Structural and optical properties of sprayed CuInS2 films

Polycrystalline CuInS2 thin films have been prepared by spray pyrolysis of aqueous solution of copper chloride, indium chloride and thiourea onto heated glass substrates. It is shown that the parameters critical to structural and optical properties of sprayed CuInS2 films are growth temperature and ion ratio of Cu/In in spraying solution. Excess of copper in starting solution promotes the recrystallization and growth of crystallites in the film. The X-ray diffraction patterns confirm that the use of copper-rich solutions reduces the temperature required for single-phase composition of CuInS2 films from 380 degrees C (Cu/In = 1) to 290 degrees C (Cu/In = 1.25). The formation of CuInS2 in spray process and chemical nature of additional phases in the films are discussed. Growth temperatures in the range of 320-380 degrees C at Cu/In > 1 are determined as optimal for depositing orientated in the (112) direction CuInS2 thin films with chalcopyrite structure. Sprayed chalcopyrite CuInS2 films have absorption coefficient similar to 10(5) cm(-1) in visible and red region of spectra and optical band gap 1.45 eV. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.