探討共軛高分子中電子予體-電子受體的比例和排列方式對光電性質的影響

Effects of the ratio and arrangement of donor and acceptor on the electronic and optical properties of conjugated polymers

劉于璇(Yu-Hsuan Liu)

指導教授 ： 黃慶怡

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01967

摘要

為了探討含有電子予體與電子受體之共軛高分子影響太陽能電池光電轉換效率的因素，從不同分子比例、數量與排列方式的光電性質來得到關聯性。由於共軛高分子的構形特別是扭轉角度對於高分子的光電性質例如：紫外-可見光吸收光譜、分子軌域能階等都會有影響，為了能夠體現出分子的特性，因此我們從分子動力學出發，模擬分子鏈段的構形分析扭轉角度，進一步運用量子力學模擬方法來研究包含有電子予體與電子受體之共軛高分子之光電性質。
首先，我們藉由觀察Poly(thieno[3,4-b]pyrazine)(PTP)分子，我們得知當主鏈上有共軛雜環時，分子因為有很好的平面性加上分子內的電子傳遞效應，使得即使是小分子也有很廣的吸收範圍，經由小分子模擬發現當Thiophene與Thienopyrazine形成新的電子予體-電子受體分子時，形成新的分子軌域，使得新的分子能隙小於原本電子予體與電子受體的能隙，因此增加吸收範圍為200nm~700nm。進一步擴展到P3HT與PTP形成嵌段共聚合物時，紫外光-可見光吸收光譜，可觀察到吸收範圍明顯增加。因此，我們選擇主鏈包含電子予體與電子受體之 Polythiophene與Polythienopyrazine進行一系列分析。
由於此兩個材料皆擁有長烷基側鏈的影響，容易造成主鏈擁有較廣的扭轉角度分佈。因此本研究利用全原子分子動力學(AAMD)，模擬不同比例、排列之分子鏈在無序狀態下之分子構形。接著藉由量子力學(QM)模擬分子構形與紫外/可見光吸收光譜、分子能階之結果。整體上來說，以三種不同比例的嵌段共聚物來說，電子受體的比例增加，圖譜越紅位移；能隙也越小。從相同比例不同的排列方式來看，我們可觀察到各種比例Alternative的圖譜都呈現比Block紅位移且能隙也較小，只有在較長鏈段容易出現較大的扭轉角度，出現相反的趨勢。

關鍵字

共軛高分子 ； 電子予體-電子受體 ； 全原子分子動力學 ； 量子力學 ； 紫外/可見光吸收光譜

並列摘要

Since the conformation of conjugated polymer can greatly affect electronic and optical properties, we employed all-atom molecular dynamics (AAMD) simulation chain conformation and quantum mechanical (QM) methods to explore the effects of the ratio and arrangement of donor/acceptor on the electronic and optical properties of conjugated polymers.
In the study of poly(thieno[3,4-b]pyrazine) (PTP), the low band gaps observed in TP homopolymer materials are typically attributed to the fused-ring of the backbone and the oligomer series revealed broad absorption, significantly red-sifted by approximately 120~150 nm with each additional TP unit. Hence it is currently common for TP to be utilized as an ‘acceptor’ unit in a ‘donor-acceptor’ pair. In order to probe the extent and nature of ‘donor-acceptor’ properties , thiophene monomer and thieno[3,4-b]pyrazine monomer has been simulated. Through the study of monomer, when thiophene and thienopyrazine binding to form ‘donor-acceptor’, results in a lower bandgap due to the orbital mixing of the donor and the acceptor units, the UV-visible absorption spectrum reveal wide range (200~700 nm). The characteristics of these materials provide further insight to the electronic and optical properties through varying the ratio and arrangement of P3HT and PTP.
In this study, we employed AAMD to simulate the conformation of different ratio and arrangement of donor/acceptor conjugated polymer and analyze the torsion angle distribution on the main chain. In the case of the series, the long alkyl side chain on both P3HT and PTP results in more conformational flexibility, resulting in wide range distribution of main chain torsion angles. Then we employed QM to calculate UV-visible absorption spectrum and molecule orbital energy. These results demonstrate the fact that the content of acceptor increase, the overall absorption range becomes broad, and the bandgap becomes small. The absorption spectrum of alternative versus block, alternative reveals red shift, simultaneously, the band gap is smaller. Only if the alternative polymer chain reveals big torsion deviation, block copolymer shows red shift and small bandgap.

並列關鍵字

conjugated polymer ； donor-acceptor ； all atom molecular dynamics ； quamtum mechmical

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