| Summary: | 碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 102 === In this thesis, a series of novel conjugated polymers and small molecules with dithienobenzothiadiazole (DTBTD), as structural core unit were designed and synthesized by Stille coupling and Suzuki coupling reactions. The correlations between the molecular structure packing, optical and electrochemical properties were investigated.
This thesis has been divided into two parts. In the first part, conjugated polymers containing dithienobenzothiadiazole (DTBTD) as an acceptor moieties and bithiophene (BT) and dihexyl-bithiophene (BT-hex) as donor moieties were designed and synthesized using stille cross-coupling reaction. The solubility, optical absorption spectra, X-ray diffraction spectra (XRD) and electrochemical properties of the resulting polymer P(DTBTD-3EHT-BT-hex) were characterized. The solubility of the P(DTBTD-3EHT-BT-hex) polymer is significantly improved as compared to the nonalkylated P(DTBTD-3EHT-BT) polymer. In solution, P(DTBTD-3EHT-BT-hex) exhibited broad absorption covering the range from 300 to 600 nm and with the optical band gap of 1.98 eV. The energy levels of P(DTBTD-3EHT-BT-hex) polymer possesses low-lying HOMO energy level which is about -5.46 eV. Results of XRD data revealed amorphous nature of the P(DTBTD-3EHT-BT-hex) polymer. We proposed that the side chain structural modification approach can advance better designing for conjugated polymers with high power conversion efficiency.
Based on the first part of our results, we further designed and synthesized a new series of conjugated small molecules such as DTBTD-terT-hex, DTBTD-hex-BF and DTBTD-2,3-DDec-terT with dithienobenzothiadiazole as a acceptor unit, and terthiophene and benzofuran as the donor side group. The impact of these different donor side groups on their solubility, optical, XRD and electrochemical properties were investigated. The physical properties of the synthesized small molecules showed good solubility, broad absorption bands within the range from 300 to 650 nm, and optical band gaps of 1.89 eV, 2.10 eV and 1.98 eV for DTBTD-terT-hex, DTBTD-hex-BF and DTBTD-2,3-DDec-terT, respectively. Furthermore, DTBTD-terT-hex displayed red shift absorption band compared to other small molecules. The XRD results clearly indicate that the structure of DTBTD-terT-hex and DTBTD-hex-BF have regular packing and good crystallinity when compared to the DTBTD-2,3-DDec-terT. These findings offer valuable guideline for further designing dithienobenzothiadiazole based small molecules to develop high-performance BHJ organic photovoltaic cells.
In summary, we have successfully designed, synthesized and characterized a family of polymers and small molecules containing dithienobenzothiadiazole as a acceptor unit. The achievement of structure-property correlations will be benefit of developing high performance conjugated semiconductor materials.
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