Low cost copper zinc tin sulphide (CZTS) solar cells fabricated by sulphurizing sol-gel deposited precursor using 1,2-ethanedithiol (EDT)

Abstract

In this paper, we report the preparation of crystalline CZTS thin films by sol–gel method followed by sulphurization using 1,2- Ethanedithiol (EDT) at 400 °C in a three zone horizontal tubular reactor equipped with computer controlled vacuum system. These films were characterized by XRD, Raman, Hall measurements and UV–Vis-NIR spectroscopy. XRD and Raman studies confirmed highly crystalline and single phase CZTS. Hall study revealed p-type semiconducting CZTS film having charge carriers density of 1.70 × 1018 cm−3 and the resistivity (ρ) of the order of 5.00 × 10−1Ω-cm. It was found that the direct band gap of 1.44 eV for CZTS film was seen from optical study. Further, double metal oxide layers having slightly different band gap were used to form a p-n junction with CZTS film. Cadmium-free solar cells with structure ITO/ZnO/CZTS/Ag (cell-1) and ITO/ZnO/com-TiO2/CZTS/Ag (cell-2) were fabricated. Electrochemical Impedance Spectroscopy (EIS) measurements were performed in the low frequency range with applied bias of 0.1 Volt for the devices. The EIS studies showed that the solar cell with ultrathin compact TiO2 layer provide a favorable path for the efficient charge transport process at the interface. The external quantum efficiency measured at 520 nm was found to be 62.5%. Cell-2 exhibited improved photovoltaic parameters with short circuit current density (Jsc) of 4.721 mA/cm2, fill factor of 0.46 and open circuit voltage (Voc) of 400 mV. The short circuit current density and fill factor of double metal oxide layers (cell-2) were increased by 78% and 46%, respectively, as compared to single metal oxide layer (cell-1).