Fabrication Of CIGS Thin Film Solar Cells By Magnetron Sputtering And Post-selenization Processes

The CIGS solar cells take the advantages of high conversion efficiency,large optical absorption coefficient,good stability,and tunable bandgap.This thesis focuses on the CIGS thin films solar cells prepared by magnetron sputtering and post-selenization processes.Starting from the material preparation process,we first studied the phase evolution of the different metallic precursors during the alloying process,then investigate the selenization processes of different precursors using solid selenium as the selenium source which is low-toxic,easy to store,and relatively low-cost.The analysis of CIGS thin film growth and element diffusion process revealed that the metallic precursors show copper out-diffusion to the surface at the early stage of the selenization reaction,which results in the presence of a copper-depleted OVC phase at the bottom of the CIGS absorber layer.By controlling the phase structure of the metallic precursors,Cu,In,and other metal phases are converted into Cu₉?In,Ga?₄ and other alloy phases,which can effectively suppress the out-diffusion of Cu,and thus suppressing the formation of the OVC phase at the bottom of the absorber layer.Finally,the effects of the OVC phase on the interface transmission characteristics and photovoltaic performance of the CIGS solar cell were systematically studied by the temperature-dependent J-V measurements,Kelvin probe,and SCAPS theoretical simulation.In this thesis,the following conclusions have been made from the research of the above aspects:1.By studying the phase evolution and element diffusion of CIGS thin films during the selenization process,the results show that?1?the OVC phase formed at the bottom of the absorber layer is caused by Cu out-diffusion to the surface,?2?Cu₉?In,Ga?₄ is formed during the alloying process effectively reduces the diffusion of Cu elements to the surface,thus suppressing the formation of the OVC phase at the bottom of the absorber layer.2.By studying the CIGS thin-film photovoltaic cells prepared by this techniques,it can be found that reducing the OVC phase can?1?reduce the series resistance of the battery from 8.13?·cm² to 0.3?·cm²,increase the fill factor from 44.3%to 68.2%,and increase the efficiency greatly from 5.4%.To 12.54%.?2?The solar cells'back contact barrier height of the device is reduced from 123.1 mV to 6.5 mV,which demonstrates a good ohmic contact.3.Simulating the CIGS thin film devices according to the theory of SCAPS software,we can find that the carrier layer concentration at the bottom of the absorber layer has significant influence on the heterojunction band bending,distribution of electric field,thus affecting the open circuit voltage,fill factor and short-circuit current density of the solar cells.Therefore,the optimum cell efficiency can be obtained by increasing the carrier concentration at the bottom of the absorber.