Flux-Boosted Sulfide Crystal Growth: Growth of CuInS2 Crystals by NaCl–InCl3 Evaporation

Abstract

Copper–indium–gallium–sulfide–selenide (CIGSSe) is used in photovoltaic cells and photocathodes, because of its tunable optoelectronic properties, but the fabrication of CIGSSe samples usually requires a multistage process under vacuum. Herein we used a flux growth technique for the sulfide system and achieved efficient flux growth of idiomorphic copper–indium–sulfide CuInS2 crystals of size ∼5 μm from a NaCl–InCl3 flux under mild conditions at ambient pressures. We first examined the flux growth conditions such as holding temperature, solute concentration, and holding time for growing highly crystalline CuInS2 crystals. A moderate holding temperature (∼550 °C) and high solute concentration (∼70 mol %) yielded idiomorphic pure CuInS2 crystals. High-resolution transmission electron microscopy showed clear electron diffraction spots, indicating that the resultant CuInS2 crystals had a highly crystalline, intrinsic tetragonal crystal structure. Thermogravimetry-differential thermal analysis showed that the CuInS2 crystals grew efficiently during flux evaporation at 550 °C, at which the flux evaporation degree reached ∼81%. The CuInS2 crystal growth mode is discussed based on the characterization results.