Anti-solvent assisted multi-step deposition for efficient and stable carbon-based CsPbI2Br all-inorganic perovskite solar cell

Inorganic halide perovskite CsPbI2Br has attracted tremendous attentions in the photovoltaic fields in view of its improved ambient phase stability and reasonable band gap (1.91eV). Traditional one-step solution-processed CsPbI2Br absorbers, however, usually suffer from poor morphology, low crystallinity and thin thickness, which impede further promotion of device performance. Herein, an anti-solvent assisted multi-step deposition strategy for high-quality CsPbI2Br film is demonstrated, wherein different anti-solvents are first introduced in the PbI2 precursor filming processes to construct porous PbI2(DMSO) films. Then CsBr solution intercalates into the porous PbI2(DMSO) film by multi-step deposition, effectively facilitating the close contact of reactants and complete annealing reaction. CsBr drops and porosity degree of PbI2(DMSO) film are found to control the final morphology and phase composition of the perovskite film. Utilizing green ethanol (EtOH) treated PbI2 film with high porosity and randomized orientation, highly pure-phase and full-coverage CsPbI2Br films with high thickness, large grain sizes and high crystallinity are obtained after optimizing CsBr drops. Finally, carbon-based all-inorganic planar perovskite solar cells (PSCs) with absorbers prepared through above methods achieve a champion efficiency of 10.21%, which is a record value for the CsPbI2Br PSCs without hole transport layer. More importantly, the unencapsulated all-inorganic CsPbI2Br device shows a promising long-term stability with no obvious efficiency degradation when exposed in ambient atmosphere with 15-30% relative humidity (RH) at room temperature for 44 days.