| Recently, donor-acceptor (D-A) conjugated copolymers have attracted considerable attention for their potential and promising applications in organic thin film transistors (OTFTs), organic photovoltaic devices (OPVs) as charge transport materials. And the great achievements have been acquired due to the strong intermolecular interaction and the narrow band gap of the D-A copolymers. Compared with the inorganic materials and small organic molecules, the D-A conjugated copolymers show some advantages, such as flexibility, better solution processability, film-forming abilities and low-cost production and so on. At present, to design D-A copolymers is one of the most effective strategies to acquire OTFT or OPV materials with excellent device performances. Therefore, in this thesis we present some new design ideas to synthesize new kinds of D-A conjugated copolymers via modifying the structure of donor and acceptor, and study their opto-electronic properties, and also primarily explore the structure-property relationship and discuss on the fabrication and characterization of related OFET devices.The main contents of this thesis are described as follows:In Chapter1, the basic concepts, structural features of organic semiconductor materials and application prospects of polymeric semiconductor materials were briefly introduced. Then the research progress and structure-property relationship of polymeric semiconductor materials applied in OFET and polymer solar cell (PSC) were reviewed and summarized. At last the design strategies of this thesis were outlined.In Chapter2, a series of new D-A conjugated copolymers (Ⅱ-1～Ⅱ-4) were designed and synthesized, in which (3-unsubstituted oligothiophene unit acted as an electron donor and diketopyrrolopyrrole (DPP) as an electron acceptor. By controlling the reaction condition and extracting with different solvents, two polymers with different molecular weight (Ⅱ-1A, Mn=2.79×104and Ⅱ-1B, Mn=4.40×104) were obtained. The basic properties were characterized by TGA (thermogravimetric analysis), UV-vis absorption spectra and CV (cyclic voltammetry). The OFET performances of Ⅱ-1A and Ⅱ-1B were measured and the results demonstrated that the high molecular weight of the polymer plays a key role in enhancing themobility. The hole mobility of Ⅱ-1B reaches1.08cm2V-1s-1without thermal annealing and a higher hole mobility of3.46cm2V-1s-1is obtained annealed at200℃directly in an air atmosphere. This implies that introducing a longer (3-unsubstituted oligothiophene unit into the main-chain of DPP-oligothiophene copolymer can produce the pronounced p-type behavior, reduce the steric hindrance of the bulk side-chain groups and enhance the molecular ordering capability at low temperatures, which greatly improves the OTFT performances.In Chapter3, five kind of D-A conjugated copolymers (Ⅲ-1～Ⅲ-5) with fused electron-rich ring (dithieno[3,2--b:2’,3’-d]thiophene or benzo[1,2-b:4,5-b’]dithiophene) as an electron donor and DPP as an electron acceptor were designed and synthesized. The charge transport ability of Ⅲ-1was measured by OFETs and the polymer shows high mobility over1.0cm2V-1s-1.This implies that introducing a fused ring of dithieno[3,2-6:2’,3’-d]thiophene into the main-chain of DPP-based copolymer can efficiently improve the OTFT performances of the device due to strong donor-acceptor interaction and ordered π-π close packing of the polymeric chains. Furthermore, some polymers show low HOMO energy level and narrow band gap, that is favorable for improving the Voe and Jsc of PSC.In Chapter4, three kind of new D-A conjugated copolymers (Ⅳ-1～Ⅳ-3) with oligothiophene unit as an electron donor and isoindigo as an electron acceptor were designed and synthesized. The polymers with high molecular weight were obtained by Soxhlet extraction with chlorobenzene or o-dichlorobenzene.The effect of oligothiophene with different amount of thiophene groups on the optical absorption and energy level were discussed by comparison of the photophysical properties of these polymers. The charge transport abilities of IV-1A and IV-1B were measured by OFETs, and results also demonstrated that the high molecular weight of the polymer plays a key role in enhancing themobility. The hole mobility of IV-1B with relatively high molecular weight reaches0.025cm2V-1s-1(Ion/Ioff=107).In Chapter5, four conjugated copolymers (Ⅴ-1～Ⅴ-4) with fused ring of dithieno[3,2-b:2’,3’-d]thiophene, thieno[3,2-b]thiophene or benzo[1,2-b:4,5-b’]dithiophene as an electron donor and isoindigo as an electron acceptor were designed and synthesized. These polymers show low HOMO energy level, narrow band gap and good π-π stacking. It should be worthy that research demonstrated that introducing thiophene group into the sidechain of the donor can efficiently improve the intensity of absorption and lower the HOMO and LUMO energy level, which may facilitate the field-effect hole mobility and increase the Voc of PSC.In comparison with p-type and n-type polymeric charge transport materials, theambipolar materials with high and balanced electron and hole mobilities were relatively few. So exploring new ambipolar is of great interest and challenge. In Chapter6, three conjugated D-A copolymers including DPP or isoindigo unit (VI-1～VI-3) were designed and synthesized. Judging from the HOMO and LUMO energy levels of these polymers, they should be suitable as ambipolar semiconductor for the charge injection, accumulation and transport of both hole and electron. Furthermore, the effect of the introduction of thiophene and the choice of the acceptor on the property of ambipolar semiconductor was also discussed.In Chapter7, wedesigned and synthesized a one-dimensionalD-D polymerand a two-dimensional D-D polymer including benzo[1,2-b:4,5-b’]dithiophene and thiophene unit (VII-1～VII-2). Then a series of conjugated D-A copolymers containing benzo[1,2-b:4,5-b’]dithiophene unit (Ⅶ-3～Ⅶ-11) were designed and synthesized. The effect on the optical absorption,π-π stacks of main-chain and energy level by introducing different acceptorswere studied by comparison of the photophysical properties of these polymers. And the structure-property relationships were also discussed.In Chapter8, four D-A copolymers (Ⅷ-1～Ⅷ-4) using quinoxaline as electron acceptor and oligothiophene or benzo[1,2-b:4,5-b’]dithiophene as electron donor have been synthesized by Stille cupling condensation. The effect of introduction of different oligothiophene on the optical absorption and energy level were discussed by comparison of the photophysical properties of these polymers. In addition, the structure-property relationships of the corresponding polymers were primarilydiscussed.In Chapter9, five D-A copolymers (Ⅸ-1～Ⅸ-5) using thieno[3,4-b]diathiazole (TDT) as electron acceptor and oligothiophene, carbazole, benzo[1,2-b:4,5-b’]dithiophene or dithieno[3,2-b:2’,3’-d]silole as electron donor were designed and synthesized. The photophysical propertiesof IX-1were measured. All of the polymersshow narrow band gap and good π-π stacking.The charge transport ability of IX-1was measured by OFETs and the corresponding mobility reaches1.7×10-4cm2V-1s-1, which accords with the value reported by previous literatures. It is also found that these polymers show low HOMO energy level and narrow band gap, which may improve the Voc and JSC of PSC. |
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