Systematic Optical Management via Controlled Thickness MgF 2 Antireflection Coatings for High‐Efficiency Cu 2 ZnSnS 4 and Sb 2 (S,Se) 3 Solar Cells

Thin‐film solar cells based on kesterite Cu 2 ZnSnS 4 (CZTS) and antimony selenosulfide (Sb 2 (S,Se) 3 ) have emerged as promising next‐generation photovoltaic technologies owing to their earth‐abundant constituents, low toxicity, and favorable optoelectronic properties. However, Fresnel reflection losses at the illuminated interface severely limit the incident photon flux, thereby constraining further improvements in short‐circuit current density ( J sc ) and power conversion efficiency (PCE). Herein, MgF 2 antireflection coatings (ARCs) with varying thicknesses, approximately 85, 100, and 115 nm, were deposited onto devices via vacuum thermal evaporation. The theoretical optimal thickness for broadband antireflection, along with a discrete thickness series of 85, 100, and 115 nm, was derived based on key optical and physical properties, including refractive index and transmittance, in conjunction with thin‐film interference theory. MgF 2 layers with different thicknesses were integrated into complete CZTS and Sb 2 (S,Se) 3 solar cells, followed by comprehensive experimental validation and data analysis. The incorporation of the MgF 2 ARC effectively enhanced J sc , yielding CZTS devices with 11.69% efficiency and Sb 2 (S,Se) 3 devices with 10.27% efficiency. This work not only demonstrates the applicability of MgF 2 ARCs to two representative thin‐film solar cell platforms but also provides a practical theoretical framework and experimental reference for interfacial optical management in future photovoltaic devices.