Charge Transfer Modulation in the α-CsPbI₃/WS₂ Heterojunction via Band-Tailoring with Elemental Ni Doping

The performance of photovoltaic devices relies on the light-absorbing capability of the absorber layer and the lifetime of excited-state charge carriers. Combining two-dimensional transition metal dichalcogenides (TMDCs) with perovskites in heterojunctions shows immense potential due to their strong light-matter interaction, excellent charge carrier mobility, long electron-hole diffusion length, and improved stability. However, fast charge carrier recombination in TMDCs and poor charge separation at the interface limit their efficiency. In this direction, band structure modulation can be a key approach to improving the charge separation in these heterojunctions. Herein, we have fabricated a heterojunction of CsPbI₃ and WS₂ (CPI-WS₂) and modulated the band levels by incorporating Ni atoms into CPI. Experimental and theoretical analyses reveal that Ni-doping elevates both the valence and conduction bands of CPI, transforming the quasi-type II band arrangement of CPI-WS₂ into a type II configuration. The doped heterosystem shows substantial charge carrier separation at the interface, with TMDC acting as the electron extractor. This higher segregation of charges notably improves the photocurrent and photoresponsivity within the modulated heterojunctions. This study underscores the importance of doping-induced band-level engineering for promoting charge carrier separation at the TMDC-perovskite interface, advancing the design of advanced optical devices based on heterojunctions.