Structure Optimization Design And Simulation Of High Efficiency Perovskite Solar Cells

With low cost,simple process and gradually increasing photoelectric conversion efficiency,Organic-inorganic hybrid perovskite solar cell has become frontier of photoelectric field.At present,perovskite solar cells still have not been widely used,due to low energy utilization rate,PN junction energy band mismatch,low mobility of PCBM,high temperature sintering of TiO₂and high price of Spiro-OMeTAD.To explore these problems,based on continuity equation,poisson equation and drift-diffusion equation,including effect of interface defect,four kinds of bulk defect（gaussian distribution of acceptor-like states,gaussian distribution of donor-like states,conduction band tail distribution of acceptor-like states,valence band tail distribution of donor-like states）,four types of recombination（surface recombination,auger recombination,radiative recombination,SRH recombination）are considered in this study.Density functional theory is used to quantify the spin orbit coupling and calculate the material energy level.Thermionic emission model was used to calculate the process of the carrier through the energy level peak.Therefore,physical model of solar cell was established by TCAD Atlas software and was simulated.Focused on perovskite material,the structure and layers of solar cell is studied,all perovskite tandem solar cell was designed to broaden spectral utilization rate.ETL and HTL in traditional P-I-N structure were removed in turn to reduce costs and process complexity,ETL-free cell was designed by removing PCBM,and the most simplified structure cell was developed by removing TiO₂and Spiro-OMeTAD layers which was realized by direct combination of transparent electrode TCO and p-CH₃NH₃PBI₃.Energy band engineering is used to reduce band mismatch of PN junction,and double gradient band gap is used to enhance the carrier collection rate and improve the efficiency of solar cells.Firstly,based on traditional P-I-N structure,all perovskite tandem cell composed by two P-I-N junctions is designed to broaden the spectral utilization,300-700nm visible light is absorbed by the top P-I-N junction and 700-1100nm near-infrared light is absorbed by the bottom P-I-N junction.Furthermore,compared with PEDOT:PSS,Spiro-OMeTAD,CuI,CuO and CuSCN,NiO was selected as P-type layer at both P-I-N junctions.To increase performance of the cell,the best N-type layer at two P-I-N junctions was selscted among C₆₀,SnO₂,TiO₂,ZnO,PCBM and CdS,and SnO₂is located at top P-I-N junction and ZnO is located at bottom P-I-N junction.In addition,efficiency of this cell achieced to 32%after optimization thickness of perovskite.Secondly,to reduce costs and process complexity,ETL-free solar cell is designed based on the good bipolar charge transfer character of perovskite.Effects of device structure,hole transporting material,electrode material and perovskite band gap distribution on the performance of the cell were investigated.It was found that increasing gradient band gap of perovskite can reduce the energy level mismatch,reduce the heterojunction contact resistance,promote the transmission of photo-generated carriers,reduce the recombination loss,and enhance the efficiency to26.64%.Based on the concept of a simplified structure,CTL-free perovskite cell was designed with energy conversion efficiency of 20.2%Finally,based on energy band engineering method,a gradient band gap solar cell was designed by ion doping modulated perovskite.Auxiliary electric field at the front gradient band gap can improve the open circuit voltage,and double gradient band gap can broaden the spectral absorption range.Reducing band shift at Perovskite/ZnO interface lead to the efficiency increased 2.84%.The proposed method can also be used to reduce the energy band shift at CuSCN/perovskite interface,which showed that energy band engineering is effective in development of solar cell.