側鏈含有菲基–1,3–二氮雜茂之予體－受體結構規則之聚噻吩運用於異質接面太陽能電池上之合成與研究

Abstract

In this dissertation, a series of polythiophene copolymers have been synthesized to study to photovoltaic characteristics. First of all, we have used Grignard metathesis polymerization to successfully synthesize a series of regioregular polythiophene copolymers that contain electron-withdrawing and conjugated phenanthrenyl-imidazole moieties as side chains. The introduction of the phenanthrenyl-imidazole moieties onto the side chains of the regioregular polythiophenes increased their conjugation lengths and thermal stabilities and altered their band gap structures. The band gap energies, determined from the onset of optical absorption, could be tuned from 1.89 eV to 1.77 eV by controlling the number of phenanthrenyl-imidazole moieties in the copolymers. Moreover, the observed quenching in the photoluminescence of these copolymers increases with the number of phenanthrenyl-imidazole moieties in the copolymers, owing to the fast deactivation of the excited state by the electron-transfer reaction. Both the lowered bandgap and fast charge transfer contribute to the much higher external quantum efficiency of the poly(3-octylthiophene)-side-chain-tethered phenanthrenyl-imidazole than that of pure poly(3-octylthiophene), leading to much higher short circuit current density. In particular, the short circuit current densities of the device containing the copolymer having 80 mol % phenanthrenyl-imidazole, P82, improved to 14.2 mA/cm2 from 8.7 mA/cm2 for the device of pure poly(3-octylthiophene), P00, an increase of 62%. In addition, the maximum power conversion efficiency improves to 2.80% for P82 from 1.22% for P00 (pure P3OT). Second, intramolecular donor–acceptor structures prepared by binding conjugated octylphenanthrenyl-imidazole moieties covalently onto the side chains of regioregular poly(3-hexylthiophene)s exhibit lowered bandgaps and enhanced electron transfer. For instance, conjugating 90 mol% octylphenanthrenyl-imidazole moieties onto poly(3-hexylthiophene) chains reduced the optical bandgap from 1.91 to 1.80 eV, and the electron transfer probability was at least twice than that of pure poly(3-hexylthiophene) when blended with [6,6]-phenyl-C61-butyric acid methyl ester. The lowered bandgap and the fast charge transfer both contribute to the much higher external quantum efficiencies—and, thus, much higher short-circuit current densities—for the copolymers presenting octylphenanthrenyl-imidazole moieties, relative to those of pure poly(3-hexylthiophene)s. In particular, the short-circuit current density of a device containing the copolymer presenting 90 mol% octylphenanthrenyl-imidazole moieties improved to 13.7 mA/cm2 from 8.3 mA/cm2 for the device containing pure poly(3-hexylthiophene)—an increase of 65%. In addition, the maximum power conversion efficiency was 3.45% for the copolymer presenting 90 mol% octylphenanthrenyl-imidazole moieties. Finally, PHPIT, a new kind of intramolecular D–A side-chain-tethered hexylphenanthrenyl-imidazole polythiophene has been synthesized. The visible light absorption of the PHPIT/PCBM blend is enhanced by the presence of the electron-withdrawing hexylphenanthrenyl-imidazole. The EQE of the device was maximized when the PHPIT/PCBM blend experienced annealing at 120 °C for 30 min. The more-balanced electron and hole mobilities and the enhanced visible and internal light absorptions in the devices consisting of annealed PHPIT/PCBM blends both contributed to a much higher short-circuit current density, which in turn led to a power conversion efficiency as high as 4.1%, despite the fact that PHPIT is only comprised of ca. 20 repeating units.