One-pot thermolysis synthesis of CuInS₂ nanoparticles with chalcopyrite-wurtzite polytypism structure

CuInS₂ nanoparticles as the visible (wurtzite, 1.67 eV) or near infrared (chalcopyrite, 1.50 eV) light absorbing material in thin film solar cells, were synthesized using facile, one step heating up method by dissolving of CuCl, InCl₃ and SC(NH₂)₂ as precursors in oleylamine (OLA) alone or in combination with oleic acid (OA) and 1-octadecene (ODE) as solvent. The phase, size, morphology, and size distribution were controlled by the coordination ability between solvent molecules and metal precursors, reaction temperature and time. The presence of higher amounts of thiourea or OA to OLA led to the formation of chalcopyrite phase in comparison to wurtzite structure. Also, higher reaction temperatures (>240 °C) resulted in favour of more chalcopyrite phase and higher crystallinity but the nanoparticles got agglomerated. As synthesized nanoparticles was characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, high resolution-transmission electronic microscopy, ultraviolet–visible-near infrared, photoluminescence. The high resolution TEM confirmed the existence of chalcopyrite structure along with wurtzite structure in the nanocrystal (polytypism). Well controlled chalcopyrite CuInS₂ triangular pyramidal shape with an average size ranging from ~10–20 nm size was obtained by using 20 ml OLA or 20 ml OLA along with 4 ml OA and ODE, respectively, with 210 °C heating up and 4 h annealing time.