Impact of Minor Phases on the Performances of CZTSSe Thin-Film Solar Cells

Cu2ZnSn(S1–xSex)4 (CZTSSe) alloys are promising candidates for low-cost and high-efficiency thin-film solar cells. Compared to CdTe and Cu(InxGa1–x)Se2, CZTSSe uses chemicals found more abundantly on earth. This key aspect as well as its optical properties—band gap range of 1.0–1.5 eV and absorption coefficient larger than 104 cm–1—makes CZTSSe a feasible option for photovoltaic thin-film technologies scalable to TW/year. The key limitation to high efficiency in this technology remains a deficit in the open-circuit voltage with respect to the band gap: many groups have linked this drawback of CZTSSe solar cells to the presence of minor phases. This review aims to summarize what is known about CZTSSe minor phases and their impact on device characteristics.