Solution processed copper zinc tin sulfide thin films for thermoelectric device applications

Abstract

In this work, Cu2ZnSnS4 (CZTS) thin film has been fabricated on a soda-lime glass substrate through an economical green chemical route employing nebulizer assisted spray pyrolysis technique. The deposition is carried out under ambient atmospheric pressure without annealing and sulphurization. An investigation was done to reveal the temperature dependence of various characteristics especially the thermoelectric property of this Earth-abundant, nontoxic CZTS films in the range of 300 °C–375 °C. This study reveals the thermoelectric conversion capability of the material in addition to its photovoltaic conversion application. XRD spectra revealed the formation of tetragonal structured kesterite CZTS peaks preferentially oriented along [112] direction. The film thickness and size of the crystallites is found to increase with temperature up to 350 °C while the dislocation density and microstrain decreased. Raman spectra exhibit a phase pure CZTS layer free from secondary and tertiary phases at a substrate temperature of 300 °C whose composition seems to be off stoichiometric with a Cu/(Zn + Sn) ratio of 0.78. The surface morphological analysis shows a dense, smooth and compact surface for the 350 °C sample. The bandgap was found to vary in the range of 1.52–1.74 eV. Refractive index, extinction coefficient and electrical characteristics of the prepared films endorse its usage as an absorber material for thin-film photovoltaic energy conversion. The Seebeck coefficient of 350 °C grown film is found to be 153 μV/K and the corresponding power factor increases to 5.76 × 10−3 W/mK−2 which recommends its utility in the thermoelectric devices.