Dual Role of Cu‐Chalcogenide as Hole‐Transporting Layer and Interface Passivator for p–i–n Architecture Perovskite Solar Cell

Abstract Inorganic hole‐transport layers (HTLs) are widely investigated in perovskite solar cells (PSCs) due to their superior stability compared to the organic HTLs. However, in p–i–n architecture when these inorganic HTLs are deposited before the perovskite, it forms a suboptimal interface quality for the crystallization of perovskite, which reduces device stability, causes recombination, and limits the power conversion efficiency of the device. The incorporation of an appropriate functional group such as sulfur‐terminated surface on the HTL can enhance the interface quality due to its interaction with perovskite during the crystallization process. In this work, a bifunctional Al‐doped CuS film is wet‐deposited as HTL in p–i–n architecture PSC, which besides acting as an HTL also improves the crystallization of perovskite at the interface. Urbach energy and light intensity versus open‐circuit voltage characterization suggest the formation of a better‐quality interface in the sulfide HTL–perovskite heterojunction. The degradation behavior of the sulfide‐HTL‐based perovskite devices is studied, where it can be observed that after 2 weeks of storage in a controlled environment, the devices retain close to 95% of their initial efficiency.