Interfacial engineering has been shown to play a vital role in boosting the performance of perovskite solar cells in the past few years. Here we demonstrate that caesium bromide (CsBr), as an interfacial modifier between the electron collection layer and the CH₃NH₃PbI_3−xCl_x absorber layer, can effectively enhance the stability of planar heterojunction devices under ultra violet (UV) light soaking. Additionally, the device performance is improved due to the alleviated defects at the perovskite-titania heterojunction and enhanced electron extraction.

Hypophosphorous acid (HPA) additive could effectively reduce the Sn vacancy density of CsSnIBr ₂ films and achieve highly thermal stable PSCs.