低能隙高分子與其組成單元的階級結構形成機制與光電物理性質關係之系統性分析與研究

Abstract

低能隙(Low band gap)高分子為當前高效率bulk-heterojunction (BHJ) polymer solar cells (PSCs)與organic field-effect transistors (OFETs)中的重要單元, 在達成PSCs光電轉換效率>8%與電荷載子遷移率(charge carrier mobility) > 5.5 cm2V-1s-1 (amorphous silica-based FETs)的過程中,微觀分子結構與巨觀元件效能間的橋梁-階級結構(hierarchical structure)將扮演重要角色. 因此, 本計畫將系統性的研究低能隙高分子與其組成單元,即電子施體(electron donor moiety, D)與電子受體(electron acceptor moiety, A),的階級結構形成機制與其對元件效能的影響. 並藉由探討分子結構,階級結構與元件效能的關係,找尋提升元件效能的關鍵參數,以達到提升元件效能的目的. 低能隙高分子具有複雜的分子結構與分子間作用力.本研究將系統中牽涉到的變因(分子結構與物理作用力)進行拆解,並在三個層級上進行研究. 首先,針對低能隙高分子的主要組成單元進行研究. 探討不同的架橋原子, 不同的側鏈結構, 以及不同環數目的polycyclic aromatic結構, 對其排列行為以及元件效能的影響. 在第二階段,利用耦合反應連接D, A單元以形成D-A, D-A-D,及A-D-A型態的共軛性分子, 藉此引入D, A單元並存的複雜分子結構與dipole-dipole分子間作用力, 來探討低能隙高分子中重複單元(repeat units, i.e. D-A)的可能排列方式與其排列行為對元件性質的影響. 最後, 利用耦合反應將具有雙官能基取代的D, A單元進行共聚反應, 以形成低能隙高分子. 在這個階段的研究中, 將搭配在前兩階段中對D, A單元的階級結構與元件效能的認識, 來解析低能隙高分子其高分子鏈的階級結構形成機制,並透過對低能隙高分子規則結構的了解,來進一步提升當前BHJ PSCs與OFETs的元件效能.

As a main component in the high performance bulk-heterojunction (BHJ) polymer solar cells (PSCs) and organic field-effect transistors (OFETs), wide varieties of low band gap (LBG) conjugated polymers have been developed. To further enhance the performances of BHJ PSCs and OFETs, and achieve > 8% power conversion efficiency (PCE) for PSCs and charge mobility > 5.5 cm2V-1s-1 (amorphous silica-based FETs) for the OFETs. The hierarchical structures of a series of specifically designed LBG polymers, and their constituent Donor/Acceptor units will be synthesized and studied. The study is aimed to identify the relationships among molecular structure, hierarchical structure and device performance of LBG polymers, and find out the key parameters for improving the device performances of PSCs and OFETs. LBG polymers possess complicate molecular structures and intermolecular interactions. In this proposal, we break down the molecular structures of LBG polymers and study the relationships among molecular structures, hierarchical structures, and device performances at three stages. At first stage, how the hierarchical structures and device performances are affected by (1) the length of π conjugating systems, (2) the types of the bridge atoms, and (3) the side chain structures of the donor units will be studied. At the second stage, D-A, D-A-D and A-D-A type conjugated molecules will be synthesized to introduce complex molecular structures and intermolecular interactions into the molecular systems. This part of study focus on finding out the preferred arrangements of the repeating units of LBG polymers in their ordered structures. At the finally stage, a series of LBG polymers will be synthesized and characterized. The formation mechanism of the hierarchical structures of the LBG polymers will be carefully studied and analyzed based on the understanding of the D/A type small molecules obtained from the first two stages. To achieve PCEs > 8% and charge mobilities > 5.5 cm2V-1s-1, the PSCs and OFETs performance will be optimized based on the conditions of forming well-defined hierarchical structures of LBG polymers.