Barrier reinforcement for enhanced perovskite solar cell stability under reverse bias

Stability of perovskite solar cells (PSCs) under light, heat, humidity and their combinations have been notably improved recently. However, PSCs have poor reverse-bias stability that limits their real-world application. Here we report a systematic study on the degradation mechanisms of p–i–n structure PSCs under reverse bias. The oxidation of iodide by injected holes at the cathode side initialize the reverse-bias-induced degradation, then the generated neutral iodine oxidizes metal electrode such as copper, followed by drift of Cu+ into perovskites and its reduction by injected electrons, resulting in localized metallic filaments and thus device breakdown. A reinforced barrier with combined lithium fluoride, tin oxide and indium tin oxide at the cathode side reduces device dark current and avoids the corrosion of Cu0. It dramatically increases breakdown voltage to above −20 V and improved the T90 lifetime of PSCs to ~1,000 h under –1.6 V. The modified minimodule also maintained over 90% of its initial performance after 720 h of shadow tests. The stability of perovskite photovoltaics under reverse bias is limited and thus an issue for real-world applications. Nengxu Li and colleagues report the underlying degradation mechanism at the cathode side and a multilayer barrier to minimize it.