Fabrication and photovoltaic properties of Cu2ZnSnS4/i-a-Si/n-a-Si thin film solar cells

Abstract Cu 2 ZnSnS 4 (CZTS) films were successfully prepared by sulfurization of Zn/Sn/Cu multilayers at different temperatures from 350–575 C. The film sulfurized at 500 C presents no any secondary phases and Raman peaks at 251, 288, 336 and 368 cm −1 are observed with the main Raman peak locating at 336 cm −1 . The surface of the Cu 2 ZnSnS 4 film is compact and the thickness of film is about 1 μm. The mapping and point characterization of energy dispersive spectrometer show that the composition element ratios are close to the stoichiometry of Cu 2 ZnSnS 4 . The absorption coefficient of Cu 2 ZnSnS 4 film is larger than 10 4  cm −1 in the visible light region of 400-800 nm and the direct band gap of the Cu 2 ZnSnS 4 film is estimated to be about 1.5 eV. The effect of intrinsic amorphous silicon layer is obvious and Cu 2 ZnSnS 4 /i-a-Si/n-a-Si solar cell shows much higher conversion efficiency and more obvious diode rectifying effect than Cu 2 ZnSnS 4 /n-a-Si solar cell. The reverse saturation current density of Cu 2 ZnSnS 4 /i-a-Si/n-a-Si hetero junction has a value around 1.42 × 10 −3  mA/cm 2 and the ideal diode factor of this junction is estimated to be about 2.85. The open circuit voltage, short circuit current density and fill factor of this Cu 2 ZnSnS 4 /i-a-Si/n-a-Si solar cell are 562 mV, 12.3 mA/cm 2 and 43.8%, respectively, and the conversion efficiency is calculated to be about 3.03%.