合成星狀噻吩-呋喃小分子於溶液製程有機太陽能電池的應用

Abstract

本研究設計合成含噻吩-呋喃共軛臂鏈之星狀(star-shaped,S)小分子並應用於溶液製程有機太陽能電池。利用雙噻吩(bi-thiophene,TT)為S之核心，逐步反應形成含有四個噻吩-呋喃共軛臂鏈之S-TT。進一步比較以TT為中心含兩個噻吩-呋喃共軛臂鏈之線性(linear,L)小分子材料(L-TT)，探討多維共軛臂鏈對小分子光電物理性質之影響。此系列S-TT與L-TT在一般有機溶劑有良好的溶解度。因S-TT 有較多的共軛臂鏈，因此比 L-TT 具備更好的熱穩定性。由紫外光-可見光光譜發現，S-(TT)在薄膜狀態下其吸收波長較L-(TT)紅位移，顯示多維共軛臂鏈的導入能有效提供分子間引力，幫助成膜性。由光電子光譜實驗顯示，多維共軛臂鏈可有效改變TT核心的旋轉角度，並有效調控HOMO能階。理論計算結果推測，多維共軛臂鏈能有效調整小分子之能階與多維方向的電子分佈。初步將小分子材料與PC61BM混摻(1:1,w/w)製備成太陽能電池之主動層，元件採用反式結構，其中氧化锌作為元件電子選擇層和三氧化鉬為電洞選擇層，再使用銀為陽極和氧化銦錫為陰極。在 AM 1.5 照度下S-(TT)之光伏參數:開路電壓為0.81 V，短路電流為1.62 mAcm -2，填充因子為0.30，轉換效率為0.40%。L-(TT)之開路電壓為0.88V，短路電流為 1.09mAcm-2，填充因子為0.33，轉換效率為0.32 %。結果顯示多維共軛臂鏈的導入能有效增加小分子吸收太陽光特性，增加光電轉換效率。

A novel four-arm star-shaped (S) small molecule based on oligo(thienylfuran)s as conjugated arms and bithiophene (TT) as central core, was synthesized for solution-processable organic solar cells (OSC). To systematically investigate the characteristics of multi-dimensional conjugated systems, a two-arm linear-shaped (L) small molecule based on the same conjugated arms as that of S-TT was further synthesized. S-TT, as well as L-TT, both presented satisfactory solubility in common organic solvents. The nature of addition arms of S-(TT) exhibited better thermal stability than did L-(TT). According to the UV-vis measurements, the onset wavelengths of S-(TT) displayed a red-shift about 38 nm from solution state to film state, which is larger than that of L-(TT)(~7 nm). This implies that the addition conjugated arms of S-(TT) would incur a dense packing between molecules in film state. The tailoring of HOMO levels of L-TT and S-TT could be accomplished by utilizing the twisted central TT core. Computational analysis provided further evidences that the additional conjugated arms of multi-dimensional conjugated systems were capable of adjusting energy levels and electronic distribution. Inverted OSCs with ZnOx and MoO3 as an electron extraction layer and a hole extraction layer, respectively were fabricated by spin-coating the blend of L-TT or S-TT as donor and the fullerene derivative (PC61BM) as acceptor. The preliminary photovoltaic performances indicate that the photocurrent and power conversion efficiency were benefited greatly by inserting multi-dimensional conjugated arms in small molecule.