Passivation of 2D Cs₂PbI₂Cl₂ Nanosheets for Efficient and Stable CsPbI₃ Quantum Dot Solar Cells

Inorganic CsPbI₃ perovskite quantum dots (PQDs) possess remarkable optical properties, making them highly promising for photovoltaic applications. However, the inadequate stability resulting from internal structural instability and the complex external surface chemical environment of CsPbI₃ PQDs has hindered the development of CsPbI₃ PQD solar cells (PQDSCs). In this work, the capping layer composed of inorganic two-dimensional (2D) Ruddlesden-Popper (RP) phase Cs₂PbI₂Cl₂ nanosheets (NSs) is introduced, which may be effectively treated to improve the surface properties of the CsPbI₃ PQD film. This modification serves to passivate defects by filling cesium and iodine vacancies while optimizing the energy band arrangement and preventing humidity intrusion, leading to the meliorative stability and photovoltaic performance. The optimized CsPbI₃ PQDSCs achieve an enhanced power conversion efficiency (PCE) of 14.73%, with the superb stability of only a 16% efficiency loss after being exposed to ambient conditions (30 ± 5% RH) for 432 h.