Bifunctional Stabilization of All-Inorganic α-CsPbI₃ Perovskite for 17% Efficiency Photovoltaics

The all-inorganic α-CsPbI₃ perovskite with the most suitable band gap faces serious challenges of low phase stability and high moisture sensitivity. We discover that a simple phenyltrimethylammonium bromide (PTABr) post-treatment could achieve a bifunctional stabilization including both gradient Br doping (or alloying) and surface passivation. The PTABr treatment on CsPbI₃ only induces less than 5 nm blue shift in UV-vis absorbance but significantly stabilize the perovskite phase with much better stability. Finally, the highly stable PTABr treated CsPbI₃ based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion efficiency up to 17.06% and stable output of 16.3%. Therefore, this one-step bifunctional stabilization of perovskite through gradient halide doping and surface organic cation passivation presents a novel and promising strategy to design stable and high performance all-inorganic lead halide.