Synthesis And Properties Of Organic Photovoltaic Materials Based On Thiophene Derivatives And Benzothiadiazole Groups

The research status of organic solar cells(OSCs) and their typical organic donor materials were reviewed in this dissertation. As is known to all, there are some factors to mainly influence performance of organic photovoltaic materials, such as the matched spectra between absorption of organic donor materials and sun light, molecular energy levels, carrier mobility and solubility. In order to further study the relationship between molecular structure and photovoltaic property, three series of photovoltaic materials were designed and synthesized, including the low band gap one-dimensional(1D) and two-dimensional(2D) polymers based on quinoxaline(Q), benzothiadiazole(BT) and thiophene units, as well as the star-shaped small molecules(SMs) based on triphenylamine(TPA) and BT units. Their molecular structure were characterized by 1H NMR, 13 C NMR, Time-of-?ight mass spectra(TOF-MS) and elemental analysis. Their thermal stability, electrochemical, photophysical and photovoltaic properties were investigated by thermal gravimetric analysis(TGA), differential scanning calorimetry(DSC), cyclic voltammetry(CV), UV-visible absorption spectroscopy(UV-vis) and solution-processed bulk heterojunction(BHJ) solar cells, respectively. The studied results are mainly presented as follows:1. A novel polymer of PBT-TTQ-F based on the Q and BT units was designed and synthesized. For comparison, its counterpart of PBT-TTQ-H without the fluorine atom was prepared at the same time. Significantly red-shifted UV-vis absorption profile and improved photovoltaic properties were observed in the PBT-TTQ-F polymer by attaching fluorine atoms to the polymer backbone. Under the optimized condition, bulk heterojunction polymer solar cells(PSCs) based on PBT-TTQ-F exhibited a higher power conversion efficiency(PCE) of 3.05% with a short-circuit current(Jsc) of 9.48 m A/cm2 and a fill factor(FF) of 48.6%. The PCE, Jsc and FF values are 1.2-1.7 times higher than those values of the PBT-TTQ-H based devices.2. A type of the 2D D-A polymers of Th2TT-BT-Th2 and Th2TT-BT-Th4 containing different thienyl numbers in main-chain was designed and synthesized with the BT acceptor(A) unit and the donor(D) unit of 3,6-di(4,5-dioctyl-2-thienyl) thienothiophene(TT-Th2), in which the Th2TT-BT-Th2 and Th2TT-BT-Th4 contain one and two thienyl spacers between the D and A units in the backbone, respectively. It was found that increasing thienyl spacer’s amounts can increase the conjugated content and broaden the absorption spectrum for polymers, as well as improve the PCE and Jsc values for their PSCs. The maximum PCE of 3.34% and Jsc of 12.6 mA/cm2 were achieved in the Th2TT-BT-Th4-based PSCs., which is 2.1 and 3.0 times higher than those corresponding values in the Th2TT-BT-Th2-based devices, respectively.3. A type of the star-shaped photovoltaic SMs were designed and synthesized based on a core of the TPA unit, three arms of the BT units, and three terminals of carbazol(Cz) units. Effect of the substituted positions of Cz and the sequence of thienyl spacer on the photovoltaic performances was investigated. It demonstrates that TPA(BT-3Cz)3 with 3-carbazolyl(3Cz) unit exhibited better photovoltaic performance than the TPA(BT-2Cz)3 with 2-carbazolyl(2Cz) unit in the solution-processing OSCs. The maximum PCE about 4% was displayed in the TPA(BT-3Cz)3-based devices. After embedding a thienyl spacer between the BT and 3Cz units, the resulting molecule of TPA(BT-T-3Cz)3 exhibited significantly more improved photovoltaic performance than the TPA(T-BT-3Cz)3 with a thienyl spacer between the TPA and BT units. The maximum PCE of 5.07% and Jsc of 10.6 mA/cm2 were achieved in the TPA(BT-T-3Cz)3-based OSCs, in which the PCE value is one of the highest PCE values among the TPA-based star shaped SMs in OSCs.