Room Temperature Processed Tin Perovskites

Perovskites have become attractive semiconductors in photovoltaic devices due to their unique optoelectronic properties; however, with lead-based perovskite approaching the theoretical device limit, all-perovskite tandems have become increasingly of interest but are limited due to the limitations of tin-based perovskites. Sn-based perovskites have emerged due to their similar band structure, bandgap tunability, and higher Schockley- Queisser limit. Despite this potential, they currently lag in terms of stability and efficiency compared to their lead-based counterparts, primarily due to high defect densities from rapid thin-film formation and Sn vacancies caused by oxidation. While Sn oxidation is detrimental to device performance and stability, controlled crystallization is hypothesized to reduce uncoordinated Sn(II) and enhance overall device performance and stability.<br/><br/>Researchers have extensively employed additive, cation, and solvent engineering to control the crystallization of Sn-based perovskites, though understanding of the process remains limited. We aimed to deepen our understanding of the crystallization of Sn-based perovskites and how it differs from Pb-based perovskites. Utilizing additive engineering, we are able to preferentially orient a FASnI₃ film along the [001] and [010] planes, indicative of more controlled crystal growth. While having preferential growth is consistent in using many ammonium-based additives, we are able to grow FASnI₃ thin films completely at room temperature, minimizing the amount of added energy into the system to oxidize Sn(II), as elevated temperatures are known to increasing oxidize Sn(II). Upon exposure to ambient conditions, x-ray photoelectron spectroscopy (XPS) measurements have shown increased stability of the engineered FASnI₃ with significantly less Sn(IV) content compared to pure FASnI₃ and 10.48% power conversion efficiency when implemented into a p-i-n solar device.