Fabrication And Research Of Silver And Germanium Co-doped (Cu,Ag)₂Zn(Sn,Ge)Se₄ Thin Film Solar Cells

Each day brings further evidence that the concept of green and sustainable development has ingrained into the human mindset,and the aware of the utilization of solar energy has become promot than we used to.Solar cells have been vigorously studied because of their good application prospects.Quaternary compound semiconductor material copper zinc tin selenium(Cu₂Zn Sn Se₄,CZTSe)is widely used as an absorber layer materials for thin-film solar cells because of its low cost,high absorption coefficient and earth-abundant elements composition.However,due to the intrinsic defects and defect clusters in CZTSe thin film,it is difficult to improve the efficiency of CZTSe thin film solar cells.In order to achieve higher device efficiency,herein,Ag and Ge ions were doped into CZTSe by solution method to improve the defects in CZTSe thin film solar cells.The specific contents and main research results of this paper are as follows:(1)CZTSe thin films and devices were prepared under different selenization time,and the best selenization time was explored.Through the analysis of CZTSe thin films prepared under different selenization time,it was found that when the selenization time was 15 min,the thin film surface was flat and compact.Meanwhile,the CZTSe thin film had good crystal quality and showed the best overall properties.After making the CZTSe thin film into device,we finally obtained device efficiency of 7.81%under the selenization time of 15 min.(2)Studying the effects of Ag doping and Ge doping on the properties of CZTSe thin films and solar cells.Firstly,we prepared(Cu_1-xAg_x)₂Zn Sn Se₄(CAZTSe)and Cu₂Zn(Sn_1-xGe_x)Se₄(CZTGSe)thin films with different Ag contents and different Ge contents by solution method using the best selenization time.Besides,we tested and analyzed the crystal structure and micromorphology of those thin films using means of XRD,SEM and other test methods.Finally,CAZTSe and CZTGSe thin film solar cells were prepared according to the standard structure of CZTSe thin film solar cells and the performances of both thin film solar cells were studied.The results show that compared with undoped CZTSe thin films and solar cells,Ag doping not only changed the carrier concentration of CZTSe thin films,but also improvd the open circuit voltage(V_oc)of CZTSe thin film solar cells.Finally,when the Ag-doped concentration was 5%,the device efficiency of 8.56%was achieved.Similarly,compared with undoped CZTSe thin film solar cells,Ge doping not only increased the V_oc of the device,but also improved the fill factor of the device.Finally,a high device efficiency of 10.04%was obtained.(3)The properties of CZTSe thin films and devices are further improved by co-doping Ag and Ge ions.(Cu_1-xAg_x)₂Zn(Sn_1-xGe_x)Se₄(CAZTGSe)thin films and devices with Ag/(Ag+Cu)ratio of 5%and different Ge/(Ge+Sn)ratios were prepared by solution method at optimum selenization time.The effects of Ag and Ge ions on CZTSe thin films and devices were investigated.It is found that the incorporation of Ag and Ge ions plays a synergistic role in improving the performance of CZTSe thin films and devices.Compared with only Ag-doped CZTSe thin films,the surfaces of Ag and Ge ions co-doped CAZTGSe thin films were more uniform and compact,which could reduce the carrier recombination loss.Compared with only Ge-doped CZTSe thin films,CAZTGSe thin films had better longitudinal grain growth and good contact with the substrate,which was conducive to the collection of photogenerated carriers.Finally,we achieved CAZTGSe thin film solar cells with the highest efficiency of 10.12%when the Ag/(Ag+Cu)ratio was 5%and Ge/(Ge+Sn)ratio was 25%.