High‐Quality Cs₂AgBiBr₆ Double Perovskite Film for Lead‐Free Inverted Planar Heterojunction Solar Cells with 2.2 % Efficiency

Abstract All‐inorganic double‐metal perovskite materials have recently gained much attention due to their three dimensionality (3D) and non‐toxic nature to replace lead‐based perovskite materials. Among all those double perovskite materials, theoretical works have demonstrated that Cs 2 AgBiBr 6 shows high stability and possesses a suitable band gap for solar‐cell applications. However, the film‐forming ability of Cs 2 AgBiBr 6 is found to be the utmost challenge hindering its development in thin‐film solar‐cell devices. In this work, a high‐quality Cs 2 AgBiBr 6 film with ultra‐smooth morphology, micro‐sized grains, and high crystallinity is realized via anti‐solvent dropping technology and post‐annealing at high temperature. After optimization, the first example of an inverted planar heterojunction solar‐cell device based on Cs 2 AgBiBr…