染料敏化太陽能電池之釕化合物

Abstract

本研究利用Wittig-Horner reaction以及Suzuki coupling，合成出2,2'-bipyridine衍生之配位子：包括引入2-或3-位置取代carbazole，以及fluorene單元之化合物，並以之合成一系列Grätzel-型釕金屬光敏化染料。本系列釕金屬染料的UV吸收光譜在530~550 nm範圍可觀測得金屬→配位子之電荷轉移吸收(metal-to-ligand charge-transfer)，當在bipyridine和carbazole、fluorene中間引入雙鍵後，由於有效共軛長度之增加，使吸收峰的波長有明顯的紅位移。以這些釕金屬染料為光敏劑製成染料敏化太陽能電池(dye-sensitized solar cells, DSSCs) ，展現不錯的光電轉換效率。其中染料Ru-vinyl-fluorene有最好的元件效率，參數為：光電轉換效率η = 4.90%；開環電壓Voc = 0.63 V；短路電流Jsc = 11.14 mA/cm2；填充因子FF = 0.70。其光電轉換效率，可達到在相同的條件下製作與量測，以Grätzel染料N719 (cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium (II) bis-tetrabutylammonium) 製成標準元件 (η=7.11%) 的69%。推測較佳的光收成與染料之吸附度導致Ru-vinyl-fluorene元件有較高的效率。

A series of 2,2'-bipyridine derivatives, incorporating 2- or 3-substituted carbazole, or fluorene unit, have been synthesized via Wittig-Horner reaction and Suzuki coupling. These compounds have been successfully used as ligands for Grätzel-type ruthenium dyes. The metal-to-ligand charge-transfer bands in these complexes appeared in the range of 530~550 nm. A prominent red shift of the MLCT band was observed as an olefinic entity was inserted between the 2,2'-bipyridine and the carbazole or fluorene unit to increase the effective conjugation length. Dye-sensitized solar cells based on these sensitizers exhibited good performance. Among them, Ru-vinyl-fluorene-based cell had the best performance ：η (power conversion efficiency), 4.90%；VOC (open-circuit voltage), 0.63 V；JSC (short-circuit current), 11.14 mA/cm2；FF (fill factor), 0.70. The conversion efficiency reaches ~69% of the standard device (η=7.11%) based on N719 (cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium (II) bis-tetrabutylammonium) fabricated and measured under similar condition. The more effective light-harvesting and higher dye density on TiO2 may be the main reasons for better efficiency of Ru-vinyl-fluorene-based cell.