應用於染料敏化太陽能電池新穎苯咪唑型釕錯合物染料之合成與元件性質研究

Abstract

我們成功的合成一系列以Benzimidazole為基本架構的釕金屬錯合物染料，應用於染料敏化太陽能電池。有別於文獻中常見的以Bipyridine為主體的染料( 如N719、Z907 )，本系列的染料有合成簡單、成本更低廉的優點，並以大量的染料吸附於TiO2奈米粒子表面而提高光電流，故元件效能可以與N719相當。由先前的研究中得知，benzimidazole接上benzyl基團時( 以RD5為代表 )，光電轉換效率達最佳值。與N719比較起來，雖然效率相去不遠，但仍有以下缺點：(1)電子-電洞再結合反應速率高於N719，以致於光電壓( Voc )低於N719；(2) 吸光系數較低，故單一分子的光利用率較不理想。在本論文中，我們藉由修飾RD5的推拉電子基團，成功的減少電荷再結合的發生而有效的提升元件的Voc，其中以包含兩個氟原子取代基的RD12效果最為顯著；我們並利用光電壓/光電流瞬態衰減技術研究其元件的動力學過程，來解釋Voc提升的原因。另一方面，我們利用Thiophene基團來增長分子的共軛，其中加入兩個Thiophene基團的RD18釕金屬錯合物成功的將吸光系數由RD12的8000 M-1 cm-1提升到RD18的17000 M-1 cm-1，因此RD18成為本論文中光電轉換效率最高者；經過一系列的元件最佳化工程調整後，其Jsc為19.731 mA cm-2、Voc為0.758 V、填充因子為0.704、整體元件光電轉換效率達到10.58 %，比相同條件下的N719元件(η= 9.3 % )還要優越，是極具潛力的新一代光敏染料。

We design a series of benzimidazole-based heteroleptic complexs (RD series) for Dye-Sensitized Solar Cell applications. Being different with the dyes based on bipyridine-ligand we generally known, for example: N719 and Z907. The dyes we design have the advantages of simply synthesis and low costing. The power conversion efficiency of RD series dyes is comparable with N719 by large amounts of dye-loading. We knew the benzimidazole-based dye contain benzyl group had the best power conversion efficiency. Compare to N719, RD series had some defect: (1) Back reaction rate was too fast, caused the Voc was reduced. (2) The extinction coefficient was lower, against thin film device development. In our study, we design some kind of electron-acceptor or donor group, expect to reduce the back reaction rate to improve Voc value. RD12 which was design two fluoro-substituted had the best performance among this series. We used transient photocurrent/photovoltage decays measurements the thin-film samples were performed to understand the effect of fluorine atoms on cell performance. On other hand, we design thiophene group to improve the extinction coefficient. The complex contain two thiophene group (RD18) successfully increased extinction coefficient from 8000 to 17000, and it is the dye had the best power conversion efficiency among RD series. Upon optimization, the device made of the RD18 dye gives Jsc/mA cm-2 = 19.731, Voc/V = 0.758, FF = 0.704, and η= 10.58 %.