Promoted Charge Extraction in All-Inorganic CsPbBr₃ Perovskite Solar Cells by a CsPbX₃ (X = Br and I) Quantum Dot Interface Layer

Inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted wide attention due to their low cost and excellent resistance to ultraviolet light, oxygen, and temperature. However, the mechanism of CsPbBr3 crystallization is relatively complex due to the lower solubility of CsBr in N,N-dimethylformamide. Also, the excessively high valence band offset between CsPbBr3 and a hole transport layer (HTL), such as Spiro-OMeTAD, is the main factor limiting the improvement in efficiency. Herein, based on the top-down vertical crystallization mechanism of polycrystalline CsPbBr3 prepared by multistep spin coating, we obtained the optimal window period for conversion to CsPbBr3 through regulating the annealing time and the deposition number of CsBr. Then, perovskite quantum dots (QDs) were used as an intermediate layer between the perovskite and HTL, which can diffuse into grain boundaries and passivate defects in the CsPbBr3 film. The solar cell fabricated by QD modification yields a champion power conversion efficiency (PCE) of 7.23% compared to 5.15% for the unmodified devices. Moreover, the CsPbBr3 PSC device without encapsulation exhibits an enhanced long-term stability under atmospheric conditions due to the high hydrophobicity of the QD coating. Finally, high-PCE and stable devices were ultimately obtained due to the excellent stability of the prepared CsPbBr3 coupled with quantum dot modification.