Effect of solvent on the characteristic properties of nebulizer spray pyrolyzed Cu2ZnSnS4 absorber thin films for photovoltaic application

Cu2ZnSnS4 (CZTS) thin films are the most promising absorber layer for thin film solar photovoltaics. The nebulizer assisted spray pyrolysis technique was employed to deposit the CZTS absorber thin films on bare soda lime glass substrate at a temperature of 350 degrees C without annealing and sulfurization. Different solvents such as Dimethyl sulfoxide (DMSO), Ethylene diamine, 2-Methoxy ethanol and Water were used. The influence of these solvents on the structural, morphological, compositional, optical and electrical properties were studied using an X-ray diffractometer, Raman spectrometer, Scanning electron microscope annexed with energy dispersive X-ray spectrometer, Atomic force microscope, UV-vis spectrophotometer and a digital current source meter. The X-ray diffraction pattern reveals the formation of CZTS in all the solvents with preferential peak along [112] direction and the size of the crystallites is found to vary from 21 nm for DMSO to 34 nm for water. Raman analysis exhibited a phase pure film for all the solvents except the film prepared from DMSO which reveals a peak for the presence of Cu2S. The morphological and compositional analysis shows better texture with uniform coverage on the glass substrate and off stoichiometric ratio for all the deposited films. From the optical analysis it is seen that the prepared films show a broad absorption spectra in the visible region and the band gap was found to lie in the range of 1.15 eV to 1.51 eV. The current voltage characterization in dark shows significant increase in current with the applied voltage for all the films with DMSO film recording the lowest. Hall measurements revealed a carrier concentration of 1.93 x 10(18) cm(-3), mobility of 13.67 cm(2)/V s and a conductivity of 42.27 x 10(-2) Omega(-1) cm(-1) for water. From this study, we infer that the CZTS film deposited using precursor solution derived from water exhibits phase purity along with enhanced photovoltaic properties at a substrate temperature of 350 degrees C through nebulizer assisted spray pyrolysis technique.