Synthesis and Properties of Conjugated Polyelectrolyte and Wide-Bandgap Conjugated Polymers

• Main Authors: ZHOU, YI-LING, 周羿伶
• Other Authors: RWEI, SYANG-PENG
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/2p549s

碩士 === 國立臺北科技大學 === 分子科學與工程系有機高分子碩士班 === 107 === The molecular design of conjugated polymers to be used in organic photovoltaics usually incorporates electron-withdrawing groups into the polymer backbone to achieve a deep LUMO level, which is beneficial to realizing high-open-circuit-voltage solar cells. In this work, a benzothiadiazole unit or a diester thiophene unit are introduced into the polymer mainchain to lower their HOMOs, and the optical, electrochemical and crystalline properties of the resulting products are extensively investigated. This thesis consists of two parts. Firstly, a conjugated polyelectrolyte (BTFLSO3K) containing benzothiadiazole units is synthesized to replace PEDOT:PSS as a hole transport material of p-i-n structured perovskite solar cells. The wavelength of maximum absorption of the BTFLSO3K solution locates at 522 nm which red-shifts to 544 nm in the solid film, indicating the polymer chains can pack into ordered structures. As expected, the HOMO level of BTFLSO3K (-5.40 eV) is deeper than that of PEDOT:PSS (-5.20 eV), evidenced by the photoemission spectra. Consequently, the substitution of PEDOT:PSS with BTFLSO3K as hole-transporting layer significantly improves the power conversion efficiency from 11.7% to 15.5%, that is equivalent to a 31% increment. Moreover, the results from contact angle measurements indicate the BTFLSO3K and PEDOT:PSS films have static water contact angle of 53.1° and 10.6°, respectively. A more hydrophobic surface will be more efficient to resist the invasion of water moisture and then to increase the environmental stability of perovskite solar cells. In the second part, a series of wide-bandgap conjugated polymers containing diester thiophene units, namely C8T, C8F, C8TT, C8TF, C16TT, and C16TF, are synthesized to potentially replace P3HT as the electron donor of newly developed small-molecule electron acceptor, such as ITIC, for developing high-efficiency organic solar cells. UV-vis absorption spectra show that all products possess strong absorption in the range of 400 to 600 nm with absorption coefficients over 40 L/g·cm. The photoemission spectroscopy results reveal that these polymers have HOMOs of around -5.14 ~ -5.57 eV, which are apparently deeper than that of P3HT (-5.11 eV) and those compounds with fluorine substitutions exhibit relatively low-lying HOMOs. Moreover, the X-ray diffraction patterns of polymer films demonstrate that the insertion of thiophene rings as conjugated spacer and the replacement of thiophene with difluorothiophene as building block significantly improve the packing ability of polymer chains into a lamellar structure.