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 Cs₂AgBiBr₆ shows high stability and possesses a suitable band gap for solar-cell applications. However, the film-forming ability of Cs₂AgBiBr₆ is found to be the utmost challenge hindering its development in thin-film solar-cell devices. In this work, a high-quality Cs₂AgBiBr₆ 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 Cs₂AgBiBr₆ 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.