in Optical physics in semiconductor hetero-
Engineering from Wuhan National structures from Penn State
Laboratory for Optoelectronics, University. His efforts at NREL
Huazhong University of Science emphasize relating basic inter-
and Technology in 2018. He was facial properties to technologically
a visiting PhD student in University relevant device level behaviors in
of Nebraska Lincoln and University traditional and novel semicon-
Jinhui Tong of Colorado Boulder from 2016 to Joseph J. Berry ductor heterostructures including
2018. His current research is oxides, organics and most recently
focus on Pb/Sn based perovskite hybrid semiconducting materials. He is also a principle investigator on
solar cells. the NREL lead Department of Energy, Center for Hybrid Organic
Inorganic Semiconductors for Energy (CHOISE) Energy Frontier
Research Center, exploring basic aspect of hybrid materials (www.
choise-efrc.org).

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Finally, we discuss the challenges and future opportunities for

further developing 2D perovskites for a wide range of applications.

2. Chemical and crystal structure

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The standard 3D perovskites have a general structure of ABX3,

and six halide anions (X site; e.g., I, Br, and Cl) coordinated
to a divalent metal cation (B site; e.g., Sn2+ and Pb2+) form a BX6
octahedral framework (Fig. 2a).57 Twelve monovalent cations
(A site; e.g., MA+, FA+, and Cs+) occupy the centers of four BX6
octahedra. Each of the A, B, and X sites can contain one or
multiple elements, allowing flexibility in adjusting the properties
of the perovskite. Whether or not certain compositions can form a
stable perovskite structure is often estimated based on a simple
geometric consideration, the Goldschmidt tolerance factor (t),58
Fig. 1 Illustration of 2D perovskites with structure tunability for a variety rA þ rX
of optoelectronic applications. t ¼ pffiffiffi
2ðrB þ rX Þ

the tolerance factor is relaxed. For instance, a library of organic where rA, rB, and rX are the corresponding ionic radii. Essentially,
ligands has been demonstrated in 2D hybrid perovskites, and when t is in the range of B0.8–1.0, a stable 3D perovskite
the inorganic layer thickness can also be tuned synthetically. structure can be formed.48 Moreover, the octahedral factor
This rich chemical tunability provides unique opportunities to (m = rB/rX; m is normally between 0.4 and 0.9) can be used
control their structural distortion, quantum and dielectric con- to empirically evaluate whether a B-site atom prefers an octa-
finement, exciton–phonon coupling, and Rashba splitting, which, hedral coordination of the X-site atom (as opposed to other
in turn, modulate their optical, electronic, and spin properties. coordination numbers).59,60
For this reason, 2D perovskites have shown tremendous potential The 2D perovskite is generally described with a formula
for photoemission (exciton vs. broad emission), spintronic, and (A 0 )m(A)n1BnX3n+1, where A 0 can be divalent (m = 1) or mono-
photodetector applications (Fig. 1). valent (m = 2) cations that form a bilayer or monolayer con-
In this review, we discuss recent advances of 2D perovskites for necting the inorganic (A)n1BnX3n+1 2D sheets, where n
various optoelectronic applications. First, we discuss the structure indicates the layer thickness of metal halide sheets that can
and optoelectronic properties of 2D perovskites, including band be adjusted by tuning precursor composition (Fig. 2a).61,62
structure, optical properties, and charge transport. We then high- Generally, the organic A 0 -site cation can be arbitrarily long so
light recent achievements of using 2D perovskite in solar cells and that large, high-aspect-ratio cations (e.g., aliphatic- or aromatic-
then go beyond solar cells to examine applications including light- based cations) can be employed. Note that the geometry of a 2D
emitting diodes (LEDs), spintronic applications, and photodetectors. octahedral arrangement typically contains a BX42 inorganic

Matthew C. Beard is a Senior Kai Zhu is a senior scientist in

Research Fellow at the National the Chemistry and Nanoscience
Renewable Energy Laboratory Science Center at the National
and is Director of the Center for Renewable Energy Laboratory
Hybrid Organic Inorganic Semicon- (NREL). He received his PhD
ductors for Energy (CHOISE) an degree in physics from Syracuse
Energy Frontier Research Center University in 2003. His research
funded by the Office of Science interests have included characteri-
within the US. Department of zation and modeling of hydro-
Energy. He received his PhD genated amorphous silicon thin
from Yale University in 2002. film solar cell, III–V wide-
His research interest includes bandgap light emitting diodes,
Matthew C. Beard hot-carrier utilization (slowed Kai Zhu dye-sensitized solar cells, and
hot-carrier cooling and multiple Li-ion batteries and super-
exciton generation), reduced dimensionality in solar energy capacitors. His current research focuses on perovskite solar cells,
conversion, photochemical energy conversion, and the use of including material development, device fabrication, and fundamental
ultrafast transient spectroscopies in tracking energy conversion characterization on charge-carrier dynamics and device operating
processes. principles.

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Fig. 2 (a) Schematic comparing 2D and 3D perovskite structures. (b) Schematic of different oriented families of 2D perovskites: h100i plane,
A 0 2An1BnX3n+1; h110i plane, A 0 2AmBmX3m+2; and h111i plane, A 0 2Aq1BqX3q+2. Cuts along h100i, h110i and h111i directions (grey parts) result in the
corresponding different types of 2D perovskites. Reproduced with permission from ref. 56. Copyright 2019, Wiley-VCH.

unit, and the negative charge from the additional anion needs of h110i-oriented perovskites as absorbers in solar cells, which
to be balanced by a positive charge (e.g., A 0 2BX4 when n = 2 and is likely caused by the difficulty of modulating the thickness of
A 0 is a monovalent cation). It is worth noting that the limit the inorganic layers in these materials and few cations that can
n = N corresponds to the 3D perovskite, whereas n = 1 stabilize their structures.56,65 The h111i-oriented 2D perovskites
represents the pure 2D, and 1 o n r 5 is often known as have a formula A 0 2Aq1BqX3q+2 (q 4 1) and can only be
quasi-2D. More importantly, a mixture of 3D perovskite and constructed from group 15 B3+ ions (e.g., Bi, Sb, As).66 The
low-n phases (e.g., n r 3) can form even in the case of high h111i-oriented perovskites are attractive solar cell absorbers
n values (e.g., n = 30–60),20 which we refer to as quasi-3D due to their p-type-like character and relatively small effective
perovskites. With the increase of n, the differences of thermo- masses for both holes and electrons; however, their strong
dynamic stability in the high-n structures become smaller, excitonic nature appears to limit the performance for solar
which makes it difficult to prepare phase-pure high-n structures.63 cells thus far in their development.48 In this review, we focus on
Thus, the n value of such perovskites is usually described based on the commonly reported h100i-oriented 2D perovskites. This
the precursor composition. class of materials can be further divided into Ruddlesden–
We can conceptually obtain 2D halide perovskite layers by Popper (RP) phases (Fig. 3a),67,68 Dion–Jacobson (DJ) phases
cutting along the h100i, h110i, and h111i crystallographic (Fig. 3b),69–71 and the phases with alternating cations in the
planes of the corresponding 3D perovskite structure, leading interlayer space (ACI) (Fig. 3c).72,73
to three 2D perovskite families with different orientations For the most commonly studied RP-phase 2D perovskites, a
(i.e., h100i, h110i, and h111i; Fig. 2b). The general formula of relatively weak van der Waals gap forms between a bilayer of
h100i-oriented 2D perovskites is A 0 2An1BnX3n+1, and their monovalent cations and two adjacent lead halide sheets. The
inorganic sheets are obtained by taking n layers along the RP compositions are generally described as A 0 2An1BnX3n+1,69
100 direction of the 3D perovskites. This structure represents where A 0 is aryl ammonium or alkyl cation (typical examples
the most commonly studied 2D halide perovskites. Because the include phenylethylammonium (PEA+) and butylammonium
h110i-oriented perovskite layer is often highly distorted, inter- (BA+)); small A cation is typically Cs+, FA+, or MA+; B site is
esting behaviors such as of the formation of self-trapped Sn2+ or Pb2+; and the X site is I, Br, or Cl. For the RP phase,
excitons, and broad-band/white-light emission at room the inorganic layers are often offset by one octahedral unit and
temperature.64 In addition, there are few reports on the use present certain in-plane displacement (Fig. 3a). Alternatively,

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Fig. 3 Examples of RP-, DJ-, and ACI-phase 2D perovskite structures. (a) Ca4Mn3O10 (left) and (BA)2(MA)2Pb3I10 (n = 3; right); (b) CsBa2Ta3O10 (left) and
(3AMP)(MA)2Pb3I10 (n = 3; right). Reproduced with permission from ref. 69. Copyright 2018, American Chemical Society. (c) (Gua)(MA)nPbnI3n+1 (n = 1, 2, 3).
Reproduced with permission from ref. 72. Copyright 2017, American Chemical Society.

diamine compounds with two amino groups can avoid any gaps arrangement of lead halide inorganic sheets and bulky organic
by forming hydrogen bonds on both ends with the two adjacent interlayers results in a multiple-quantum-well (MQW) electronic
inorganic sheets,74 leading to a more stable DJ-phase 2D structure (Fig. 5a).145 The high organic and inorganic dielectric
perovskite with A 0 An1BnX3n+1 stoichiometry. The typical exam- contrast leads to a huge electron–hole binding energy (Eb) in 2D
ples are 3-(aminomethyl)piperidinium (3AMP+) and 4-(amino- perovskites.146 Time-resolved terahertz spectroscopy has verified
methyl)piperidinium (4AMP+). Adjacent layers in the DJ phase that charge transport is preferred along the inorganic planes for
have no offsets and are stacked on top of each other (Fig. 3b). prototypical 2D perovskites.147 The excitons can be stabilized by 2D
For ACI-phase 2D perovskite with the formula A 0 AnBnX3n+1,72 perovskite MQWs, even at ambient temperatures. Various possibi-
the small A cation not only resides in the lead halide sheets but lities based on the MQW structure make 2D perovskite an inter-
also fills in the interlayer with the large A 0 cation, adopting the esting material system for room-temperature photoelectric and
layer-stacking characteristics of both DJ and RP structures fundamental physical applications.
(Fig. 3c). Note that guanidinium (Gua+) is the only cation that The 2D confinement effect directly influences the bandgap
is reported, so far, to form the ACI structure. Obviously, the (Eg) of 2D perovskite materials. For an RP hybrid perovskite, the
interlayer distance varies with the choice of spacing cation A 0 , Eg depends on the well width,148 and the total Eg energy is
and the RP phases have larger interlayer distance due to the determined by the base 3D structure and extra quantization
requirement of a bilayer of spacer organic cations. energies of the electron and hole.149 The optical Eg of
Many bulky organic cations have been reported to incorpo- A 0 2An1BnX3n+1 perovskite generally decreases as the n value
rate into a 2D perovskite and later into a solar cell; the reported increases. For example, the Eg value for BA2An1PbnI3n+1 perov-
bulky cations for RP- and DJ-phase 2D perovskites are summar- skites decrease with increased layer thickness from 2.24 eV
ized in Fig. 4. In general, the properties determining whether a (n = 1) to 1.52 eV (n = N) due to quantum-confinement effects
cation is suitable as a spacer include: (1) the net positive charge associated with dimensional increase (Fig. 5b and c).150 The
and degree of substitution of the perovskite anchoring site size and electronegativity of the halide and metal ions can also
(primary ammonium 4 secondary amine 4 tertiary amine 4 affect Eg, which increases as their size decreases. Pb has a lower
quaternary amine, in descending order); (2) hydrogen-bonding Pauling electronegativity in comparison to Sn, so the Pb elec-
ability; (3) space-filling ability (linear cross cations 4 branch tronic states are higher in the band structure.99 This flexibility
irregular cations); and (4) stereochemical configuration (aromatic of bandgap tuning, as well as composition tailoring for 3D/2D
hydrocarbons o flexible aliphatic hydrocarbons).65 multi-dimensional perovskite, can facilitate various optoelec-
tronic applications with targeted optical Eg materials.
Excitons have an essential influence on charge transport in
3. Basic optoelectronic properties semiconductors.151 The 2D structure generally shows a large
exciton binding energy (Eb) of several hundred meV (Fig. 5d),
In this section, we discuss some basic optoelectronic properties which significantly enhances the interaction between electrons
of 2D perovskites, including the electronic band structure, and holes compared to 3D perovskites.152 For quasi-3D perovs-
optical properties and charge transport dynamics. kites (i.e., 3D perovskite mixed with 2D perovskites), Eb is
smaller and is comparable to 3D perovskites.153 Because of
3.1. Band structure and optical properties this MQW band structure and large Eb values, low-n (e.g., n o 5)
In the layer-structured 2D perovskites, the large-sized organic cation 2D perovskites often exhibit significant transport barrier across
interlayers can limit charge carriers within a two-dimensional range. the adjacent 2D perovskite sheets. To address this challenge,
These interlayers also act as dielectric regulators, determining the various efforts have focused on controlling the growth of the
electrostatic force on the electron–hole pairs.144 The alternating inorganic perovskite framework perpendicular to the substrate

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Fig. 4 Summary of different bulky cations for RP- and DJ-phase 2D perovskites. RP phases: RP1, ethylammonium (EA+, m = 1),75,76 propan-1-
ammonium (m = 2),77,78 butan-1-ammonium (BA, m = 3),7,79,80 pentan-1-ammonium (m = 4),81 hexane-1-ammonium (m = 5),81 heptan-1-ammonium
(m = 6),82 octan-1-ammonium (m = 7),82 nonan-1-ammonium (m = 8);82 decan-1-ammonium (m = 9),82,83 undecan-1-ammonium (m = 10);83 RP2,
2-(methylthio)ethylamine (MTEA);84 RP3, allylammonium (ALA);85 RP4, but-3-yn-1-ammonium (BYA);86 RP5, 2-fluoroethylammonium;87 RP6, isobutyl-
ammonium (iso-BA);88 RP7, ammonium 4-butyric acid (GABA);89 RP8, 5-ammonium valeric acid (5-AVA);90 RP9, heteroatom-substituted alkyl-
ammonium;91 RP10, cyclopropylammonium;92,93 RP11, cyclobutylammonium;92,93 RP12, cyclopentylammonium;92,93 RP13, cyclohexylammonium;92,93
RP14, cyclohexylmethylammonium;94 RP15, 2-(1-cyclohexenyl)ethylammonium;95,96 RP16, (carboxy)cyclohexylmethylammonium (TRA);97 RP17, phenyl-
trimethylammonium (PTA);98 RP18, benzylammonium (BZA);99–104 RP19, phenylethylammonium (PEA);50,100,101,105–108 RP20, propyl phenyl ammonium
(PPA);100,101 RP21, 4-methylbenzylammonium;109 RP22, 4-fluorophenylethylammonium (F-PEA);106,110–113 RP23, 2-(4-chlorophenyl)ethanaminium
(Cl-PEA);111 RP24, 2-(4-bromophenyl)ethanaminium (Br-PEA);111 RP25, perfluorophenethylammonium (F5-PEA);114 RP26, 4-methoxyphenethylammonium
(MeO-PEA);112 RP27, 2-(4-stilbenyl)ethanammonium (SA);115 RP28, 2-(4-(3-fluoro)stilbenyl)ethanammonium (FSA);115 RP29, 2-thienylmethylammonium
(ThMA);116 RP30, 2-(2-thienyl)ethanaminium;116 RP31, 2-(40 -methyl-5 0 -(7-(3-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)-[2,20 -bithiophen]-5-yl)-
ethan-1-aminium (BTM);117 RP32, 1-(2-naphthyl)methanammonium (NMA);118 RP33, 2-(2-naphthyl)ethanammonium (NEA);118 RP34, naphthalene-O-
ethylammonium;119 RP35, pyrene-O-ethylammonium;119 RP36, perylene-O-ethylammonium;119 RP37, 3-iodopyridinium (IPy);97 RP38, carbazole
alkylammonium (CA-C4).120 DJ phases: DJ1, propane-1,3-diaminium (PDA, m = 3);121 butane-1,4-diaminium (BDA, m = 4);122–126 pentane-1,5-
diaminium (m = 5);125 hexane-1,6-diaminium (HDA, m = 6);124,125 heptane-1,7-diaminium (m = 7);125 octane-1,8-diaminium (ODA, m = 8);124,125
nonane-1,9-diaminium (m = 9)125 decane-1,10-diaminium (m = 10);126 dodecane-1,12-diaminium (m = 12);126,127 DJ2, N1-methylethane-1,2-
diammonium (N-MEDA);128 DJ3, N1-methylpropane-1,3-diammonium (N-MPDA);128 DJ4, 2-(dimethylamino)ethylammonium (DMEN);129 DJ5,
3-(dimethylamino)-1-propylammonium (DMAPA);129 DJ6, 4-(dimethylamino)butylammonium (DMABA);129 DJ7, protonated thiourea cation;130 DJ8,
2,2 0 -dithiodiethanammonium;91,131 DJ9, 2,2 0 -(ethylenedioxy)bis(ethylammonium) (EDBE);132 DJ10, 2-(2-ammonioethyl)isothiouronium;133 DJ11,
2-methylpentane-1,5-diammonium;121 DJ12, N-(aminoethyl)piperidinium;97 DJ13, N-benzylpiperazinium;134 DJ14, piperazinium;134 DJ15, 3-(amino-
methyl)piperidinium (3AMP);69 DJ16, 4-(aminomethyl)piperidinium (4AMP);69 DJ17, 1,4-bis(aminomethyl)cyclohexane;135 DJ18, m-phenylene-
diammonium;136 DJ19, histammonium (HA);99 DJ20, 2-(ammoniomethyl)pyridinium;137 DJ21, N,N-dimethyl-p-phenylenediammonium (DPDA);138
DJ22, 1,4-phenylenedimethanammonium (PDMA);139 DJ23, 4-amidinopyridinium;140 DJ24, benzimidazolium;141 DJ25, 1,5-diammonium-
naphthalene;126 DJ26, 5,5 0 -bis(ammoniumethylsulfanyl)-2,2 0 -bithiophene (BAESBT);142 DJ27, 5,500 0 -bis(aminoethyl)-2,2 0 :5 0 ,200 :500 ,200 0 -quaterthiophene
(AEQT).143

to facilitate vertical charge transport for efficient charge collec- also results in interesting and tunable exciton–phonon,158
tion in PV devices.154–157 exciton–photon,159 and exciton–exciton coupling,160,161 as well
Although the large Eb in low-n 2D perovskites may be as the formation of self-trapped excitons (which leads to broad-
detrimental for charge separation in solar cells, it can be band emission) and many other paths for relevant optoelec-
beneficial for other optoelectronic applications beyond solar tronic applications.
cells. For instance, the excitonic effect can significantly
promote radiative recombination, which leads to higher photo- 3.2. Charge-transport dynamics
luminescence quantum yield (PLQY) in perovskite-based LED The confining nature of 2D perovskite results in anisotropic
devices, making them excellent candidates for high-efficiency conductivity and carrier mobility along various crystallographic
LEDs. Additionally, the excitonic character in 2D perovskites directions. In general, when measured along the plane of the

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Fig. 5 (a) Schematic of n = 1 2D perovskite structure with alternating organic and inorganic sheets along with the corresponding MQW energy diagram
(Eexc and Eg are the optical bandgap and electronic bandgap of the inorganic framework, respectively; organic cations have a larger HOMO–LUMO gap).
The constant dielectric contrast (e1 and e2 for inorganic and organic layers, respectively) is also presented. Reproduced with permission from ref. 56.
Copyright 2019, Wiley-VCH. (b) Typical optical emission and absorption spectra of (BA)2(MA)n1PbnI3n+1 perovskites. Reproduced with permission from
ref. 79. Copyright 2017, Cell Publishing Group. (c) Band energy diagrams of BA2MAn1PbnI3n+1 perovskites. Reproduced with permission from ref. 150.
Copyright 2014, ACS Publishing Group. (d) Comparison of the relationship between bandgap Eg and exciton binding energy Eb in various low-D and 3D
perovskites. Reproduced with permission from ref. 152. Copyright 2016, ACS Publishing Group.

inorganic sheet, the conductivity and mobility are much better absent from the literature. The tunneling barrier height can
in comparison to that measured perpendicular to the sheets. vary depending on the following two primary effects: (1) the
The challenge of out-of-plane charge transfer is caused by the intermolecular coupling between adjacent organic cations, and
relatively high resistive, low mobility organic interlayer between (2) the energy arrangement between the perovskite transport
adjacent higher mobility inorganic conductive sheets. In addi- belt and the oxidation or reduction potential of organic cations.
tion, the charge-transfer behavior of 2D perovskite also shows a Based on these considerations, we divide the strategies to
strong dependence on the n value. In RP 2D perovskite films, improve charge transport of 2D perovskites into four parts: (1)
the holes transfer from high-n QWs or the bulk to low-n phase process engineering (e.g., hot casting154,155 and solvent ratio
along with electrons flowing in the opposite direction.85,162 An tuning165–169); (2) additive engineering (e.g., NH4SCN,170,171
optimized n distribution of the QWs will enable more-efficient NH4Cl,170 MACl,172 PbI2,173 and HI174) to tune the orientation
charge transfer across 2D structures with mixed n values. In of 2D perovskite films; (3) engineering based on small cations
addition, as the ratio of the number of inorganic perovskite (e.g., FA+,62,175 MA+, or Cs+ (ref. 156 and 157)) to align perovskite
plates per organic spacer increases, the mobility increases 2D sheets and orientation of corresponding 2D perovskite
significantly as a continuous inorganic pathway is achieved. films; and (4) engineering based on choice of bulky cations
The orientation of the 2D perovskite layers is critical to the (e.g., F-PEA and MeO-PEA106,112,114,164,176,177) to adjust the
device performance: when the inorganic plates are arranged coupling between perovskite 2D sheets and the energy levels
parallel to the charge-collection direction, better device perfor- of organic layers. These strategies have been used mainly in
mance can usually be obtained. low-n 2D perovskite in solar cells, and we discuss the details of
The charge-transport mechanism between inorganic layers how these strategies affect charge transport in the next section.
has been proposed to be mediated by a tunneling process163,164
with the organic molecules acting as barriers. Tunnel junctions
have two key factors affecting charge transport: tunneling 4. Application in solar cells
distance and barrier height. The latter is more complex and
unpredictable than the former. The out-of-plane charge trans- Here, we discuss the application of 2D perovskites in solar cells.
port is generally believed to increase when the interlayer This section is organized in four parts: (1) the application of
distance decreases,164 although a systematic study is still low-n 2D (n r 5) perovskites as absorbers in devices; (2) 3D/2D

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mixed perovskites as absorbers in devices; (3) 2D perovskite the quasi-2D perovskite film did show great promise regarding
as an interfacial layer on the bottom and top surface of 3D stability after 40 days of storage under ambient conditions
perovskite; and (4) Pb-free 2D perovskites as absorbers in with 52% relative humidity (RH), whereas the 3D counterpart
devices. degraded quickly within 4–5 days.50
The 2D perovskite film surface is normally rough, and there
4.1. 2D and quasi-2D perovskites with n r 5 are many defects at the surface/boundary of 2D perovskites
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4.1.1. Process engineering. Although water (or moisture) is prepared with the normal one-step process due to the rapid
sometimes beneficial to device preparation, a humid environ- crystallization process.150,153 In addition, charge transport is
ment is usually considered as a key factor that accelerates the anisotropic for directions across and within the 2D sheets;
degradation of PSCs under practical operation conditions.150 In thus, it is strongly affected by the crystal orientation relative
2014, Karunadasa et al. demonstrated the first quasi-2D per- to the substrate.150 Tsai et al. first reported the hot-casting
ovskites (PEA2MA2Pb3I10; n = 3) in mesoscopic PSCs. Although method for preparing 2D perovskite (BA)2(MA)3Pb4I13 (n = 4).154
the cell efficiency (4.73%) was low at that time (Table 1), Interestingly, hot casting promoted the growth-oriented 2D

Table 1 Representative 2D (n r 5) perovskite absorbers of PSCs based on process engineering

Perovskite Device structure PCE (%) Stability Year[Ref.]

PEA2MA2Pb3I10 (n = 3) Device A 4.73 N/A 201450
(BA)2(MA)3Pb4I13 (n = 4) Device B 12.52 100% of PCE after 2250 h, dark, 65% RHa 2016150
(Gua)(MA)3Pb3I10 (n = 3) Device B 16.65 84% of PCE after 2400 h, darkb 2019178
(BA)2(MA)3Pb4I13 (n = 4) Device B with PEIE on PCBM and 14.9 N/A 2018179
changing Al to Ag
(BA)2(MA)3Pb4I13 (n = 4) ITO/PTAA/PVK/C60/BCP/Ag 17.26 96% of PCE after 2000 h, darka 2019180
(PEA)2MA4Pb5I16 (n = 5) Device B with PEIE on PCBM and 18.04 96.1% of PCE after 8 months, darka 2019181
changing Al to Ag
(BA)2(MA)3Pb4I13 (n = 4) Device A 11.8 90% of PCE after 30 days, dark, 60  5% RHa 2019165
(BA)2(MA)3Pb4I13 (n = 4) Device B with LiF on PCBM 12.15 85% of PCE after 330 h, dark, 60  5% RHa 2018166
(PEA)2MA4Pb5I16 (n = 5) Device A 12.29 N/A 2019167
(BA,Gua)2MA4Pb5I16 (n = 5) ITO/PCP-Na/PVK/PCBM/BCP/Ag 15.86 91% of PCE after 700 h, dark, 55  5% RHb 2019169
RH, relative humidity; PVK, perovskite; PCP-Na, 3,3 0 -[(2-([1,1 0 -biphenyl]-4-yl)-4H-cyclopenta[2,1-b:3,4-b 0 ]dithiophene-4,4-diyl)bis(propane-1-sulfonate)].
Device A: FTO/c-TiO2/PVK/spiro-OMeTAD/Au. Device B: ITO/PEDOT:PSS/PVK/PCBM/Al. a Encapsulated devices or non-encapsulated devices in Ar or
N2 atmosphere. b Non-encapsulated devices in air.

Fig. 6 (a) Grazing-incidence wide-angle X-ray scattering (GIWAXS) comparison of room-temperature cast (left) and hot-cast (right) (BA)2(MA)3Pb4I13
perovskite films. X-ray scattering intensity is related to the color scale. Reproduced with permission from ref. 154. Copyright 2016, Nature Publishing
Group. (b) Atomic force microscopy (AFM) phase images (left) and 2D GIWAXS pattern (right) of a drop-cast 2D-perovskite film prepared at 50 1C.
Reproduced with permission from ref. 179. Copyright 2018, Wiley-VCH. (c) Schematics of the crystallization process using DMF solvent (case 1) and
DMSO/DMF solvent (case 2). Reproduced with permission from ref. 165. Copyright 2019, ACS Publishing Group. (d) Schematics showing the effect of the
mixed solvent DMSO : DMF (5 : 5) on 2D perovskite crystal growth. Reproduced with permission from ref. 167. Copyright 2019, Wiley-VCH.

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perovskite films with the inorganic framework more aligned complex lead to different growth directions, which create
vertically to the substrate (Fig. 6a), which would enable better structural mismatches and random boundaries. However, by
pathways of charge transport. The corresponding 2D devices using a mixed solvent (DMF/DMSO 5 : 5), only one intermediate
exhibited better stability compared to their 3D counterpart. The complex is formed after anti-solvent extraction and before
device performance was brought over 10% for the first time for annealing. As a result, one direction of perovskite growth is
2D PSCs. Since this study, the hot-casting method has become a enhanced and the 2D perovskites exhibit preferred orientation/
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standard approach for preparing various 2D PSCs.174,178 How- alignment (Fig. 6d). Consistent with the improved quality of the
ever, this method is difficult as it requires precise control of the 2D perovskite films, the devices based on mixed solvents
substrate temperature, which can then affect the batch-to-batch (DMF : DMSO, 5 : 5) also showed 480% performance improve-
reproducibility. Gao et al. deposited the precursor solutions by ment (from 6.78% to 12.29%) over those made with pure DMF
a substrate-heated drop-casting method, which allowed self- by using the anti-solvent extraction method.
assembly into uniform and oriented 2D-(BA)2(MA)3Pb4I13 (n = 4) It is worth noting that at present, different reports often
perovskite films in air (Fig. 6b), yielding PSCs with PCE of up to conclude different growth mechanisms, despite the reported
14.9%.179 Zhao et al. proposed a slow post-annealing (SPA) use of the same growth methods. More detailed mechanistic
process for BA2MA3Pb4I13 (n = 4) 2D PSCs, and a favorable studies are required to obtain a deeper, more actuate under-
alignment of bandgap energy within 2D perovskite (from standing of how the hot-casting or solvent processing routes
bottom (n = 1) to top (n = N)) was achieved due to gradients impact the crystallization process.
in vertical distribution of different perovskite phases after 4.1.2. Additive engineering. Additives can also assist the
SPA. As a result, they obtained the champion performance of growth of vertically oriented 2D perovskite films.170–173 Chen
17.26%.180 Hu et al. reported another strategy by introducing a et al. first added ammonium thiocyanate (NH4SCN) into a
vacuum poling treatment to arrange different-n-value nanoplates room-temperature, one-step, spin-coated process method.171
and to enforce uniform nucleation during crystallization.181 Using After introducing the NH4SCN, one can clearly observe
this approach, a PCE of 18.04% based on (PEA)2MA4Pb5I16 (n = 5) vertical-oriented larger grains perpendicular to the substrate
was demonstrated. with almost no grain boundary, resulting in increased carrier
When 2D perovskite films are formed from the hot-casting lifetime and transport mobility, leading to improved efficiency
process, heterogeneous nucleation mainly occurs at the gas/ and shelf life of the unencapsulated device. Later, they applied
liquid interface, which helps to form a thin sheet-like capping NH4SCN to (PEA)2(MA)4Pb5I16 (n = 5) films, and the device
layer on the outmost surface of the perovskite film. As a result, performance improved from 0.56% to 11.01% due to the highly
the rapid volatilization of DMF facilitates homogeneous nuclea- crystalline, vertically orientated 2D perovskite films (Fig. 7a)
tion, resulting in the formation of randomly oriented perovs- and improved electron/hole transport.182 With the cooperation
kite grains in the inner layer. To address this issue, Fan et al. of NH4Cl and NH4SCN to further enhance the crystallization
fabricated the devices through mixed solvent engineering of and charge transport, PSC based on (PEA)2(MA)4Pb5I16 (n = 5)
DMF/DMSO, which improved PCE from B6% (pure DMF) to obtained an efficiency of 14.1%.170
B11% (DMF/DMSO 1 : 3).165 By using DMF/DMSO solvent In 3D PSCs, MACl is shown to slow down the speed of
engineering, the solvent volatilization process is used to perovskite film formation and benefit the film coverage, resulting
modulate the crystallization process which makes the perovs- in much-improved performance.183,184 Chen et al. reported using a
kite cover act as the seed—thus promoting the subsequent MACl-assisted method to prepare highly oriented 2D-perovskite
perovskite crystallization perpendicular to the inner layer of the (ThMA)2(MA)2Pb3I10 (n = 3) thin films, resulting in improved PCE
perovskite film (Fig. 6c). In another study, Huang et al. showed from 1.74% to more than 15%.185 After applying a MACl treatment,
that specific solvents strongly affect the crystallization kinetics the 2D perovskite formed a unique nanorod-shape morphology,
and crystal orientation of the resulting 2D perovskites by and showed a significant increase in crystal size, out-of-plane
hot-casting.166 Among several solvents, dimethylacetamide orientation (Fig. 7b), and carrier lifetime. Other groups have
(DMAC) shows weak coordination to Pb and ammonium salts, reported similar phenomena.186 PbI2 as a typical Lewis acid can
suitable boiling point, and low polarity; thus, it is easy to also form self-induced passivation in 2D-perovskite films with
remove during solution processing, and it can facilitate rapid reduced surface defects.173
crystallization of 2D perovskites. As a result of proper solvent Chen et al. recently introduced a second spacer cation (SSC+)
selection, a PCE from 7.33% (from DMF) to 12.15% (from approach by adding PEAI into the BA2MA4Pb5I16 (n = 5) perovskite
DMAC) was demonstrated. precursor solution.187 If PEAI is not added, a large number of the
For the anti-solvent method, the mechanism of formation nuclei will precipitate from the precursor solution, resulting in
are different according to Zhang’s recent report.167 The coordi- small-grained perovskite films. However, after adding PEAI, the
nation strength of the solvent with perovskite precursor affects presence of precursor agglomerates may induce preferential
the formation of intermediate complexes and the subsequent nucleation and reduce the nucleation density, facilitating the
growth of the 2D perovskite layer. Perovskite structure and formation of large grains (Fig. 7c). This approach leads to the
intermediate complexes coexist after anti-solvent extraction demonstration of a PCE of 14.09% and B10% degradation of an
and before thermal annealing of the DMF based precursor. unsealed device after 1000 h air exposure. They also used Gua+ as
During annealing, the existing perovskite and intermediate the SSC+ and obtained a similar result in a follow-up study.188

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Fig. 7 (a) GIWAXS patterns of perovskite films without (left) and with (right) addition of NH4SCN in (PEA)2(MA)4Pb5I16 (n = 5). Schematic showing the
effect of SCN additive on perovskite crystal orientation. Reproduced with permission from ref. 182. Copyright 2018, Wiley-VCH. (b) SEM images, GIWAXS
results, and schematic of proposed packing structures of 2D (ThMA)2(MA)2Pb3I10 (n = 3) perovskite films with MACl. Reproduced with permission from
ref. 185. Copyright 2018, ACS Publishing Group. (c) Illustration of the formation of the 2D perovskite film without or with PEAI addition by second spacer
cation. Reproduced with permission from ref. 187. Copyright 2018, Wiley-VCH. (d) Schematic of sequential two-step post-treatment for GuaMA4Pb4I13
film fabrication. Reproduced with permission from ref. 190. Copyright 2019, Wiley-VCH.

Although using excessive additives can lead to better crystal- 4.1.3. Small-cation engineering. Previous reports have
linity, it also results in a large gap between grains, thus shown that Cs+ can effectively assist the crystallization of more
reducing the PV performance.189 Chen et al. reported a sequen- stable 3D perovskite due to entropy gains if phase segregation
tial post-treatment process to make ACI 2D PSCs with high is avoided.191,192 The surface morphology and apparent grain
performance, where they sequentially used guanidinium thio- size of the 2D perovskite film are improved (Fig. 8a) by replacing
cyanate (GuaSCN) and MACl as post-treatment agents (Fig. 7d).190 MA+ with Cs+ based on the hot-casting method,156 thereby redu-
GuaSCN treatment has a significant effect on the perovskite cing the trap density, increasing the mobility of charge carriers,
morphology, leading to the fusion of segregated grains into and improving the thermal stability. The enhanced film quality
dense and ordered grains. The trap state can be further and the corresponding structural and optoelectronic properties
passivated by subsequent MACl treatment; as a result, the significantly improved PCE from 12.3% to 13.68% (Table 3).
performance is enhanced to 15.27% (Table 2). Moreover, the 5% Cs+-doped devices only exhibited a degradation

Table 2 Representative 2D (n r 5) perovskite absorbers of PSCs based on additive engineering

Type Perovskite Device structure PCE (%) Stability Year[Ref.]

NH4SCN (BA)2(MA)2Pb3I10 (n = 3) Device A 6.89 100% of PCE after 24 days, darka 2017171
NH4SCN (PEA)2(MA)4Pb5I16 (n = 5) Device A 11.01 78.5% of PCE after 160 h, dark, 55  5% RHb 2018182
NH4SCN + NH4Cl (PEA)2(MA)4Pb5I16 (n = 5) Device A 14.1 490% of PCE after 45 days, dark, 30% RHb 2018170
MACl (ThMA)2(MA)2Pb3I10 (n = 3) Device A 15.42 90% of PCE after 1000 h, darka 2018185
PEAI BA2MA4Pb5I16 (n = 5) Device A 14.09 490% of PCE after 1000 h, dark, 25  5% RHb 2019187
GuaI BA2MA4Pb5I16 (n = 5) Device A 16.26 94% of PCE after 1200 h, dark, 25  5% RHb 2019188
GuaSCN+ MACl GAMA4Pb4I13 (n = 4) Device A 15.27 75% of PCE for 480 h, dark, 50% RHb 2019190

RH, relative humidity; PVK, perovskite. Device A: ITO/PEDOT:PSS/PVK/PCBM/BCP/Ag. a Encapsulated devices or non-encapsulated devices in Ar or
N2 atmosphere. b Non-encapsulated devices in air.

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Fig. 8 (a) Plan-view and cross-section view of scanning electron microscopy (SEM) images of (BA)2(Cs0.05MA0.95)3Pb4I13 (n = 4) and (BA)2(MA)3Pb4I13 (n = 4)
perovskite films. Reproduced with permission from ref. 156. Copyright 2017, Wiley-VCH. (b) SEM images and GIWAXS patterns of (BA)2(MA1–xFAx)3Pb4I13
films (x = 0, and 0.4). Reproduced with permission from ref. 62. Copyright 2018, ACS Publishing Group. (c) 2D XRD patterns and (d) conductive atomic force
microscopy (C-AFM) imaging for the perovskite films of BA2MA4Pb5I16 (n = 5) (left) and BA2(Cs0.02MA0.64FA0.34)4Pb5I16 (n = 5) (right). Reproduced with
permission from ref. 175. Copyright 2019, Wiley-VCH.

of 11% from its initial PCE value after 1400 h air exposure with boundary, and stronger crystallographic texture (Fig. 8c and d).
30% RH. In addition, the corresponding perovskite films with the triple
It was further reported that incorporating a suitable amount cations showed a longer carrier lifetime and higher conductivity.
of FA+ can effectively control BA2(MAxFA1x)3Pb4I13 (n = 4) Compared with devices prepared by mono A-cation (MA+), PCE of
crystallization kinetics for enlarging crystal grains with 2D BA2(Cs0.02MA0.64FA0.34)4Pb5I16 (n = 5) devices with triple cations
increased crystallinity (Fig. 8b), leading to high-quality films increased from 7.80% to 14.23%. Recently, Zhou et al. also
with limited nonoriented phases and reduced recombination reported a similar effect and demonstrated a PCE of 15.58%
centers.62 In situ photoluminescence (PL) techniques showed based on BA2(MA0.76FA0.19Cs0.05)3Pb4I13 (n = 4) with 8.6% excess
that the low-n-number 2D phase was formed early, then n = N PbI2.157 The approach based on these triple cations is also found
perovskite was eventually formed. After the introduction of 20% to be effective for mixed Pb/Sn perovskites (BA)2(FA0.85Cs0.15)3
FA+, the BA2(MA0.8FA0.2)3Pb4I13 (n = 4) perovskite-based devices (Pb0.6Sn0.4)4I13 (n = 4).193
displayed the highest performance of 12.81%, resulting from 4.1.4. Bulky-cation engineering. Although PEA+ and BA+
enhanced carrier lifetime and crystal orientation. Ke et al. represent the most commonly studied bulky cations so far,
employed MA+ and FA+ cations in 3-(aminomethyl)piperidinium other large-sized organic cations have been incorporated into
(3AMP2+)-based 2D perovskite.71 Single-cation (3AMP)(MA)3Pb4I13 2D perovskites and subsequently into solar cells. The suitability
perovskite shows a wider bandgap, more distorted inorganic of a bulky cation includes its hydrogen-bonding capacity,
structure, and smaller Pb–I–Pb angles compared to that of stereochemical configuration, and space-filling ability.65 Spin–
mixed-cation (3AMP)(MA0.75FA0.25)3Pb4I13 perovskite. Adding orbit coupling and density functional theory (DFT) calculations
a small amount of hydroiodic acid further improved film indicated that the increased length of the barrier molecule would
morphology, crystal quality, and vertical orientation, leading result in decreased electrical conductivity.100 Moreover, it was
to the demonstration of 12.04%-efficient devices based on shown that a better open-circuit voltage (Voc) could be achieved
(3AMP)(MA0.75FA0.25)3Pb4I13 (n = 4). when the charge is localized on the barrier molecule whereas a
Based on these findings, Zhang et al. first reported the use of better current density was obtained when the charge is more
mixed triple cations (MA+, FA+, and Cs+) in fabricating 2D delocalized.
BA2(Cs0.02MA0.64FA0.34)4Pb5I16 (n = 5) perovskites.175 Compared Zhang et al. recently reported the application of F-PEA by
with the traditional MA-based counterparts, the use of these introducing fluorine to the para position of PEA in 2D
mixed triple cations leads to the film formation with smooth/ perovskites.106 F-PEA can better align the stacking of perovskite
dense surface morphology, bigger grain size, fewer grain sheets and decrease the average phenyl ring centroid–centroid

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Table 3 Representative 2D (n r 5) perovskite absorbers of PSCs based on small cations engineering

Perovskite Device structure PCE (%) Stability Year[Ref.]

(BA)2(Cs0.05MA0.95)3Pb4I13 (n = 4) Device A 13.68 89% of PCE after 1400 h, dark, 30% RHa 2017156
BA2(MA0.8FA0.2)3Pb4I13 (n = 4) Device B 12.81 88% of PCE after 1300 h, dark, B40–60% RHa 201862
(3AMP)(MA0.75FA0.25)3Pb4I13 (n = 4) Device B with changing PCBM to C60 12.04 42% of PCE after 48 h, continuous light soakinga 201971
BA2(Cs0.02MA0.64FA0.34)4Pb5I16 (n = 5) Device A 14.23 74% of PCE after 600 h, dark, B15–20% RHa 2019175
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BA2(MA0.76FA0.19Cs0.05)3Pb4I13 (n = 4) Device B 15.58 80% of PCE after 1400 h, dark, 85 1Cb 2019157
(BA)2(FA0.85Cs0.15)3(Pb0.6Sn0.4)4I13 Device B 9.3 47% of PCE after 2000 h, darkb 2018193
(n = 4)
a
RH, relative humidity; PVK, perovskite. Device A: FTO/c-TiO2/PVK/spiro-OMeTAD/Au. Device B: ITO/PEDOT:PSS/PVK/PCBM/BCP/Ag. Non-
encapsulated devices in air. b Encapsulated devices or non-encapsulated devices in Ar or N2 atmosphere.

distances in the organic layer, which would result in better perovskites (with a van der Waals gap).74,164 Kanatzidis et al.
interlayer electronic coupling and higher out-of-plane conduc- first reported PSCs based on DJ-phase perovskites (amino-
tivity (Fig. 9a). Using the anti-solvent deposition method at methyl)piperidinium (3AMP) and 4-(aminomethyl)piperidi-
room temperature, the efficiency of 13.64% was achieved by nium (4AMP).69 The Pb–I–Pb angles of 3AMP-based perovskite
(F-PEA)2MA4Pb5I16 (n = 5)-based PSCs in the absence of any are bigger than that of perovskite based on 4AMP, indicating
additives (Table 4). In addition, F-PEA-based 2D PSCs displayed more orbitals overlap between the I p and Pb s,196 thus
improved thermal stability relative to PEA-based devices. The resulting in a reduced bandgap (Fig. 9b). The structural change
same results were later confirmed by other reports.111,112,194 In also led to the difference in device performance. Specifically,
another recent study, Wang et al. report a method of using devices based on 4AMP-based perovskite (n = 4) showed a lower
4-aminoethyl pyridine (4-AEP) as a bi-functional organic cation PCE of 4.24% compared to 3AMP-based counterpart (7.32%);
to adjust the crystallization rate of 2D perovskite.195 4-AEP not the higher performance associated with 3AMP largely results
only can react with PbI2 to form 2D perovskite but can also from the smaller bandgap and improved transport property.
coordinate with Pb2+ (pyridyl unit) to slow down the crystal- Later, Ma et al. proposed propane-1,3-diammonium (PDA) with
lization rate, thus controlling the nucleation growth. As a reduced cation length to form 2D perovskites.164 Compared to
result, the device based on (4-AEP)2MA4Pb5I16 (n = 5) perovskite BA-based 2D perovskites, charge transport across neighboring
achieved a PCE of 11.68%, which is higher than that of inorganic perovskite layers are greatly enhanced. As a result,
PEA-based devices prepared under the same condition. the corresponding devices achieved a high PCE of 13.0% with
The bulky cations of DJ-phase perovskites with two amino improved stability. Other bulky cations (e.g., (aminomethyl)pyr-
groups can form a single layer with hydrogen bonds to the two idinium (4AMPY), (adamantan-1-yl)methanammonium (A), and
neighboring inorganic sheets. This structural feature was 1,4-phenylenedimethanammonium (PDMA)) are also reported
shown to improve the material stability compared to RP-type as candidates to the DJ-type 2D perovskites.71,139,177

Fig. 9 (a) The structures of n = 1 2D perovskites (PEA)2PbI4 (left) and (F-PEA)2PbI4 (right) along with time-resolved microwave conductivity results of
transport across and within the 2D sheets. Reproduced with permission from ref. 106. Copyright 2019, ACS Publishing Group. (b) Average axial and
equatorial angles of (4AMP)PbI4 and (3AMP)PbI4 along with the definitions of the respective axial and equatorial Pb–I–Pb angles. Reproduced with
permission from ref. 69. Copyright 2018, ACS Publishing Group. (c) Top-view SEM images of (Gua)(MA)3Pb3I10 (n = 3) films without and with MACl additive
along with an illustration of different n distribution of QWs and n-dependent electron flow direction. Reproduced with permission from ref. 51. Copyright
2019, Wiley-VCH. (d) SEM image and crystal structures of (BEA)0.5MA3Pb3I10 perovskite with alternating BEA2+ and MA+ cations in the interlayer space.
Reproduced with permission from ref. 197. Copyright 2019, Wiley-VCH.

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Table 4 Representative 2D (n r 5) perovskite absorbers of PSCs based on bulky cations engineering

Perovskite Device structure PCE (%) Stability Year[Ref.]

(F-PEA)2(MA)4Pb5I16 (n = 5) Device A with m-TiO2 on c-TiO2 13.64 65% of PCE after 76 h, dark, 70 1Ca 2019106
F-PEA2MA2Pb3I10 (n = 3) FTO/NiOx/PVK/PC61BM/BCP/Ag 5.83 N/A 2019111
(F-PEA)2(MA)4Pb5I16 (n = 5) Device B with changing C60 to PCBM 14.5 90% of PCE after 40 days, dark, 40–50% RHa 2019112
(4-AEP)2MA4Pb5I13 (n = 5) Device A with changing c-TiO2 to C60 11.68 95% of PCE after 1000 h, dark, 30% RHa 2019195
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(3AMP)(MA)2Pb3I10 (n = 3) Device B with changing ITO to FTO 7.32 N/A 201869

PDAMA3Pb4I13 (n = 4) Device B 13.0 90% of PCE after 1000 h, dark, 85% RHb 2018164
(3AMPY)(MA)3Pb4I13 (n = 4) Device B with changing Ag to Al 9.2 N/A 201971
A2FA2Pb3I10 (n = 3) Device A with m-TiO2 on c-TiO2 7.8 84% of PCE after 800 h, MPPT, 2019177
continuous light soakinga
(Gua)(MA)3Pb3I10 (n = 3) Device B with changing Ag to Al 7.26 N/A 201772
and C60/BCP to PCBM
(Gua)(MA)3Pb3I10 (n = 3) Device A (changing spiro-OMeTAD 16.48 88% of PCE after 240 days, dark, 30–40% RHa 201973
to PCBM)
(Gua)(MA)3Pb3I10 (n = 3) Device A 18.48 95% of PCE after 131 days, dark, 30–40% RHb 201951
(BEA)0.5Cs0.15(FA0.83MA0.17)2.85- Device A 17.39 93% of PCE after 500 h, continuous light soakinga 2019197
Pb3(I0.83Br0.17)10 (n = 3)
a
RH, relative humidity; PVK, perovskite. Device A: FTO/c-TiO2/PVK/spiro-OMeTAD/Au. Device B: ITO/PEDOT:PSS/PVK/C60/BCP/Ag. Non-
encapsulated devices in air. b Encapsulated devices or non-encapsulated devices in Ar or N2 atmosphere.

The ACI-type 2D perovskites adopt a larger crystal symmetry 4.2. 3D/2D mixed perovskite
and different stacking, which can decrease the bandgap com- The pure 2D (n = 1) PSCs do not exhibit efficiencies as high as
pared to RP perovskites with the same n values. Kanatzidis et al. 3D PSCs due to their larger bandgaps and restricted transport
reported the first ACI 2D perovskite (Gua)(MA)nPbnI3n+1 across the organic spacer layers. In contrast, 3D/2D multi-
(n = 1–3) along with the application in solar cells with a good dimensional perovskites formed by incorporating 2D perovs-
performance of 7.26%.72 Later, Zhao et al. compared anti- kites into 3D perovskites (using bulky cations to replace small
solvent and hot-casting methods to get more insight into the amounts of organic cations in the precursor solution) has
kinetic transformation process.73 The formed intermediate recently appeared to be a promising approach to balance good
phases, (Gua)2PbI4 perovskite, is critical to the subsequent device performance with long-term operational stability.198
transformation into (Gua)(MA)3Pb3I10 (n = 3) perovskites. This Based on the previous report of better stability of low-n 2D
material was able to achieve a PCE of 14.68% via use of an anti- perovskites,50 Yao et al. reported a facile two-step method to
solvent approach. MACl was later added to the precursor to form uniform, compact (MAPbI3)1x[(PEI)2PbI4]x 3D/2D perovs-
further improve the (Gua)(MA)3Pb3I10 (n = 3) films’ morphology kite films. By spin-coating an initial PbI2 and polyethylenimine
and QW’s distribution (Fig. 9c), resulting in the an impressive hydriodide (PEIHI) mixed solution, then coated with a CH3NH3I
PCE (18.48%) for 2D PSCs.51 1,4-Butanediamine (BEA) was used layer to produce a film.199 The in situ-formed (PEI)2PbI4 incorpora-
as a bulky organic cation to form a new type of 2D perovskite in tion was shown to retard perovskite growth and promote the
which BEA2+ and MA+ alternating cations are in the interlayer formation of a continuous uniform film, and the formation of
space (B-ACI) (Fig. 9d), this combines advantages of DJ and ACI 3D perovskite crystals with domains hindered by increasing
perovskites.197 Devices based on (BEA)0.5MA3Pb3I10 perovskite the number of 2D materials. A champion PCE of 15.2% was
reached a performance of 14.86%, which further increased to obtained from this approach for a (MAPbI3)0.98[(PEI)2PbI4]0.02
17.39% by alloying with Cs, FA, and Br into the composition film and displayed better humidity stability than the reference
((BEA)0.5Cs0.15(FA0.83MA0.17)2.85Pb3(I0.83Br0.17)10). 3D MAPbI3-based devices (Table 5).

Table 5 Representative 3D/2D mixed-perovskite absorbers of perovskite solar cells

Perovskite Device structure PCE (%) Stability Year[Ref.]

(MAPbI3)0.98[(PEI)2PbI4]0.02 ITO/PEDOT:PSS/PVK/PC61BM/LiF/Ag 15.2 84% of PCE after 14 days, dark, 50% RHa 2015199
(DA2PbI4)0.05MAPbI3 ITO/TiO2/PVK/spiro-OMeTAD/MoO3/Ag 19.05 80% of PCE after 60 days, darkb 2019225
(PEA2PbI4)0.017(MAPbI3) FTO/c-TiO2/m-TiO2/PVK/spiro-OMeTAD/Ag 19.84 96% of PCE after 100 h, darka 2019200
(AVA2PbI4)0.03(MAPbI3)0.97 FTO/TiO2/ZrO2/PVK/C 10.10 100% of PCE after 10 000 h, 55 1C, 201752
continuous light soakingb
BA0.09(FA0.83Cs0.17)0.91Pb(I0.6Br0.4)3 FTO/SnO2/PC61BM/PVK/spiro-OMeTAD/Au 17.2 80% of PCE after 1000 h, air, darka 201755
(BzDA)(Cs0.05MA0.15FA0.8)9- FTO/c-TiO2/m-TiO2/PVK/spiro-OMeTAD/Au 15.6 80% of PCE after 84 h, dark, 20–50% RHa 2019210
Pb10(I0.93Br0.07)31 (n = 10)
CA2MA39Pb40I121 (n = 40) ITO/SnO2/PVK/spiro-OMeTAD/Au 6.6 59% of PCE after 264 h, dark, 77% RHa 2018120
Gua0.1[Cs0.1(FA0.83MA0.17)0.9]0.9- ITO/SnO2/PVK/spiro-OMeTAD/MoO3/Ag 21.12 N/A 2019218
Pb(I0.83Br0.17)3
a b
RH, relative humidity; PVK, perovskite. Non-encapsulated devices in air. Encapsulated devices or non-encapsulated devices in Ar or N2
atmosphere.

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Park et al. used a small amount of PEAI to fabricate showed only 20% performance degradation after 1000 h in air and
(PEA2PbI4)0.017(MAPbI3)0.983 PSCs, and the devices showed almost 4000 h with encapsulation under light illumination. A
comparable performance and better stability compared to similar trend was also observed with other bulky salts, such as
that of MAPbI3-based devices. However, the small amount of (2-chloroethylamine) (CEA+), 2-thiophenemethylammonium
incorporated PEA2PbI4 still resulted in a lower short-circuit (ThMA) and dimethylamine (DMA).202–209
current density (Jsc) than that of MAPbI3-based devices.200 Ammonium salts containing a short-branched chain than
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Later, by applying AVA2PbI4 into a printable MAPbI3-based commonly used PEA+ and BA+ may exhibit better charge-
mesoporous HTM-free device, Nazeeruddin et al. demonstrated transport properties when used in 2D perovskites. Lioz Etgar
a performance of 11.2% by (AVA2PbI4)0.03(MAPbI3)0.97 on a et al. introduced 1,4-benzenedimethanamonium iodide (BzDAI)
10  10 cm2 module; the device exhibited no degradation in with a relatively short length and aromatic ring with free
performance after testing for 410 000 h under continuous p-electrons to enhance the charge transport.210 The PSCs with
illumination at 55 1C.52 FA- and Cs-based perovskites generally (BzDA)(Cs0.05MA0.15FA0.8)9Pb10(I0.93Br0.07)31 (n = 10) achieved an
exhibit better stability than MA-based ones for 3D perovskites.31 efficiency of 15.6%, and the devices also exhibited better
Based on this consideration, Snaith et al. introduced BA+ into stability under humidity and illumination. Some other bulky
a mixed-cation 3D FA0.83Cs0.17Pb(IyBr1y)3 perovskite.55 They cations (e.g., carbazole alkylammonium iodide derivative (CAI)
found the formation of 2D perovskite flakes scattered among and phenyltrimethylammonium (PTA)) also showed the same
highly oriented 3D perovskite grains; these 2D perovskite struc- trend.98,120,211
tures significantly reduced nonradiative charge recombination Using bulky, large-sized organic halide salts (e.g., BAI and
(Fig. 10a). As a result, a BA0.05(FA0.83Cs0.17)0.95Pb(I0.8Br0.2)3-based PEAI) has been shown to reduce the defect density of 3D
PSC was achieved with a PCE of 20.6%. The energetic alignment perovskites. However, the formation of RP-type 2D perovskites
across the 3D/2D interface is found to be similar to a standard within these structures could reduce Jsc of devices due to
type-I or type-II heterojunction due to the wider bandgap of 2D quantum-confinement effects. Recently, addition of guanidinium
perovskite.124,201 By further increasing ratios of BA+ cations and cations (Gua+) have been reported to form highly stable 3D
Br anions, BA0.09(FA0.83Cs0.17)0.91Pb(I0.6Br0.4)3 perovskite was devel- crystalline structures to improve the solar cell performance for
oped with enhanced device stability; the corresponding devices MAPbI3- or FAPbI3-based PSCs.212–217 In another study, a large Gua

Fig. 10 (a) Schematic of self-assembled 3D/2D perovskite structure along with the electronic band structures (VB: valence band; CB: conduction band).
Reproduced with permission from ref. 55. Copyright 2017, Nature Publishing Group. (b) Photographs of perovskite films prepared with different molar
ratio of Gua. The pristine perovskite composition is Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3. Reproduced with permission from ref. 218. Copyright 2019, Royal
Society of Chemistry. (c) AFM (left) and SEM (right) images of CsPbI3xEDAPbI4 (x values indicated) perovskite films. Reproduced with permission from
ref. 220. Copyright 2017, American Association for the Advancement of Science (AAAS). (d) High-resolution transmission electron microscopy (HRTEM)
image of the perovskite grain-boundary region with 7% GuaSCN additive. The pristine perovskite composition is (FASnI3)0.6(MAPbI3)0.4. Reproduced with
permission from ref. 54. Copyright 2019, American Association for the Advancement of Science (AAAS).

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cation was incorporated into Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3 involving a cation exchange reaction. The 2D perovskite inter-
perovskites to form Guax(CsFAMA)1x mixed-cation perovskites.218 facial layer is expected to enhance moisture resistance and
The color of the corresponding perovskite films changed from black reduce surface defects by combining large hydrophobic cations
for 0% Gua+ to brown for 40% Gua+ (Fig. 10b). Incorporation of 10% with effective charge-transfer properties.227 In addition, Herz
Gua+ resulted in the best device performance (PCE of 21.12%) with et al. found that the blue-shift emission from the quasi-2D
higher carrier lifetime and lower trap density due to the strong region overlaps the absorption spectrum of 3D perovskite,
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passivation from the Gua+ additive. which leads to efficient heterogeneous photon recovery.228
In addition to increasing the stability against heat and Structural analysis has been commonly used to verify the
moisture, the use of 2D perovskite is also often reported as formation of the 2D perovskite structure on top the 3D perov-
an effective additive for phase stabilization in inorganic skite absorber in a device stack. Nazeeruddin et al. demon-
CsPbI3155,219–221 or FAPbI3,222–224 which are known to have strated the layered 2D perovskite PEA2PbI4 with distinct X-ray
phase instabilities with respect to the a-to-d phase transition diffraction (XRD) features on top of the 3D Cs0.1FA0.74MA0.13-
at room temperature. Zhang et al. recently demonstrated the PbI2.48Br0.39 perovskite films (Fig. 11a).229 When incorporating
use of a small amount of 2D EDAPbI4 (ethylenediamine, the PEA2PbI4 perovskite top layer, the PSCs exhibit a higher
EDA) perovskite into the CsPbI3 perovskite to significantly PCE of 20.1% (Table 6). In addition, the devices exhibited less
enhance the phase stability of a-CsPbI3.220 Following this than 15% of performance degradation under illumination in
preparation approach, the apparent grain size of CsPbI3 ambient air at 50 1C over 800 h. Other groups also reported
xEDAPbI4 decreased with increasing EDAPbI4 content and the similar results of PEAI.230–232 Based on the application of PEAI,
number of pinholes was much reduced (Fig. 10c), resulting in Grätzel et al. recently introduced five fluorine atoms to PEAI
the all-inorganic PSC with a PCE of 11.8%. Other studies have forming pentafluorophenylethylammonium iodide (F5PEAI) and
also shown enhanced phase stability of CsPbI3 PSCs by using applied its IPA solution for the post-growth treatment of the 3D
other 2D perovskite additives.155,221 These results show that perovskite absorber.233 The X-ray photoelectron spectroscopy
the construction of quasi-2D or 3D/2D mixed perovskites repre- (XPS) depth profiling of fluorine (F) and X-ray reflectivity (XRR)
sents an effective approach to enhance phase stability of peak width (Fig. 11b) established the presence of B8–9 nm 2D
inorganic CsPbI3 perovskite. perovskite on the top. The 2D layer also enhances interfacial
FAPbI3 is another well-known perovskite composition that charge collection and enables the device performance of 422%.
also has a significant phase-stability issue. Adding a small Unencapsulated PSCs only showed 10% degradation after
amount of Cs+ to FAPbI3 to form CsFAPbI3 is one effective 1000 hours under illumination in ambient air.
way to improve the phase stability by tuning the tolerance Seo et al. reported the use of a mixed solvent (o-dichloro-
factor;27 however, it generally widens the bandgap, leading to benzene : IPA = 97 : 3, v/v) containing n-hexyl trimethyl ammo-
a reduction of Jsc. Incorporating a certain amount of 2D nium bromide (HTAB) solution and spin-coated on top of the
BA2Pb(I/Br)4 into the perovskite precursor facilitates the 3D perovskite surface to form a wide-bandgap perovskite layer,
formation of phase-pure FA-based perovskite. Further passivation which is confirmed by HRTEM of the device cross-section near
of grain boundaries by semiconducting molecules with Lewis base the interface region (Fig. 11d).21 The HTAB molecule comprises
groups significantly improved charge-carrier dynamics, leading to a functionalized moiety (N+(CH3)3) and an aliphatic moiety
devices with PCE of 20.62% and improved stability.224 The (C6H13). The C6H13 could form van der Waals interactions
benefits of incorporating PEA+-based 2D structures into 3D between the perovskite and organic HTM, which would
perovskites were also reported by other groups.222,223 Comple- promote the self-assembly of P3HT. As a result, they attained
mentary additives PEAI and Pb(SCN)2 were used to improve a a PCE of 23.3%, and the encapsulated devices maintained
wide-bandgap (1.68 eV) PSC with an efficiency of B20%.22 Tong more than 95% of their initial PCE for 1370 h with maximum
et al. applied GuaSCN to low-bandgap Sn–Pb mixed-perovskite power-point tracking (MPPT) under continuous light soaking at
thin films to improve their structural and optoelectronic pro- room temperature. Some other organic cations, with optimized
perties resulting from the formation of a 2D structure at grain concentration, have also shown similar results with enhanced
boundaries (Fig. 10d).54 New strategies to ‘‘design’’ 2D-PPAs stability and efficiency; these organic cations include BAI,226
with enhanced charge transport are necessary for further cyclopropylammonium iodide (CAI),234 octylammonium iodide
advancing efficient and stable 2D-PPA based-3D PSCs. (OAI),226,235 dodecylammonium iodide (DAI),235 5-ammonium
valeric acid iodide (5-AVAI),236 n-butylammonium bromide
4.3. Interface modification with 2D perovskites (BABr),237 long-chain aliphatic alkylammonium chloride
A 2D perovskite thin layer can also be added to the top of a 3D (CmH2m+1NH3Cl, m = 8, 10, 12),238 and 3-(nonafluoro-tert-
perovskite absorber as an interfacial layer between the perovs- butyloxy)propylamine hydroiodide (A43).239
kite absorber and charge-transport/contact layer; this inter- For the pure 2D perovskite, many achievements have been
facial engineering was also shown to improve the perovskite made in determining the properties of the films, such as charge
absorber layer with lower defect densities and longer carrier transfer between QW and n-layer distribution.162,240 However,
lifetimes.226 The 2D interfacial layer is usually processed by the influence of the cationic chemical dependence of 2D/3D
spin coating an isopropanol (IPA) solution containing long- heterostructures on charge collection and final PV performance
chain alkyl-ammonium halides on top of a 3D perovskite has not been fully developed. This is important for ensuring

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Fig. 11 (a) XRD spectra (left) and XRD pattern (right) for the L-CFM/P film at X-ray incident angles of 0.31 (for surface) and 51 (for interior). CFMPIB
represents pristine 3D perovskite and L-CFM/P represents pristine 3D perovskite with a 2D perovskite layer. Reproduced with permission from ref. 229.
Copyright 2018, Royal Society of Chemistry. (b) XRR data of pure 2D, 3D, and 2D/3D perovskite films. Reproduced with permission from ref. 233.
Copyright 2019, American Association for the Advancement of Science (AAAS). (c) Schematic illustration of fabricating the 2D/3D heterostructure and the
schematic model of the 2D/3D hierarchical structure. Reproduced with permission from ref. 25. Copyright 2019, American Chemical Society. (d) SEM
images of a pristine 3D perovskite surface (left) and the surface of the wide-bandgap low-D perovskite layer on the pristine perovskite (right); cross-
section HRTEM images of the pristine perovskite (left) and the wide-bandgap low-D perovskite layer on pristine perovskite (right) near the surface. Scale
bars: 1 mm (SEM); 10 nm (HRTEM). Reproduced with permission from ref. 21. Copyright 2019, Nature Publishing Group.

Table 6 Representative 2D perovskites used for interface modification to improve the performance and stability of perovskite solar cells

PCE
Type Perovskite Device structure (%) Stability Year[Ref.]
BAI (Cs0.05(MA0.17FA0.83)0.95- Device A 15.74 86% of PCE after 100 h, 2018226
Pb(I0.83Br0.17)3) 450% RH, darka
PEAI Cs0.1FA0.74MA0.13PbI2.48Br0.39 Device A 20.1 90% of PCE after 800 h, 50 1C, MPPT, 2018229
continuous light soakingb
PEAI Cs0.05(MA0.17FA0.83)0.95- Device A 18.51 90% of PCE after 1000 h, dark, 2018230
Pb(I0.83Br0.17)3 60  10% RHa
F-PEAI Cs0.1(MA0.17FA0.83)Pb(I0.83Br0.17)3 Device A 20.54 99% of PCE after 36 d, dark, 2019231
10–30% RHa
PEAI (FAPbI3)0.85(MAPbBr3)0.15 Device A 24.66 90% of PCE, over 600 h, MPPT, 2019232
continuous light soakinga
F5PEAI Cs0.04FA0.92MA0.04PbI3 Device A 22.16 90% of PCE after 1000 h, 40% RH, MPPT, 2019233
continuous light soakinga
HTAB (FAPbI3)0.95(MAPbBr3)0.05 Device A (changing 23.3 495% of PCE after 1370 h, MPPT, 201921
spiro-OMeTAD to P3HT) continuous light soakingb
CAI MAPbIxCl3x Device B 13.86 54% of PCE after 220 h, dark, 450% RHa 2016234
5-AVA (FAPbI3)0.88(CsPbBr3)0.12 Device A (changing 16.75 98% of PCE after 63 days, dark, 10% RHa 2018236
spiro-OMeTAD to CuSCN)
BABr Cs0.17FA0.83Pb(I0.6Br0.4)3 Device A (changing 19.8 N/A 2019237
c-TiO2/m-TiO2 to SnO2)
A34 Cs0.1FA0.74MA0.13PbI2.48Br0.39 Device A 20.13 N/A 2018239
PEAI–FAI FAPbI3 Device A 21.15 52% of PCE after 60 days, dark, 2019253
mixture 30–40% RHa
C6Br (FAPbI3)0.92(MAPbBr3)0.08 Device A 23.4 85% of PCE after 500 h, MPPT, 2019242
continuous light soakingb
BAI CsPbI2Br Device A (without m-TiO2) 14.5 80% of PCE after 25 days in 10% 2019251
RH and then another 25 days
in 25% RH, darka
a
Device A: FTO/c-TiO2/m-TiO2/PVK/spiro-OMeTAD/Au. Device B: ITO/PEDOT:PSS/PVK/PCBM/rhodamine 101/LiF/Ag. Non-encapsulated devices.
b
Encapsulated devices or non-encapsulated devices in Ar or N2 atmosphere.

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effective charge extraction from the 2D interfacial layer. Along energy offset at the heterojunction may also produce an energy
this direction, Liu et al. conducted a study to deepen the barrier hindering charge transfer across the 2D/3D heterojunc-
understanding of how interface engineering or composition tion. More studies should focus on developing the synthesis
adjustment can affect the 2D and 3D interface in FAPbI3-based control to form a transparent 2D capping layer with controlled
solar cells (Fig. 11c).25 They found that better QW distribution energy levels and/or the layer thickness (i.e., n value) of the 2D
with faster charge-transfer mechanics can improve carrier structures.197,252 Design of new bulky organic cations that
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mobility and charge collection and can reduce recombination. could form stable 2D structures with enhanced plane-to-plane
The 2D/3D film based on PEA : FA (1 : 1) achieves a balance charge transport along with new ways to control the 2D
between charge transport within QWs and passivation at the structure/composition will further advance the performance
2D/3D heterojunction, resulting in an efficiency of 21.15%, and stability of 2D-modified 3D PSCs.106,175
which is significantly higher than that of the 3D counterpart
(19.02%). In addition to the performance improvement, the 4.4. Lead-free 2D perovskites
device also displayed impressive long-term environmental One research topic in the perovskite field is evaluating Pb
stability. A similar effect was also found in the PEAI-treated alternatives so as to reduce the potential toxic impact from
MAPbI3 devices.241 Pb.254–256 For this reason, some researchers have explored
So far, most studies have focused on the structure and quasi-2D perovskites by replacing Pb2+ with Sn2+,257 such as
optoelectronic properties of the 2D perovskite layer. Bawendi PEA2FAn1SnnI3n+1,258 where a 2D/3D (PEA,FA)SnI3 bulk hetero-
et al. recently pointed out that the deposition method is a critical junction structure was shown to exhibit improved device per-
factor for manufacturing high-efficiency 2D/3D PSCs.242 In this formance and stability. In another study, different bulky
study, the precursor and solvent (linear alkylammonium bromide/ cations benzylammonium (BzA+) and histammonium (HA2+)
chloroform) were combined as a selective precursor dissolution were applied to form BzA2Pb1xSnxI4 and HAPb1xSnxI4
strategy to effectively form a transparent 2D perovskite layer onto perovskites.99 The inorganic frameworks of Sn-based 2D per-
the 3D perovskite thin film. This strategy passivated defects, ovskite (n = 1) is less distorted than that of 2D Pb-based
resulting in improved carrier lifetime and Voc. As a result, they perovskites,255 leading to slightly smaller bandgaps (Fig. 12a).
obtained a champion PCE of 23.4% with a certified stabilized PCE Kanatzidis et al. first used triethylphosphine (TEP) as an
of 22.6% based on n-hexylammonium bromide (C6Br). intermediate coordinating ligand to improve film quality of
Treatment of ammonium salt or derivatives to 3D perovskite PEA2MA3Sn4I13 (n = 4, Fig. 12b), resulting in a PCE of 2.53%
films could lead to the formation of an organic cation layer (Table 7).259 By increasing the 2D layer thickness to nine,
rather than a 2D capping layer; these organic cations could also (PEA)2(FA)8Sn9I28 showed much better stability compared to
passivate defects and improve the performance of PSCs. Some 3D FASnI3-based devices.260 Importantly, (PEA)2(FA)8Sn9I28 also
additional candidates include octylammonium iodide (OAI),243 showed much improved Voc (0.59 V) compared to 3D FASnI3,
tetra-ethyl ammonium (TEA),244 mixed hydroiodic acid and leading to an efficiency of 5.94%. The improved Voc in the
oleylamine (OLA-HI),245 MABr/FAI,246 choline iodine (CHI),247 quasi-2D perovskites was attributed to a lower defect density
PEAI,13,248 phenyltrimethylammonium bromide (PTABr),249 associated with suppressed Sn2+ oxidation. By further improv-
and GuaBr.250 The underlying mechanisms are still not known ing the n number, PEA2FA49Sn50I151-based solar cells showed
as to why some cations can form 2D capping layer under 9% efficiency for Sn-based PSCs, which is much better than the
particular process conditions whereas some cannot; however, 6% efficiency for the control device based on 3D FASnI3.261
several reports have clear evidence (2D XRD, GIWAXS, SEM, or Huang et al. first used the mixed bulky organic cations PEA and
HRTEM) to support the formation of a 2D perovskite layer on BA in 2D Sn-based perovskites to control the crystallization
3D perovskite.21,25,226,229,237,242 process.262 Combining BA+ and PEA+ to (BA0.5PEA0.5)2FA3Sn4I13
It is challenging to realize the formation of a 2D capping (n = 4) 2D perovskites effectively suppressed the intermediate
layer for all-inorganic Cs-based perovskites. To address this phase that hinders the uniform nucleation of the perovskite
challenge, Lin et al. demonstrated an in situ growth method to crystals, resulting in improved perovskite morphology and
form 2D/3D heterostructured on inorganic CsPbI2Br perovskite.251 orientation (Fig. 12c) along with a higher PCE of 8.82%.
By adding some DMSO in the alkyl-ammonium halide IPA Sn(II)-Based DJ-type 2D perovskite, (4AMP)(FA)n1SnnI3n+1
solutions to tune the conversion process, they were able to was recently reported by Zhou et al. in solar cells with a
demonstrate a type-II heterojunction between the 2D and 3D performance of over 4%; the unencapsulated device showed
perovskites, which resulted in enhanced hole collection and 9% degradation after 100 h under 1 sun illumination in N2
reduced carrier recombination. As a result, both device perfor- atmosphere at 45 1C (Fig. 12d).263 They further investigated a
mance and stability against humid environment were improved series of DJ-type 2D Pb-free perovskites of (diammonium)-
compared to the control device without the 2D perovskite surface (FA)n1SnnX3n+1 (n = 1–4) with the target to overcome the charge-
treatment. transport limitation.264 The diammonium candidates include
Thus, forming a 2D capping layer or just an organic cation anthra[2,3-b:7,8-b0 ]bis(5-thiopheneylmethanammonium) (ATMA),
layer can passivate surface defects (and possibly bulk defects); 2,10-hexacenediyldimethanammonium (HMA), 2,9-pentacene-
but it also can form a heterojunction to decrease nonradiative diyldimethanammonium (PMA), 2,8-tetracenediyldimethan-
recombination and enhance charge-carrier separation. The ammonium (TMA), or 2,6-anthracenediyldimethanammonium

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Fig. 12 (a) Structure of (HA)SnI4 (left) and (BZA)2SnI4 (right). Reproduced with permission from ref. 99. Copyright 2017, American Chemical Society.
(b) SEM images (top: surface view; bottom: cross-section view) of PEA2MA3Sn4I13 films without (left) and with (right) TEP additive. Reproduced with
permission from ref. 259. Copyright 2017, American Chemical Society. (c) An illustration of the crystal-growth process in Sn-based 2D perovskites of BA
and/or PEA. Reproduced with permission from ref. 262. Copyright 2019, American Chemical Society. (d) Energy-level diagram, J–V curves, and stability
for hole transport layer (HTL)-free PSCs based on (4AMP)(FA)3Sn4I13 (n = 4). Reproduced with permission from ref. 263. Copyright 2019, American
Chemical Society.

Table 7 Representative Pb-free 2D perovskites absorbers used for Pb-free PSCs

Perovskite Device structure PCE (%) Stability Year[Ref.]

Bn2SnI4 (n = 1) FTO/c-TiO2/m-TiO2/PVK/Au 2.35 N/A 2019257
a
PEA2MA3Sn4I13 (n = 4) FTO/c-TiO2/PVK/PTAA/Au 2.53 90% of PCE after 1 month, dark 2017259
(PEA)2(FA)8Sn9I28 (n = 9) ITO/NiOx/PVK/PCBM/Al 5.94 96% of PCE after 100 h, darka 2017260
PEA2FA49Sn50I151 (n = 50) ITO/PEDOT:PSS/PVK/PCBM/BCP/Al 9.0 59% of PCE after 76 h, dark, 20% RHb 2018261
(BA0.5PEA0.5)2FA3Sn4I13 (n = 4) ITO/PEDOT:PSS/PVK/C60/LiF/Al 8.82 59% of PCE after 8 days, darka 2019262
(4AMP)(FA)3Sn4I13 (n = 4) FTO/TiO2/ZrO2/PVK/C 4.22 91% of PCE after 100 h, continuous light soaking 45 1Ca 2019263
a b
Encapsulated devices or non-encapsulated devices in Ar or N2 atmosphere. Non-encapsulated devices in air.

(AMA). Through DFT calculation, three compounds— precise tuning of their broadband emission, spin lifetime/
(TMA)(FA)3Sn4I13, (PMA)(FA)3Sn4I13, and (ATMA)(FA)3Sn4I13—were population, magnetic ordering, along with associated optical,
identified to have a type-II band alignment (staggered bandgap) electrical, and magnetic properties. Below we summarize some
and fast charge transport. of the pioneering work of using hybrid 2D perovskites for
optoelectronic applications beyond solar cells, including LEDs,
spintronics-devices, and photodetectors.
5. Application beyond solar cells 5.1. Light-emitting diodes
In addition to solar cell applications, the excitonic character Two-dimensional metal halide perovskites have emerged as a
and versatile structure in the hybrid 2D perovskites also opens promising candidate for high-performance light-emitting
the door to other optoelectronic applications. For instance, diodes (LEDs) in the past few years. The superior properties
the excitonic effect in low-n 2D perovskites can significantly of 2D layered perovskites as electroluminescent materials,
promote radiative recombination, which leads to higher when compared to their 3D counterparts, can be summarized
PLQY in perovskite-based LED devices, making them excellent as follows.
candidates for high-efficiency LEDs. The structural versatility (1) 2D perovskites generally possess much larger exciton
(i.e. organic or inorganic component, dimensionality, crystal- binding energies (hundreds of meV)265,266 due to dielectric
line phase, impurity doping), if engineered properly, can allow and quantum confinement of the layered structure, which

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leads to an enhanced radiative recombination and thus emitting at 410 nm with a low external quantum efficiency
higher PLQY. (EQE) of 0.04% at 6 V at room temperature.276 In 2018, Sargent
(2) The formation of cascaded energy structures within 2D and co-workers systematically investigated the relationship
perovskite films with mixed n (layer thickness) can promote rapid between PLQY and electron–phonon interaction by preparing
and efficient energy transfer from lower-n quantum wells to high-quality n = 1 2D perovskite single crystals.277 Through
higher-n quantum wells (in sub-ns), leading to a reduced exciton tuning the molecular structures of organic ammonium cations,
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quenching effect and enhanced radiative recombination. they were able to control crystal rigidity and electron–phonon
(3) The incorporation of hydrophobic organic ligands and interactions, which leads to modulation of their PLQY. Their
the enhanced van der Waals interactions between the organic results showed that the greater the structure rigidity is, the
molecules result in a significantly enhanced ambient and brightest the emitter. Their optimized structure with PhC2
thermal stability compared to 3D perovskites with no such crystals, namely PEA2PbBr4, displayed a PLQY of 79%, although
hydrophobic molecules. LED devices based on this formula were not fabricated. To
(4) The rich chemical tunability of 2D perovskites, including address the challenges associated with strong electron–phonon
both organic and inorganic subcomponents, enables unprecedented interaction in n = 1 2D perovskites, the field has shifted focus to
opportunities to tune their optical and electrical properties for a using quasi-2D (1 o n o N) layered perovskites as electro-
much broader range of applications such as broadband emission, luminescent layers.
circular-polarized emission, and detection. 5.1.2. LEDs based on quasi-2D layered perovskites. In
Here, we summarize recent progress in LEDs based on 2D 2016, several breakthroughs were reported showing that
layered perovskites (single-layer vs. quasi-2D and RP vs. DJ), electroluminescent layers based on quasi-2D perovskites can
excluding 3D ABX3-type perovskite thin films, 2D nanoplatelets/ display better performance than even their 3D counterparts
nanosheets, or quantum dots, which can be found (Table 8). In the PEA2(MA)n1PbnBr3n+1 (n = 1–4) system, Lee
elsewhere.17,267–272 et al. demonstrated that the quasi-2D perovskites displayed a
5.1.1. LEDs based on single-layer n = 1 2D perovskites. The much higher current efficiency and luminance than 3D
usage of RP-type 2D perovskites as electroluminescent layers MAPbBr3 and 2D n = 1 PEA2PbBr4.278 By tuning the ratio of
within an LED can be traced back to Nurmikko’s273 and MAPbBr3 and PEA2PbBr4, they were able to achieve a high
Saito’s274 work in the 1990s, where the optical properties of current efficiency of 4.90 cd A1 and a luminance of 2935 cd
single-layered (n = 1) PEA2PbI4 were investigated and LED m2. The iodide-based analogue PEA2(MA)n1PbnI3n+1 (n = 5)
devices fabricated. However, they found that a very high has been demonstrated by Sargent and co-workers to outper-
(B24 V) turn-on voltage was needed, and the electrolumines- form 3D MAPbI3 (n = N) for near-infrared emission, with an
cence efficiency and quantum yield was minimal at room EQE of 8.8% and a radiance of 80 W sr1 m2.61 They further
temperature.274 It still remains difficult to fabricate high- ascribed the superior performance to a cascading energy trans-
efficiency LEDs based on n = 1 2D perovskites, even though fer that funnels photoexcitations to the lowest-bandgap phase
they intrinsically possess a higher exciton binding energy. The within mixed quasi-2D perovskite thin film (Fig. 13a). Soon
poor performance is ascribed to poor out-of-plane (layer-to- after that report, Huang and co-workers demonstrated quasi-2D
layer) charge transport at low voltages due to the insulating perovskite LEDs based on (NMA)2(FAPbI3)n1PbnI3n+1 with a
organic ligands and fast nonradiative exciton quenching at recorded EQE of 11.7% and radiance of 82 W sr1 m2.279
room temperature due to powerful exciton–phonon coupling Similarly, they also attributed the superior device performance
within the layers. The poor charge transport within the n = 1 2D to the funneling mechanism, which occurs within sub-ns time-
system results in a high voltage to turn on the electrolumines- scales and outcompetes nonradiative exciton quenching and
cence. The electron–phonon interactions, both for acoustic and increases radiative recombination (Fig. 13b and c). By embed-
optical phonons, is found to be orders of magnitude higher ding the quasi-2D perovskites into a high-bandgap polymer
than found in GaAs quantum wells, leading to low PLQY at forming a bulk heterojunction, Di and co-workers reported
room temperature.275 For these reasons, there has been rather LEDs with a record EQE of 20.1%.280 The polymer component
slow progress in LEDs based on n = 1 2D perovskite active layers is stated to significantly suppress the bulk and interfacial non-
over the last few decades. In 2016, Jin et al. used 2D layered radiative relaxation process. The same energy-funnel concept is
PEA2PbBr4 nanoplates and fabricated color-pure violet LEDs also applied within the bromide system,281 PEA2(MA)n1PbnBr3n+1,

Table 8 Summary of representative highly efficient 2D and quasi-2D perovskite LEDs

Perovskite composition Wavelength (nm) EQE (%) CE (cd A1) Lmax (cd m2) Radiance (W sr1 m2) Year[Ref.]
PEA2PbBr4 410 0.04 — — — 2016276
PEA2(MA)n1PbnBr3n+1 526 7.4 4.9 8400 — 2017281
PEA2(MA)n1PbnI3n+1 B760 8.8 — — 80 201661
(NMA)2(FAPbI3)n1PbnI3n+1 763 11.7 — — 82 2016279
(NMA)2(FAPbI3)n1PbnI3n+1/poly-HEMA 795 20.1 — — — 2018280
PEA2(FAPbBr3)2PbBr4 532 14.36 62.43 9120 — 2018283
(BAB)FAn1PbnX3n+1 776 4.2 — — 88.5 2019284

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Fig. 13 (a) Electronic band structure of ITO, TiO2, F8, MoO3, Au electrode, and quasi-2D perovskites with different layer thicknesses (n numbers).
Reproduced with permission from ref. 61. Copyright 2016, Nature Publishing Group. (b) Schematic illustration of cascade energy transfer in quasi-2D
perovskite thin films. Reproduced with permission from ref. 279. Copyright 2016, Nature Publishing Group. (c) EQE and energy conversion efficiency as a
function of current density for the NFPI6B and NFPI quasi-2D perovskite LEDs. Reproduced with permission from ref. 279. Copyright 2016, Nature
Publishing Group. (d) Operational lifetimes of DJ and RP structure perovskite-based LEDs. Reproduced with permission from ref. 284. Copyright 2019,
American Association for the Advancement of Science.

showing an EQE of 7.4% and luminescence of 8400 cd m2 for mixed-phase quasi-2D perovskite can promote efficient energy
green LEDs. By mixing PEA with IPA (iso-propylammonium), funneling from lower n to higher n, growing phase-pure 2D
Sargent and co-workers showed that the mixed cation can desta- perovskite is also an important route for improving device
bilize n = 1 phase, and lead to the formation of only quasi-2D stability. Very recently, the stability of LED-based on quasi-2D
perovskites with n = 2, 3, and 4 phases.282 Their perovskite films perovskites has been dramatically improved by using the DJ
showed a record PLQY of 88% at 477 nm. The corresponding rather than RP structure. Ning and co-workers demonstrated
LEDs device displayed stable sky-blue emission with a maximum that LEDs based on the DJ quasi-2D perovskites ((BAB)-
luminance of 2480 cd m2 achieved at 490 nm. You and FAn1PbnX3n+1 (BAB: 1,4-bis(aminomethyl)benzene; X: Br, I))
co-workers reported other green LEDs based on PEA2(FAPbBr3)2- exhibit a T50 of over 100 hours, which is nearly two orders of
PbBr4 (n = 3).283 With optimized phase engineering and surface magnitude longer compared to LEDs based on RP quasi-2D
passivation, they achieved a current efficiency of 62.4 cd A1 and perovskite systems (Fig. 13d).284 Their optimized LEDs exhibit
EQE of 14. 36%. The mixture of different phases (different layer an EQE of 5.2% with a maximum radiance of 88.5 W sr1 m2.
thicknesses or n numbers) does not seem to be detrimental to Therefore, it is clear that a balance of LED device efficiency
LED performance; however, careful phase engineering to favor and stability requires careful optimization of organic ligands,
directional energy funneling is extremely important, and an crystallographic structure, phase engineering, and crystalline
ongoing challenge, for LEDs based on quasi-2D perovskites. orientation of quasi-2D perovskites.
In addition to the superior LED performance when 5.1.3. Broadband emission in 2D perovskites. Another
compared to 3D perovskites, quasi-2D perovskite also exhibit interesting optical property of 2D perovskites, in addition
improved stability. Huang and co-workers demonstrated a T50 to their excitonic emission, is broadband emission enabled
(the amount of time for the EQE to drop to half its initial value) by the rich chemical tunability in 2D metal halide perovskites.
of 2 h under a constant current density of 10 mA cm2, which is If the broadband emission covers the visible spectrum,
two orders of magnitude better than that based on 3D perovs- then the emitters can be used as single-source white-light
kites (T50 = 1 min).279 Recently, using phase-pure RP-type 2D emitters at a high quantum efficiency to produce great
perovskites based on BA2(MA)n1PbnI3n+1, Kanatzidis, Mohite, energy-efficiency compared to current mixed phosphor based
and co-workers achieved efficient electroluminescence with technology. The development of metal halide perovskites as
a radiance of 35 W sr1 m2 at 744 nm and a significantly single-source white-light emitters is a young, yet-emerging
enhanced stability (T50 4 14 h) compared to quasi-2D or 3D field. In 2014, seminal work from Karunadasa and co-workers
perovskite systems.285 Their results suggest that although demonstrated bright broadband visible emission in 2D perovskite

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Table 9 Summary of representative broadband-emitting 2D perovskites

Perovskite composition PLQY (%) CRI CIE (x, y) Year[Ref.]

(EDBE)PbBr4 9 84 (0.39, 0.42) 2014132
(EDBE)PbCl4 2 81 (0.33, 0.39) 2014132
(N-MEDA)PbBr4 0.5 82 (0.36, 0.41) 2014128
(N-MEDA)PbBr3.5Cl0.5 — 85 (0.31, 0.36) 2014128
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a-(DMEN)PbBr4 — 73 (0.28, 0.36) 2017129

(AEA)PbBr4 — 87 (0.29, 0.34) 2017122
(CyBMA)PbBr4 1.5 — (0.23, 0.29) 2017287
(EA)4Pb3Br0.5Cl9.5 — 83 (0.30, 0.35) 201776
PEA2PbI4:Sn (0.36%) 6.0 — — 2019289
PEA2PbI4:Sn (1%) 23 — — 2020292

which displays a PLQY of 9% with a CRI of 84. In 2017, Kanatzidis

and co-workers reported another white-light-emitting (110)
perovskite, namely a-(DMEN)PbBr4, which emits cold white light
with a CRI of 73.129 The first example of a (001) white-light-
emitting perovskite is (EDBE)PbCl4, which emits cold white light
with a CRI of 81 and a PQLY of 2%. Subsequently, other (001)
white-light-emitting perovskites have been reported including
(C6H11NH3)2PbBr4,286 (H3NC6H4(CH2)2NH3)PbBr4 or (AEA)-
PbBr4,122 (CyBMA)PbBr4 (CyBMA: cis-1,3-bis(ammoniomethyl)-
cyclohexane),287 and (EA)4Pb3BrxCl10x (EA: CH3CH2NH3+).76
However, the demonstrated 2D perovskite compounds are still
quite limited and the PLQYs observed to date remain low. An
improved atomistic understanding is needed to elucidate the
underlying mechanism and origin of the bright broadband
emission of these materials to enable higher PLQY.
Although some research groups attributed the broadband
Fig. 14 (a) Crystal structure of the (110) 2D (EDBE)PbBr4 perovskite and its emission to crystal defects that serve as the broadband color
PL emission. Inset shows the crystal photographs. Reproduced with centers,290,291 the mechanism of the broadband emission in
permission from ref. 132. Copyright 2014, American Chemical Society. these 2D perovskite systems is generally believed to be exciton
(b) Nuclear coordinate diagram for exciton self-trapping and detrapping
self-trapping (Fig. 14b), where photoexcitation induces an
process in 2D perovskites. Reproduced with permission from ref. 289.
Copyright 2019, Wiley-VCH. (c) Schematic illustration of the three for- excited-state lattice distortion mediated through the strong
mation mechanisms of self-trap excitons: intrinsic, defect, and extrinsic. electron–lattice coupling.122,288 Ultrafast pump–probe spectro-
Reproduced with permission from ref. 288. Copyright 2018, American scopy results suggest that the photogenerated excitons self-trap
Chemical Society. (d) Schematic illustration of dopant-induced extrinsic in sub-ps (B400 fs), which is followed by luminescence,
self-trap exciton and PL spectra of PEA2PbI4, PEA2SnI4, and PEA2PbI4:Sn
and the lattice distortion leads to homogeneous emission
(0.36%). Reproduced with permission from ref. 122. Copyright 2017, Royal
Society of Chemistry. broadening.64 The presence of multiple self-trapped exciton
states can further broaden the emission inhomogeneously.
Additionally, reducing the temperature generally leads to
(EDBE)PbX4 (Fig. 14a)132 and (N-MEDA)PbBr4xClx,128 (N-MEDA: an enhanced broadband emission compared to free-exciton
N1-methylethane-1,2-diammonium; EDBE: 2,2-(ethylenedioxy) emission. This temperature-dependent emission property can
bis(ethylammonium); X: Cl, Br). Since those results, several be understood by the thermodynamics of the self-trapping
white-light-emitting 2D perovskites have been developed as and de-trapping processes (Fig. 14b),122 where the higher tem-
single-source white-light phosphors (Table 9). From the stand- perature provides enough activation energy to de-trap back to the
point of crystal structures, strong white-light emission has been free-exciton state from self-trapped exciton (kBT 4 Ea,detrap),
discovered in both corrugated (110) and (001) Pb–Br and Pb–Cl thereby reducing the broadband emission and increasing the
perovskite-based layered systems. The reported 2D (110) free-exciton emission. Therefore, although only a few 2D perovs-
layered perovskites that exhibit broadband emission are kites have been reported as white-light emitters, broadband
(N-MEDA)PbBr4xClx, (N-MEDA)PbBr4, and a-(DMEN)PbBr4129 emission in perovskites, in theory, can be generalized if
(a-DMEN: N1,N1-dimethylethane-1,2-diammonium). For instance, the thermodynamic activation energies of self-trapping and
by tuning the halide composition in (110) (N-MEDA)PbBr4xClx, de-trapping process are optimized at specific temperatures.
Karunadasa128 and co-workers were able to improve the emis- Thus far, most reported broadband-emitting 2D perovskites
sion’s color-rendering index (CRI) from 82 to 85, yet the PLQY was have been discovered with the special design of organic amines,
only 0.5–1.5%. The PLQY was subsequently improved with their where the broadband emission is ascribed to the intrinsic self-
second white-light-emitting (110) perovskite (EDBE)PbBr4,132 trapped excitons (Fig. 14c). More recently, Chen and co-workers

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demonstrated that impurity Sn dopants can trigger extrinsic excitons with Jahn–Teller-like octahedral distortions can lead
self-trapping of excitons in PEA2PbI4, giving broadband red-to- to the observed broadband emission.293
near-infrared emission at room temperature (Fig. 14d).289 A
similar observation has recently been reported by Mitzi and 5.2. Spintronic application
co-workers, which suggests that metal impurities, even at trace Because of strong spin–orbital coupling (SOC) associated with
levels, should be considered more carefully when preparing heavy elements (e.g., Pb and I), hybrid metal halide perovskites
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these crystals and films, as they could have a fundamental are considered attractive candidates for spintronics and spin
impact on their optical and electronic properties.292 This optoelectronics. In conjunction with inversion asymmetry, SOC
introduces a new strategy—namely, dopant-induced extrinsic in perovskites further leads to an effective magnetic field that
exciton self-trapping approach (Fig. 14c)—to the development lifts the degeneracy of the carrier spin states within the
of broadband-emitting perovskites. However, this field is still in conduction and/or valence bands, which is often referred to
its infancy, and more materials need to be investigated. A as the Rashba effect.294 The spin-degenerate parabolic band is
generalized theory and a mechanism of broadband emission, now split into two spin-polarized bands, and the new parabolic
across different hybrid material systems, are very much needed bands can be described by E  (k) = (h 2k2/2m*)  aR|k|, where aR
for discovering next-generation white-light phosphors. For is the Rashba splitting parameter (Fig. 15a). Thus far, spin-
instance, the community is still searching for a simple and optoelectronic devices based on 3D perovskites have been
general correlation between broadband emission and structure investigated both theoretically and experimentally,40,295–297
dimensionality, crystal distortions (e.g., in-plane and out-of- although the relative role of bulk and surface Rashba contribu-
plane octahedral distortion), and impurity dopants. Karunadasa tions is still under debate.298,299 This is because crystal struc-
and co-workers have shown an interesting linear correlation tures of perovskite in bulk (i.e., tetragonal or orthorhombic)
between the most considerable measured out-of-plane distortion present inversion symmetry, where the Rashba effect should be
Dout (1801  yout) and the ratio of broadband emission vs. forbidden. As such, it is proposed that the Rashba effect is a
excitonic emission at a given temperature, after rigorously test- surface effect due to a structural distortion at the surface; but it
ing over 50 other structural parameters.122 DFT calculations by is likely that surface reconstruction penetrates several hundred
Yan and co-workers revealed that a low electronic dimension- nanometers towards the bulk interior. In many cases, large
ality, rather than the structural dimensionality, is a prerequisite Rashba splitting has been experimentally observed (by angle-
for forming broadband emission, and only the self-trapped resolved photoelectron spectroscopy (ARPES),300 for instance),

Fig. 15 (a) Schematic illustration of Rashba splitting that generates two parabolic branches with opposite spin orientations. Reproduced with permission
from ref. 306. Copyright 2017, American Association for the Advancement of Science. (b) Photomodulation spectrum of PEA2PbI4 film (excited at 2.8 eV)
compared to that of a silicon wafer. Reproduced with permission from ref. 306. Copyright 2017, American Association for the Advancement of Science.
(c) Illustration of spin dynamics measurements. (d) Spin coherent lifetime in excited states for n = 1–4 and 3D MAPbI3 single crystals. (c) and (d) are
reproduced with permission from ref. 309. Copyright 2018, American Chemical Society.

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suggesting they could be promising candidates for spintronic Their result opens up new avenues for using these 2D perovskites
applications. Reduced dimensionality, namely from 3D perovskite for opto-spin logic applications. In the quasi-2D perovskite
to 2D perovskite, can further reduce the symmetry, resulting in an systems, the same group recently demonstrated that the ultrafast
enhanced Rashba effect. This is similar to many aspects of 2D energy funneling from low-n to high-n perovskites, as shown in
heterostructures in traditional semiconductors where the Rashba LEDs, also preserves their spin information, thus achieving spin
effect is often observed.301 Additionally, the rich chemical funneling in the quasi-2D perovskite films with thickness up to
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tunability of 2D perovskites—including controllable distortions 600 nm.311 Using 2D perovskites for (optical) spin manipulation is
of the inorganic framework, inorganic layer thickness, and an intriguing and exciting research direction; however, the spin
organic components—makes 2D perovskites an exciting platform lifetime of these systems are generally very short at high tempera-
to investigate their structure–Rashba-effect relationships; it also ture. Future research should focus on (1) understanding the
brings new opportunities for spintronic applications. Here we structure–Rashba-effect and structure–spin-lifetime correlation,
summarized recent advances in spintronic devices based on 2D and (2) demonstrating other spintronic devices, such as spin
hybrid perovskites, neglecting those based on 3D perovskites light-emitting diodes and spin valves.
which can be found in other literature reports.295,297,302–305 5.2.2. Chiral 2D layered perovskite systems. The chemical
5.2.1. Rashba splitting in 2D perovskite. Based on the tunability of 2D perovskites also offers a unique opportunity to
electroabsorption and photoinduced absorption spectra, directly incorporate chiral organic molecules in between the
Vardeny and co-workers reported a giant Rashba splitting in inorganic layers, introducing chirality into the hybrid frame-
2D n = 1 PEA2PbI4, with Rashba energy of (40  5) meV and work. Understanding how chirality can affect the Rashba effect,
Rashba parameter of (1.6  0.1) eV (Fig. 15b).306 Further DFT and how their synergetic effects can provide spin-control within
calculations showed that the Rashba splitting originates from this hybrid layered system, may bring new opportunities for
the broken inversion symmetry due to Pb atom displacement spintronic applications. In 2018, Sargent and co-workers
from the octahedral center. This resulted in the Rashba band reported 3% spin-polarized photoluminescence at zero
splitting in the plane perpendicular to the 2D barriers. How- magnetic fields at 2 K in 2D Pb–Br perovskite multilayers that
ever, a subsequent report from Mohammed and co-workers incorporated chiral organic molecules, suggesting that the spin
using both DFT calculations and time-resolved PL argued that degree of freedom of hybrid perovskites can be controlled by
intrinsic, large Rashba splitting only occurs in the 2D perov- the chirality of the incorporated organic cations.312 This is
skite crystals with even number of inorganic layers, namely subsequently confirmed by Li and co-workers, who reported
PEA2MAPb2I7 (n = 2), but not in the n = 1 or n = 3 crystals.307 an average degree of circularly polarized photoluminescence
Their results highlight the importance of the layer thickness in (CPL) of 9.6% and 10.1% at 77 K for (R-MBA)2PbI4 and
2D perovskites for Rashba splitting. The presence of Rashba (S-MBA)2PbI4 (MBA: C6H5CH(CH3)NH3), respectively.313 How-
splitting in 2D BA2MAPb2I7 (n = 2) was also recently confirmed ever, it should be noted that the demonstrated spin-polarized
by Hall and co-workers, in which time-resolved circular dichroism photoluminescence is likely intrinsically limited because the PL
techniques were used to probe the carrier spin-relaxation emission of n = 1 2D chiral perovskite is rather weak. As such,
dynamics.308 Their simulations of the measured spin dynamics more direct spin manipulation and associated demonstration
show a Rashba spin splitting of 10 meV at an electron energy of in a spintronic device based on chiral perovskites should be
50 meV above the bandgap. Also, a 2018 report measured the both intriguing and insightful.
spin-relaxation dynamics to ‘‘indirectly’’ probe the Rashba In a recent study, Lu et al. demonstrated that a polarized
effects in 2D perovskite systems.309 In this study, Beard and spin-transport through 2D chiral hybrid perovskites can be effec-
co-workers used a circularly polarized pump–probe method tively manipulated depending on the handedness of the organic
(Fig. 15c) to study the spin-coherence dynamics in 2D perovs- molecules, which occurs via the chiral-induced spin selectivity
kite single crystals with different layer thicknesses (n = 1–4, N). (CISS) mechanism (Fig. 16).314 Magnetic conductive probe AFM
They found that the spin-coherence lifetime increases with studies showed the highest spin-polarization transport of up to
increasing layer thickness from n = 1 to n = 4, followed by a 86%, which is much larger than previously reported in chiral self-
decrease from n = 4 to N (Fig. 15d). These results were assembled monolayer systems (typically in the range of 30% to
attributed to two counteracting contributions: (1) Rashba split- 50%315–317), as carriers transfer through multiple chiral layers
ting increases the spin-coherence lifetime from the n = N to the undergoing a spin-polarized tunneling process. Magnetoresistance
layered systems; and (2) phonon scattering, which increases for measurements in spintronics devices further confirm the spin-
smaller n values, decreases the spin-coherence lifetime due to filtering effect enabled by the chiral organic layers, forming half
spin–lattice relaxation. They proposed that the Elliot–Yafet (EY) spin-valve devices based on a single ferromagnetic electrode. The
mechanism is the main cause for spin depolarization. successful demonstration of the CISS effect in these 2D chiral
Using 2D perovskites to manipulate spin polarization has also perovskite films opens the door for future spintronic applications
been demonstrated recently. In the (F-PEA)2PbI4 thin film, Sum based on chiral hybrid materials.
and co-workers demonstrated a room-temperature spin-selective
optical Stark effect (OSE).310 They found that the exciton spin 5.3. Photodetector
states can be selectively tuned by B6.3 meV using circularly Compared to 3D perovskites, which have drawn extensive
polarized optical pulses without any external photonic cavity. attention for next-generation photodetectors,318–321 the

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6. Conclusion and outlook

Since the first application of 2D perovskite absorbers in solar
cells in 2014, the best PCE of 2D PSCs has improved to B19%
to date. This points out the promise of using or incorporating
2D perovskites for solar cells. In addition, 2D perovskites also
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display tremendous potential in LED, broadband emission,

spintronic, and photodetector applications, and they serve as
a prototype system to understand many fundamental struc-
ture–property relationships including spin–orbital coupling,
Rashba effect, exciton–phonon coupling, and light–matter
interactions. To further advance or explore the unique char-
acteristics of 2D perovskites for all these applications, more
efforts are required to focus on materials design, growth
controls, and the fundamental physical and chemical proper-
ties of 2D organic–inorganic hybrid halide perovskites. Below
we discuss key scientific challenges as well as our perspective
Fig. 16 Schematic illustration of magnetic conductive probe AFM mea- on future research directions for 2D perovskites.
surements (a) and chirality dependence in out-of-plane charge transport
(b–d). Reproduced with permission from ref. 314. Copyright 2019,
American Association for the Advancement of Science. 6.1. Phase purity of 2D perovskite thin films
The as-prepared 2D films almost always contain different n
values, which presents a challenge to enabling different appli-
development of 2D perovskites for photodetectors is still in its cations, but also complicates the scientific understanding of
infancy. Due to the poorly controlled crystalline orientation, various physical and chemical properties of 2D perovskite
phases, and anisotropic transport properties in microcrystal- structures, which, in turn, presents another challenge for
line films, 2D perovskite-based photodetectors usually require tailoring materials design. Thus, it is necessary to develop
the use of single crystals; however, the growth of large-area, synthetic tools and controls to obtain pure-phase 2D perovskite
high-quality, shape-controlled 2D perovskite single crystals structures. Similarly, continued efforts on developing strategies
remains a significant challenge. As such, advances in 2D to manipulate the growth orientation of 2D perovskite to either
perovskite-based photodetectors is strongly tied to the growth use or avoid the limitation of the anisotropic properties of 2D
of 2D perovskite single crystals.322 Thus far, surface-tension- structures is crucial for the future development of this field.
driven crystal growth has been shown to be the most effective
approach to grow photodetector-quality 2D perovskite single 6.2. Anisotropic charge transport in 2D perovskites
crystals. In 2018, Priya and co-workers reported the growth of
The vastly different charge-transport properties along the out-
quasi-2D perovskite single-crystal membranes based on the
of-plane and in-plane directions for 2D perovskites will remain
surface-tension effect, where the growth rate of the precursor
an active area of research for various optoelectronic applica-
molecules at the water/air interface is much higher than those
tions. In addition, mixed bulky cations for 2D perovskite also
in bulk solution.248 Their photodetector based on the BA2PbI4
shows promising results that should be pursued.324,325 Accu-
(n = 1) shows a shallow dark current (1013 A), higher on/off
rate description of the crystal structure of 2D perovskites is
ratio (B104), and faster response time compared to those with
essential for revealing the role of bulky cations in perovskite
higher n numbers. More recently, Liu and co-workers coupled
formation and charge transport. In addition, a molecular
the inverse temperature crystallization method with surface-
library should be established by investigating the effect of
tension control to achieve preferential crystallization of 2D
different molecular lengths, conjugated groups, functional
perovskite single crystals at the solution/air interfaces.323 Using
units, and the substituent groups on the charge-transfer capa-
this method, they were able to obtain high-quality, 36 mm-sized
city and other properties.
2D PEA2PbI4 single crystals with a high aspect ratio. Photo-
detector devices based on different crystal facets, namely (001)
and (010), show very different properties. The photodetectors 6.3. Quantum efficiency and stability
based on the (010) planes show much less photo-response than PLQY is a key parameter for characterizing the emission proper-
those based on the (001) planes. Based on the (001) plane, the ties of 2D perovskites. At present, the PLQY for 2D structures
photodetectors display responsivity as high as 139.6 A W1, remains low at room temperature because of the fast non-
EQE of 37719.6%, detectivity of 1.89  1015 Jones, and response radiative exciton quenching due to the strong exciton–lattice
speed as fast as trise = 21 ms and tdecay = 37 ms. Their photo- coupling. Strategies in both molecular design and device engi-
detector performance based on 2D PEA2PbI4 single crystals is so neering need to be explored to inhibit the nonradiative recom-
far among the highest reported for all perovskite planar bination in these systems. Meanwhile, a balance between
photodetectors. quantum efficiency and stability need to be considered.

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6.4. Fundamental structure–property relationships support of PV applications of 2D perovskites from the

Given all the observed interesting optical, electronic, and spin De-risking Halide Perovskite Solar Cells program, funded by
properties in 2D perovskites, little is known about the struc- the U.S. Department of Energy, Office of Energy Efficiency and
tural origin of these properties at the atomic level. In particular, Renewable Energy, Solar Energy Technologies Office. The views
general correlations between the crystallographic structural expressed in the article do not necessarily represent the views of
the DOE or the U.S. Government. The U.S. Government retains
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characters (e.g., dimensionality, distortions, impurity dopants)

and broadband emission, Rashba effect, spin coherent lifetime, and the publisher, by accepting the article for publication,
and spin polarization still need to be rigorously tested and acknowledges that the U.S. Government retains a nonexclusive,
established. The challenge here stems not only from the paid-up, irrevocable, worldwide license to publish or reproduce
difficulties associated with the synthetic output, but also on the published form of this work or allow others to do so, for
developing direct, unambiguous characterization methods and U.S. Government purposes.
theory to probe the optical, electronic, and spin properties.
Understanding these key structure–property relationships can
further provide synthetic guidance for the next-generation References
hybrid materials for targeted optoelectronic applications. This
is a new, exciting area where synthetic, spectroscopic, and 1 M. Grätzel, Acc. Chem. Res., 2017, 50, 487–491.
computational tools will be heavily involved, and it provides a 2 J.-P. Correa-Baena, M. Saliba, T. Buonassisi, M. Grätzel,
tremendous playground and opportunities for chemists, physicists, A. Abate, W. Tress and A. Hagfeldt, Science, 2017, 358,
and engineers to unveil the mystery of hybrid materials. 739–744.
Finally, it is worth emphasizing that for solar cell applica- 3 Best Research-Cell Efficiency Chart, National Renewable
tions even if 2D perovskites may not be used as the primary Energy Laboratory, https://www.nrel.gov/pv/cell-efficiency.
light absorber, these low-dimensional materials can still play html, Augest, 2019.
important roles to improve the conventional 3D perovskite 4 Y. Rong, Y. Hu, A. Mei, H. Tan, M. I. Saidaminov, S. I. Seok,
based photovoltaic devices. More research efforts will likely M. D. McGehee, E. H. Sargent and H. Han, Science, 2018,
focus on 2D/3D mixed perovskites, where 2D perovskite can 361, eaat8235.
serve as a passivating agent or capping layer for improving the 5 D. Weber, Z. Naturforsch. B, 1978, 33, 1443.
stability and efficiency of devices. At present, as many of these 6 D. Weber, Z. Naturforsch. B, 1979, 34, 939.
behaviors in these 2D systems have not yet been clearly defined, 7 D. B. Mitzi, C. A. Feild, W. T. A. Harrison and A. M. Guloy,
developing tools to identify/control/study the materials and Nature, 1994, 369, 467–469.
their properties represents a pressing need for the field. More 8 D. B. Mitzi, S. Wang, C. A. Feild, C. A. Chess and
studies should focus on developing the synthetic control to A. M. Guloy, Science, 1995, 267, 1473–1476.
form a transparent 2D capping layer with controlled energy 9 A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, J. Am.
levels and/or the layer thickness (i.e., n value) of the 2D Chem. Soc., 2009, 131, 6050–6051.
structures. Design of new bulky organic cations that could 10 H.-S. Kim, C.-R. Lee, J.-H. Im, K.-B. Lee, T. Moehl,
form stable 2D structures with enhanced plane-to-plane charge A. Marchioro, S.-J. Moon, R. Humphry-Baker, J.-H. Yum,
transport along with new ways to control the 2D structure/ J. E. Moser, M. Grätzel and N.-G. Park, Sci. Rep., 2012,
composition will further advance the performance and stability 2, 591.
of 2D/3D PSCs.106,175 11 M. M. Lee, J. Teuscher, T. Miyasaka, T. N. Murakami and
H. J. Snaith, Science, 2012, 338, 643–647.
12 D. Bi, C. Yi, J. Luo, J.-D. Décoppet, F. Zhang,
Conflicts of interest S. M. Zakeeruddin, X. Li, A. Hagfeldt and M. Grätzel, Nat.
Energy, 2016, 1, 16142.
There are no conflicts to declare. 13 Q. Jiang, Y. Zhao, X. Zhang, X. Yang, Y. Chen, Z. Chu,
Q. Ye, X. Li, Z. Yin and J. You, Nat. Photonics, 2019, 13,
Acknowledgements 460–466.
14 N. J. Jeon, H. Na, E. H. Jung, T.-Y. Yang, Y. G. Lee, G. Kim,
The work was supported by the U.S. Department of Energy H.-W. Shin, S. Il Seok, J. Lee and J. Seo, Nat. Energy, 2018, 3,
under Contract No. DE-AC36-08GO28308 with Alliance for 682–689.
Sustainable Energy, Limited Liability Company (LLC), the 15 W. S. Yang, B.-W. Park, E. H. Jung, N. J. Jeon, Y. C. Kim,
Manager and Operator of the National Renewable Energy D. U. Lee, S. S. Shin, J. Seo, E. K. Kim, J. H. Noh and
Laboratory. The authors thank the support on fundamental S. I. Seok, Science, 2017, 356, 1376–1379.
design and characterization of 2D perovskite materials from 16 W. S. Yang, J. H. Noh, N. J. Jeon, Y. C. Kim, S. Ryu, J. Seo
the Center for Hybrid Organic Inorganic Semiconductors for and S. I. Seok, Science, 2015, 348, 1234–1237.
Energy (CHOISE), an Energy Frontier Research Center funded 17 M. Abdi-Jalebi, Z. Andaji-Garmaroudi, S. Cacovich,
by the Office of Basic Energy Sciences, Office of Science within C. Stavrakas, B. Philippe, J. M. Richter, M. Alsari, E. P.
the U.S. Department of Energy. The authors also appreciate the Booker, E. M. Hutter, A. J. Pearson, S. Lilliu, T. J. Savenije,

1178 | Energy Environ. Sci., 2020, 13, 1154--1186 This journal is © The Royal Society of Chemistry 2020
 View Article Online

Review Energy & Environmental Science

H. Rensmo, G. Divitini, C. Ducati, R. H. Friend and 35 F. Zhang, W. Shi, J. Luo, N. Pellet, C. Yi, X. Li, X. Zhao,
S. D. Stranks, Nature, 2018, 555, 497. T. J. S. Dennis, X. Li, S. Wang, Y. Xiao, S. M. Zakeeruddin,
18 N. Ahn, D.-Y. Son, I.-H. Jang, S. M. Kang, M. Choi and D. Bi and M. Grätzel, Adv. Mater., 2017, 29, 1606806.
N.-G. Park, J. Am. Chem. Soc., 2015, 137, 8696–8699. 36 M. Sun, F. Zhang, H. Liu, X. Li, Y. Xiao and S. Wang,
19 J. Burschka, N. Pellet, S.-J. Moon, R. Humphry-Baker, J. Mater. Chem. A, 2017, 5, 13448–13456.
P. Gao, M. K. Nazeeruddin and M. Grätzel, Nature, 2013, 37 J. A. Christians, P. Schulz, J. S. Tinkham, T. H. Schloemer,
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

499, 316. S. P. Harvey, B. J. Tremolet de Villers, A. Sellinger, J. J. Berry

20 A. Mei, X. Li, L. Liu, Z. Ku, T. Liu, Y. Rong, M. Xu, M. Hu, and J. M. Luther, Nat. Energy, 2018, 3, 68–74.
J. Chen, Y. Yang, M. Grätzel and H. Han, Science, 2014, 345, 38 F. Zhang, Z. Wang, H. Zhu, N. Pellet, J. Luo, C. Yi, X. Liu,
295–298. H. Liu, S. Wang, X. Li, Y. Xiao, S. M. Zakeeruddin, D. Bi and
21 E. H. Jung, N. J. Jeon, E. Y. Park, C. S. Moon, T. J. Shin, M. Grätzel, Nano Energy, 2017, 41, 469–475.
T.-Y. Yang, J. H. Noh and J. Seo, Nature, 2019, 567, 511–515. 39 J.-J. Guo, Z.-C. Bai, X.-F. Meng, M.-M. Sun, J.-H. Song,
22 D. H. Kim, C. P. Muzzillo, J. Tong, A. F. Palmstrom, Z.-S. Shen, N. Ma, Z.-L. Chen and F. Zhang, Sol. Energy,
B. W. Larson, C. Choi, S. P. Harvey, S. Glynn, J. B. 2017, 155, 121–129.
Whitaker, F. Zhang, Z. Li, H. Lu, M. F. A. M. van Hest, 40 X. Liu, F. Zhang, Z. Liu, Y. Xiao, S. Wang and X. Li, J. Mater.
J. J. Berry, L. M. Mansfield, Y. Huang, Y. Yan and K. Zhu, Chem. C, 2017, 5, 11429–11435.
Joule, 2019, 3, 1734–1745. 41 Y. Bai, Q. Dong, Y. Shao, Y. Deng, Q. Wang, L. Shen,
23 W. Chen, Y. Wu, Y. Yue, J. Liu, W. Zhang, X. Yang, H. Chen, D. Wang, W. Wei and J. Huang, Nat. Commun., 2016,
E. Bi, I. Ashraful, M. Grätzel and L. Han, Science, 2015, 350, 7, 12806.
944–948. 42 X. Zheng, J. Troughton, N. Gasparini, Y. Lin, M. Wei,
24 S. Yang, S. Chen, E. Mosconi, Y. Fang, X. Xiao, C. Wang, Y. Hou, J. Liu, K. Song, Z. Chen, C. Yang, B. Turedi,
Y. Zhou, Z. Yu, J. Zhao, Y. Gao, F. De Angelis and J. Huang, A. Y. Alsalloum, J. Pan, J. Chen, A. A. Zhumekenov,
Science, 2019, 365, 473–478. T. D. Anthopoulos, Y. Han, D. Baran, O. F. Mohammed,
25 T. Niu, J. Lu, X. Jia, Z. Xu, M.-C. Tang, D. Barrit, N. Yuan, E. H. Sargent and O. M. Bakr, Joule, 2019, 3, 1963–1976.
J. Ding, X. Zhang, Y. Fan, T. Luo, Y. Zhang, D.-M. Smilgies, 43 F. Bella, G. Griffini, J.-P. Correa-Baena, G. Saracco,
Z. Liu, A. Amassian, S. Jin, K. Zhao and S. Liu, Nano Lett., M. Grätzel, A. Hagfeldt, S. Turri and C. Gerbaldi, Science,
2019, 19, 7181–7190. 2016, 354, 203–206.
26 A. R. b. M. Yusoff and M. K. Nazeeruddin, Adv. Energy 44 Y. Jiang, L. Qiu, E. J. Juarez-Perez, L. K. Ono, Z. Hu, Z. Liu,
Mater., 2018, 8, 1702073. Z. Wu, L. Meng, Q. Wang and Y. Qi, Nat. Energy, 2019, 4,
27 M. Saliba, T. Matsui, J.-Y. Seo, K. Domanski, J.-P. Correa- 585–593.
Baena, M. K. Nazeeruddin, S. M. Zakeeruddin, W. Tress, 45 F. Zhang, D. H. Kim and K. Zhu, Curr. Opin. Electrochem.,
A. Abate, A. Hagfeldt and M. Grätzel, Energy Environ. Sci., 2018, 11, 105–113.
2016, 9, 1989–1997. 46 D. Thrithamarassery Gangadharan and D. Ma, Energy
28 G. E. Eperon, T. Leijtens, K. A. Bush, R. Prasanna, T. Green, Environ. Sci., 2019, 12, 2860–2889.
J. T.-W. Wang, D. P. McMeekin, G. Volonakis, R. L. Milot, 47 L. Etgar, Energy Environ. Sci., 2018, 11, 234–242.
R. May, A. Palmstrom, D. J. Slotcavage, R. A. Belisle, 48 B. Saparov and D. B. Mitzi, Chem. Rev., 2016, 116,
J. B. Patel, E. S. Parrott, R. J. Sutton, W. Ma, F. Moghadam, 4558–4596.
B. Conings, A. Babayigit, H.-G. Boyen, S. Bent, F. Giustino, 49 S. Yang, Y. Wang, P. Liu, Y.-B. Cheng, H. J. Zhao and
L. M. Herz, M. B. Johnston, M. D. McGehee and H. J. Snaith, H. G. Yang, Nat. Energy, 2016, 1, 15016.
Science, 2016, 354, 861–865. 50 I. C. Smith, E. T. Hoke, D. Solis-Ibarra, M. D. McGehee and
29 A. Swarnkar, A. R. Marshall, E. M. Sanehira, B. D. H. I. Karunadasa, Angew. Chem., Int. Ed., 2014, 53,
Chernomordik, D. T. Moore, J. A. Christians, 11232–11235.
T. Chakrabarti and J. M. Luther, Science, 2016, 354, 92–95. 51 T. Luo, Y. Zhang, Z. Xu, T. Niu, J. Wen, J. Lu, S. Jin, S. Liu
30 Q. Zhao, A. Hazarika, X. Chen, S. P. Harvey, B. W. Larson, and K. Zhao, Adv. Mater., 2019, 31, 1903848.
G. R. Teeter, J. Liu, T. Song, C. Xiao, L. Shaw, M. Zhang, 52 G. Grancini, C. Roldán-Carmona, I. Zimmermann,
G. Li, M. C. Beard and J. M. Luther, Nat. Commun., 2019, E. Mosconi, X. Lee, D. Martineau, S. Narbey, F. Oswald,
10, 2842. F. De Angelis, M. Graetzel and M. K. Nazeeruddin, Nat.
31 Z. Li, M. Yang, J.-S. Park, S.-H. Wei, J. J. Berry and K. Zhu, Commun., 2017, 8, 15684.
Chem. Mater., 2016, 28, 284–292. 53 P. Chen, Y. Bai, M. Lyu, J.-H. Yun, M. Hao and L. Wang,
32 W. Travis, E. N. K. Glover, H. Bronstein, D. O. Scanlon and Sol. RRL, 2018, 2, 1700186.
R. G. Palgrave, Chem. Sci., 2016, 7, 4548–4556. 54 J. Tong, Z. Song, D. H. Kim, X. Chen, C. Chen, A. F.
33 X. Zheng, B. Chen, J. Dai, Y. Fang, Y. Bai, Y. Lin, H. Wei, Palmstrom, P. F. Ndione, M. O. Reese, S. P. Dunfield,
X. C. Zeng and J. Huang, Nat. Energy, 2017, 2, 17102. O. G. Reid, J. Liu, F. Zhang, S. P. Harvey, Z. Li, S. T.
34 F. Zhang, D. Bi, N. Pellet, C. Xiao, Z. Li, J. J. Berry, Christensen, G. Teeter, D. Zhao, M. M. Al-Jassim,
S. M. Zakeeruddin, K. Zhu and M. Grätzel, Energy Environ. M. F. A. M. van Hest, M. C. Beard, S. E. Shaheen,
Sci., 2018, 11, 3480–3490. J. J. Berry, Y. Yan and K. Zhu, Science, 2019, 364, 475–479.

This journal is © The Royal Society of Chemistry 2020 Energy Environ. Sci., 2020, 13, 1154--1186 | 1179
 View Article Online

Energy & Environmental Science Review

55 Z. Wang, Q. Lin, F. P. Chmiel, N. Sakai, L. M. Herz and 74 S. Ahmad, P. Fu, S. Yu, Q. Yang, X. Liu, X. Wang, X. Wang,
H. J. Snaith, Nat. Energy, 2017, 2, 17135. X. Guo and C. Li, Joule, 2019, 3, 794–806.
56 C. Ortiz-Cervantes, P. Carmona-Monroy and D. Solis-Ibarra, 75 T. Nakajima, H. Yamauchi, T. Goto, M. Yoshizawa,
ChemSusChem, 2019, 12, 1560–1575. T. Suzuki and T. Fujimura, J. Magn. Magn. Mater., 1983,
57 F. Zhang, S. Wang, X. Li and Y. Xiao, Curr. Nanosci., 2016, 31-34, 1189–1190.
12, 137–156. 76 L. Mao, Y. Wu, C. C. Stoumpos, B. Traore, C. Katan, J. Even,
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

58 V. M. Goldschmidt, Naturwissenschaften, 1926, 14, M. R. Wasielewski and M. G. Kanatzidis, J. Am. Chem. Soc.,
477–485. 2017, 139, 11956–11963.
59 C. Li, X. Lu, W. Ding, L. Feng, Y. Gao and Z. Guo, Acta 77 B. Doudin and G. Chapuis, Acta Crystallogr., Sect. B: Struct.
Crystallogr., Sect. B: Struct. Sci., 2008, 64, 702–707. Sci., 1990, 46, 180–186.
60 W. A. Dunlap-Shohl, Y. Zhou, N. P. Padture and D. B. Mitzi, 78 E. R. Peterson and R. D. Willett, J. Chem. Phys., 1972, 56,
Chem. Rev., 2019, 119, 3193–3295. 1879–1882.
61 M. Yuan, L. N. Quan, R. Comin, G. Walters, R. Sabatini, 79 C. C. Stoumpos, C. M. M. Soe, H. Tsai, W. Nie,
O. Voznyy, S. Hoogland, Y. Zhao, E. M. Beauregard, J.-C. Blancon, D. H. Cao, F. Liu, B. Traoré, C. Katan,
P. Kanjanaboos, Z. Lu, D. H. Kim and E. H. Sargent, Nat. J. Even, A. D. Mohite and M. G. Kanatzidis, Chem, 2017,
Nanotechnol., 2016, 11, 872. 2, 427–440.
62 N. Zhou, Y. Shen, L. Li, S. Tan, N. Liu, G. Zheng, Q. Chen 80 P. Cheng, P. Wang, Z. Xu, X. Jia, Q. Wei, N. Yuan, J. Ding,
and H. Zhou, J. Am. Chem. Soc., 2018, 140, 459–465. R. Li, G. Zhao, Y. Cheng, K. Zhao and S. F. Liu, ACS Energy
63 C. M. M. Soe, W. Nie, C. C. Stoumpos, H. Tsai, J.-C. Lett., 2019, 4, 1830–1838.
Blancon, F. Liu, J. Even, T. J. Marks, A. D. Mohite and 81 D. G. Billing and A. Lemmerer, Acta Crystallogr., Sect. B:
M. G. Kanatzidis, Adv. Energy Mater., 2018, 8, 1700979. Struct. Sci., 2007, 63, 735–747.
64 T. Hu, M. D. Smith, E. R. Dohner, M.-J. Sher, X. Wu, 82 A. Lemmerer and D. G. Billing, Dalton Trans., 2012, 41,
M. T. Trinh, A. Fisher, J. Corbett, X. Y. Zhu, H. I. 1146–1157.
Karunadasa and A. M. Lindenberg, J. Phys. Chem. Lett., 83 W.-W. Zhong, Y.-Y. Di, Y.-X. Kong, D.-F. Lu and J.-M. Dou,
2016, 7, 2258–2263. J. Chem. Thermodyn., 2014, 72, 100–107.
65 L. Mao, C. C. Stoumpos and M. G. Kanatzidis, J. Am. Chem. 84 H. Ren, S. Yu, L. Chao, Y. Xia, Y. Sun, S. Zuo, F. Li, T. Niu,
Soc., 2019, 141, 1171–1190. Y. Yang, H. Ju, B. Li, H. Du, X. Gao, J. Zhang, J. Wang,
66 B. Vargas, R. Torres-Cadena, J. Rodrı́guez-Hernández, L. Zhang, Y. Chen and W. Huang, Nat. Photonics, 2020,
M. Gembicky, H. Xie, J. Jiménez-Mier, Y.-S. Liu, DOI: 10.1038/s41566-019-0572-6.
E. Menéndez-Proupin, K. R. Dunbar, N. Lopez, P. Olalde- 85 A. H. Proppe, R. Quintero-Bermudez, H. Tan, O. Voznyy,
Velasco and D. Solis-Ibarra, Chem. Mater., 2018, 30, S. O. Kelley and E. H. Sargent, J. Am. Chem. Soc., 2018, 140,
5315–5321. 2890–2896.
67 C. C. Stoumpos, D. H. Cao, D. J. Clark, J. Young, J. M. 86 D. Solis-Ibarra and H. I. Karunadasa, Angew. Chem., Int.
Rondinelli, J. I. Jang, J. T. Hupp and M. G. Kanatzidis, Ed., 2014, 53, 1039–1042.
Chem. Mater., 2016, 28, 2852–2867. 87 C. Lermer, S. T. Birkhold, I. L. Moudrakovski, P. Mayer,
68 W. Paritmongkol, N. S. Dahod, A. Stollmann, N. Mao, L. M. Schoop, L. Schmidt-Mende and B. V. Lotsch, Chem.
C. Settens, S.-L. Zheng and W. A. Tisdale, Chem. Mater., Mater., 2016, 28, 6560–6566.
2019, 31, 5592–5607. 88 Z.-X. Wang, W.-Q. Liao, H.-Y. Ye and Y. Zhang, Dalton
69 L. Mao, W. Ke, L. Pedesseau, Y. Wu, C. Katan, J. Even, Trans., 2015, 44, 20406–20412.
M. R. Wasielewski, C. C. Stoumpos and M. G. Kanatzidis, 89 N. Mercier, CrystEngComm, 2005, 7, 429–432.
J. Am. Chem. Soc., 2018, 140, 3775–3783. 90 N. Ashari-Astani, F. Jahanbakhshi, M. Mladenović,
70 I.-H. Park, Q. Zhang, K. C. Kwon, Z. Zhu, W. Yu, K. Leng, A. Q. M. Alanazi, I. Ahmadabadi, M. R. Ejtehadi,
D. Giovanni, H. S. Choi, I. Abdelwahab, Q.-H. Xu, T. C. Sum M. I. Dar, M. Grätzel and U. Rothlisberger, J. Phys. Chem.
and K. P. Loh, J. Am. Chem. Soc., 2019, 141, 15972–15976. Lett., 2019, 10, 3543–3549.
71 X. Li, W. Ke, B. Traoré, P. Guo, I. Hadar, M. Kepenekian, 91 A. Lemmerer and D. G. Billing, CrystEngComm, 2010, 12,
J. Even, C. Katan, C. C. Stoumpos, R. D. Schaller and 1290–1301.
M. G. Kanatzidis, J. Am. Chem. Soc., 2019, 141, 92 D. G. Billing and A. Lemmerer, CrystEngComm, 2009, 11,
12880–12890. 1549–1562.
72 C. M. M. Soe, C. C. Stoumpos, M. Kepenekian, B. Traoré, 93 D. G. Billing and A. Lemmerer, CrystEngComm, 2007, 9,
H. Tsai, W. Nie, B. Wang, C. Katan, R. Seshadri, 236–244.
A. D. Mohite, J. Even, T. J. Marks and M. G. Kanatzidis, 94 X.-N. Li, P.-F. Li, W.-Q. Liao, J.-Z. Ge, D.-H. Wu and
J. Am. Chem. Soc., 2017, 139, 16297–16309. H.-Y. Ye, Eur. J. Inorg. Chem., 2017, 938–942.
73 Y. Zhang, P. Wang, M.-C. Tang, D. Barrit, W. Ke, J. Liu, 95 D. G. Billing and A. Lemmerer, Acta Crystallogr., Sect. C:
T. Luo, Y. Liu, T. Niu, D.-M. Smilgies, Z. Yang, Z. Liu, S. Jin, Cryst. Struct. Commun., 2006, 62, m269–m271.
M. G. Kanatzidis, A. Amassian, S. F. Liu and K. Zhao, J. Am. 96 G. S. Lorena, H. Hasegawa, Y. Takahashi, J. Harada and
Chem. Soc., 2019, 141, 2684–2694. T. Inabe, Chem. Lett., 2014, 43, 1535–1537.

1180 | Energy Environ. Sci., 2020, 13, 1154--1186 This journal is © The Royal Society of Chemistry 2020
 View Article Online

Review Energy & Environmental Science

97 Y. Takahashi, R. Obara, K. Nakagawa, M. Nakano, J.-y. Tokita 120 R. Herckens, W. T. M. Van Gompel, W. Song, M. C. Gélvez-
and T. Inabe, Chem. Mater., 2007, 19, 6312–6316. Rueda, A. Maufort, B. Ruttens, J. D’Haen, F. C. Grozema,
98 Z. Li, N. Liu, K. Meng, Z. Liu, Y. Hu, Q. Xu, X. Wang, S. Li, T. Aernouts, L. Lutsen and D. Vanderzande, J. Mater. Chem.
L. Cheng and G. Chen, Nano Lett., 2019, 19, 5237–5245. A, 2018, 6, 22899–22908.
99 L. Mao, H. Tsai, W. Nie, L. Ma, J. Im, C. C. Stoumpos, 121 A. B. Corradi, A. M. Ferrari, G. C. Pellacani, A. Saccani,
C. D. Malliakas, F. Hao, M. R. Wasielewski, A. D. Mohite F. Sandrolini and P. Sgarabotto, Inorg. Chem., 1999, 38,
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

and M. G. Kanatzidis, Chem. Mater., 2016, 28, 7781–7792. 716–721.

100 B.-E. Cohen, M. Wierzbowska and L. Etgar, Sustainable 122 M. D. Smith, A. Jaffe, E. R. Dohner, A. M. Lindenberg and
Energy Fuels, 2017, 1, 1935–1943. H. I. Karunadasa, Chem. Sci., 2017, 8, 4497–4504.
101 M. E. Kamminga, H.-H. Fang, M. R. Filip, F. Giustino, 123 M. Amami, R. Zouari, A. Ben Salah and H. Burzlaff, Acta
J. Baas, G. R. Blake, M. A. Loi and T. T. M. Palstra, Chem. Crystallogr., Sect. E: Struct. Rep. Online, 2002, 58,
Mater., 2016, 28, 4554–4562. m357–m359.
102 M. Braun and W. Frey, Z. Kristallogr. – New Cryst. Struct., 124 M. Safdari, P. H. Svensson, M. T. Hoang, I. Oh, L. Kloo and
1999, 214, 331–332. J. M. Gardner, J. Mater. Chem. A, 2016, 4, 15638–15646.
103 W.-Q. Liao, Y. Zhang, C.-L. Hu, J.-G. Mao, H.-Y. Ye, P.-F. Li, 125 X. Li, J. Hoffman, W. Ke, M. Chen, H. Tsai, W. Nie,
S. D. Huang and R.-G. Xiong, Nat. Commun., 2015, 6, 7338. A. D. Mohite, M. Kepenekian, C. Katan, J. Even,
104 Y. Jin, C.-H. Yu and W. Zhang, J. Coord. Chem., 2014, 67, M. R. Wasielewski, C. C. Stoumpos and M. G. Kanatzidis,
1156–1173. J. Am. Chem. Soc., 2018, 140, 12226–12238.
105 J. Calabrese, N. L. Jones, R. L. Harlow, N. Herron, 126 A. Lemmerer and D. G. Billing, CrystEngComm, 2012, 14,
D. L. Thorn and Y. Wang, J. Am. Chem. Soc., 1991, 113, 1954–1966.
2328–2330. 127 K. Pradeesh, G. S. Yadav, M. Singh and G. Vijaya Prakash,
106 F. Zhang, D. H. Kim, H. Lu, J.-S. Park, B. W. Larson, J. Hu, Mater. Chem. Phys., 2010, 124, 44–47.
L. Gao, C. Xiao, O. G. Reid, X. Chen, Q. Zhao, P. F. Ndione, 128 E. R. Dohner, E. T. Hoke and H. I. Karunadasa, J. Am.
J. J. Berry, W. You, A. Walsh, M. C. Beard and K. Zhu, J. Am. Chem. Soc., 2014, 136, 1718–1721.
Chem. Soc., 2019, 141, 5972–5979. 129 L. Mao, Y. Wu, C. C. Stoumpos, M. R. Wasielewski and
107 G. C. Papavassiliou, I. B. Koutselas, A. Terzis and M. G. Kanatzidis, J. Am. Chem. Soc., 2017, 139, 5210–5215.
M. H. Whangbo, Solid State Commun., 1994, 91, 695–698. 130 M. Daub and H. Hillebrecht, Z. Kristallogr. - Cryst. Mater.,
108 D. B. Mitzi, J. Solid State Chem., 1999, 145, 694–704. 2018, 233, 555.
109 G. C. Papavassiliou, G. A. Mousdis, C. P. Raptopoulou and 131 N. Louvain, W. Bi, N. Mercier, J.-Y. Buzaré, C. Legein and
A. Terzis, Z. Naturforsch. B, 2000, 55, 536. G. Corbel, Dalton Trans., 2007, 965–970.
110 H. Dammak, S. Elleuch, H. Feki and Y. Abid, Solid State 132 E. R. Dohner, A. Jaffe, L. R. Bradshaw and H. I.
Sci., 2016, 61, 1–8. Karunadasa, J. Am. Chem. Soc., 2014, 136, 13154–13157.
111 H. Pan, X. Zhao, X. Gong, Y. Shen and M. Wang, J. Phys. 133 Y. Li, G. Zheng and J. Lin, Eur. J. Inorg. Chem., 2008,
Chem. Lett., 2019, 10, 1813–1819. 1689–1692.
112 W. Fu, H. Liu, X. Shi, L. Zuo, X. Li and A. K.-Y. Jen, Adv. 134 A. Bonamartini Corradi, A. M. Ferrari, L. Righi and
Funct. Mater., 2019, 29, 1900221. P. Sgarabotto, Inorg. Chem., 2001, 40, 218–223.
113 K. Kikuchi, Y. Takeoka, M. Rikukawa and K. Sanui, Curr. 135 M. K. Rayner and D. G. Billing, Acta Crystallogr., Sect. E:
Appl. Phys., 2004, 4, 599–602. Struct. Rep. Online, 2010, 66, m660.
114 J. Hu, I. W. H. Oswald, H. Hu, S. J. Stuard, M. M. Nahid, 136 D. B. Mitzi, C. D. Dimitrakopoulos and L. L. Kosbar, Chem.
L. Yan, Z. Chen, H. Ade, J. R. Neilson and W. You, ACS Mater., 2001, 13, 3728–3740.
Mater. Lett., 2019, 1, 171–176. 137 H. Yu, Z. Wei, Y. Hao, Z. Liang, Z. Fu and H. Cai, New
115 I.-H. Park, L. Chu, K. Leng, Y. F. Choy, W. Liu, J. Chem., 2017, 41, 9586–9589.
I. Abdelwahab, Z. Zhu, Z. Ma, W. Chen, Q.-H. Xu, G. Eda 138 M. P. Hautzinger, J. Dai, Y. Ji, Y. Fu, J. Chen, I. A. Guzei,
and K. P. Loh, Adv. Funct. Mater., 2019, 29, 1904810. J. C. Wright, Y. Li and S. Jin, Inorg. Chem., 2017, 56,
116 X.-H. Zhu, N. Mercier, A. Riou, P. Blanchard and P. Frère, 14991–14998.
Chem. Commun., 2002, 2160–2161. 139 Y. Li, J. V. Milić, A. Ummadisingu, J.-Y. Seo, J.-H. Im, H.-S.
117 Y. Gao, E. Shi, S. Deng, S. B. Shiring, J. M. Snaider, Kim, Y. Liu, M. I. Dar, S. M. Zakeeruddin, P. Wang,
C. Liang, B. Yuan, R. Song, S. M. Janke, A. Liebman- A. Hagfeldt and M. Grätzel, Nano Lett., 2019, 19, 150–157.
Peláez, P. Yoo, M. Zeller, B. W. Boudouris, P. Liao, 140 Y. Li, G. Zheng, C. Lin and J. Lin, Cryst. Growth Des., 2008,
C. Zhu, V. Blum, Y. Yu, B. M. Savoie, L. Huang and 8, 1990–1996.
L. Dou, Nat. Chem., 2019, 11, 1151–1157. 141 C. Lermer, S. P. Harm, S. T. Birkhold, J. A. Jaser, C. M.
118 K.-z. Du, Q. Tu, X. Zhang, Q. Han, J. Liu, S. Zauscher and Kutz, P. Mayer, L. Schmidt-Mende and B. V. Lotsch,
D. B. Mitzi, Inorg. Chem., 2017, 56, 9291–9302. Z. Anorg. Allg. Chem., 2016, 642, 1369–1376.
119 J. V. Passarelli, D. J. Fairfield, N. A. Sather, M. P. 142 X.-H. Zhu, N. Mercier, P. Frère, P. Blanchard, J. Roncali,
Hendricks, H. Sai, C. L. Stern and S. I. Stupp, J. Am. Chem. M. Allain, C. Pasquier and A. Riou, Inorg. Chem., 2003, 42,
Soc., 2018, 140, 7313–7323. 5330–5339.

This journal is © The Royal Society of Chemistry 2020 Energy Environ. Sci., 2020, 13, 1154--1186 | 1181
 View Article Online

Energy & Environmental Science Review

143 D. B. Mitzi, K. Chondroudis and C. R. Kagan, Inorg. Chem., 164 C. Ma, D. Shen, T.-W. Ng, M.-F. Lo and C.-S. Lee, Adv.
1999, 38, 6246–6256. Mater., 2018, 30, 1800710.
144 K. Zheng and T. Pullerits, J. Phys. Chem. Lett., 2019, 10, 165 J. Zhang, L. Zhang, X. Li, X. Zhu, J. Yu and K. Fan, ACS
5881–5885. Sustainable Chem. Eng., 2019, 7, 3487–3495.
145 X. Hong, T. Ishihara and A. V. Nurmikko, Phys. Rev. B: 166 J. Qiu, Y. Zheng, Y. Xia, L. Chao, Y. Chen and W. Huang,
Condens. Matter Mater. Phys., 1992, 45, 6961–6964. Adv. Funct. Mater., 2019, 29, 1806831.
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

146 Z. Guo, X. Wu, T. Zhu, X. Zhu and L. Huang, ACS Nano, 167 L. Gao, F. Zhang, C. Xiao, X. Chen, B. W. Larson, J. J. Berry
2016, 10, 9992–9998. and K. Zhu, Adv. Funct. Mater., 2019, 29, 1901652.
147 R. L. Milot, R. J. Sutton, G. E. Eperon, A. A. Haghighirad, 168 C. J. Dahlman, R. A. DeCrescent, N. R. Venkatesan,
J. Martinez Hardigree, L. Miranda, H. J. Snaith, R. M. Kennard, G. Wu, M. A. Everest, J. A. Schuller and
M. B. Johnston and L. M. Herz, Nano Lett., 2016, 16, M. L. Chabinyc, Chem. Mater., 2019, 31, 5832–5844.
7001–7007. 169 X. Lian, J. Chen, Y. Zhang, S. Tian, M. Qin, J. Li,
148 P. Gao, A. R. Bin Mohd Yusoff and M. K. Nazeeruddin, Nat. T. R. Andersen, G. Wu, X. Lu and H. Chen, J. Mater. Chem.
Commun., 2018, 9, 5028. A, 2019, 7, 18980–18986.
149 J. A. Sichert, Y. Tong, N. Mutz, M. Vollmer, S. Fischer, 170 W. Fu, J. Wang, L. Zuo, K. Gao, F. Liu, D. S. Ginger and
K. Z. Milowska, R. Garcı́a Cortadella, B. Nickel, A. K. Y. Jen, ACS Energy Lett., 2018, 3, 2086–2093.
C. Cardenas-Daw, J. K. Stolarczyk, A. S. Urban and 171 X. Zhang, G. Wu, S. Yang, W. Fu, Z. Zhang, C. Chen,
J. Feldmann, Nano Lett., 2015, 15, 6521–6527. W. Liu, J. Yan, W. Yang and H. Chen, Small, 2017,
150 D. H. Cao, C. C. Stoumpos, O. K. Farha, J. T. Hupp and 13, 1700611.
M. G. Kanatzidis, J. Am. Chem. Soc., 2015, 137, 7843–7850. 172 J. Qing, X.-K. Liu, M. Li, F. Liu, Z. Yuan, E. Tiukalova,
151 Q. Zhang, R. Su, W. Du, X. Liu, L. Zhao, S. T. Ha and Z. Yan, M. Duchamp, S. Chen, Y. Wang, S. Bai, J.-M. Liu,
Q. Xiong, Small Methods, 2017, 1, 1700163. H. J. Snaith, C.-S. Lee, T. C. Sum and F. Gao, Adv. Energy
152 J. S. Manser, J. A. Christians and P. V. Kamat, Chem. Rev., Mater., 2018, 8, 1800185.
2016, 116, 12956–13008. 173 H. J. Jung, C. C. Stompus, M. G. Kanatzidis and
153 T. M. Koh, V. Shanmugam, J. Schlipf, L. Oesinghaus, V. P. Dravid, Nano Lett., 2019, 19, 6109–6117.
P. Müller-Buschbaum, N. Ramakrishnan, V. Swamy, 174 Y. Chen, Y. Sun, J. Peng, W. Zhang, X. Su, K. Zheng,
N. Mathews, P. P. Boix and S. G. Mhaisalkar, Adv. Mater., T. Pullerits and Z. Liang, Adv. Energy Mater., 2017,
2016, 28, 3653–3661. 7, 1700162.
154 H. Tsai, W. Nie, J.-C. Blancon, C. C. Stoumpos, 175 L. Gao, F. Zhang, X. Chen, C. Xiao, B. W. Larson,
R. Asadpour, B. Harutyunyan, A. J. Neukirch, S. P. Dunfield, J. J. Berry and K. Zhu, Angew. Chem., 2019,
R. Verduzco, J. J. Crochet, S. Tretiak, L. Pedesseau, 131, 11863–11867.
J. Even, M. A. Alam, G. Gupta, J. Lou, P. M. Ajayan, 176 B. Febriansyah, T. M. Koh, Y. Lekina, N. F. Jamaludin,
M. J. Bedzyk, M. G. Kanatzidis and A. D. Mohite, Nature, A. Bruno, R. Ganguly, Z. X. Shen, S. G. Mhaisalkar and
2016, 536, 312. J. England, Chem. Mater., 2019, 31, 890–898.
155 F. Li, Y. Pei, F. Xiao, T. Zeng, Z. Yang, J. Xu, J. Sun, B. Peng 177 J. V. Milić, J.-H. Im, D. J. Kubicki, A. Ummadisingu,
and M. Liu, Nanoscale, 2018, 10, 6318–6322. J.-Y. Seo, Y. Li, M. A. Ruiz-Preciado, M. I. Dar,
156 X. Zhang, X. Ren, B. Liu, R. Munir, X. Zhu, D. Yang, J. Li, S. M. Zakeeruddin, L. Emsley and M. Grätzel, Adv. Energy
Y. Liu, D.-M. Smilgies, R. Li, Z. Yang, T. Niu, X. Wang, Mater., 2019, 9, 1900284.
A. Amassian, K. Zhao and S. Liu, Energy Environ. Sci., 2017, 178 H. Gu, C. Liang, Y. Xia, Q. Wei, T. Liu, Y. Yang, W. Hui,
10, 2095–2102. H. Chen, T. Niu, L. Chao, Z. Wu, X. Xie, J. Qiu, G. Shao,
157 Y. Jiang, X. He, T. Liu, N. Zhao, M. Qin, J. Liu, F. Jiang, X. Gao, G. Xing, Y. Chen and W. Huang, Nano Energy, 2019,
F. Qin, L. Sun, X. Lu, S. Jin, Z. Xiao, T. Kamiya and Y. Zhou, 65, 104050.
ACS Energy Lett., 2019, 4, 1216–1224. 179 C. Zuo, A. D. Scully, D. Vak, W. Tan, X. Jiao, C. R. McNeill,
158 D. B. Straus, S. Hurtado Parra, N. Iotov, J. Gebhardt, D. Angmo, L. Ding and M. Gao, Adv. Energy Mater., 2019,
A. M. Rappe, J. E. Subotnik, J. M. Kikkawa and 9, 1803258.
C. R. Kagan, J. Am. Chem. Soc., 2016, 138, 13798–13801. 180 G. Wu, X. Li, J. Zhou, J. Zhang, X. Zhang, X. Leng, P. Wang,
159 A. Brehier, R. Parashkov, J. S. Lauret and E. Deleporte, M. Chen, D. Zhang, K. Zhao, S. Liu, H. Zhou and Y. Zhang,
Appl. Phys. Lett., 2006, 89, 171110. Adv. Mater., 2019, 31, 1903889.
160 M. Braun, W. Tuffentsammer, H. Wachtel and H. C. Wolf, 181 J. Zhang, J. Qin, M. Wang, Y. Bai, H. Zou, J. K. Keum,
Chem. Phys. Lett., 1999, 303, 157–164. R. Tao, H. Xu, H. Yu, S. Haacke and B. Hu, Joule, 2019, 3,
161 K. Ema, M. Inomata, Y. Kato, H. Kunugita and M. Era, 3061–3071.
Phys. Rev. Lett., 2008, 100, 257401. 182 X. Zhang, G. Wu, W. Fu, M. Qin, W. Yang, J. Yan, Z. Zhang,
162 J. Liu, J. Leng, K. Wu, J. Zhang and S. Jin, J. Am. Chem. Soc., X. Lu and H. Chen, Adv. Energy Mater., 2018, 8, 1702498.
2017, 139, 1432–1435. 183 M. Kim, G.-H. Kim, T. K. Lee, I. W. Choi, H. W. Choi, Y. Jo,
163 Y. Chen, S. Yu, Y. Sun and Z. Liang, J. Phys. Chem. Lett., Y. J. Yoon, J. W. Kim, J. Lee, D. Huh, H. Lee, S. K. Kwak,
2018, 9, 2627–2631. J. Y. Kim and D. S. Kim, Joule, 2019, 3, 2179–2192.

1182 | Energy Environ. Sci., 2020, 13, 1154--1186 This journal is © The Royal Society of Chemistry 2020
 View Article Online

Review Energy & Environmental Science

184 Y. Zhao and K. Zhu, J. Phys. Chem. C, 2014, 118, 9412–9418. 205 T. Zhou, H. Lai, T. Liu, D. Lu, X. Wan, X. Zhang, Y. Liu and
185 H. Lai, B. Kan, T. Liu, N. Zheng, Z. Xie, T. Zhou, X. Wan, Y. Chen, Adv. Mater., 2019, 31, 1901242.
X. Zhang, Y. Liu and Y. Chen, J. Am. Chem. Soc., 2018, 140, 206 S. Heo, G. Seo, K. T. Cho, Y. Lee, S. Paek, S. Kim,
11639–11646. M. Seol, S. H. Kim, D.-J. Yun, K. Kim, J. Park, J. Lee,
186 T. Niu, H. Ren, B. Wu, Y. Xia, X. Xie, Y. Yang, X. Gao, Y. Chen L. Lechner, T. Rodgers, J. W. Chung, J.-S. Kim, D. Lee,
and W. Huang, J. Phys. Chem. Lett., 2019, 10, 2349–2356. S.-H. Choi and M. K. Nazeeruddin, Adv. Energy Mater.,
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

187 X. Lian, J. Chen, M. Qin, Y. Zhang, S. Tian, X. Lu, G. Wu 2019, 9, 1902470.

and H. Chen, Angew. Chem., Int. Ed., 2019, 58, 9409–9413. 207 C.-T. Lin, J. Lee, J. Kim, T. J. Macdonald, J. Ngiam, B. Xu,
188 X. Lian, J. Chen, Y. Zhang, M. Qin, T. R. Andersen, J. Ling, M. Daboczi, W. Xu, S. Pont, B. Park, H. Kang, J.-S. Kim,
G. Wu, X. Lu, D. Yang and H. Chen, J. Mater. Chem. A, 2019, D. J. Payne, K. Lee, J. R. Durrant and M. A. McLachlan, Adv.
7, 19423–19429. Funct. Mater., 2020, 30, 1906763.
189 X. Lian, J. Chen, Y. Zhang, M. Qin, J. Li, S. Tian, W. Yang, 208 E. Shirzadi, A. Mahata, C. Roldán Carmona, F. De Angelis,
X. Lu, G. Wu and H. Chen, Adv. Funct. Mater., 2019, P. J. Dyson and M. K. Nazeeruddin, ACS Energy Lett., 2019,
29, 1807024. 4, 2989–2994.
190 Y. Zhang, J. Chen, X. Lian, M. Qin, J. Li, T. R. Andersen, 209 H. Chen, Q. Wei, M. I. Saidaminov, F. Wang, A. Johnston,
X. Lu, G. Wu, H. Li and H. Chen, Small Methods, 2019, Y. Hou, Z. Peng, K. Xu, W. Zhou, Z. Liu, L. Qiao, X. Wang,
3, 1900375. S. Xu, J. Li, R. Long, Y. Ke, E. H. Sargent and Z. Ning, Adv.
191 C. Yi, J. Luo, S. Meloni, A. Boziki, N. Ashari-Astani, Mater., 2019, 31, 1903559.
C. Grätzel, S. M. Zakeeruddin, U. Röthlisberger and 210 B.-E. Cohen, Y. Li, Q. Meng and L. Etgar, Nano Lett., 2019,
M. Grätzel, Energy Environ. Sci., 2016, 9, 656–662. 19, 2588–2597.
192 L. T. Schelhas, Z. Li, J. A. Christians, A. Goyal, P. Kairys, 211 L. Iagher and L. Etgar, ACS Energy Lett., 2018, 3, 366–372.
S. P. Harvey, D. H. Kim, K. H. Stone, J. M. Luther, K. Zhu, 212 N. D. Pham, C. Zhang, V. T. Tiong, S. Zhang, G. Will,
V. Stevanovic and J. J. Berry, Energy Environ. Sci., 2019, 12, A. Bou, J. Bisquert, P. E. Shaw, A. Du, G. J. Wilson and
1341–1348. H. Wang, Adv. Funct. Mater., 2019, 29, 1806479.
193 D. Ramirez, K. Schutt, Z. Wang, A. J. Pearson, E. Ruggeri, 213 N. De Marco, H. Zhou, Q. Chen, P. Sun, Z. Liu, L. Meng,
H. J. Snaith, S. D. Stranks and F. Jaramillo, ACS Energy E.-P. Yao, Y. Liu, A. Schiffer and Y. Yang, Nano Lett., 2016,
Lett., 2018, 3, 2246–2251. 16, 1009–1016.
194 J. Hu, I. W. H. Oswald, S. J. Stuard, M. M. Nahid, N. Zhou, 214 D. J. Kubicki, D. Prochowicz, A. Hofstetter, M. Saski,
O. F. Williams, Z. Guo, L. Yan, H. Hu, Z. Chen, X. Xiao, P. Yadav, D. Bi, N. Pellet, J. Lewiński, S. M. Zakeeruddin,
Y. Lin, Z. Yang, J. Huang, A. M. Moran, H. Ade, J. R. Neilson M. Grätzel and L. Emsley, J. Am. Chem. Soc., 2018, 140,
and W. You, Nat. Commun., 2019, 10, 1276. 3345–3351.
195 Y. Li, H. Cheng, K. Zhao and Z.-S. Wang, ACS Appl. Mater. 215 A. D. Jodlowski, C. Roldán-Carmona, G. Grancini,
Interfaces, 2019, 11, 37804–37811. M. Salado, M. Ralaiarisoa, S. Ahmad, N. Koch, L. Camacho,
196 C. Katan, L. Pedesseau, M. Kepenekian, A. Rolland and G. de Miguel and M. K. Nazeeruddin, Nat. Energy, 2017, 2,
J. Even, J. Mater. Chem. A, 2015, 3, 9232–9240. 972–979.
197 P. Li, C. Liang, X.-L. Liu, F. Li, Y. Zhang, X.-T. Liu, H. Gu, 216 R. J. Stoddard, A. Rajagopal, R. L. Palmer, I. L. Braly,
X. Hu, G. Xing, X. Tao and Y. Song, Adv. Mater., 2019, A. K. Y. Jen and H. W. Hillhouse, ACS Energy Lett., 2018,
31, 1901966. 3, 1261–1268.
198 A. Krishna, S. Gottis, M. K. Nazeeruddin and F. Sauvage, 217 L. Hong, J. Milic, P. Ahlawat, M. Mladenovic, D. J. Kubicki,
Adv. Funct. Mater., 2019, 29, 1806482. F. Jahanbakhshi, D. Ren, M. Gelvez-Rueda, M. A. Ruiz-
199 K. Yao, X. Wang, F. Li and L. Zhou, Chem. Commun., 2015, Preciado, A. Ummadisingu, Y. Liu, C. Tian, L. Pan, S. M.
51, 15430–15433. Zakeeruddin, A. Hagfeldt, F. C. Grozema, U. Rothlisberger,
200 J. Chen, D. Lee and N.-G. Park, ACS Appl. Mater. Interfaces, L. Emsley, H. Han and M. Grätzel, Angew. Chem., Int. Ed.,
2017, 9, 36338–36349. 2019, DOI: 10.1002/anie.201912051.
201 S. V. Morozov, D. I. Kryzhkov, A. N. Yablonsky, A. V. 218 S. Wu, Z. Li, J. Zhang, T. Liu, Z. Zhu and A. K. Y. Jen, Chem.
Antonov, D. I. Kuritsin, D. M. Gaponova, Y. G. Sadofyev, Commun., 2019, 55, 4315–4318.
N. Samal, V. I. Gavrilenko and Z. F. Krasilnik, J. Appl. Phys., 219 A. Thote, I. Jeon, J.-W. Lee, S. Seo, H.-S. Lin, Y. Yang,
2013, 113, 163107. H. Daiguji, S. Maruyama and Y. Matsuo, ACS Appl. Energy
202 G. Liu, H. Zheng, X. Xu, S. Xu, X. Zhang, X. Pan and S. Dai, Mater., 2019, 2, 2486–2493.
Adv. Funct. Mater., 2019, 29, 1807565. 220 T. Zhang, M. I. Dar, G. Li, F. Xu, N. Guo, M. Grätzel and
203 Y. Wang, H. Xu, F. Wang, D. Liu, H. Chen, H. Zheng, L. Ji, Y. Zhao, Sci. Adv., 2017, 3, e1700841.
P. Zhang, T. Zhang, Z. D. Chen, J. Wu, L. Chen and S. Li, 221 Y. Jiang, J. Yuan, Y. Ni, J. Yang, Y. Wang, T. Jiu, M. Yuan
Chem. Eng. J., 2019, 123589, DOI: 10.1016/j.cej.2019.123589. and J. Chen, Joule, 2018, 2, 1356–1368.
204 L. Zhou, Z. Lin, Z. Ning, T. Li, X. Guo, J. Ma, J. Su, C. Zhang, 222 J.-W. Lee, Z. Dai, T.-H. Han, C. Choi, S.-Y. Chang, S.-J. Lee,
J. Zhang, S. Liu, J. Chang and Y. Hao, Sol. RRL, 2019, N. De Marco, H. Zhao, P. Sun, Y. Huang and Y. Yang, Nat.
3, 1900293. Commun., 2018, 9, 3021.

This journal is © The Royal Society of Chemistry 2020 Energy Environ. Sci., 2020, 13, 1154--1186 | 1183
 View Article Online

Energy & Environmental Science Review

223 D. S. Lee, J. S. Yun, J. Kim, A. M. Soufiani, S. Chen, Y. Cho, 242 J. J. Yoo, S. Wieghold, M. C. Sponseller, M. R. Chua,
X. Deng, J. Seidel, S. Lim, S. Huang and A. W. Y. Ho-Baillie, S. N. Bertram, N. T. P. Hartono, J. S. Tresback, E. C.
ACS Energy Lett., 2018, 3, 647–654. Hansen, J.-P. Correa-Baena, V. Bulović, T. Buonassisi,
224 T. Niu, J. Lu, M.-C. Tang, D. Barrit, D.-M. Smilgies, Z. Yang, S. S. Shin and M. G. Bawendi, Energy Environ. Sci., 2019,
J. Li, Y. Fan, T. Luo, I. McCulloch, A. Amassian, S. Liu and 12, 2192–2199.
K. Zhao, Energy Environ. Sci., 2018, 11, 3358–3366. 243 M. Jung, T. J. Shin, J. Seo, G. Kim and S. I. Seok, Energy
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

225 X. Huang, Q. Cui, W. Bi, L. Li, P. Jia, Y. Hou, Y. Hu, Z. Lou Environ. Sci., 2018, 11, 2188–2197.
and F. Teng, RSC Adv., 2019, 9, 7984–7991. 244 S. Yang, Y. Wang, P. Liu, Y.-B. Cheng, H. J. Zhao and
226 T. M. Koh, V. Shanmugam, X. Guo, S. S. Lim, O. Filonik, H. G. Yang, Nat. Energy, 2016, 1, 15016.
E. M. Herzig, P. Müller-Buschbaum, V. Swamy, S. T. Chien, 245 A. Dutta, S. K. Dutta, S. Das Adhikari and N. Pradhan,
S. G. Mhaisalkar and N. Mathews, J. Mater. Chem. A, 2018, Angew. Chem., Int. Ed., 2018, 57, 9083–9087.
6, 2122–2128. 246 E. M. Sanehira, A. R. Marshall, J. A. Christians, S. P. Harvey,
227 B. Liu, M. Long, M. Cai, L. Ding and J. Yang, Nano Energy, P. N. Ciesielski, L. M. Wheeler, P. Schulz, L. Y. Lin,
2019, 59, 715–720. M. C. Beard and J. M. Luther, Sci. Adv., 2017, 3, eaao4204.
228 S. G. Motti, T. Crothers, R. Yang, Y. Cao, R. Li, 247 Y. Wang, M. I. Dar, L. K. Ono, T. Zhang, M. Kan, Y. Li,
M. B. Johnston, J. Wang and L. M. Herz, Nano Lett., L. Zhang, X. Wang, Y. Yang, X. Gao, Y. Qi, M. Grätzel and
2019, 19, 3953–3960. Y. Zhao, Science, 2019, 365, 591–595.
229 K. T. Cho, G. Grancini, Y. Lee, E. Oveisi, J. Ryu, O. Almora, 248 Y. Wang, T. Zhang, M. Kan, Y. Li, T. Wang and Y. Zhao,
M. Tschumi, P. A. Schouwink, G. Seo, S. Heo, J. Park, Joule, 2018, 2, 2065–2075.
J. Jang, S. Paek, G. Garcia-Belmonte and M. K. Nazeeruddin, 249 Y. Wang, T. Zhang, M. Kan and Y. Zhao, J. Am. Chem. Soc.,
Energy Environ. Sci., 2018, 11, 952–959. 2018, 140, 12345–12348.
230 P. Chen, Y. Bai, S. Wang, M. Lyu, J.-H. Yun and L. Wang, 250 D. Luo, W. Yang, Z. Wang, A. Sadhanala, Q. Hu, R. Su,
Adv. Funct. Mater., 2018, 28, 1706923. R. Shivanna, G. F. Trindade, J. F. Watts, Z. Xu, T. Liu,
231 Q. Zhou, L. Liang, J. Hu, B. Cao, L. Yang, T. Wu, X. Li, K. Chen, F. Ye, P. Wu, L. Zhao, J. Wu, Y. Tu, Y. Zhang,
B. Zhang and P. Gao, Adv. Energy Mater., 2019, 9, 1802595. X. Yang, W. Zhang, R. H. Friend, Q. Gong, H. J. Snaith and
232 H. Min, M. Kim, S.-U. Lee, H. Kim, G. Kim, K. Choi, R. Zhu, Science, 2018, 360, 1442–1446.
J. H. Lee and S. I. Seok, Science, 2019, 366, 749–753. 251 M. Tai, Y. Zhou, X. Yin, J. Han, Q. Zhang, Y. Zhou and
233 Y. Liu, S. Akin, L. Pan, R. Uchida, N. Arora, J. V. Milić, H. Lin, J. Mater. Chem. A, 2019, 7, 22675–22682.
A. Hinderhofer, F. Schreiber, A. R. Uhl, S. M. Zakeeruddin, 252 B. Chen, P. N. Rudd, S. Yang, Y. Yuan and J. Huang, Chem.
A. Hagfeldt, M. I. Dar and M. Grätzel, Sci. Adv., 2019, Soc. Rev., 2019, 48, 3842–3867.
5, eaaw2543. 253 T. Niu, J. Lu, X. Jia, Z. Xu, M.-C. Tang, D. Barrit, N. Yuan,
234 C. Ma, C. Leng, Y. Ji, X. Wei, K. Sun, L. Tang, J. Yang, J. Ding, X. Zhang, Y. Fan, T. Luo, Y. Zhang, D.-M. Smilgies,
W. Luo, C. Li, Y. Deng, S. Feng, J. Shen, S. Lu, C. Du and Z. Liu, A. Amassian, S. Jin, K. Zhao and S. Liu, Nano Lett.,
H. Shi, Nanoscale, 2016, 8, 18309–18314. 2019, 19, 7181–7190.
235 H. Kim, S.-U. Lee, D. Y. Lee, M. J. Paik, H. Na, J. Lee and 254 F. Giustino and H. J. Snaith, ACS Energy Lett., 2016, 1, 1233–1240.
S. I. Seok, Adv. Energy Mater., 2019, 9, 1902740. 255 F. Hao, C. C. Stoumpos, D. H. Cao, R. P. H. Chang and
236 J. Chen, J.-Y. Seo and N.-G. Park, Adv. Energy Mater., 2018, M. G. Kanatzidis, Nat. Photonics, 2014, 8, 489.
8, 1702714. 256 T. Miyasaka, A. Kulkarni, G. M. Kim, S. Öz and A. K. Jena,
237 S. Gharibzadeh, B. Abdollahi Nejand, M. Jakoby, Adv. Energy Mater., 2019, 1902500.
T. Abzieher, D. Hauschild, S. Moghadamzadeh, J. A. 257 I. Zimmermann, S. Aghazada and M. K. Nazeeruddin,
Schwenzer, P. Brenner, R. Schmager, A. A. Haghighirad, Angew. Chem., Int. Ed., 2019, 58, 1072–1076.
L. Weinhardt, U. Lemmer, B. S. Richards, I. A. Howard and 258 C. Ran, J. Xi, W. Gao, F. Yuan, T. Lei, B. Jiao, X. Hou and
U. W. Paetzold, Adv. Energy Mater., 2019, 9, 1803699. Z. Wu, ACS Energy Lett., 2018, 3, 713–721.
238 M. S. de Holanda, R. Szostak, P. E. Marchezi, L. G. T. A. 259 D. H. Cao, C. C. Stoumpos, T. Yokoyama, J. L. Logsdon,
Duarte, J. C. Germino, T. D. Z. Atvars and A. F. Nogueira, T.-B. Song, O. K. Farha, M. R. Wasielewski, J. T. Hupp and
Sol. RRL, 2019, 3, 1900199. M. G. Kanatzidis, ACS Energy Lett., 2017, 2, 982–990.
239 K. T. Cho, Y. Zhang, S. Orlandi, M. Cavazzini, 260 Y. Liao, H. Liu, W. Zhou, D. Yang, Y. Shang, Z. Shi, B. Li,
I. Zimmermann, A. Lesch, N. Tabet, G. Pozzi, G. Grancini X. Jiang, L. Zhang, L. N. Quan, R. Quintero-Bermudez,
and M. K. Nazeeruddin, Nano Lett., 2018, 18, 5467–5474. B. R. Sutherland, Q. Mi, E. H. Sargent and Z. Ning, J. Am.
240 X. Zhang, R. Munir, Z. Xu, Y. Liu, H. Tsai, W. Nie, J. Li, Chem. Soc., 2017, 139, 6693–6699.
T. Niu, D.-M. Smilgies, M. G. Kanatzidis, A. D. Mohite, 261 S. Shao, J. Liu, G. Portale, H.-H. Fang, G. R. Blake, G. H. ten
K. Zhao, A. Amassian and S. Liu, Adv. Mater., 2018, Brink, L. J. A. Koster and M. A. Loi, Adv. Energy Mater.,
30, 1707166. 2018, 8, 1702019.
241 Y. Hu, J. Schlipf, M. Wussler, M. L. Petrus, W. Jaegermann, 262 J. Qiu, Y. Xia, Y. Zheng, W. Hui, H. Gu, W. Yuan, H. Yu,
T. Bein, P. Müller-Buschbaum and P. Docampo, ACS Nano, L. Chao, T. Niu, Y. Yang, X. Gao, Y. Chen and W. Huang,
2016, 10, 5999–6007. ACS Energy Lett., 2019, 4, 1513–1520.

1184 | Energy Environ. Sci., 2020, 13, 1154--1186 This journal is © The Royal Society of Chemistry 2020
 View Article Online

Review Energy & Environmental Science

263 M. Chen, M.-G. Ju, M. Hu, Z. Dai, Y. Hu, Y. Rong, H. Han, 282 J. Xing, Y. Zhao, M. Askerka, L. N. Quan, X. Gong, W. Zhao,
X. C. Zeng, Y. Zhou and N. P. Padture, ACS Energy Lett., J. Zhao, H. Tan, G. Long, L. Gao, Z. Yang, O. Voznyy,
2019, 4, 276–277. J. Tang, Z.-H. Lu, Q. Xiong and E. H. Sargent, Nat. Commun.,
264 M.-G. Ju, J. Dai, L. Ma, Y. Zhou, W. Liang and X. C. Zeng, 2018, 9, 3541.
J. Mater. Chem. A, 2019, 7, 16742–16747. 283 X. Yang, X. Zhang, J. Deng, Z. Chu, Q. Jiang, J. Meng,
265 D. B. Straus and C. R. Kagan, J. Phys. Chem. Lett., 2018, 9, P. Wang, L. Zhang, Z. Yin and J. You, Nat. Commun., 2018,
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

1434–1447. 9, 570.
266 C. Katan, N. Mercier and J. Even, Chem. Rev., 2019, 119, 284 Y. Shang, Y. Liao, Q. Wei, Z. Wang, B. Xiang, Y. Ke, W. Liu
3140–3192. and Z. Ning, Sci. Adv., 2019, 5, eaaw8072.
267 L. Zhang, Y. Liu, Z. Yang and S. Liu, J. Energy Chem., 2019, 285 H. Tsai, W. Nie, J.-C. Blancon, C. C. Stoumpos,
37, 97–110. C. M. M. Soe, J. Yoo, J. Crochet, S. Tretiak, J. Even,
268 B. R. Sutherland and E. H. Sargent, Nat. Photonics, 2016, A. Sadhanala, G. Azzellino, R. Brenes, P. M. Ajayan,
10, 295–302. V. Bulović, S. D. Stranks, R. H. Friend, M. G. Kanatzidis
269 Y.-H. Kim, H. Cho and T.-W. Lee, Proc. Natl. Acad. Sci. and A. D. Mohite, Adv. Mater., 2018, 30, 1704217.
U. S. A., 2016, 113, 11694–11702. 286 A. Yangui, D. Garrot, J. S. Lauret, A. Lusson, G. Bouchez,
270 Y.-H. Kim, H. Cho, J. H. Heo, T.-S. Kim, N. Myoung, E. Deleporte, S. Pillet, E. E. Bendeif, M. Castro, S. Triki, Y. Abid
C.-L. Lee, S. H. Im and T.-W. Lee, Adv. Mater., 2015, 27, and K. Boukheddaden, J. Phys. Chem. C, 2015, 119, 23638–23647.
1248–1254. 287 I. Neogi, A. Bruno, D. Bahulayan, T. W. Goh, B. Ghosh,
271 H. Zhu, Y. Fu, F. Meng, X. Wu, Z. Gong, Q. Ding, R. Ganguly, D. Cortecchia, T. C. Sum, C. Soci, N. Mathews
M. V. Gustafsson, M. T. Trinh, S. Jin and X. Y. Zhu, Nat. and S. G. Mhaisalkar, ChemSusChem, 2017, 10, 3765–3772.
Mater., 2015, 14, 636–642. 288 M. D. Smith and H. I. Karunadasa, Acc. Chem. Res., 2018,
272 X. Gong, Z. Yang, G. Walters, R. Comin, Z. Ning, 51, 619–627.
E. Beauregard, V. Adinolfi, O. Voznyy and E. H. Sargent, 289 J. Yu, J. Kong, W. Hao, X. Guo, H. He, W. R. Leow, Z. Liu,
Nat. Photonics, 2016, 10, 253–257. P. Cai, G. Qian, S. Li, X. Chen and X. Chen, Adv. Mater.,
273 X. Hong, T. Ishihara and A. V. Nurmikko, Phys. Rev. B: 2019, 31, 1806385.
Condens. Matter Mater. Phys., 1992, 45, 6961–6964. 290 E. P. Booker, T. H. Thomas, C. Quarti, M. R. Stanton,
274 M. Era, S. Morimoto, T. Tsutsui and S. Saito, Appl. Phys. C. D. Dashwood, A. J. Gillett, J. M. Richter, A. J. Pearson,
Lett., 1994, 65, 676–678. N. J. L. K. Davis, H. Sirringhaus, M. B. Price, N. C. Greenham,
275 K. Gauthron, J. S. Lauret, L. Doyennette, G. Lanty, A. Al D. Beljonne, S. E. Dutton and F. Deschler, J. Am. Chem. Soc.,
Choueiry, S. J. Zhang, A. Brehier, L. Largeau, O. Mauguin, 2017, 139, 18632–18639.
J. Bloch and E. Deleporte, Opt. Express, 2010, 18, 291 Q. Zhang, Y. Ji, Z. Chen, D. Vella, X. Wang, Q.-H. Xu, Y. Li
5912–5919. and G. Eda, J. Phys. Chem. Lett., 2019, 10, 2869–2873.
276 D. Liang, Y. Peng, Y. Fu, M. J. Shearer, J. Zhang, J. Zhai, 292 T. Li, X. Chen, X. Wang, H. Lu, Y. Yan, M. C. Beard and
Y. Zhang, R. J. Hamers, T. L. Andrew and S. Jin, ACS Nano, D. B. Mitzi, ACS Energy Lett., 2019, 347–352, DOI: 10.1021/
2016, 10, 6897–6904. acsenergylett.9b02490.
277 X. Gong, O. Voznyy, A. Jain, W. Liu, R. Sabatini, 293 X. Wang, W. Meng, W. Liao, J. Wang, R.-G. Xiong and
Z. Piontkowski, G. Walters, G. Bappi, S. Nokhrin, Y. Yan, J. Phys. Chem. Lett., 2019, 10, 501–506.
O. Bushuyev, M. Yuan, R. Comin, D. McCamant, S. O. 294 E. I. Rashba, Sov. Phys. Solid State, 1960, 2, 1109–1122.
Kelley and E. H. Sargent, Nat. Mater., 2018, 17, 550–556. 295 M. Kepenekian and J. Even, J. Phys. Chem. Lett., 2017, 8,
278 J. Byun, H. Cho, C. Wolf, M. Jang, A. Sadhanala, 3362–3370.
R. H. Friend, H. Yang and T.-W. Lee, Adv. Mater., 2016, 296 P. Odenthal, W. Talmadge, N. Gundlach, R. Wang,
28, 7515–7520. C. Zhang, D. Sun, Z.-G. Yu, Z. Valy Vardeny and Y. S. Li,
279 N. Wang, L. Cheng, R. Ge, S. Zhang, Y. Miao, W. Zou, C. Yi, Nat. Phys., 2017, 13, 894.
Y. Sun, Y. Cao, R. Yang, Y. Wei, Q. Guo, Y. Ke, M. Yu, Y. Jin, 297 J. Wang, C. Zhang, H. Liu, R. McLaughlin, Y. Zhai,
Y. Liu, Q. Ding, D. Di, L. Yang, G. Xing, H. Tian, C. Jin, S. R. Vardeny, X. Liu, S. McGill, D. Semenov, H. Guo,
F. Gao, R. H. Friend, J. Wang and W. Huang, Nat. Photo- R. Tsuchikawa, V. V. Deshpande, D. Sun and Z. V.
nics, 2016, 10, 699. Vardeny, Nat. Commun., 2019, 10, 129.
280 B. Zhao, S. Bai, V. Kim, R. Lamboll, R. Shivanna, F. Auras, 298 E. Mosconi, T. Etienne and F. De Angelis, J. Phys. Chem.
J. M. Richter, L. Yang, L. Dai, M. Alsari, X.-J. She, L. Liang, Lett., 2017, 8, 2247–2252.
J. Zhang, S. Lilliu, P. Gao, H. J. Snaith, J. Wang, 299 X. Che, B. Traore, C. Katan, M. Kepenekian and J. Even,
N. C. Greenham, R. H. Friend and D. Di, Nat. Photonics, Phys. Chem. Chem. Phys., 2018, 20, 9638–9643.
2018, 12, 783–789. 300 D. Niesner, M. Wilhelm, I. Levchuk, A. Osvet, S. Shrestha,
281 L. N. Quan, Y. Zhao, F. P. Garcı́a de Arquer, R. Sabatini, M. Batentschuk, C. Brabec and T. Fauster, Phys. Rev. Lett.,
G. Walters, O. Voznyy, R. Comin, Y. Li, J. Z. Fan, H. Tan, 2016, 117, 126401.
J. Pan, M. Yuan, O. M. Bakr, Z. Lu, D. H. Kim and 301 Y. A. Bychkov and É. I. Rashba, J. Exp. Theor. Phys., 1984,
E. H. Sargent, Nano Lett., 2017, 17, 3701–3709. 39, 78.

This journal is © The Royal Society of Chemistry 2020 Energy Environ. Sci., 2020, 13, 1154--1186 | 1185
 View Article Online

Energy & Environmental Science Review

302 K. Liao, X. Hu, Y. Cheng, Z. Yu, Y. Xue, Y. Chen and X. R. Wang, D. Song, O. Voznyy, M. Zhang, S. Hoogland,
Q. Gong, Adv. Opt. Mater., 2019, 7, 1900350. W. Gao, Q. Xiong and E. H. Sargent, Nat. Photonics, 2018,
303 P. Odenthal, W. Talmadge, N. Gundlach, R. Wang, 12, 528–533.
C. Zhang, D. Sun, Z.-G. Yu, Z. Valy Vardeny and Y. S. Li, 313 J. Ma, C. Fang, C. Chen, L. Jin, J. Wang, S. Wang, J. Tang
Nat. Phys., 2017, 13, 894–899. and D. Li, ACS Nano, 2019, 13, 3659–3665.
304 Y. Yang, M. Yang, K. Zhu, J. C. Johnson, J. J. Berry, J. van de 314 H. Lu, J. Wang, C. Xiao, X. Chen, R. Brunecky, J. J. Berry,
Published on 18 February 2020. Downloaded by Indian Institute of Technology Roorkee on 7/30/2025 5:45:27 AM.

Lagemaat and M. C. Beard, Nat. Commun., 2016, 7, 12613. K. Zhu, M. C. Beard and Z. V. Vardeny, Sci. Adv., 2019,
305 D. Sun, C. Zhang, M. Kavand, K. J. van Schooten, 5, aay0571.
H. Malissa, M. Groesbeck, R. McLaughlin, C. Boehme 315 B. P. Bloom, V. Kiran, V. Varade, R. Naaman and
and Z. V. Vardeny, 2016, arXiv preprint arXiv:1608.00993. D. H. Waldeck, Nano Lett., 2016, 16, 4583–4589.
306 Y. Zhai, S. Baniya, C. Zhang, J. Li, P. Haney, C.-X. Sheng, 316 P. C. Mondal, C. Fontanesi, D. H. Waldeck and R. Naaman,
E. Ehrenfreund and Z. V. Vardeny, Sci. Adv., 2017, Acc. Chem. Res., 2016, 49, 2560–2568.
3, e1700704. 317 V. Kiran, S. R. Cohen and R. Naaman, J. Chem. Phys., 2017,
307 J. Yin, P. Maity, L. Xu, A. M. El-Zohry, H. Li, O. M. Bakr, 146, 092302.
J.-L. Brédas and O. F. Mohammed, Chem. Mater., 2018, 30, 318 L. Dou, Y. Yang, J. You, Z. Hong, W.-H. Chang, G. Li and
8538–8545. Y. Yang, Nat. Commun., 2014, 5, 5404.
308 S. B. Todd, D. B. Riley, A. Binai-Motlagh, C. Clegg, 319 Y. Fang, Q. Dong, Y. Shao, Y. Yuan and J. Huang, Nat.
A. Ramachandran, S. A. March, J. M. Hoffman, I. G. Hill, Photonics, 2015, 9, 679–686.
C. C. Stoumpos, M. G. Kanatzidis, Z.-G. Yu and K. C. Hall, 320 M. Ahmadi, T. Wu and B. Hu, Adv. Mater., 2017,
APL Mater., 2019, 7, 081116. 29, 1605242.
309 X. Chen, H. Lu, Z. Li, Y. Zhai, P. F. Ndione, J. J. Berry, 321 F. P. Garcı́a de Arquer, A. Armin, P. Meredith and
K. Zhu, Y. Yang and M. C. Beard, ACS Energy Lett., 2018, 3, E. H. Sargent, Nat. Rev. Mater., 2017, 2, 16100.
2273–2279. 322 Akriti, E. Shi and L. Dou, Trends Chem., 2019, 1, 365–367.
310 D. Giovanni, W. K. Chong, H. A. Dewi, K. Thirumal, 323 Y. Liu, H. Ye, Y. Zhang, K. Zhao, Z. Yang, Y. Yuan, H. Wu,
I. Neogi, R. Ramesh, S. Mhaisalkar, N. Mathews and G. Zhao, Z. Yang, J. Tang, Z. Xu and S. Liu, Matter, 2019, 1,
T. C. Sum, Sci. Adv., 2016, 2, e1600477. 465–480.
311 D. Giovanni, J. W. M. Lim, Z. Yuan, S. S. Lim, M. Righetto, 324 N. Zhou, B. Huang, M. Sun, Y. Zhang, L. Li, Y. Lun,
J. Qing, Q. Zhang, H. A. Dewi, F. Gao, S. G. Mhaisalkar, X. Wang, J. Hong, Q. Chen and H. Zhou, Adv. Energy
N. Mathews and T. C. Sum, Nat. Commun., 2019, 10, 3456. Mater., 2019, 1901566.
312 G. Long, C. Jiang, R. Sabatini, Z. Yang, M. Wei, L. N. Quan, 325 M. Long, T. Zhang, D. Chen, M. Qin, Z. Chen, L. Gong,
Q. Liang, A. Rasmita, M. Askerka, G. Walters, X. Gong, X. Lu, F. Xie, W. Xie, J. Chen and J. Xu, ACS Energy Lett.,
J. Xing, X. Wen, R. Quintero-Bermudez, H. Yuan, G. Xing, 2019, 4, 1025–1033.

1186 | Energy Environ. Sci., 2020, 13, 1154--1186 This journal is © The Royal Society of Chemistry 2020