Design And Synthesis Of D（A-Ar）₂ Type Organic Small Molecular Photovoltaic Materials And Investigation Of Photoelectric Properties

Under the double restriction of the fossil energy shortage and environmental protection increasingly severe,energy and environment problems have become the key and important problems to be solved in the world.In recent years,organic photovoltaic materials(OPV)have drawn a great deal of attention due to their advantages such as cleanliness,light weight,low cost,wide source of raw materials and the ability to be made into flexible large-area devices.In particular,small molecular organic solar cells(SM-OSCs)have many advantages:relatively simple synthesis and purification process,good monodispersity,clear structure,little change between batches,no end group pollution,Furthermore,small molecular organic solar cells(SM-OSCs)have more variable molecular structure,structure is more controllable,and has high carrier mobility.In this thesis,the important progress of small molecular organic solar cells(SM-OSCs)is systematically reviewed and introduced.For the shortage of high-efficiency organic small molecular donor materials and lack of design theory guidance for designing high-performance molecules.A series of linear SM-OSCs donor materials with D(A-Ar)2 type framework based diketopyrrolopyrrole(DPP),isoindigo(ⅡD)and benzothiadiazole(BT)as birdged acceptor units were designed and synthesized for application in OSCs.Their influences of different structure modification on photovoltaic performance were characterized and systematically investigated.The relationships between the molecular structures and photovoltaic performance were further investigated,and some excellent-performance of small molecular photovoltaic materials were obtained.The main achievements and conclusions of this thesis are as follows:1)Three novel SMs were designed and synthesized,in which bianthracene was used as the donor core and thiophene-diketopyrrolopyrrole(DPP)used as the acceptor units.The influences of different molecular configurations on absorption,HOMO/LUMO energy level,planarity,as well as photovoltaic properties of these SMs were systematically investigated.It is found that the AAN(T-DPP)2 has longer conjugate lengths,red-shift UV absorption spectra,and a wider absorption range.As a result,the AAN(T-DPP)2/PC71BM based OSCs exhibits a best power conversion efficiency of 2.33%with open circuit voltage(Voc)of 0.86 V,a short circuit current(Jsc)of 6.82 mA/cm2 and fill factor(FF)of 39.80%.2)Three π-conjugated SMs with D(A-Ar)2 molecular frameworks are designed and synthesized as the donor materials in organic solar cells(OSCs).Containing tetrafluorobenzene(TFB)as central donor(D)core,thiophene as π-bridge,2-octylthiophene(T)as terminal(Ar)unit,as well as the different arm of acceptor(A)units,pyridine-diketopyrrolopyrrole(PyDPP),thiophene-diketopyrrolopyrrole(TDPP)and isoindigo(IID),namely DTTFB(PyDPP-T)2,DTTFB(TDPP-T)2 and DTTFB(IID-T)2,respectively.The impacts on the photovoltaic performance of introducing fluorine atoms and combining different acceptor arms into the backbone were investigated.As a result,DTTFB(TDPP-T)2/PC71BM based OSCs presents a PCE value of 5.15%,a Jsc value of 12.44 mA/cm2 and a FF value of 59.5%.which is about 2.8 and 1.6 times higher than that of DTTFB(PyDPP-T)2/PC71BM and DTTFB(IID-T)2/PC71BM based cells,respectively.Obviously,introducing different acceptor units as arms onto the D(A-Ar)type SMs could be a promising strategy for designing high-performance TFB-based linear molecular donor materials.3)Three linear SMs with a D(A-Ar)2 framework,based on fluorinated 2,2’-bithiophene(FBT)as donor(D)central core,2-octylthiophene(Ar)units as end-capping units,pyridine-flanked diketopyrrolopyrrole(PyDPP),isoindigo(IID)and thiophene-flanked diketopyrrolopyrrole(TDPP)as accepting(A)units,denoted as FBT(PyDPP-T)2,FBT(IID-T)2 and FBT(TDPP-T)2,respectively.have been designed and synthesized for application in organic solar cells(OSCs).The impacts of fluorinated central cores and different acceptor units on photovoltaic properties are systematically investigated.An impressively improved PCE of 9.00%was obtained in the FBT(TDPP-T)2/PC71BM based cells due to an enhanced Jsc of 16.14 mA cm-2 and FF of 73.52%,which is among the highest reported for D(A-Ar)2-type SM-based solar cells with a PCE up to 9.0%so far.4)Three linear small molecules(SMs)with D(A-Ar)2 framework,based on pyran-bridged indacenodithiophene(IDTP)as central donor(D)core,coupled with fluorine-substituted benzothiadiazole(DFBT)as bridged accepting(A)unit,and particularly by using carbazole(Cz),2-octylthiophene(T)and 2-octylthiothiophene(TS)units as terminal aromatic(Ar)groups,were designed and synthesized for application in small molecular organic solar cells.The influences of heteroatom-substituted on photovoltaic properties are systematically investigated.Encouragingly,the optimized device based on IDTP(BT-TS)2 exhibited an outstanding efficiencies up to 7.33%with Voc,Jsc and FF of 0.84 V,13.26 mA/cm2 and 66%,which is is 1.45 times and 1.71 times higher than that of the other SMS based devices,respectively.5)Three D(A-Ar)2 type linear small molecules,using fluorinated 2,2’-bithiophene(FBT)as central building core,thiophene-flanked diketopyrrolopyrrole(TDPP)as acceptor bridged units,2-octylthio-thiophene(TS)unit,2-octyl-thiazole(TZ)unit and 2-octylthio-thiazole(TZS)as end-capping units,namely FBT(TDPP-TS)2,FBT(TDPP-TZ)2 and FBT(TDPP-TZS)2,respectively.have been synthesized for application in OSCs.The influences of different terminal groups on photovoltaic properties of these SMs were systematically investigated.After optimization,FBT(TDPP-TZS)2/PC71BM based device significantly enhances an efficiency from 6.96 to 8.91%,which is attributed to the enhanced simultaneously Voc,Jsc and FF.