Selenium Thin‐Film Photovoltaics: A Review of Material Properties, Fabrication Strategies, and Emerging Applications

As a historic photovoltaic material with a wide bandgap (~1.9 eV), selenium has regained research interest for indoor photovoltaics due to its spectral match with indoor light sources. This review summarizes recent advances in the material properties, fabrication techniques, and device engineering of Se‐based solar cells. Se combines attractive practical merits, including earth abundance, low toxicity, intrinsic environmental stability, and compatibility with low‐temperature processing. However, the one‐dimensional structure of its ideal photovoltaic phase—trigonal selenium—poses challenges for controlling thin‐film orientation. Through the development of various preparation techniques, such as close‐space sublimation and melt processing, combined with interface engineering (e.g., forming Se–O bonds, introducing Te adhesion layers) and transport‐layer optimization, the certified efficiency of Se solar cells has reached 10%. Notably, under indoor illumination, Se cells have achieved efficiencies of over 20% and have been successfully used to power Internet‐of‐Things devices, demonstrating considerable application potential. Continued optimization of film quality and device architecture are expected to expand Se photovoltaics toward flexible electronics and tandem integration.