| As the energy in the world becomes increasingly scarce and the stronger awareness of energy conservation and environmental protection,people have paid more and more attentions to the research and application of the thin film solar cells.In recent years,the Cu2ZnSnS4（CZTS）based solar cells have become a hot topic because of its high absorption coefficient,suitable band gap energy,environmental friendliness,high theoretical conversion efficiency and low cost.At present,the study of the CZTS based solar cells is concentrated on the CZTS/CdS heterojunction.However,the CdS buffer layer is poisonous and it can cause absorption loss due to its low band gap.It is necessary to substitute the CdS buffer layer with other materials.Among them In2S3 is one of the most promising candidate materials because of its nontoxic and higher band gap in comparison with CdS.This work has been carried out under the above-mentioned background and by the support of the national project.Main contents and results of this study are as follows:1.The performance of the CZTS/In2S3 heterojunction solar cell is investigated by the SCAPS-1D.We investigate the influence of the structural parameters of the CZTS absorber layer,the In2S3 buffer layer,working temperature and the parasitic resistor on the cell performance.The structure optimization parameters were achieved:The thickness of the CZTS absorber layer is 3 μm and buffer layer is 20 nm;the optimal concentration for the absorber layer and the buffer layer are 1×1017 cm-3.The CZTS defect density should be controlled under 1×1013 cm-3.At the same time,we can find that the shunt and series resistances mainly affect the fill factor;the increased working temperature has a strong influence on the solar cell efficiency and the temperature coefficient is calculated to be about-0.17%/K.After optimization,CZTS solar cell has the optimal photovoltaic property:short circuit current density:23.37 mA/cm2,open circuit voltage:0.958 V,fill factor:86.13%,conversion efficiency:19.28%.2.Ag and Sn-doped In2S3 thin films were prepared using thermal evaporation method.The influences of Ag and Sn impurity on the structural,morphology,optical and electrical properties of the In2S3 films have been studied.The X-ray diffraction spectra reveal the formation of cubic In2S3 phase.The optical properties illustrate that the Ag doping results in a reduction of optical band gap while Sn doping leads to widening of the band gap.Besides,both the Ag and Sn doping exhibit a decrease in resistivity and a significant improvement in carrier concentration.3.The band alignment at the CZTS/In2S3 interface was measured by X-ray photoemission spectroscopy（XPS）.The valence and conduction band offsets were determined to be 0.46 eV and 0.82 eV,respectively,which indicate that the CZTS/In2S3 belongs to type I semiconductor heterojunction.The research of this article lays a foundation for the preparation of the high efficiency,low cost and Cd free environmentally friendly CZTS/In2S3 heterojunction solar cell.Therefore this article has a certain theoretical and practical significance. |
