Synthesis And Properties Of The Thienoisoindigo-based Organic Semiconductors

With the rapid development of organic electronics,the design and synthesis of?-conjugated organic semiconductors have become the hotspot in the fields of materials chemistry.To date,the organic compounds with an electron push and pull moieties(donor-acceptor,D-A)are the most popular materials among all kinds of organic semiconductors,which can finely tune the molecular energy levels,solubility and planarity,etc.In the last few years,organic field-effect transistors and solar cells based on D-A structure organic semiconductors with outstanding performance have been achieved.Thienoisindigo(TII)is a new electron-withdrawing moiety with a polar bicyclic lactam structure.TII structure is thienopyrrolone units by replacing the benzene rings of isoindigo with thiophenes,which might further enhance planarity along the backbone and promote intermolecular ?-? stacking by the further effective conjugation.In this thesis,with the goal to develop new type and high performance organic semiconductors,we designed and synthesized a series of TII-based small molecular and polymer materials,and applied these materials in OFET and OPV devices.Moreover,we also systematically investigated the relationship between the microstructures of these materials and devices performance.The detailed works are listed as follows:1)TII compound was synthesized from 3-bromothiophene,and optical and electrochemical properties were investigated by UV-vis absorption spectroscopy and cyclic voltammetry(CV).Then,TII-based and DPP-based small molecular materials(M1-M4)were prepared with benzene,phenylacetylene or trifluorotoluene as donor units.Density functional theory(DFT)calculations reveal that the model molecular geometry of M2 is almost flat.All the materials exhibit long wavelength absorption and low band-gap properties by using UV,vis absorption and CV measurements.2)Three D-A-D type TII-based small molecular materials were synthesized with triphenylamine(TII(TPA)2),benzofuran(TII(BFu)2)or naphthalene(TII(Na)2)as donor units,these materials are thermally stable.The HOMO energy levels of TII(TPA)2,TII(BFu)2 and TII(Na)2 are-4.82 eV,-5.09 eV and-5.08 eV,respectively.The optical band-gaps of three small molecular materials are 1.46 eV,1.49 eV and 1.53 eV,respectively.The performance of OFET devices show the almost similar hole mobilities as high as 1.28×10-3 cm2 V-1 s-1 for TII(BFu)2 and 1.29×10-3 CIcm2 V-1 s-1 for TII(Na)2.However,the hole mobility of TII(TPA)2 is 2.64×10-4 cm2 V-1 s-1,which is much lower than other TII-based materials.3)Three D-A type TII-based conjugated polymers were synthesized via Suzuki or Sonogashira coupling reaction with carbazole(P(TII-Cz)),1,4-diethynylbenzene(P(TII-BEN))and 9,10-diethynylanthracene(P(TII-ANT))as donor moieties,respectively.The thermal,optical and electrochemical properties of the polymers were also investigated.All three polymers exhibit broad and near-infrared absorption,the optical band gaps are 1.52 eV,1.49 eV and 1.24 eV,respectively.Moreover,P(TII-Cz),P(TII-BEN)and P(TII-ANT)were applied in supercapacitor electrodes to evaluate their electrochemical properties by using CV and GCD tests.These materials exhibit specific capacity of 21.7 F g-1 for P(TII-Cz),40.3 F g-1 for P(TII-BEN)and 23.1 F g-1 for P(TII-ANT)at a current density of 0.5 A g-1.The highest hole mobilities were 3.44×10-3 cm2 V-1 s-1 for P(TII-Cz),4.38×10-3 cm2 V-1 s-1 for P(TII-BEN)and 9.40×10-3 cm2 V-1 s-1 for P(TII-ANT)in bottom-gated/top-contact field-effect transistors.For understanding structure-property relationships,the microstructures of three polymers were investigated by X-ray diffraction and atomic force microscopy.4)Due to wide absorption in the UV-vis-NIR region,appropriate HOMO and LUMO energy levels,and hole mobility characteristics,TII-based materials were applied in conventional bulk-heterojunction solar cells(ITO/PEDOT:PSS/active layer/Al).These photovoltaic devices show the best PCE of 1.24%for TII(BFu)2,1.04%for TII(Na)2,1.59%for P(TII-BEN)and 1.90%for P(TII-ANT).The microstructures of TII-based materials mixed with PC71BM were tested by X-ray diffraction and atomic force microscopy.