Current-voltage characteristics of Cu₂ZnSnS₄ absorber layer for energy harvesting devices

Environment friendly Copper-Zinc-Tin-Sulphide (CZTS)/Cadmium sulphide (CdS) thin film solar cells have been fabricated by sequential vacuum thermal evaporation technique. The developed CZTS films having the thickness of 1μm from layer by layer deposition of Cu: ZnS: Sn precursors having various compositional ratios (2:1:1, 2:1.5:1 and 2:2:1). Structural and morphological information of CZTS films were analyzed by XRD, Raman and SEM. The structural analysis showed increase with thickness and grain size increases whereas strain and dislocation density decreases. UV–vis absorption studies revealed that CZTS thin films have an optical band gap around 1.5 eV and it shows a large absorption coefficient (>104 cm−1). Four probe and Hall measurements indicate that CZTS thin film has the resistivity from 1.5–2.96 Ω-cm and the hole concentration from the value 9.1 × 1016–2.09 × 1018 N (cm−3). The deposited film CZTS were annealed at 500°C, to avoid forming binary compounds. Thin film solar cell has the structure of ITO/Mo/CZTS/CdS/i-ZnO/Al-grid/ITO exhibits the photovoltaic conversion efficiency of 5.6% under Air Mass (AM) 1.5 conditions and its photovoltaic performances were examined. This approach is favoured due to cell efficiency has a very large influence on the acceptable manufacturing cost of a PV module.