High-Quality Cs2 AgBiBr6 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 VOC =1.01 V, JSC =3.19 mA/cm2 , and FF=69.2 %. Besides, the device shows no hysteresis and a high stability.