Mitigating Ion Migration with an Ultrathin Self‐Assembled Ionic Insulating Layer Affords Efficient and Stable Wide‐Bandgap Inverted Perovskite Solar Cells

Abstract

AbstractWide‐bandgap perovskite solar cells (PSCs) are attracting increasing attention because they play an irreplaceable role in tandem solar cells. Nevertheless, wide‐bandgap PSCs suffer large open‐circuit voltage (VOC) loss and instability due to photoinduced halide segregation, significantly limiting their application. Herein, a bile salt (sodium glycochenodeoxycholate, GCDC, a natural product), is used to construct an ultrathin self‐assembled ionic insulating layer firmly coating the perovskite film, which suppresses halide phase separation, reduces VOC loss, and improves device stability. As a result, 1.68 eV wide‐bandgap devices with an inverted structure deliver a VOC of 1.20 V with an efficiency of 20.38%. The unencapsulated GCDC‐treated devices are considerably more stable than the control devices, retaining 92% of their initial efficiency after 1392 h storage under ambient conditions and retaining 93% after heating at 65 °C for 1128 h in an N2 atmosphere. This strategy of mitigating ion migration via anchoring a nonconductive layer provides a simple approach to achieving efficient and stable wide‐bandgap PSCs.