Solvent Engineering for Ambient-Air-Processed, Phase-Stable\nCsPbI3 in Perovskite Solar Cells

Inorganic CsPbI3 perovskite\nsolar cells (PSCs) owning\ncomparable photovoltaic performance and enhanced thermal stability\ncompared to organic–inorganic hybrid perovskites have attracted\nenormous interest in the past year. However, it is still a challenge\nto stabilize the desired black α-CsPbI3 perovskites\nin ambient air for photovoltaic applications. Herein, sequential solvent\nengineering including the addition of hydroiodic acid (HI) and subsequent\nisopropanol (IPA) treatment for fabricating stable and working CsPbI3 PSCs is developed, and a novel low-temperature phase-transition\nroute from new intermediate Cs4PbI6 to stable\nα-CsPbI3 is also released for the first time. As\nsuch, the as-prepared PSCs give a relatively high power conversion\nefficiency (PCE) of 4.13% (reverse scan), and the steady-state power\noutput of 1.88% is confirmed for the selected cell with an initial\nPCE of 3.13%. To the best of our knowledge, this is the first demonstration\nof fabricating CsPbI3 inorganic PSCs under fully open-air\nconditions.