Theoretical and experimental investigations on the bulk photovoltaic effect in lead-free perovskites MASnI3 and FASnI3

Abstract

Perovskite solar cells based on the lead free hybrid organic–inorganic CH₃NH₃SnI₃ (MASnI₃) and CH₄N₂SnI₃ (FASnI₃) perovskites were fabricated, and the photoelectric conversion efficiency (PCE) was assessed. FASnI₃'s PCE was higher than MASnI₃'s efficiency. To study the different photovoltaic properties, we calculated their structural, electronic, and optical properties using density functional theory via the Perdew–Burke–Ernzerhof and spin–orbit coupling (PBE-SOC) methods. The results show that FASnI₃ exhibits an appropriate band gap, substantial stability, marked optical properties, and significant hole and electron conductive behavior compared with MASnI₃. The interaction of organic cations (FA⁺) with the inorganic framework of FASnI₃ was stronger than that with MASnI₃, so they affected the band length and band angle distribution, causing the structure of the FASnI₃ and MASnI₃ to change. The calculations also demonstrated that energy splitting was evident in FASnI₃ due to the spin–orbit coupling effect, however, it was moderate in MASnI₃, which was caused by the H bond effect. This research not only furthers the understanding of these functional materials, but also can assist the development of highly efficient and stable non-lead perovskite solar cells.