Molecular Design And Theoretical Study On Photovoltaic Properties Of Organic Solar Cell Donor-acceptor Materials

Organic solar cells are widely concerned by researchers all over the world because of their advantages of low cost,flexibility,light weight and environmental friendliness.Organic solar cells can be divided into monolayer organic solar cells,double heterojunction organic solar cells,and bulk heterojunction organic solar cells.The properties of organic solar cell devices are closely related to their acceptor materials.In this paper,we design a series of acceptors for organic solar cells and study their feasibility as organic solar cell device materials using density functional theory and time-dependent density functional theory.This paper is mainly carried out from the following three aspects:(1)Two different A-D-A type organic solar cell acceptors A1-A2 were designed using perylene as donor unit,2-(3-cyanobutyl)indene as acceptor unit and thiophene as π bridge.Based on Density Functional Theory(DFT),the frontier molecular orbitals,the positions of HOMO and LUMO energy levels and the distribution of electrostatic potential were analyzed.Time-dependent Density Functional Theory(TD-DFT)was used to analyze the electron excited state properties such as the distribution of hole electrons and ultraviolet absorption peaks.The effects of alkyl chain position and πbridge on the optical properties and charge transfer rate of organic solar cell acceptors are studied,which provides a theoretical basis for the synthesis of efficient organic solar cell acceptors.(2)We designed an A-D-A type organic solar cell acceptors with benzothiadiazole as the core,as the donor unit,and 2-(3-cyanodimethyl)indione as the terminal group as the acceptor unit.The atoms on benzothiadiazole molecular structure were replaced by O,S,Se and methyl,respectively.A total of four acceptors Q-CH3,Q-O,Q-S and Q-Se were obtained.Meanwhile,F atom with low electronegativity was introduced to adjust the electron-absorbing capacity of the acceptor unit,thus increasing the charge transfer capacity of the molecule.Alkoxy groups are introduced to increase the solubility of organic molecules.DFT and TD-DFT were used to study their hole and electron distribution,absorption uv spectral range,HOMO and LUMO energy level position,electrostatic potential distribution and other parameters.The influence degree of various substituent groups on the characteristics of acceptors in organic synthetic solar cells was studied in depth.The results show that the absorption peak red shift of SE substituent acceptor is the most obvious,and the band gap is smaller.The acceptor of methyl group has the largest vibrator strength and the highest charge transfer rate.(3)A series of non-fullerene acceptors with a thick ring structure as donor unit and the 2-(3-cyanokylidene)endophenone terminal group as acceptor unit was designed.The alkoxy group was introduced to increase the solubility of organic molecules.The effects of π-bridge addition and π-conjugated thick-ring structure on the band gap and light absorption properties of these molecules were investigated by analyzing their hole and electron distribution,absorption range of UV spectrum,HOMO and LUMO energy level positions,electrostatic potential distribution and other parameters.The results show that C2 with π bridge structure is the best acceptor.