Effect of formamidinium (FA) ions on mixed ‘A’-site based bromide perovskite (APbBr₃) thin films

Hybrid organic-inorganic perovskites (HOIPs) have become promising candidates for future photovoltaics (PV) with significant advancements in their performance over recent years. Along with PV, HOIPs possess applications in photodiodes, photodetectors, photocatalysis, and memory devices. Generally, perovskites are structurally flexible to accommodate various cations on their respective sites through compositional engineering, thereby altering the characteristic material properties of the system. HOIPs have ABX₃ structures, in which organic or inorganic moieties occupy the monovalent ‘A’ site. In this work, the effect of formamidinium (FA) on the optical and morphological properties of HOIPs using two different bromide perovskites - FA_0.5MA_0.4Cs_0.1PbBr₃ and MA_0.9Cs_0.1PbBr₃ - is examined. After ‘FA’ modification, we noticed a reduction in the bandgap and an increase in the grain size of the FA_0.5MA_0.4Cs_0.1PbBr₃ perovskite compared with the MA_0.9Cs_0.1PbBr₃ perovskite. As a result, a better photocurrent response during photoelectrochemical analysis and an improved power conversion efficiency (PCE) for photovoltaic devices were detected with the FA-modified HOIP (FA_0.5MA_0.4Cs_0.1PbBr₃).