Heterojunction lithiation engineering and diffusion-induced defect passivation for highly efficient Sb2(S,Se)3 solar cells

High-quality heterojunctions are crucial for achieving high power conversion efficiency (PCE) in the antimony selenosulfide (Sb2(S,Se)3) solar cells. Here, we introduce lithium fluoride (LiF) doping of the precursor solution to improve the conductivity, morphology, and n-type characteristics of cadmium sulfide (CdS) films. In addition, Li-ions have high mobility, which enhances in situ diffusion into the Sb2(S,Se)3 absorber layer during subsequent hydrothermal deposition. Li effectively passivates selenium vacancies (VSe) and antimony anti-site (SbS) defects through the formation of Li–S(e) bonds. This lithiation process not only realizes a twofold optimization of the CdS buffer layer and the Sb2(S,Se)3 absorber layer, but also yields a favorable energy level arrangement and a wider depletion region at the CdS/Sb2(S,Se)3 heterojunction. By this way, we have achieved a champion PCE of 10.76% compared to a certified value of 10.50% for Sb2(S,Se)3 solar cells, which is the highest certified efficiency reported for Sb-based solar cells so far. This study provides a convenient method to optimize dual functional layers and heterojunctions for high-performance Sb2(S,Se)3 solar cells.