Strain regulation for phase-pure and stable wide-bandgap FAPbBr3 perovskite solar cells

Abstract

Wide-bandgap lead bromide perovskites are ideal candidates for perovskite solar cells (PSCs) requiring high open-circuit voltages (V_OC), particularly as front absorbers in multiple-junction architectures. However, the formation of a photoinactive non-perovskite δ-phase (δ-FAPbBr₃) is a critical issue that inhibits the photovoltaic performance of the devices. In this work, we introduce sodium 4-chlorobenzenesulfonate (4Cl-BZS) to inhibit the formation of the δ-phase and release lattice strain, thus preparing perovskite thin films with a pure phase. Consequently, inverted FAPbBr₃ solar cells achieve a champion power conversion efficiency (PCE) of 10.57% and a high V_OC of 1.63 V, representing one of the best performances for this configuration. Furthermore, unencapsulated devices retain over 90% of their initial efficiency after 1400 h of aging under 50% relative humidity, demonstrating excellent environmental stability.