Investigation of effects of the film homogeneity on the cell efficiency of Cu2ZnSnS4 (CZTS) based thin film solar cell

In the first stage of this study, various metallic stacking order layers were utilized and the most promising one determined. In the second stage of this study, the effect of pre-annealing treatment of Mo/Cu/Sn in the determined stacking order (Mo/Cu/Sn/Zn/Cu) on the properties of Cu2ZnSnS4 (CZTS) thin films was investigated. CZTS thin films were grown on Mo coated glass by DC magnetron sputtering deposition of metallic precursor layers, followed by a thermal annealing step in Rapid Thermal Processing (RTP) system. Mo/Zn/Sn/Cu and Mo/Cu/Sn/Zn/Cu were used as metallic stacking order layers, 500, 550, and 600 °C values were selected as the reaction temperatures. The GDOES data showed that increasing the reaction temperature gave rise to enhancement in the homogeneity of the films and Mo/Cu/Sn/Zn/Cu stacking order was appeared more promising one in terms of the homogeneity of the film. XRD and Raman spectra of the films exhibited and proved formation of CZTS structure and other secondary phases. In the second stage of this study, the Mo/Cu/Sn structure of the Mo/Cu/Sn/Zn/Cu stacking order was exposed to pre-annealing treatment at 200 and 380 °C to see impact of the pre-annealing treatment and pre-annealing temperature. XRD and Raman spectra of the films proved formation of CZTS structure. GDOES data revealed that pre-annealing treatment enhanced homogeneity of films. PL and optical band gap values showed that the pre-annealing treatment did not change the optical properties of the films. The best solar cell performance was achieved with 2.2 % conversion efficiency in the CZTS samples which are pre-annealed at 200 °C.