Strain regulation for Phase-Pure and Stable Wide-Bandgap FAPbBr₃ Perovskites Solar Cells

Abstract

Wide-bandgap lead bromide perovskites are ideal candidates for perovskite solar cells (PSCs) requiring high open-circuit voltages (VOC), particularly as front absorbers in multiple-junction architectures. However, the formation of the 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 δ-phase and release lattice strain thus preparing perovskite thin films with pure phase. Consequently, inverted FAPbBr3 solar cells achieve a champion power conversion efficiency (PCE) of 10.57% and a high Voc 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.