The Influence Of Element Doping On The Performance Of CZTSSe Solar Cell

The kesterite Cu₂ZnSn（S,Se）₄（CZTSSe）solar cell is developed from the Cu（In,Ga）Se₂（CIGS）solar cell.Because of its adjustable optical band gap of the absorber film and high absorption coefficient(greater than 10⁴cm^-1),rich sources of materials and other characteristics,CZTSSe solar cell is one of the most promising thin-film solar cells in the future.However,the previous record of CZTSSe solar cells is 12.62%,which is far lower than the high record of CIGS solar cells（23.35%）,the main reason is that the open-circuit voltage(V_oc)and short circuit current(J_sc)values are quite different.Studies have shown that rare earth elements have excellent photoelectric properties and can increase the photo-generated current density of currents,and are widely used in many solar cell fields.In addition,Cd doping can effectively reduce Cu _Zn and Zn _Cuinversion defects in the film and improve the photovoltaic performance of the cell.In this thesis,DMSO was used as a solvent to prepare a rare earth element La-doped CZTSSe solar cell and a La and Cd co-doped CZTSSe solar cell with dual advantages.The main contents are as follows:1.The La-doped CZTSSe thin films and solar cells in different proportions were prepared by the solution method,and the thin films and cell devices were characterized and analyzed accordingly.It was found that the doping of rare earth element La can increase the crystallinity of the film,reduce the thickness of the fine-grain layer,eliminate holes,and increase the width of the depletion layer（W_d）;the doping of rare earth element La has an important effect on cell devices,and can reduce the equivalent resistance of the cell device.the open-circuit voltage increases by 15 m V,and the result is 7.4%Photoelectric conversion efficiency when La/（Cu+Zn+Sn）=7%.2.Based on the best doping ratio of La,we designed a two-step spin coating method to prepare Cd-doped CZTSSe thin film.After characterizing the film and cell devices,it is found that Cd²⁺replaces part of Zn²⁺into the CZTSSe lattice,inhibiting the formation of Cu _Zn inversion defects.Moreover,Cd doping eliminates the small particle layer of the film,reduces carrier recombination,and causes J_sc of the device to increase.Finally,the external quantum efficiency（EQE）test of the cell device found that the incorporation of Cd element further increased the light absorption of the cell device.When Cd/（Cd+Zn）=30%,we get a solar cell with a photoelectric conversion efficiency of 9.4%.