UC Santa Cruz

Perovskite materials have seen increasing interest in the field of optoelectronics over the past decade. The unique crystal structure allows for facile tuning of the bandgap via stoichiometry, and the low formation energy allows for the use of low temperature and low-cost fabrication of films. Perovskites synthesized for this work will consist of both one-step polycrystalline thin films and quantum dots synthesized via a ligand assisted reprecipitation method. Films will be fabricated using spin coating techniques. The optical properties, such as the absorbance and the photoluminescence, were used to characterize the films. Surface morphology was investigated using atomic force microscopy and scanning electron microscopy. Single carrier devices and light emitting diodes were fabricated to explore the electrical properties of the perovskite films. An antisolvent wash study was performed on polycrystalline bulk thin films of methylammonium lead bromide to find the optimum antisolvent wash for surface morphology and photoluminescence. Out of 6 antisolvents investigated, n-Butanol was found to have the lowest and most consistent surface roughness, while maintaining photoluminescence. For quantum dot perovskites, a comparison between insulating organic ligands oleylamine and oleic acid (OLA-OA) and conductive organic ligands 3,3-diphenylpropylamine and trans-cinnamic acid (DPPA-TCA) was completed. The DPPA-TCA ligands had better surface passivation, which lead to higher photoluminescence quantum yield. The surface morphology of the DPPA-TCA ligands was also improved compared to the OLA-OA ligands. DPPA-TCA ligands also had a lower turn-on voltage and increased current density in light emitting diodes. Oxide and polymer additives were incorporated into the DPPA-TCA quantum dot solutions to attempt to improve the surface morphology and consistency of the perovskite films. These additives did not offer an improvement to the film quality. Lastly, the ligand quantity of the precursor solution of the quantum dot synthesis was varied to shift the photoluminescence from green (526 nm) to blue (470 nm).