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

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 Cs₂ AgBiBr₆ shows high stability and possesses a suitable band gap for solar-cell applications. However, the film-forming ability of Cs₂ AgBiBr₆ is found to be the utmost challenge hindering its development in thin-film solar-cell devices. In this work, a high-quality Cs₂ AgBiBr₆ 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 Cs₂ AgBiBr₆ exhibits a power conversion efficiency of 2.23 % with V_OC =1.01 V, J_SC =3.19 mA/cm² , and FF=69.2 %. Besides, the device shows no hysteresis and a high stability.