Numerical Simulation Studies Of CuInS₂Solar Cells

CuInS2is one of the best ideal solar cell absorber layer materials because of its high coeffciency (105cm-1) and bandgap of1.53eV, which well matchs to sunlight spectrum. However, the best lab efficiency of CuInS2cells is about12.2%, which is far lower than the theoretical efficiency (28.6%) and the best efficiency (20.8%) of Cu(In,Ga)Se2cells. There are two mian pathways to solve the problem, which are studying the influence of absorber photoelectricity, defect, bandstructure, etc on cell performance and optimizing the cell strcture to improve cell efficiency. Hence, deeply studying influence of various material parameters on cell performance possesses academic merits and practical utilities. Moreover, we design a CuInS2cell with graded-Zn(O,S) buffer and test its performance by AMPS-1D.We have done many numerical simulation studies on the CuInS2thin solar cells. The absorption coefficiency of the absorber layer CuInS2and the transparent conducting layer ZnO:Al used for the simulation were obtained using thin films prepared by pulsed laser deposition and measured by using a UV-VIS-NIR spectrophotometer (Shimadzu, UV3600).Firstly, we study the influence of CuInS2thickness, bandgap and CdS thickness on the tapical structure (Al/ZnO:Al/CdS/CuInS2/Mo) CuInS2cell performance. The results show that optimum CuInS2thickness, bandgap and CdS thickness are around2000nm,1.40eV and40-50nm, respectively.Secondly, we refine the simulated cell structure and insert a thin interface to simulate the defect of preperaed films, and the CdS is replaced by Zn(O,S). We systematically study the influence of various parameters of absorber, buffer and interface layer on cell performance, such as relative dielectric constant EPS, defect density and back electrode barrier height, etc. The optimum parameters:Zn(O,S) buffer electron mobility μn>5cm2/V·s, doping density Nd>1018cm-3; CuInS2absorber relative dielectric constant EPS>12, defect density is5x1016cm-3, electron mobility μn>70cm2/V·s; Mo back electrode barrier<0.24eV.Finally, we study the influence of conduction band offsets and valence band offsets on cell performance and performance of CuInS2cell with different sulphur content Zn(O,S) buffer. Moreover, we design a kind of CuInS2cell with graded-Zn(O,S) buffer and test its performance by AMPS-1D. For high efficiency cell, conduction band offsets with｜△Ecba| 0.2eV and｜△Ecwb｜<0.4eV is prerequisite. The best-simulated performance of cell with single-Zn(O,S)buffer are Eff=14.6%, Jsc=23.2mA/cm2, FF=0.68and Voc=0.93V. We design the cells with graded-Zn(O,S) buffer based on the above study, and the cells possess high efficiency20.8%and a special high FF (0.86).