Dispersive optical constants and electrical properties of nanocrystalline CuInS2 thin films prepared by chemical spray pyrolysis

Abstract

Nanocrystalline CuInS2 thin films were deposited on borosilicate glass substrates via chemical spray pyrolysis method. The structural, morphological, optical, and electrical properties were studied as a function of increasing annealing temperature from 250 to 350 ̊C. XRD analysis showed mixed phases at lower temperatures with the preferred orientation shifting towards the (112) chalcopyrite CuInS2 plane at higher substrate temperature. The crystallite size increased slightly between 13 and 18 nm with increase in annealing temperature. The optical band gap was determined on basis of Tauc extrapolation method and the Wemple–Di-Domenico single oscillator model. Possible structural and quantum confinement effect may have resulted in relatively larger band gaps of 1.67–2.04 eV, relative to the bulk value of 1.5 eV. The presence of CuxS in the as-deposited and wurtzite peaks after annealing at 350 ̊C play a role in influencing the optical and electrical properties of CuInS2 thin films.