Diffusion-Driven Targeted Passivation of Selenium Vacancies via an I-Doped CdS Buffer Layer for Efficient Sb₂Se₃...

Antimony selenide (Sb₂Se₃) is an emerging photovoltaic absorber with attractive optoelectronic properties, but its device performance is largely constrained by deep-level defects, particularly selenium vacancies (V_Se), which induce severe non-radiative recombination. Herein, we report a targeted anion-defect passivation strategy by incorporating iodine into the CdS buffer layer (CdS:I). Iodine doping not only promotes the preferential (100)-oriented growth of CdS and passivates its intrinsic sulfur vacancies but also facilitates the spontaneous diffusion of iodine into the Sb₂Se₃ absorber during annealing. Density functional theory (DFT) and deep-level transient spectroscopy (DLTS) analyses confirm that the diffused iodine atoms preferentially occupy V_Se sites, forming charge-neutral I_Se defects with low formation energy. This results in a remarkable reduction in the defect capture cross-section to 4.88 × 10^-22 cm². The optimized Sb₂Se₃ solar cell achieves a high open-circuit voltage of 489.36 mV and a power conversion efficiency of 10.07%. This work provides an effective and generalizable defect-passivation route for enhancing the performance of Sb₂Se₃ and related polycrystalline photovoltaic devices.