Electrical and optical properties of single-phase CuInS₂ films prepared using spray pyrolysis

Abstract

The spray pyrolysis conditions required to prepare single-phase CuInS₂ films of good optical quality were optimized. The as-deposited films had a sphalerite structure which transformed to the chalcopyrite structure on annealing at 670 K. Single-phase and two-phase (mixture of CuInS₂ and Cu_xS) regimes were established and were correlated with the cation-to-anion and copper-to-indium ratios in the spray solution. The resistivity of both as-deposited and annealed single-phase films changed from about 10³ Ωm to about 10^-1 Ωm with increasing copper-to-indium ratio in the spray solution. An optical gap of about 1.38 eV was measured for both the sphalerite and the chalcopyrite structures. Photoconductivity was observed in the as-deposited films and was enhanced on annealing. The photosensitivity decreased as the copper excess in the spray solution was increased (up to 7%).