UNDERSTANDING THE INSTABILITY ASSOCIATED WITH PEROVSKITE PHOTOVOLTAICS: INTRINSIC, PROCESSING AND OPERATIONAL

Abstract

Perovskite solar cells (PSCs) based on alkylammonium lead halide perovskites have been seen as a robust challenger to the conventional inorganic counterparts due to their advantages in adaptability and cost efficiency. However, PSCs are still suffering from poor stability which puts a shadow on their imminent commercialization. The work in this thesis will investigate the instability of PCSs in different aspects. First, we identify a degradation mechanism that’s associated with the intrinsic instability of perovskite materials. Specifically, metallic Pb can be formed via irreversible β-proton elimination of Pb-amine complex, where amines originate from the proton transfer of alkylammoniums. Improved intrinsic stability can be realized by the proper choice of alkylammoniums without β-proton. Second, we focus on the side reaction between alkylammoniums in the perovskite precursor solution during processing. We find that the addition of Iodine (I2) into the precursor solution greatly slows down the side re- action between methylammonium (MA) and formamidinium (FA) during annealing, presumably due to the strong interaction between triiodide (I−) and alkylammoni- ums. We achieve a better bottom interfacial stability by suppressing the side reaction during processing. Finally, we aim to improve theoperational stability of PSCs under thermal stress. Iodine generated from perovskites under thermal stress can catalyze perovskite degradation in the form of I−. Besides, these oxidized iodine species can migrate to transport layers and impair carrier transport. We develop a redox-active thiol layer at the perovskite-transport layer interface that can recycle the detrimental oxidized iodine species back to iodide. PSCs with thiol interlayer show a significant improvement in thermal stability.