Preparation and characterization of Cu2ZnSnS4 thin films with various compositions deposited by a dual thermal evaporation technique

Abstract

Cu2ZnSnS4 (CZTS) thin films were deposited successfully with four different compositions, namely, Cu-rich, Sn-rich, Zn-rich and near-stoichiometric CZTS, by a dual thermal evaporation technique to investigate the effect of stoichiometry on the physical properties of the deposited films. The thin films were characterized by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–VIS–NIR spectroscopy in the as-deposited state and after annealing in nitrogen at 350 °C for 30 min. It was found that the stoichiometry of the film played a critical role in the physical properties and stability after annealing. Increasing the amount of each element compared to that of the others impacted the colour, preferred orientation, grain size, microstrain, dislocation density, surface morphology, transmittance, reflectance, absorbance and band gap of the thin films. A (112) preferred orientation was obtained, and this orientation became more pronounced after the annealing of all films. The stoichiometry of the films changed after annealing due to re-evaporation of the sulfur, and the Cu-rich film was the most stable of the films studied herein. The estimated band gap (Eg) for the as-deposited films varied between 1.53 eV and 2.3 eV and were reduced to 1.1 eV for the Cu-rich film after annealing.