Synthesis of AgInSnS₄ thin films by adding tin (Sn) into the chalcopyrite structure of AgInS₂ using spray pyrolysis

AgInSnS₄ thin films were prepared by adding a tin salt to the starting solution used for preparing chalcopyrite AgInS₂ thin films by spray pyrolysis The AgInSnS₄ films were grown at substrate temperatures in the 300-400 °C range, using an alcoholic solution comprised of silver acetate, indium chloride, tin chloride and thiourea. The tin chloride content in the starting solution was gradually varied in terms of the molar ratio x = [Sn]/([S] + [Ag]) from 0 to 0.5 to obtain Sn-doped chalcopyrite AgInS₂ (x < 0.2) and spinel-like AgInSnS₄ (x = 0.2-0.4). X-ray diffraction studies indicated that AgInSnS₄ has a cubic spinel-like structure with lattice parameter of 10.77 A. All AgInSnS₄ thin films exhibited p-type conduction, and their room temperature conductivity ranged from 10^{- 1} to 10^{- 2} S/cm. The conductivity versus 1/T plots for this material showed an Arrhenius-like behavior, from which two activation energies of E_a1 = 0.23-0.40 eV and E_a2 = 0.07-0.20 eV were determined. These results suggest that the grain boundary scattering and the ionization of shallow acceptors dominate the charge carrier transport in the sprayed AgInSnS₄ thin films. The AgInSnS₄ absorption spectrum revealed an energy gap around E_g = 1.89 eV, which was associated to direct-allowed transitions. To our knowledge, the quaternary compound has been prepared for the first time using spray pyrolysis.