Enhancing Perovskite Solar Cell Durability via Strategic Cation Management in Chalcogenide-Based Hole Transport Layer

Copper-chalcogenide-based inorganic holetransport layers (HTLs) are widely studied in perovskite solar cells (PSCs) because of their favorable valence band maximum and their ability to passivate interfacial defects through Pb-S interactions. These compounds are shown to produce stable PSCs because of their high intrinsic stability. However, the density functional theory (DFT) calculations and X-ray photoelectron spectroscopy analysis presented here reveal that the presence of Cu in the HTL can weaken the interfacial Pb-S interactions and compromise the device stability. A clear inverse relationship is observed between the stability of perovskite film and the Cu-concentration in the HTL underneath. Therefore, to minimize the detrimental effect of Cu, this work explores Cu-deficient chalcopyrite compounds, CuIn₃S₅ and Cu(In_xGa_(1-x))₃S₅, as HTLs for PSCs, which results in improved device stability. DFT calculations reveal that incorporating gallium into the HTL reduces the HTL-perovskite interfacial energy, which results in further enhancement of device stability. The average T₈₀ lifetimes (the time to retain 80% of the initial efficiency) under ambient conditions for the NiO, CuIn₃S₅, and Cu(In_0.3Ga_0.7)₃S₅ HTL-based devices are 200, 449, and 656 h, respectively. These findings underscore the significant roles of cations and anions of the inorganic transport layer in enhancing the stability of the PSCs.