Dependence of the properties of copper zinc tin sulfide thin films prepared by electrochemical deposition on sulfurization temperature

Abstract

Copper zinc tin sulfide (CZTS, Cu2ZnSnS4) is a low band gap semiconductor that is attractive for use in solar cells. We investigated the dependence of the structure and properties of CZTS thin films on the temperature used to sulfurize precursor thin films composed of copper, zinc and tin fabricated by electrochemical deposition. The precursor films were sulfurized in a furnace with three zones, which allowed fine control of the sulfurization temperature between 250 and 400 °C. X-ray diffraction and Raman spectroscopic measurements confirmed that the films were composed of CZTS following sulfurization. The grain size and crystallinity of the films increased with sulfurization temperature. The composition of CZTS also varied with sulfurization temperature. The proportions of Cu and Zn increased while that of Sn decreased with increasing sulfurization temperature. Absorption and reflectance spectra revealed that the absorption coefficients and band gaps of the CZTS films varied with sulfurization temperature between 3–4.1 × 104 cm−1 and 1.4–1.53 eV, respectively. Solar cells containing CZTS sulfurized at 400 °C showed a maximum efficiency of 2.04 %, which was attributed to the higher crystallinity and larger grain size of CTZS compared with thin films sulfurized at lower temperatures. Our results show that control of sulfurization temperature is an important factor in optimizing the performance of CZTS thin films in solar cells.