Interface Engineering in a CdS-Modified PbS Nanosheet-FAPbI3 Heterostructure Enabling High-Performance Perovskite Solar Cells

Regulating strain in perovskite films via utilizing the crystal structure relationship between solid-phase materials (SPMs) and perovskite is an effective method to achieve high-performance perovskite solar cells. It is crucial to investigate and manipulate the heterointerfaces between perovskites and SPMs since the mismatched crystal structure and energy band structure of SPMs will bring recombination sites to the heterointerfaces. In this work, CdS-modified PbS nanosheets (CPS) were prepared through cation exchange with (200)-preferred PbS nanosheets. The wide-band gap CdS charge-blocking layer of CPS nanosheets distributed at the grain boundaries effectively passivates the heterointerfaces in FAPbI3-CPS heterostructures (FAPI-CPS). Further, it potentially blocks carrier transportation and suppresses carrier recombination at grain boundaries and in FAPbI3-PbS nanosheet heterointerfaces. Attributed to the CdS layer, the FAPI-CPS devices achieve an enhanced power conversion efficiency. CPS nanosheets with an interplanar spacing slightly smaller than that of α-FAPbI3 could provide compressive strain to FAPbI3 at the FAPI-CPS heterointerfaces, leading to significantly improved device stability. The unencapsulated FAPI-CPS solar cells maintained 92% of their initial PCE after being stored at 20 ± 5 °C, 20 ± 5% RH for 2500 h.