Alumina Nanoparticle Interfacial Buffer Layer for Low‐bandgap Lead‐tin Perovskite Solar Cells

Mixed lead-tin (Pb:Sn) halide perovskites are promising absorbers with narrow-bandgaps (1.25–1.4 eV) suitable for high-efficiency all-perovskite tandem solar cells. However, solution processing of optimally thick Pb:Sn perovskite films is notoriously difficult compared to neat-Pb counterparts. This is partly due to the rapid crystallization of Sn-based perovskites, resulting in rougher films. These rough films complicate subsequent layers’ conformal coating, leading to contact between the absorber and the top metal electrode in completed devices, reducing VOC, fill factor, efficiency, and stability. This study employs alumina nanoparticles distributed on the surface of rough Pb:Sn perovskite films as an interfacial buffer layer. The approach improves the conformality of the electron-transport layer and boosts the efficiency and stability of the devices.