Synthesis And Properties Of D-A-type Oligomers And Conjugated Polymers Based On Benzodithiophene-4,8-dione Used As Elactron-donating Materials

With development of economy and society,energy issue and environmental pollution are becoming more and more serious.It is urgent to develop clean,safe,pollution-free and sustainable energy.Compared with other new energy sources,such as water,wind,geothermal and tidal energy,solar energy has some advantages of territorial unlimitation,noise and non-pollution,and so on.Therefore,how to utilize solar energy efficiently has become an important research issue for scientists.In this area,organic solar cell(OSCs)has been widely concerned and studied resulting from their merits on low cost,light weight,flexibility and so on.In this dissertation,the development and working principle of organic solar cells are systematically introduced,and their research status of organic photovoltaic materials based on benzodithiophene(BDT),benzothiadiazole(BT),benzodithiophene-4,8-dione(BDD)units are presented systematically.In view of the scientific problems,such as few electron-donoring materials with high power conversion efficiency(PCE)and unclear relationship between molecular structures and photovoltaic properties,a series of D-A oligomers and polymers based on benzodithiophene-4,8-dione(BDD)unit were designed and synthesized and characterized detailedly.Their photophysical,electrochemical and charge transporting properties,as well as morphologies and photovoltaic performances in solution-processing bulk-heteroj untion organic photovoltaic cells were systematically studied.The orbital energy levels and optimal molecular structures of these oligomers and polymers are simulated by theoretical calculation.The relationship among molecular structure and energy level,photophysics,electrochemistry,charge transport and photovoltaic properties of D-A oligomers and polymers are preliminarily revealed.With the oligomers and polymer donors excellent photovoltaic performance were obtained.The contents of this thesis are listed as follows:(1)Oligomer donor materials based on thiophene donor unit and BDD acceptor unit with D-(A-D)n(n = 2,3,4)framework were designed and synthesized.The effect of the number of D-A repeated units on absorption,electrochemical energy levels and photovoltaic properties of oligomers was systematically studied.It is found that with an increase of the number of D-A units,their molar extinction coefficients of the oligomers in solution are increased,as well as the absorption spectra are red-shifted and the HOMO levels are ascended.Furthermore,5T4BDD exhibits better photovoltaic performance due to the greater conjugation degree and broader absorption.The PCE of 0.51%is obtained in the 5T4BDD based using PC71BM as receptor was.(2)A small molecule and an oligomer donor with the structure of D-(A-D)n(n =1,2)based on two-dimensional benzodithiophene(BDT)as donor unit and benzodithiophene-4,8-dione(BDD)as receptor unit were designed and synthesized.In comparison with the small molecule,effect of the number of D-A repeated units on photophysics,electrochemistry,molecular planarity,intermolecular stacking behavior and photovoltaic properties of the oligomer were systematically studied.The oligomer exhibited stronger intermolecular stacking behavior,and thus showed better photovoltaic properties.The PCE of 7.89%is obtained in the oligomer-based BHJ-OSCs using ITIC non-fullerene as acceptor with a Voc of 0.90 V,a Jsc of 13.23 mA/cm2 and a FF of 65.6%,respectively.(3)A series of(A1-A2)n-typed polymeric donors were designed and synthesized,using BDD,BT or fluorinated benzothiadiazolium(2FBT)as A1 and A2 units.The effect of fluorine substitution on thermal stability,photophysical,electrochemical and photovoltaic properties of polymers was systematically investigated.The results show that introduction of fluorine atom can reduce the HOMO energy level of polymer distinctly.The(A1-A2)n-typed polymeric donors based on BDD and BT have good solubility and charge transport properties.The polymer PBDDBT shows better photovoltaic performance because of its better film formation and proper aggregation ability.The PCE of 1.59%is obtained in the polymers-based BHJ-OSCs using PC71BM as acceptor.