Theoretical Simulation Of Performances In CIGS Thin-film Solar Cells With Cadmium-free Buffer Layer

CIGS is a direct band gap semiconductor material,forbidden bandwidth is 1.04 e V.By changing the Ga doping concentration can make the forbidden bandwidth of CIGS continuous vary between 1.04 ~ 1.67 eV,to better matched with the solar spectrum.Traditional buffer layer of CIGS solar cells iSCd S and its forbidden gap is 2.4 e V.At the same time,we know that Cd element is toxic,and there is pollution to the environment.So it is necessary to ensure the performance of the CIGS solar cells to reduce the use of toxic substances,and find alternative CdS buffer layer material,improve the performance of the CIGS solar cells,it is the research emphasis in this paper.ZnS is n-type ?-? direct band gap compound semiconductor material,and the forbidden bandwidth is 3.77 e V at room temperature.Because the non-toxic no-pollution,larger forbidden bandwidth,cheap accessible raw materials,low cost advantages to be the ideal buffer layer material of CIGS solar cell.In this paper,using the simulation software wxAMPS to simulate ZnO/ZnS(n)/CIGS(p)?ZnO/ZnS(n)/CIGS(i)/CIGS(p)two type solar cells with ZnS is administered buffer layer.Based on two kinds of structure of each part of the solar cell thickness,carrier concentration,effect of defect states on the performance of solar cells,the device response of solar cells under different temperature,as well as we simulating different Ga doped concentration for CIGS,to concluded that the affection of above various factors for performance of the battery.Comparingthe advantages and disadvantages of two batteries structure.Through comparison we found that:In ZnO/ZnS(n)/CIGS(p)structure optimal ZnS thickness was 0.04 um,doping concentration was 2e18cm-3;density of ZnS defect states has little effect on the performance of the battery;Absorbing layer CIGS optimal thickness was 2.5 um,doping concentration 2e16cm-3;the smaller the density of defect states,the better performance of solar cells.At the same time,we found that the Ga doping concentration had a great influence on the performance of the battery,CIGS optimal forbidden bandwidth is about 1.3839 e V;When the temperature of the environment is in the vicinity of 255 K,the comprehensive performance of solar cell performance is the most outstanding.In the structure of ZnO/ZnS(n)/CIGS(i)/CIGS(p)type solar cell optimal ZnS thickness was 0.04 um,optimal doping concentration was 5e17cm-3,overall,defect mode's influence on the solar battery is not obvious;The thickness of the intrinsic layer of CIGS is suitable for 0.5 um.The greater the density of defect states,the greater the influence on solar cells.When the defect concentrations less than 5e14cm-3,at this time,have less effect on the battery performance;For absorbing layer CIGS proper thickness is 2 um,In theory,we hope that the higher the doping concentration.Both open circuit voltage and efficiency as the doping concentration increases linearly rising,but the increase of CIGS carrier concentration is a difficult problem at present,the lower the defect density of states,the better the performance of battery,at the same time we found the ZnO/ZnS(n)/CIGS(i)/CIGS(p)structure of the optimal forbidden bandwidth of CIGS is 1.3839 e V.Ambient temperature at 280 K,ZnO/ZnS(n)/CIGS(i)/CIGS(p)structure solar cells has the best comprehensive performance.Based on the simulation of two kinds structure solar cells,we finally got in 300 K electricity conversion efficiency of 23.0448% and 27.2882% respectively of two kinds of CIGS solar cells with ZnS as buffer layer structure design.Compared with the current best conversion efficiency of 22.3% of CIGS solar cell with Cd S as the buffer layer,the conversion efficiency is improved on the basis of improving the problem of Cd S pollution.The practical application of future batteries can provide some guidance.