應用於染料敏化太陽能電池新穎釕錯合物之合成與鑑識

Abstract

染料敏化太陽能電池為前瞻性技術產品，在製程上有其低成本的優勢，在1993年DSSC染料突破10%時，電池的穩定性成為未來商品化重要一環。為了使染料敏化太陽能電池商業化，以提高電池穩定度為目標，在此論文中我們成功合成出一系列可用於染料敏化太陽能電池非硫氰酸釕金屬染料，以取代傳統較不穩定的硫氰酸釕金屬染料。本系列染料在設計上 (1)以釕原子為中央金屬，保留兩個2,2'-联吡啶-4,4'-二甲酸用以聯結二氧化鈦半導體製成的奈米粒子；(2)將原本的硫氰酸單芽基取代為碳氮配位phenylbenzimidazol (PBI)為主體的雙芽基，以增加染料穩定度。在PBI主體上更加入不同形式的修飾，並探討各種不同設計對染料敏化太陽能電池元件的影響。選擇以PBI為主結構，同時修飾的甲基苯環還可以防止染料與電解液發生逆向反應；為了提高元件的開路電壓及短路電流，因而對PBI結構進行加入氟原子及接上共軛噻吩長碳鏈修飾，而得到了向內 (CT1)及向外 (CT2)不同的染料，將CT2元件效能最佳化而得到8.3 %效率。最後我們設計了三邊不對稱的染料 (T35F)以雙芽基團上修飾高吸光特性的噻吩官能基取代雙羧酸芽基，去提升光學性質及抑制逆向反應，另一方面以碳氮配位取代硫氰酸可以提高穩定度，並調整染料HOMO的能階使染料與電池更匹配，將T35F染料進行元件效率測試，得到短路電流為16.8 mA cm-2、開路電壓726 mV、填充因子0.738，最終效率為9.0 %，優於傳統硫氰酸染料N3在相同條件下製成的元件 (8.7 %)來的更高。

Dye-sensitized solar cells (DSSC) are considered as promising devices for solar energy conversion, with the potential to significantly decrease the production costs. The breakthrough was achieved in 1993 with the demonstration of a DSSC system reaching more than 10 % efficiency. Besides efficiency, stability is more important for commercialization of the device to the market.We design a series of novel thiocyanate-free cyclometalleted ruthenium sensitizers for DSSC application. Each of these complexes contains a metal ligated by: (i) a bidentate 2,2-bipyridine- 4,4-dicarboxylic acid (dcbpy) ligand to anchor to the TiO2 surface; (ii) a cyclometalating ligand with electron withdrawing groups to ensure a sufficiently high oxidation potential for dye regeneration in the DSSC. Selecting phenylbenzimidazole as cyclometalating ligand and decorated with methylbenzene has an effect to retard charge recombination that resulted in an increase of electron lifetime. In order to increasing the stability and getting highly efficient solar cell, we decorate an n-hexyl thiophene group attaching to fluoro-substituted phenylbenzimidazole provide inward (CT1) and outward (CT2) sensitizers. The photovoltaic performance of CT2 affording a conversion efficiency of 8.3%. Finally, we degsin a tris-heteroleptic cyclometalated Ru sensitizer (T35F) to replace one dcbpy with a bidentate ligand capable of suppressing recombination and enhance the light- harvesting properties. In addition, removing the thiocyanate can improve device stable and adjusts the HOMO level of the sensitizer to potentially compromise dye regeneration. The photovoltaic performance of T35F exhibited a short-circuit photocurrent density of 16.8 mA cm-2, an open-circuit voltage of 0.726 V, and a fill factor of 0.738, affording an overall conversion efficiency of 9.0 %. The efficiency of T35F sensitizer is higher than that of traditional thiocyanate sensitizer N3 (8.7 %).