Design, Synthesis And Photoelectric Properties Of Novel Two-Dimensional Conjugated Polymer Material

Conjugated polymers which is characterized by good structure tenability, wide sources of raw materials and a variety of ways to regulate the energy level, improve the light absorption capacity and conductivity, have already attracted significant research attention. Combining the electronic-rich unit and an electron-withdrawing unit, the donor-acceptor type conjugated polymer can form a push-pull electronic structure which can enlarge the conjugation length, decrease the alternating bond lengths and optical bandgap. In addition, intramolecular charge transfer occurred between the donor unit and the acceptor unit can promote the red shift of the absorption. Two-dimensional conjugated polymers are expected to broaden the absorption spectrum, promote isotropic charge transport of polymer backbone to get better balance of the carrier mobility. And the properties can be tuned by main chain structure adjust, side chain engineering, conjugation length enlargement. In this thesis, we have synthesized a series of conjugated polymers and researched the photovoltaic properties of these materials as the donor materials for bulk heteroj unction polymer solar cells (PSCs). The electrochromic properties of two-dimensional conjugated polymers materials have been explored. Theoretical calculations have been combined to provide a reasonable explanation and property prediction. This thesis mainly includes the following research works:1. In this chapter, we prepared a series of polymers PIDFDQ, PIDFDPP, PIDFPyT based on indenofluorene (IDF) derivative for a donor unit, diphenyl quinoxaline (DQ), thiophene-flanked diketopyrrolopyrrole (DPP), thiadiazolo[3,4-c]pyridine (Pyt) as the acceptor unit, respectively. Due to the strong steric hindrance between IDF and DQ unit, the polymer PIDFDQ gave rise to a limited absorption spectral and hence the PSC device based on PIDFDQ yield a device efficiency of only 0.50% and the short circuit current of 1.80 mA/cm2. The introduction of stronger acceptor unit PyT lead the polymer PIDFPyT possess a reduced optical band gap and the short-circuit current was greatly improved to 5.24 mA/cm2 and the PCE reached 1.39%. Because of the excellent planarity and lower steric hindrance of DPP units, the absorption spectra of polymer PIDFDPP was significantly broadened and the PCE based on PIDFDPP was improved to 1.69% with a short circuit current of 6.57 mA/cm2.2. In this chapter, we have synthesized three two-dimensional conjugated polymers PIDTTPABTl, PIDTTPABT2 and PIDTTPABT3 by employing the IDT and TPA units to construct the main chain and benzodithiazole(BT) linked by different electron withdrawing units as the side chain. The polymers possessed a limited absorption spectrum, which was induced by the poor planarity. By introducing the DPP unit in the main chain, the copolymer PIDTTPABTDPP presented a significantly improved optical absorption with abroadened and red shifted wavelength.3, In this chapter, the electrochromic properties of the two-dimensional conjugated polymer PIDTTPABT was investigated. The spectroelectrochemical test showed the optical contrast of PIDTTPABT of 20% with a response time of 3.72 s at 453 nm and the optical contrast of 15% with a response time of 2.07 s at 672 nm. Color can be reversibly changed between brown and green. To further explore the structure-electrochromic properties relationship of the two-dimensional polymer, we syntheisized a new polymer PBTTPABT with the main chain and side chain both combined with the TPA and BT units. The spectroelectrochemical properties was studied and the tests showed that the optical contrast and response time of PBTTPABT were 8.5% and 0.96 s at 508 nm and 25% and 4.26 s at 710 run, respectively. The color can be reversibly transited between red and light green close to transparent. These properties indicate that both PIDTTPABT and PBTTPABT have good application potential in electrochromic fields. In comparison, polymer PBTTPABT with the D-A structure in the main chain showed superior performance with respect to PIDTTPABT.4. In this chapter, a series of two-dimensional conjugated polymers P1-P9 planarity were studied by the density functional theory. The backbone structure of P1-P4 is constructed by IDT and TPA units and with the side chain characterized as the BT unit connected by the different electron withdrawing units. Different from P1-P4, the IDT unit was substituted with BDT unit for P5-P8. The results showed that the planarity of the polymer can be improved to some extent when IDT was replaced by BDT. And different electron withdrawing unit connected to the BT unit have almost no effect on the polymer main chain configuration. By introducing thienylenevinylene unit between TPA and IDT, polymer P9 showed a greatly improved planarity with the dihedral angle only 9.65°. The same method can be employed to adjust the planarity of the side chain, by optimizing the planar configuration. Different electron-withdrawing ability of the side chain has influence on the polymer HOMO and LUMO levels, thereby affecting the polymer bandgap and absorption spectroscopy. And stronger electron withdrawing side chain resulted in lower energy level. Theoretically, P5-P9 are expected to have a superious ability to capture photons, good exciton separation capacity at donor-acceptor interface. The results are helpful for the future of the polymer design.