Development of kesterite Cu ₂ZnSn(S _1-x, Se _x) ₄ (CZTSS)-based thin film solar cells with in and ga free absorber materials

Chalcogenide-based semiconductors, such as CuInSe ₂, CuGaSe ₂, Cu(In, Ga)Se ₂ (CIGS), and CdTe have attracted considerable interest as efficient materials in thin film solar cells (TFSCs). Currently, CIGS and CdTe TFSCs have demonstrated the highest power conversion efficiency (PCE) of over 11% in module production. However, commercialized CIGS and CdTe TFSCs have some limitations due to the scarcity of In, Ga, and Te and the environmental issues associated with Cd and Se. Recently, kesterite CZTS, which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of 10 ⁴ cm ^-1, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTSbased thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. The recent development of kesterite-based CZTS thin film solar cells is summarized in this work. The new challenges for enhanced performance in CZTS thin films are examined and prospective issues are addressed as well.