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 (V_Se) and antimony anti-site (Sb_S) 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.