Chalcostibite CuSbS 2 has attracted attention as an environmentally friendly material in thermoelectric (TE) field. Our investigations into the TE properties of high-quality p-type CuSbS 2 single crystals revealed that they exhibit a uniquely low thermal conductivity caused by the active lone-pair electrons in Sb 3+ ions. The electrical conductivity was improved by the high density of shallow acceptor Cu vacancies and the absence of potential barriers to carrier transport. Consequently, the figure of merit for the Cu-poor CuSbS 2 single crystal reached 0.5 at 700 K, which is 25 times higher than that of the reported polycrystalline sample.

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I–III–VI2 Chalcopyrite Cu(In1−x Ga x )Se2 (CIGS) has attracted attention as absorbing layer in photovoltaic (PV) device. In this study, we investigated the fundamental properties of CIGS single crystals, and fabricated single crystal-based PV device. CIGS single crystals without secondary phase were successfully grown by In-solvent traveling heater method (THM). The conversion of conduction type from n- to p-type can be observed above 0.3 of Ga ratio x because of high acceptor defect concentration. PV device based on high-quality CIGS bulk single crystal demonstrates high open-circuit voltage of 0.765 V with the efficiency of 12.6%.