Simulation Of Device Performance Of CsPbI₃ Hole-Transport-Layer-Free Perovskite Solar Cells

Due to high efficiency and low cost,perovskite solar cells have great application prospects.However,there are still many obstacles to commercialization,such as the stability issue.For perovskite solar cells,the commonly used absorber and hole transport layer is the organic-inorganic hybrid perovskite and Spiro-OMe TAD,both of which have stability issue.Compared with organic-inorganic hybrid perovskites,the inorganic perovskite CsPbI₃exhibits improved stability.Thanks to the biploar nature of perovskite,the perovskite solar cells can work without a hole transport layer.Removing the hole transport layer not only avoids the stability issue caused by this layer but also simplifies the device structure and reduces the fabrication cost.In this dissertation,the device performance of hole-transport-layer-free perovskite solar cells based on CsPbI₃was systematically studied by using the solar cell simulation software SCAPS-1D.（1）The initial model of hole-transport-layer-free solar cell FTO/Ti O₂/CsPbI₃/C was simulated and verified through comparison between simulated results and reported experimental results.By comparing FTO/Ti O₂/CsPbI₃/C cell with FTO/Ti O₂/CsPbI₃/Spiro-OMe TAD/C cell,it was found that the lowering of barrier height is an important factors limiting the performance of the hole-transport-layer-free solar cell.The influence of hole doping concentration in CsPbI₃and the work function of back electrode on device performance were studied.It is found that properly increasing the hole doping concentration in CsPbI₃and the work function of back electrode can increase the built-in barrier height,open circuit voltage and cell efficiency.For the FTO/Ti O₂/CsPbI₃/Au and FTO/Ti O₂/CsPbI₃/C cell,the optimal hole doping level is 10¹⁶cm^-3and the best efficiency is 15.60%and13.87%,respectively.（2）To improve the utilization of solar spectrum,the narrow band perovskite Cs Sn I₃is added to FTO/Ti O₂/CsPbI₃/C cell to form FTO/Ti O₂/CsPbI₃/Cs Sn I₃/C heterojunction solar cell.In the CsPbI₃/Cs Sn I₃heterojunction cell,due to the extended absorption spectrum and reduced dark saturation current density,the short circuit current,open circuit voltage and cell efficiency were greatly increased.The absorber thickness of FTO/Ti O₂/CsPbI₃/Cs Sn I₃/Au（C）solar cells was systematically optimized under different CsPbI₃doping concentration and Cs Sn I₃defect concentration.After optimization,a photoelectric conversion efficiency of 19.99%and 19.59%was obtained for the FTO/Ti O₂/CsPbI₃/Cs Sn I₃/Au cell and FTO/Ti O₂/CsPbI₃/Cs Sn I₃/C cell,respectively.（3）A stable inorganic perovskite CsPbI₂Br was added into FTO/Ti O₂/CsPbI₃/Au（C）cell and hole-transport-layer-free solar cells with double-layer,triple-layer and gradient-layer absorber were constructed and simulated.These three kinds of cells were compared with each other and with the FTO/Ti O₂/CsPbI₃/C cell.Under the same conditions,the cell with gradient absorption layer CsPbI₃-CsPbI₂Br showed best open circuit voltage,fill factor and cell efficiency.By optimizing the thickness,the defect concentration and the doping concentration of the gradient absorption layer,a photoelectric conversion efficiency of 19.16%and 18.69%was obtained for the FTO/Ti O₂/CsPbI₃-CsPbI₂Br/Au cell and FTO/Ti O₂/CsPbI₃-CsPbI₂Br/C cell,respectively.These results provide useful reference for manufacturing efficient and stable perovskite hole transport layer free solar cells.