Theoretical Study On The Mechanism Of Intramolecular Charge Transfer Regulated By External Electric Field In Pyrazine Derivatives

Organic materials realize the photoelectric conversion process from light energy to electrical energy through the Donor-acceptor heterojunction structure.Compared with inorganic solar cells,organic solar cells have the advantages of strong flexibility,convenient production and low cost,but low photoelectric conversion efficiency is a factor that cannot be ignored to restrict their promotion.Solving this problem requires a better understanding of the physical mechanisms of organic photoelectric conversion.Charge separation and charge recombination,as important steps in photoelectric conversion,will affect the efficiency of photoelectric conversion.Marcus theory has been widely used to study charge transfer processes in donor-acceptor systems.There are many factors that affect the rate of charge transfer,including vibration frequency and external electric field.Therefore,density functional theory is used to simulate excited state dipole moment,Gibbs free energy,recombination energy and electron coupling,and the charge transfer of pyrazine molecules is studied by Marcus theory calculation.In this paper,the charge transfer process of donor（D）3-（4-（di（[1,1-biphenyl]-4-yl）amino）phenyl）（dp TPA）and acceptor（A）acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile（APDC）（dp TPAAP）molecule under different external electric fields(F_ext)was first studied.The dipole moment of excited state,Gibbs free energy,recombination energy and electron coupling are theoretically simulated,and the charge transfer rate of dp TPAAP system under different F_ext is calculated and analyzed according to Marcus theory,and the results show that positive F_ext has a significant influence on the charge separation rate in the process of charge separation and charge recombination.Next,the charge transfer process under different external electric fields of the near-infrared material molecule N,N-diphenyl-9,9′-spirobi[fluorene]-2-amine（SDPA）:acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile（APDC）（SDPA-APDC）is a photoactive layer.The theoretical simulation of the excited state dipole moment,Gibbs free energy,recombination energy and electron coupling under zero electric field and different F_ext,and the Gibbs free energy（ΔG）were calculated by two different theoretical methods,and it was found that the Coulomb gravitational modified free energy calculation method was more reliable.According to Marcus theory,the charge transfer rate of SDPA-APDC system under different F_ext was calculated,and the results showed that the charge separation rate and charge recombination rate were significantly affected by F_ext.The results provide a theoretical basis for the influence of external electric field on the giving-acceptor heterojunction（interface）in the photoactive layer of organic solar cells.It not only helps to understand the influence of external electric fields on organic semiconductors and their interface characteristics,but also provides a reference for the design and development of new devices.