Structural and optical properties of sprayed CuInS 2 films

Abstract

Polycrystalline CuInS 2 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 CuInS 2 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 CuInS 2 films from 380°C ( Cu/In=1 ) to 290°C ( Cu/In=1.25 ). The formation of CuInS 2 in spray process and chemical nature of additional phases in the films are discussed. Growth temperatures in the range of 320–380°C at Cu/In>1 are determined as optimal for depositing orientated in the (112) direction CuInS 2 thin films with chalcopyrite structure. Sprayed chalcopyrite CuInS 2 films have absorption coefficient ∼10 5 cm −1in visible and red region of spectra and optical band gap 1.45 eV.