Minimizing voltage losses in Sn perovskite solar cells by Cs2SnI6 passivation

Stability and oxidation are major bottlenecks in improving the performance of Sn-based perovskite solar cells. In this study, we present the formation of an n-type Cs₂SnI₆ double-perovskite (Sn-DP) layer on a (PEAI)_0.15(FAI)_0.85SnI₂ perovskite (Sn-P) layer using an orthogonal solution-processable spray-coating method. This novel approach achieves a minimized V_oc loss of 0.38 V and a PCE of 12.9% under 1 sun conditions. The n-type DP layer effectively passivates tin vacancies, suppresses Sn²⁺ oxidation, reduces defects, and enhances electron extraction. Furthermore, the Sn-DP/Sn-P-based solar cells exhibit excellent light-soaking stability for 1000 h in the air under continuous one sun illumination, which is attributed to the stable Sn⁴⁺ state of the DP layer. Our experimental and theoretical investigations reveal that the type-II band alignment between Sn-DP and Sn-P enhances the stability of the solar cells. The proposed Sn-DP/Sn-P architecture offers a promising pathway for developing Sn-based solar cells.