Phase transformation and grain growth in spray deposited wurtzite CuInS2 films

We report the processing of large-grained chalcopyrite-CuIn(S,Se)2 (ch-CISSe) films using spray deposition of wurtzite-CuInS2 (wz-CIS) nanoparticle ink and subsequent selenization. Wurtzite to chalcopyrite phase trans-formation and grain growth were studied at varying selenization temperatures of 350, 400, 450, 500 and 550 degrees C for 15 min. On annealing in selenium (Se) atmosphere at 400 degrees C, the film transformed from wurtzite to chal-copyrite phase completely, while the grain growth took place at higher temperatures (500-550 degrees C), requiring greater amounts of Se substitution (Se/Se + S > 0.7). Differential scanning calorimetry (DSC) indicates that the phase transformation temperature is sensitive to the heating rate and has a second-order character.