CdS Induced Passivation toward High Efficiency and Stable Planar Perovskite Solar Cells

In perovskite solar cells, the halide vacancy defects on the perovskite film surface/interface will instigate charge recombination, leading to a decrease in cell performance. In this study, cadmium sulfide (CdS) has been introduced into the precursor solution to reduce the halide vacancy defects and improve the cell performance. The highest efficiency of the device reaches 21.62%. Density functional theory calculation reveals that the incorporated Cd²⁺ ions can partially replace Pb²⁺ ions, thus forming a strong Cd-I bond and effectively reducing iodide vacancy defects (V_I); at the same time, the loss of the charge recombination is significantly reduced because V_I is filled by S^2- ions. Besides, the substitution of Cd²⁺ for Pb²⁺ could increase the generation of PbI₂, which can further passivate the grain boundary. Therefore, the stability of the cells, together with the efficiency of the power conversion efficiencies (PCEs), is also improved, maintaining 87.5% of its initial PCEs after being irradiated over 410 h. This work provides a very effective strategy to passivate the surface/interface defects of perovskite films for more efficient and stable optoelectronic devices.