Document Type

Dissertation - Open Access

Award Date

2021

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering and Computer Science

First Advisor

Qiquan Qiao

Abstract

Perovskite solar cells (PSCs) have seen significant improvement in photovoltaic performance in recent days. However, the performance of PSCs is limited by the defects present at grain boundaries (GB). The study adapted here discusses the nanoscale spatial realization of grain boundary defects and its passivation in perovskite solar cells. Conventional MAPbI3 and state- of-the-art Cs5(MA0.17FA0.83)95Pb(I0.83Br0.17)3-FAMACs perovskite GBs were studied in detail using atomic force microscopy. The density of trap states calculation by kelvin probe force microscopy (KPFM) shows that FAMACs perovskites have lower defects at GB compared with MAPbI3 perovskites. This improvement is caused by the less activation energy of the point defects in FAMACs due to mixing of cations and anions in perovskite structure compared with MAPbI3 perovskites. FAMACs perovskite GBs are less dominated by the defect ion migration evident from the negligible local dark-current hysteresis at GBs. To further passivate defects at the GB, FAMACs perovskite was post-treated by using an organic halide salt named phenylhydrazinium iodide (PHI). Defects analysis and passivation at GB of FAMACs perovskite were evaluated using atomic force microscopy technique through mapping of carrier recombination lifetime (τr), transport time (τt) and diffusion length (LD). These spatially resolved charge carrier dynamics parameters reveal substantial variations at GB of control and passivated perovskites. Defects analysis and passivation at GB of FAMACs perovskite through charge carrier dynamics nanoscale mapping, KPFM and CAFM demonstrate that optimized concentration of PHI can passivates the positively charged defects and significantly improves charge carrier dynamics at GB compared to control sample. This improvement in nanoscale charge transport in passivated FAMACs gives a PCE of ~20% whereas MAPbI3 and non-passivated FAMACs perovskites show ~17% and ~ 18% PCE, respectively. This clearly indicates that GB passivation in FAMACs reduces the positively charged defects and gives champion PCE of ~20%.

Number of Pages

111

Publisher

South Dakota State University

Rights

Copyright © 2021 the Author

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