Phase Control of Cs‐Pb‐Br Derivatives to Suppress 0D Cs4PbBr6 for High‐Efficiency and Stable All‐Inorganic CsPbBr3 Perovskite Solar Cells

The precise phase control of Cs-Pb-Br derivatives from 3D CsPbBr3 to 0D Cs4 PbBr6 highly determines the photovoltaic performance of all-inorganic CsPbBr3 perovskite solar cells (PSCs). Herein, the preferred phase conversion from precursor to Cs-Pb-Br derivatives is revealed by theoretically calculating the Gibbs free energies (∆G) of various phase conversion processes, allowing for a simplified multi-step solution-processable spin-coating method to hinder the formation of detrimental 0D Cs4 PbBr6 phase and enhance the photovoltaic performance of a PSC because of its large exciton binding energy, which is regarded as a recombination center. By further accelerating the interfacial charge extraction with a novel 2D transition metal dichalcogenide ReSe2 , the hole-free CsPbBr3 PSC achieves a champion efficiency of 10.67% with an impressive open-circuit voltage of 1.622 V and an excellent long-term stability. This work provides an in-depth understanding on the precise Cs-Pb-Br perovskite phase control and the effect of derivatives on photovoltaic performance of advanced CsPbBr3 PSCs.