Effect Of ZnO Intermediate Layer And Na Doping On Cu₂ZnSnS₄ Film Solar Cells

Energy is the necessity of industrial development and even the development of global society,and the fossil energy which is used most now,will cause serious pollution to the environment after burning,on the other hand,it will also face the trend of exhaustion.Looking for renewable and pollution-free clean energy is imminent.Looking for renewable and pollution-free clean energy is imminent.As a very promising green energy,solar energy has been widely used as one of the most important energy sources.Solar cell is the core device of direct conversion of solar energy into electric energy,and thin film solar cell is widely concerned in recent years because of its advantages in raw material consumption and photoelectric conversion efficiency.Cu2ZnZnS4（CZTS）semiconductor compounds have become the ideal materials for the preparation of high efficiency thin film solar cells because of their rich raw materials,innocuity and suitable direct band gap（1.4-1.6eV）and high light absorption coefficient(≥10⁴cm^-1)in the visible region.In this paper,CZTS absorption layer was grown on Mo glass by magnetron sputtering physical vapor deposition and spin coating chemical liquid deposition,CdS buffer layer was deposited by chemical water bath method,and intrinsic ZnO and ITO window layer were grown by magnetron sputtering method.In the process of preparation of CZTS absorption layer film,the curing process is very important for the growth of the material.The curing process directly determines the crystal properties such as grain size,preferred orientation crystal surface,micro morphology and stoichiometric ratio.In addition,the interface combination of Mo/CZTS and CZTS/CdS in multilayer thin film device structure will affect the open circuit voltage,short circuit current,series resistance and filling factor of CZTS solar cell.In this paper,the vulcanization process,interface microstructure,composition and energy band structure of CZTS film are studied（1）The crystal structure,micro morphology and film thickness of CZTS films were studied systematically.The results show that the surface morphology of the CZTS film obtained by re vulcanization after the pre coating alloy is better than that of the CZTS film directly vulcanized.The technological parameters of alloy and vulcanization,such as time,temperature and atmosphere pressure,were further studied.The results show that the surface morphology of CZTS is the best,and the final efficiency is the highest for1.063%.（2）ZnO interlayer was deposited between Mo electrode and CZTS absorption layer by magnetron sputtering,which reduced the thickness of secondary phase MoS₂film and the series resistance of battery.The growth parameters of CZTS absorption layer were adjusted to maintain the unity of chemical element measurement.The results show that when the ratio of Cu/（Zn+Sn）=0.67 and Zn/Sn=1.05 is maintained,the thicker ZnO interlayer can still effectively avoid the formation of ZnS secondary phase;howeVer,due to the different Gibbs free energy changes,the samples with different ZnO content have different CZTS morphology and formation mechanism;after the ZnO interlayer is adopted,the final conversion efficiency reaches 4.19%.（3）CZTS:Na precursor was deposited by chemical solution spin coating.The precursor consists of 7 layers of CZTS at the bottom and 1 layer of Na doped CZTS at the top.After vulcanization,Na doped CZTS films and solar cells were obtained.The effect of Na doping on the energy band structure and photovoltaic performance of the interface between CZTS and CdS heterojunction was first reported.The results show that 10%Na doping can reduce the CBO of cliff band arrangement between CZTS and CdS from 0.25eV to 0.1eV,and improve the photoelectric conversion efficiency by 44%.