Advances in Chemical Engineering and Science, 2023, 13, 289-300

https://www.scirp.org/journal/aces
ISSN Online: 2160-0406
ISSN Print: 2160-0392

Effect of Defects at the Buffer Layer

CdS/Absorber CIGS Interface on CIGS
Solar Cell Performance

Boureima Traoré, Soumaïla Ouédraogo, Marcel Bawindsom Kébré, Daouda Oubda,

Issiaka Sankara, Adama Zongo, François Zougmoré

Laboratoire de Matériaux et Environnement (LA.M.E)-UFR/SEA, Département de Physique, Université Joseph Ki-ZERBO,

Ouagadougou, Burkina Faso

How to cite this paper: Traoré, B., Oué- Abstract

draogo, S., Kébré, M.B., Oubda, D., Sanka-
ra, I., Zongo, A. and Zougmoré, F. (2023) This scientific paper presents a study investigating the effects of defects at the
Effect of Defects at the Buffer Layer CdS/ CdS/CIGS and CdS/SDL interfaces on the performance of CIGS solar cells.
Absorber CIGS Interface on CIGS Solar Cell
The objective of this study is to analyze the influence of defects at the inter-
Performance. Advances in Chemical Engi-
neering and Science, 13, 289-300. face between the CdS buffer layer and the CIGS absorber, as well as the sur-
https://doi.org/10.4236/aces.2023.134020 face defect layer (SDL), on CIGS solar cell performance. The study explores
three key aspects: the impact of the conduction band offset (CBO) at the
Received: August 7, 2023
CdS/CIGS interface, the effects of interface defects and defect density on per-
Accepted: September 25, 2023
Published: September 28, 2023
formance, and the combined influence of CBO and defect density at the CdS/
SDL and SDL/CIGS interfaces. For interface defects not exceeding 1013 cm−2,
Copyright © 2023 by author(s) and we obtained a good efficiency of 22.9% when −0.1 eV < CBO < 0.1 eV. By
Scientific Research Publishing Inc.
analyzing the quality of CdS/SDL and SDL/CIGS junctions, it appears that
This work is licensed under the Creative
Commons Attribution International
defects at the SDL/CIGS interface have very little impact on the performances
License (CC BY 4.0). of the CIGS solar cell. By optimizing the electrical parameters of the CdS/SDL
http://creativecommons.org/licenses/by/4.0/ interface defects, we achieved a conversion efficiency of 23.1% when −0.05 eV
Open Access < CBO < 0.05 eV.

Keywords
Numerical Simulation, CdS/CIGS Interface, Interface Defects, Conduction
Band Offset (CBO), Surface Defect Layer (SDL)

1. Introduction
Today, thin films occupy a prominent place in the field of photovoltaic solar
cells due to their low production cost and excellent conversion efficiency of up
to 23.35% [1]. All these record efficiencies are closely linked to the quality of the

DOI: 10.4236/aces.2023.134020 Sep. 28, 2023 289 Advances in Chemical Engineering and Science
B. Traoré et al.

buffer layer/absorber interface. The CdS/CIGS interface plays an important role

in the separation of electron-hole pairs [2]. The CdS/CIGS interface is a region
where the atomic arrangement is strongly disturbed, thus creating atomic inter-
diffusion phenomena [3]. Annealing conditions [2] and post-deposition treat-
ments, which require high temperatures, can modify the properties of the CdS/
CIGS interface. This change in interface properties can lead to interface defects
[4]. The difference in optical and electrical properties between the buffer layer
and the absorber leads to detuning at the band level, resulting in a band offset at
the CdS/CIGS interface [5]. Several studies performed with X-ray photoelectron
spectrometry (XPS) have shown the presence of very thin In-rich n-type layers
( CuIn 3Se5 ) on the surface of the CIGS absorber [2] [4]. This thin layer, identi-
fied as a surface defect layer is commonly referred to as (SDL). These studies
have also shown that the composition of the absorber surface is different from
that of the CIGS absorber volume [6] [7] [8]. The impact of defects at the CdS/
CIGS interface on the operation of the CIGS-based solar cell is not yet well un-
derstood, and is the subject of several theoretical and experimental studies. Con-
sequently, can the presence of this layer of surface defects at the CdS/CIGS in-
terface significantly impact solar cell performance? After highlighting the three
types of defects that limit cell performance at the CdS/CIGS interface, a detailed
study of interface defects and conduction band offset at the CdS/CIGS interface
will be carried out. Taking into account the surface defect layer (SDL), a study
will also be carried out on the CdS/SDL and SDL/CIGS interfaces. Our aim is to
study the impact of these defects at the CdS/CIGS and CdS/SDL and SDL/CIGS
interfaces on the performance of the CIGS-based solar cell.

2. Device Model and Simulation Details

Numerical simulation is used to study the influence of solar cell parameters on
these electrical characteristics without performing the experiment. In this work,
we will use the SCAPS-1D software [9] [10] to perform our numerical simula-
tions. SCAPS-1D uses the finite-difference method with well-defined boundary
conditions to solve the basic equations: the Poisson equation, the continuity eq-
uations and transports equation of electrons respectively of holes. SCAPS is used
to replicate and investigate all the available research-level CIGS solar cells with
various buffer layers. From the solution provided by SCAPS simulation, output
such as current voltage characteristics in the dark and under illumination can be
obtained as a function of temperature.
The structure of the CIGS-based thin-film solar cell comprises a mechanical
substrate, a molybdenum (Mo) back contact, a p-type CIGS absorber that forms
the P-N heterojunction with the n-type CdS buffer layer, a transparent conduc-
tive oxide (OTC) window layer and an aluminum-nickel metal grid front con-
tact. Its structure (ZnO:i)/(CdS/(CIGS/Mo)) is shown in Figure 1(a). The second
structure (ZnO:i)/(CdS/(SDL/CIGS)/Mo) studied with SDL is shown in Figure
1(b).

DOI: 10.4236/aces.2023.134020 290 Advances in Chemical Engineering and Science

 B. Traoré et al.

Figure 1. Structure of the CIGS solar cell with SDL (a) and without SDL (b).

Figure 2. Energy band diagram of the cell when the conduction band
of CIGS is above (CBO > 0) (a) and below (CBO < 0) (b) that of CdS.

At the interface between the CdS buffer layer and the CIGS absorber, Schmid
et al have shown the presence of a thin surface defect layer (SDL) rich in n-type
indium (Figure 1(b)). This thin layer is identified as a defect and formed by
atomic inter diffusion between the CdS buffer layer and the CIGS absorber [11].
With a gap wider than that of the CIGS at volume [2] [12] this layer is formed
on the surface of the CIGS. Figure 2 shows the energy band diagram of the solar
cell of the i-ZnO/(CdS/(CIGS/Mo)) structure. In Figure 2(a), the conduction
band of the CdS buffer layer is above that of the CIGS absorber, resulting in a
peak (CBO > 0) at the CdS/CIGS interface. As for Figure 2(b), the conduction
band of CdS is below that of the CIGS absorber, resulting in a cliff (CBO < 0) at
the CdS/CIGS interface.
The properties of the different layers and interfaces used for the numerical
simulation are summarized in Table 1. These properties were obtained from
theoretical and experimental results [11] [13] [14] [15].
The solar cell temperature is maintained at 300 K and is illuminated under
standard conditions by an AM 1.5 G spectrum that accounts for both direct and
diffuse radiation. In order to validate our results, we compared the J-V characte-
ristic curves of our numerical simulation with that performed experimentally by

DOI: 10.4236/aces.2023.134020 291 Advances in Chemical Engineering and Science

B. Traoré et al.

Table 1. Parameters used to simulate the CIGS solar cell CIGS.

Layers properties
i-Zno CdS SDL CIGS
Thickness (nm) 300 50 15 2500
Band gap (eV) 3.3 2.4 1.3 1.25
Electron Affinity (eV) 4.55 Variable Variable Variable
Diélectric relative Permittivity 9.00 10 13.6 13.6
Effective densité of state in
3.1 ∗1018 3.1 ∗1018 2 ∗1018 2 ∗1018
BC (cm−3)
Effective densité of state in
1.8 ∗1019 3.1 ∗1018 1.5 ∗1019 1.5 ∗1019
BV (cm−3)
Electrons thermal velocity (cm/s) 2.4 ∗107 3.1 ∗107 3.9 ∗107 3.9 ∗107
Holes thermal velocity (cm/s) 1.3 ∗107 1.6 ∗107 1.4 ∗107 1.4 ∗107
Electrons Mobility (cm2/Vs) 100 72 10 100
Holes Mobility (cm2/Vs) 31 20 1.25 12.5

Doping concentration (cm−3) 1 ∗1017

( D) 5 ∗10 17
( D) 1 ∗1013
( D) 1 ∗1016 ( A )

Bulk defect properties

Bulk defect Density (cm−3) 1 ∗1016 5 ∗1016 1 ∗1014 1 ∗1014
Capture cross-section
1 ∗10−15 1 ∗10−15 5 ∗10−13 Variable
electrons (cm2)
Capture cross-section holes (cm2) 5 ∗10−13 5 ∗10−13 5 ∗10−15 5 ∗10−15
Interface Properties
CdS/SDL SDL/CIGS
Interface defect density (cm ) −2
Variable Variable
Capture cross-section
1 ∗10−15 1 ∗10−15
electrons (cm2)
Capture cross-section holes (cm2) 1 ∗10−15 1 ∗10−15

Figure 3. J-V characteristic curves compared compared with

experimental results by Pettersson et al. [11].

DOI: 10.4236/aces.2023.134020 292 Advances in Chemical Engineering and Science

 B. Traoré et al.

Pettersson. A good agreement is found between these two results, as shown in

Figure 3.

3. Result and Discussion

3.1. CdS/CIGS Interface
In the absence of the surface defect layer (SDL), the predominant defects at the
buffer layer/absorber interface are interface defects and band offset. These de-
fects are due to inter-diffusion phenomena and band alignment at the buffer
layer/absorber interface. To this end, we will study the impact of interface de-
fects on solar cell performance as a function of minority carrier lifetime in the
CIGS absorber. The same will apply to the conduction band offset on solar cell
performance.

3.1.1. Band Offset at the CdS/CIGS Interface and Minority Carrier

Lifetime in the Absorber
The conduction band offset at the CIGS/CdS interface and the minority carrier
lifetime ( τ n ) in the absorber are two very important parameters affecting the
performance of the CIGS-based solar cell CBO is represented by the difference
in electronic affinity between the absorber (CIGS) and the buffer layer (CdS). To
carry out our simulations, we will keep the electronic affinity of the absorber
constant χ CIGS = 4.5 eV by varying that of the buffer layer χ CdS from (4 eV to
5 eV) thus resulting in a variation of the conduction band offset from −0.5 eV to
0.5 eV. The lifetime of the minority carriers in the absorber will vary from 10−2 ns
to 101 ns with a step of 10 ns. Since the absorber in this cell is p-doped, the
minority charge carriers are electrons. Figure 4 shows the influence of the con-
duction band offset at the CdS/CIGS interface on the electrical parameters
( J SC ,VOC , FF ,η ) as a function of the minority carrier lifetime in the absorber.
Generally speaking, all electrical characteristics increase as the electron lifetime
in the absorber increases. When CBO < −0.2 eV, all electrical parameters of the
solar cell decrease. Open-circuit voltage ( VOC ) and conversion efficiency (ŋ) are
the characteristics most affected (Figure 4(a), Figure 4(d)). This decrease can be
explained by a high cliff depth (Figure 3(b)). The cliff decreases the potential
difference across the ZCE, thus increasing the probability of recombination at
the CdS/CIGS interface, leading to a decrease in ( VOC ). Above −0.2 eV, ( VOC ) is
almost constant. When CBO > 0.4 eV (Figure 4), solar cell performance decreases
sharply through short-circuit current density ( J SC ), efficiency η and form factor
(FF).
This decrease may be due to the high peak shown in (Figure 3(a)). This peak
acts as a barrier against photo-generated electrons in the absorber. If the peak
height exceeds 0.4 eV, the photo-generated electrons cannot cross the barrier, so
they recombine with the holes. These results are in good agreement with nu-
merical simulations carried out on the CdS/CIGS interface by Minemoto et al.
and Gloeckler et al. [16] [17]. They concluded that photogenerated carrier trans-
port is blocked if CBO > 0.4 eV, resulting in a reduction in short-circuit current

DOI: 10.4236/aces.2023.134020 293 Advances in Chemical Engineering and Science

B. Traoré et al.

Figure 4. Effect of conduction band offset at the CdS/CIGS interface on electrical para-
meters as a function of electron lifetime in the absorber.

density ( J SC ), form factor (FF) and device efficiency. When −0.1 eV < CBO <
0.1 eV, better performance is achieved with efficiency reaching 22.8%. This per-
formance can be explained by a favorable conduction band alignment at the
CdS/CIGS interface. This interval corresponds to very low values of peak height
and cliff depth. However, adjustment of the conduction band discontinuity is
necessary to improve solar cell performance.

3.1.2. Defects at the CdS/CIGS Interface and Minority Carrier Lifetime in

Absorber
In CIGS-based solar cells, the CdS/CIGS interface is susceptible to have defects
called interface defects (Dint) due to the different optoelectronic properties of
CdS and CIGS. This interface is considered to be a zone of high recombination
due to defects linked to dangling bonds. To quantify the impact that these inter-
face defects play on the operation of the CIGS solar cell, simulations are car-
ried out by varying the density of interface defects from 1010 cm−2 to 1018 cm−2.
Figure 5 shows us the influence of defects at the CdS/CIGS interface on the
electrical parameters as a function of the minority carrier lifetime in the ab-
sorber.
In general, all electrical characteristics increase with increasing electron life-
time in the absorber. When defects at the CdS/CIGS interface are less than 1013
cm−2, very good performances are obtained through the electrical parameters
as shown in Figure 5. However, interface defects greater than 1013 cm−2 leads to
a decrease of all the electrical parameters of the cell as shown in Figure 5. This is

DOI: 10.4236/aces.2023.134020 294 Advances in Chemical Engineering and Science

 B. Traoré et al.

Figure 5. Effect of defect at the CdS/CIGS interface on electrical parameters as a function

of electron lifetime in the absorber.

probably due to a Fermi level not very an favourable anchor level at this inter-
face [15]. When defects at the CdS/CIGS interface are very large (Dint > 1013
cm−2), the device’s band structure exhibits weak band curvature in the space
charge zone (SCZ), resulting in very poor cell performance.

3.1.3. Band Offset and Defect Density at the CdS/CIGS Interface

In Sections 3.1.1 and 3.1.2, we see that all electrical parameters increase as the
electron lifetime in the absorber increases, and good performance is achieved
for an electron lifetime in the absorber of 10 ns. For a deeper understanding,
we will study the influence of the conduction band offset as a function of de-
fects at the CdS/CIGS interface on the electrical parameters as represented in
Figure 6.
For low values of the conduction band offset, very poor performances are ob-
tained through the short-circuit current density ( J SC ), form factor (FF) and de-
vice efficiency η for high values of defects at the CdS/CIGS interface i.e. exceed-
ing 1015 cm−2 as shown in Figure 6(a), Figure 6(b), Figure 6(d). This study con-
firms the results obtained in Section 3.1.1. and 3.1.2. This poor performance can
be explained by a high cliff that acts as a barrier against photogenerated elec-
trons, favoring recombination phenomena via excessively high interface defects.
When CBO > 0.4 eV, the efficiency η and the form factor decrease sharply as
shown in Figure 6(c), Figure 6(d). This decrease in solar cell performance
may be due to a very high peak as shown in Figure 3(a) As for the short-circuit

DOI: 10.4236/aces.2023.134020 295 Advances in Chemical Engineering and Science

B. Traoré et al.

Figure 6. Effect of conduction band offset at the CdS/CIGS on electrical parameters as a

function of electron lifetime in the absorber.

current density, it decreases when the interface defects exceed 1015 cm−2. This
can be explained by the combined effect of the high peak and fermi level anc-
horing due to the very high interface defects. At the end of this study dedicated
to the CdS/CIGS interface, it emerges that better performances are obtained with
−0.1 eV < CBO < 0.1 eV and interface defects lower than 1013 cm−2.

3.2. CdS/SDL and SDL/CIGS Interfaces

3.2.1. Band Offset at the CdS/SDL and SDL/CIGS Interface and Minority
Carrier Lifetime in the Absorber
Figure 7 shows us the influence of the conduction band discontinuity at the CdS/
SDL and SDL/CIGS interfaces on the electrical characteristics as a function of
electron lifetime in the absorber. In general, all electrical parameters increase
with increasing electron lifetime in the absorber. When CBO < −0.1 eV, the open-
circuit voltage ( VOC ) decreases at the CdS/SDL and SDL/CIGS interfaces com-
pared with the CdS/CIGS interface, where ( VOC ) decreases when CBO < −0.3
eV. This decrease may be due to the double cliff at both interfaces. The cliff de-
creases the potential difference across the space charge zone (ZCS), thus in-
creasing the probability of recombination at both interfaces. When CBO > 0.3
eV, the open-circuit voltage ( VOC ) remains relatively constant at the CdS/SDL
interface (Figure 7(a)) and decreases sharply at the SDL/CIGS interface (Figure
7(b)). As for the short-circuit current density ( J SC ), it grows linearly with the
CBO at the CdS/SDL interface Figure 7(c). When CBO < −0.4 eV and CBO >
0.1 eV, ( J SC ), decreases at the SDL/CIGS interface Figure 7(d).

DOI: 10.4236/aces.2023.134020 296 Advances in Chemical Engineering and Science

 B. Traoré et al.

Figure 7. Effect of conduction band offset at the CdS/SDL and SDL/CIGS interface on
electrical parameters (JSC and VOC) as a function of electron lifetime in the absorber.

In the previous section, we showed that better performance is achieved when

−0.1 eV < CBO (CdS/CIGS) < 0.1 eV. Next, we will compare the conversion effi-
ciency (η) when the conduction band offset at the CdS/SDL and SDL/CIGS in-
terfaces is between −0.1 eV and 0.1 eV. At the CdS/SDL interface, the conversion
efficiency increases slightly, reaching a value of 22.9% as shown Figure 8(c). For
the SDL/CIGS interface, the conversion efficiency increases to 23.1%, i.e. an effi-
ciency gain of 0.2% (Figure 8(d)). In view of the above, we can say that an im-
provement in solar cell performance is observed when −0.1 eV < CBO (SDL/
CIGS) < 0.1 eV. This implies that defects at the SDL/CIGS interface have less
impact on solar cell performance. This may be due to the fact that the surface
defect layer has almost the same composition as the absorber volume and that
the p-n junction is formed between p-CIGS and n-SDL, not between p-CIGS and
n-CdS [6] [8].

3.2.2. Defects at the CdS/SDL and SDL/CIGS Interfaces

To quantify the impact that interface defects play on the operation of the CIGS so-
lar cell, we will simultaneously study the impact of defects at the CdS/SDL and
SDL/CIGS interfaces on electrical performance as illustrated in the figure (Figure
9). Generally speaking, very good performance is observed when defects at the
CdS/SDL and SDL/CIGS interfaces are less than 1013 cm−2. At the CdS/SDL inter-
face, performance decreases drastically when Dint ( CdS SDL ) > 1013 cm−2. At the
SDL/CIGS interface, performance decreases slightly when Dint ( SDL CIGS) >
1013 cm−2. This decrease may probably be due to an unfavorable Fermi level

DOI: 10.4236/aces.2023.134020 297 Advances in Chemical Engineering and Science

B. Traoré et al.

Figure 8. Effect of conduction band offset at the CdS/SDL and SDL/CIGS interface on
electrical parameters (η and FF) as a function of electron lifetime in the absorber.

Figure 9. Effect of defect at the CdS/SDL and SDL/CIGS interface on electrical parame-
ters.

DOI: 10.4236/aces.2023.134020 298 Advances in Chemical Engineering and Science

 B. Traoré et al.

anchoring at these interfaces [18]. At the end of our analysis, we can therefore
say that defects at the SDL/CIGS interface have less impact on solar cell perfor-
mance.

4. Conclusion
In this paper, based on numerical simulation, the SCAPS-1D software was used
to study the impact of some interface defects on solar cell performance. In the
first part of this work, a detailed study of the CdS/CIGS interface was carried
out. This study consisted in determining the impact of the conduction band off-
set and defects at the CdS/CIGS interface as a function of the minority carrier
lifetime in the absorber. It was found that very good performances are obtained
when −0.1 eV < CBO < 0.1 eV and interface defects are less than 10−13 cm2. The
second part of our study was based exclusively on CdS/SDL and SDL/CIGS in-
terfaces. A comparative study of conduction band offset as a function of minori-
ty carrier lifetime in the absorber was carried out. Subsequently, a simultaneous
study of defects at the CdS/SDL and SDL/CIGS interfaces was also carried out.
By comparing these two interfaces, it appears from this work that defects at the
SDL/CIGS interface have less impact on solar cell performance. This work can
be beneficial to the development of solar cells with good conversion efficiency.
These results show the importance of interface defects in the architecture of new
high-efficiency solar cells. These results may provide a basis for improving the
performance of CIGS-based solar cells.

Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this pa-
per.

References
[1] Nakamura, M., Yamaguchi, K., Kimoto, Y., Yasaki, Y., Kato, T. and Sugimoto, H.
(2019) Cd-Free Cu(In,Ga)(Se,S)2 Thin-Film Solar Cell with Record Efficiency of
23.35%. IEEE Journal of Photovoltaics, 9, 1863-1867.
https://doi.org/10.1109/JPHOTOV.2019.2937218
[2] Schmid, D., Ruckh, M. and Schock, H. (1996) A Comprehensive Characterization of
the Interfaces in Mo/CIS/CdS/ZnO Solar Cell Structures. Solar Energy Materials and
Solar Cells, 41-42, 281-294. https://doi.org/10.1016/0927-0248(95)00107-7
[3] Nakada, T. and Kunioka, A. (1999) Direct Evidence of Cd Diffusion into Cu(In, Ga)Se2
Thin Films during Chemical-Bath Deposition Process of CdS Films. Applied Phys-
ics Letters, 74, 2444-2446. https://doi.org/10.1063/1.123875
[4] Buffière, M. (2011) Synthèse et caractérisation de couches minces de Zn(O,S) pour
application au sein des cellules solaires à base de CuInGaSe2. Ph.D. Thesis, Univer-
sité de Nantes, Nantes.
[5] Jackson, P., Hariskos, D., Wuerz, R., Wischmann, W. and Powalla, M. (2005) Compo-
sitional Investigation of Potassium Doped Cu(In, Ga)Se2 Solar Cells with Efficiencies
up to 20.8 %. Physica Status Solidi (RRL), 8, 219-222.
https://doi.org/10.1002/pssr.201409040
[6] Okano, Y., Nakada, T. and Kunioka, A. (1998) XPS Analysis of CdS/CuInSe2 Hete-

DOI: 10.4236/aces.2023.134020 299 Advances in Chemical Engineering and Science

B. Traoré et al.

rojunction. Solar Energy Materials and Solar Cells, 50, 105-110.

https://doi.org/10.1016/S0927-0248(97)00129-3
[7] Heske, C.D., Eich, R., Fink, E., Umbach, T., Van Buuren, C., Bostedt, L., et al. (1999)
Observation of Intermixing at the Buried CdS/CIGSe Thin Film Solar Cell. Applied
Physics Letters, 74, 1451-1453. https://doi.org/10.1063/1.123578
[8] Romero, M.J., Jones, M., AbuShama, J., Yan, Y., Al-Jassim, M.M. and Noufi, R. (2003)
Layer Band Gap Widening in Cu(In,Ga)Se2 Thin Films. Applied Physics Letters, 83,
4731-4733. https://doi.org/10.1063/1.1631396
[9] Niemegeers, A., Burgelman, M., Herberholz, R., Rau, U., Hariskos, D. and Schock,
H.-W. (1998) Model for Electronic Transport in Cu(In,Ga)Se2 Solar Cells. Applied
Physics Letter, 6, 407-421.
https://doi.org/10.1002/(SICI)1099-159X(199811/12)6:6<407::AID-PIP230>3.0.CO;
2-U
[10] Niemergeers, A. and Burgelman, M. (1997) Effects of the Au/CdTe Back Contact on
IV and CV Characteristics of Au/CdTe/CdS/TCO Solar Cells. Journal of Applied
Physics, 6, 2881-2886. https://doi.org/10.1063/1.363946
[11] Pettersson, J., Edo, M. and Platzer-Björkman, C. (2012) Electrical Modeling of
Cu(In,Ga)Se2 Cells with ALD-Zn(1-x)MgxO Buffer Layers. Journal of Applied Physics,
111, Article ID: 014509. https://doi.org/10.1063/1.3672813
[12] Liao, D. and Rockett, A. (2003) Cu Depletion at the Cu(In,Ga)Se2 Surface. Applied
Physics Letters, 82, 2829-2831. https://doi.org/10.1063/1.1570516
[13] Gloeckler, M. and Sites, J. (2005) Band-Gap Grading in CuInGaSE2 Solar Cells.
Journal of Physics and Chemistry of Solids, 66, 1891-1894.
https://doi.org/10.1016/j.jpcs.2005.09.087
[14] Oubda, D., Kebre, M.B., Zougmoré, F., Njomo, D. and Ouattara, F. (2015) Numeri-
cal Simulation of Cu(In,Ga)Se2 Solar Cells Performances. Journal of Energy and Pow-
er Engineering, 55, 1047-1055.
[15] Ouédraogo, S., Zougmoré, F. and Ndjaka, J. (2013) Numerical Analysis of Copper-
Indium-Gallium-Diselenide-Based Solar Cells by SCAPS-1D. International Journal
of Photoenergy, 2013, Article ID: 421076. https://doi.org/10.1155/2013/421076
[16] Minemoto, T., Matsui, T., Takakura, H., Hamakawa, T.Y., Negami, Y., Hashimoto,
T. and Kitagawa, M. (2001) Theoretical Analysis of the Effect of Conduction Band
Offset of Window/CIS Layers on Performance of CIS Solar Cells Using Device Si-
mulation. Solar Energy Materials and Solar Cells, 67, 83-88.
https://doi.org/10.1016/S0927-0248(00)00266-X
[17] Gloeckler, M. and Sites, J. (2005) Potential of Submicrometer Thickness CuInGaSe2
Solar Cells. Journal of Applied Physics, 98, Article ID: 103703.
https://doi.org/10.1063/1.2128054
[18] Bunning, J.M., Samantilleke, A., et al. (2005) Effects of Multi-Defects at Metal/Semi-
conductor Interfaces on Electrical Properties and Their Influence on Stability and
Lifetime of Thin Film Solar Cells. Solar Energy Materials and Solar Cells, 86, 373-
384. https://doi.org/10.1016/j.solmat.2004.08.009

DOI: 10.4236/aces.2023.134020 300 Advances in Chemical Engineering and Science