Effects of complexing agent on earth-abundant environmentally friendly Cu2ZnSnS4 thin film solar cells prepared by sol–gel deposition

Abstract

Solution-processed Cu2ZnSnS4 (CZTS) thin film growth parameters using complexing agent triethanolamine (TEA) have been optimized. Effects of TEA on structural, morphological, optical and electrical properties of CZTS thin films were systematically investigated. X-ray diffraction and Raman spectroscopy of annealed CZTS thin films confirmed a pure kesterite structure with optimized TEA concentration. Surface morphology of CZTS films were analyzed by field emission scanning electron microscope and atomic force microscope, which revealed a smooth surface and systematic grain growth formation with varying TEA concentrations. p-Type conductivity was confirmed using Hall measurements and the effect of TEA concentration on electrical properties is investigated. X-ray photoelectron spectroscopy demonstrated absence of secondary phases and stoichiometric atomic ratios of multicationic quaternary CZTS thin film grown without sulphurization. UV–Vis spectra revealed a direct energy band gap ranging from 1.90 to 1.40 eV, which was found to depend upon the TEA concentration. Such band gap values are optimum for semiconductor material as an absorber layer of thin film solar cells. The CZTS thin film was further used for the fabrication of a solar cell of structure SLG/FTO/ZnO/CZTS/Al. The best solar cell showed a short-circuit current density (Jsc) of 10.78 mA/cm2, open circuit voltage (Voc) of 0.27 V, fill factor (FF) of 37% and power conversion efficiency (η) of 1.08% under air mass 1.5 (100 mW cm−2) illumination.