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. In this talk, we will discuss 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-H. Second, we focus on the side reaction between alkylammoniums in the perovskite precursor solution during processing. We find that the addition of I₂ into the precursor solution greatly slows down the side reaction between methylammonium (MA) and formamidinium (FA) during annealing, presumably due to the strong interaction between I₃^- and alkylammoniums. We achieve a better bottom interfacial stability by suppressing the side reaction during processing. Finally, we aim to improve the operational stability of PSCs under thermal stress. Iodine generated from perovskites under thermal stress can catalyze perovskite degradation in the form of I₃^-. 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.

Adviser: Barry Rand