含五苯荑之聚對苯乙烯之合成、性質研究及其在太陽能電池之應用

Abstract

在本論文主要為含五苯荑之對苯乙烯聚合物之合成，並探討不同五苯荑比例對其光電性質之影響 ，以期應用於有機共軛高分子太陽能電池元件中。 本實驗室致力於五苯荑分子的官能化，並成功合成出雙溴五苯荑，曾利用雙溴五苯荑經Heck偶合反應合成出含五苯荑之聚對苯乙烯，但聚合效率不佳，因此我們轉為開發反應活性較高的雙碘五苯荑或不同核心架構的雙乙烯五苯荑來合成含五苯荑之聚對苯乙烯。在合成部分，以五苯荑醌為起始物，經過一系列的中心苯環官能基轉換，我們成功合成出雙碘五苯荑及雙乙烯五苯荑。雙碘五苯荑能以芳香環取代反應之方式有效地提升總產率，因此利用雙碘五苯荑進行含五苯荑之聚對苯乙烯的合成，成功合成出不同含五苯荑比例的PEN-ROPPV和PEN-3ROPPV高分子。於光物理性質部分，受到五苯荑立體效應影響，兩高分子相較於一般聚對苯乙烯在吸收和螢光光譜皆有藍位移，而PEN-3ROPPV含有較低比例的五苯荑，故相較於PEN-ROPPV較為紅位移；兩分子薄膜之吸收和螢光光譜與稀釋溶液態相當類似，文獻中指出五苯荑立體效應能有效避免高分子鏈間作用。電化學方面，兩分子之氧化為一不可逆之過程。根據兩分子之HOMO及LUMO，符合作為太陽能電池之基本條件，唯獨在能帶間隙上較寬，不利於吸收可見光。予體和受體之互混溶性為影響塊材異質接面太陽能電池因素之一，引進五苯荑欲提升對聚苯乙烯與PCBM之互溶混性，但在元件效率之表現，兩者皆相當低，推測可能原因有二：(一)、高分子無法有效吸收可見光導致捕光效率差；(二)、形態上予體和受體互溶混性並未構成有效通路。因此若要有效提升元件效率則需進行結構上的改質。

In this thesis, we report the synthesis and electronic properties of pentiptycene-incorporated poly(phenylene vinylene)s (PPVs). We have also investigated the performance of these PPV-type derivatives as active materials for bulk heterojunction (BHJ) solar cells. Our lab has been devoted to the synthesis of new pentiptycene building blocks, including dibromopentiptycene. We previously used dibromopentiptycene to synthesize pentiptycene-incorporated poly(phenylene vinylene)s by Heck coupling reactions, but the overall yield and polydispersity are poor. As a result, we turn to the more reactive diiodopentiptycene and the alterative building block divinylpentiptycene. We used pentiptycene quinone as the starting material and successfully obtained diiodopentiptycene and divinylpentiptycene through multistep synthesis, and particularly the SNAr reaction of a pentiptycene triflate. Two pentiptycene incorporated PPVs PEN-ROPPV and PEN-3ROPPV have been successfully prepared. These two polymers are blue-shifted in absorption and fluorescence spectra as compared to alkyl or alkoxy-substituted PPVs. The spectra of PEN-3ROPPV are somewhat red-shifted than those of PEN-ROPPV due to its lower fraction of the pentiptycene group. Their spectra in thin film are similar to those in dilute solutions, indicating negligible aggregation of polymers backbone.The cyclic voltammetric anodic curves of these two polymers are irreversible. The energy levels of their HOMOs and LUMOs are suitable for application in BHJ solar cells with PCBM as the electron acceptor. However, the power conversion efficiency are low partly owing to poor light harvesting of the sun light. Another possible factor that is responsible to the low efficiency of solar cells is the morphology even though we had expected that pentiptycene could interact well with PCBM.