Lead-Free Flexible Perovskite Solar Cells with Interfacial Native Oxide Have >10% Efficiency and Simultaneously Enhanced Stability and Reliability

Here we demonstrate an innovative compositional and interfacial engineering approach to achieve Pb-free flexible perovskite solar cells (f-PSCs) with an unprecedented combination of the highest efficiency reported to date (10.43%), together with enhanced operational stability and mechanical reliability. The key to this approach is alloying of an FASnI₃ metal halide perovskite (MHP) thin film with Ge²⁺ to stabilize the Sn²⁺ oxidation state in the MHP, together with the use of a NiO_x hole-transport layer. We show that this results in the in situ formation of a thin amorphous GeO₂ native oxide layer at the NiO_x/FASn_0.9Ge_0.1I₃ interface. This layer not only passivates that critical interface but also enhances the interfacial mechanical bonding.