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The effect of the deposition temperature of the buffer layer In_2S_3 on the band alignment of CZTS/In_2S_3 heterostructures and the solar cell performance have been investigated.The In_2S_3 films are prepared by thermal evaporation method at temperatures of 30,100,150,and 200 ℃,respectively.By using x-ray photoelectron spectroscopy(XPS),the valence band offsets(VBO) are determined to be-0.28 ±0.1,-0.28 ±0.1,-0.34 ±0.1,and-0.42 ±0.1 eV for the CZTS/In_2S_3heterostructures deposited at 30,100,150,and 200 ℃,respectively,and the corresponding conduction band offsets(CBO)are found to be 0.3 ±0.1,0.41 ±0.1,0.22±0.1,and 0.01 ±0.1 eV,respectively.The XPS study also reveals that interdiffusion of In and Cu occurs at the interface of the heterostructures,which is especially serious at 200 ℃ leading to large amount of interface defects or the formation of CuInS_2 phase at the interface.The CZTS solar cell with the buffer layer In_2S_3 deposited at 150 ℃ shows the best performance due to the proper CBO value at the heterostructure interface and the improved crystal quality of In_2S_3 film induced by the appropriate deposition temperature.The device prepared at 100 ℃presents the poorest performance owing to too high a value of CBO.It is demonstrated that the deposition temperature is a crucial parameter to control the quality of the solar cells.
The effect of the deposition temperature of the buffer layer In_2S_3 on the band alignment of CZTS / In_2S_3 heterostructures and the solar cell performance have been investigated. In_2S_3 films are prepared by thermal evaporation method at temperatures of 30,100,150, and 200 ° C, respectively.By using v-ray photoelectron spectroscopy (XPS), the valence band offsets (VBO) were determined to be-0.28 ± 0.1, -0.28 ± 0.1, -0.34 ± 0.1, and-0.42 ± 0.1 eV for the CZTS / In_2S_3heterostructures deposited at 30, 100, 150 , and 200 ° C respectively, and the corresponding conduction band offsets (CBO) were found to be 0.3 ± 0.1, 0.41 ± 0.1, 0.22 ± 0.1, and 0.01 ± 0.1 eV, respectively. The XPS study also reveals that interdiffusion of In and Cu occurs at the interface of the heterostructures, which is especially serious at 200 ° C leading to large amount of interface defects or the formation of CuInS_2 phase at the interface. CZTS solar cell with the buffer layer In_2S_3 deposited at 150 ° C shows the best performancedue to the proper CBO value at the heterostructure interface and the improved crystal quality of In_2S_3 film induced by the appropriate deposition temperature. The device prepared at 100 ° C. presents the poorest performance due to too high a value of CBO. It is demonstrated that the deposition temperature is a crucial parameter to control the quality of the solar cells.