Non-stoichiometric effect and disorder in as-prepared Cu2ZnSnS4 films deposited at different temperatures by ultrasonic spray pyrolysis

Abstract

A better understanding of its crystal structure, the formation of possible secondary phases, defects and Cu–Zn disorder effects is needed to improve the photovoltaic device performance of CZTS films. In this direction, the effect of deposition temperature on the structural inhomogeneities, such as secondary phases and Cu–Zn disorder, etc. as well as opto-electrical properties of CZTS were experimentally examined. For this purpose, a non-stoichiometric spraying solution was prepared and ultrasonically sprayed onto glass substrates at different deposition temperatures (350 °C, 400 °C, 450 °C, and 500 °C) to obtain CZTS films. Afterward, the structural, morphological, elemental, optical, and electrical properties of the deposited films were investigated in detail. By Lorentzian deconvolution of Raman spectra, 14 Raman vibrational modes were detected and seven of these were assigned to the secondary phases. Also, the ordered-kesterite phase (337 cm−1) of CZTS was found to crystallize along with the disordered-kesterite phase (329 cm−1) due to the disorder of the cation (Cu–Zn) sublattice. Optical band gaps for CZTS films decreased from 1.89 eV to 1.42 eV with increasing in deposition temperature. It was seen that not only optical band gaps but also Cu–Zn disorder and the amount of secondary phases in CZTS films tightly depend on the deposition temperature.