Diffusion‐Driven Targeted Passivation of Selenium Vacancies via an I‐Doped CdS Buffer Layer for Efficient Sb 2 Se 3 Solar Cells

ABSTRACT Antimony selenide (Sb 2 Se 3 ) 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 Sb 2 Se 3 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 cm 2 . The optimized Sb 2 Se 3 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 Sb 2 Se 3 and related polycrystalline photovoltaic devices.