Regulation of the Charge Carrier Dynamics in Antimony Selenide Thin‐Film Solar Cells Based on the Effective Diffusion of Ions at the Heterojunction Interface

Abstract Antimony selenide (Sb₂Se₃) is regarded as a next‐generation material for high‐efficiency photovoltaic applications due to its favorable bandgap, high absorption coefficient, carrier mobility, and stability. Nonetheless, cadmiun sulfide (CdS) has low short‐wavelength transmittance, which limits photon utilization, and the suboptimal band alignment in the CdS/Sb₂Se₃ heterojunction causes significant interface recombination. In this study, a simple lithium‐ion doping method is presented and report the dual enhancement effects of lithium ions on CdS and Sb₂Se₃ layers for the first time. Lithium ions improve the CdS layer by allowing for larger grain sizes, reduces roughness, and increase transmittance in the electron transport layer. At the same time, lightweight Li ions diffuse more easily through the interface into the Sb₂Se₃ layer, resulting in improved orientation, lower defect density, and a longer carrier lifetime. Furthermore, doping with Li ions changes the band alignment of the CdS/Sb₂Se₃ junction from a “cliff‐like” to a “spike‐like” configuration, improving carrier transport and reducing carrier recombination near the interface. Ultimately, due to the benefits of Li‐ion doping, the champion device obtained have a V_OC of 0.462 V, a J_SC of 30.86 mA cm⁻², an FF of 65.46%, and an efficiency of 9.33%, representing a 15.8% increase over the undoped device.