Fabrication of Cu2CoSnS4 thin films by a facile spray pyrolysis for photovoltaic application

Abstract

The role of substrate temperature on the structural, morphological, optical, and photovoltaic properties of Cu2CoSnS4 (CCTS) thin films based on earth abundant and non toxic elements, has been presented. Thin films of CCTS have been deposited by spray pyrolysis technique. X-ray diffraction study revealed that the films are polycrystalline in nature with stannite structure. Raman analysis confirmed the phase purity of CCTS films deposited at substrate temperature of 350°C. The XPS spectra indicates oxidation states of Cu, Co, Sn, and S to be Cu+, Co2+, Sn4+, and S2− in CCTS films. FE-SEM images showed drastic variation in the morphology of the films with respect to increase in substrate temperature. EDAX spectra of the films deposited at different substrate temperatures revealed the presence of different constituent elements such as, Cu, Co, Sn and S in CCTS thin films. The energy band gap values for the films were found to be decreasing from 1.79eV to 1.42eV with respect to increase in substrate temperature. The static contact angle measurement of the films with Sodium sulphate electrolyte depicts the hydrophilic nature of the films. The photoelectrochemical solar cell has been constructed using Sodium sulphate as electrolyte, platinum as counter electrode, while CCTS thin films were used as working electrodes. The power conversion efficiency of 1.78 % and open circuit voltage of 350mV was observed for the CCTS thin films deposited at substrate temperature of 350°C.