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

本論文乃研究探討利用Grignard metathesis 來合成一系列聚噻吩高分子來探討高分子本身之光電效應。而論文的第一部份，是以合成出一系列聚(辛基-噻吩)(P3OT)衍生物，而在其側鏈上導入一菲基-1,3-二氮雜茂(phenanthrenyl-imidazole)，希望藉由導入此官能基之後可以增加高分子本身主鏈的共軛長度，不但可以將高分子本身的能隙(bandgap)降低，且具有電子傳輸的效果，而且在光激發光方面，因為隨呃導入菲基-1,3-二氮雜茂比例增加，發光淬息(quenching)現象就越來越明顯，也因為如此促使了高分子的製作成元件之後，外部量子效率(external quantum efficiencies)增加，相對的在含有比較高比例的菲基-1,3-二氮雜茂聚(辛基-噻吩)高分子之光電流(short-circuit current density)也提升了(由8.7 mA/cm2提升到14.2 mA/cm2，提升了約62%)，光電轉換效率也增加了(由1.22%提升到2.80%)。第二部份則是，利用Grignard metathesis 來合成一系列聚(己基-噻吩)(P3HT)高分子衍生物，然後將菲基-1,3-二氮雜茂末端作了修飾導入了兩個辛基長碳鏈提升溶解度，相同的，導入了辛基-菲基-1,3-二氮雜茂之後，高分子本身的能隙降低，發光淬息(quenching)現象就越來越明顯，而此系列之高分子開路光電流也提升了(由8.3 mA/cm2提升到13.7 mA/cm2，提升了約65%)，光電轉換效率改善到3.45%。第三部份，則是合成一高分子，PHPIT，在菲基-1,3-二氮雜茂末端修飾導入了三個己基官能基到單體本身之中，而此高分子與[6,6]-苯基-C61-丁酸甲酯 ([6,6]-phenyl-C61-butyric acid methyl ester) (PCBM)掺混之後，對於可見光之吸光能力增強，而製作成元件之後發現，在迴火溫度為120 oC，持續30分鐘的情況下，其外部量子效率最高，而在此條件下，也因為較為平衡的電子電動流動率也促使了較高的光電流密度，因此，此高分子在此條件下之光電轉換效率約為4.1%。

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.