以Phenothiazine為中心之雙錨基光敏染料與染敏太陽能電池

Abstract

在本論文研究中， 我們藉由Suzuki 偶合反應、Stille 偶合反應、Vilsmeier-Haack 醛化反應以及Knoevenagel 縮合反應等化學方法，合成一系列以硫二苯胺(phenothiazine)為電子予體並經由不同結構的共軛架橋連接兩個電子受體形成HL 系列之雙錨式光敏染料，並應用於染料敏化太陽能電池。 藉由循環伏安法（cyclic voltammetry）、差式脈衝伏安法（differential pulse voltammetry）以及可見-紫外光光譜儀（UV-Vis absorption spectra），我們發現相較於單錨式光敏染料，雙錨式光敏染料有更好的光收成。這些化合物也可成功製成染料敏化太陽能電池，在光照下染料分子可以順利注入電子於TiO2，以及接受電解質之電子而再生。我們也對這些分子進行理論計算之探討，並發現化合物吸光後應有良好之電荷轉移。 透過元件測試發現，雙錨式光敏染料比單錨式光敏染料確實擁有更有效的電子注入路徑，以及較佳的光收成能力。雙錨式光敏染料在共軛架橋中引入烷基鏈可有效減少染料間的堆疊並抑制暗電流，除此之外在硫二苯胺單元氮原子的位子引入2,6-bis(hexyloxy)phen-1-yl (BP-C6)基團，更將吸光範圍大幅的紅位移，同時強化抑制染料間的堆疊現象，以及降低產生暗電流的機會，引入增加支鏈的2,6-bis(ethylhexyloxy)phen-1-yl (BP-C8)基團，更強化染料抑制暗電流的能力。此HL 系列染料中，最好的光電轉換效率高達8.32%，已超越N719 (7.35%)建構之標準元件。A series of new push–pull phenothiazine-based dyes (HL) featuring various π spacers (thiophene,3-hexylthiophene, 4-hexyl-2,2’-bithiophene, 4-hexylthiazole) and double acceptors/anchors have been synthesized via Suzuki coupling, Stille coupling, Vilsmeier-Haack formylation, and Knoevenagel condensation reactions. These dyes were used as sensitizers for dye-sensitized solar cells (DSSCs). Cyclic voltammetry, differential pulse voltammetry and UV-Vis absorption spectra were used to estimate the HOMO and LUMO energy levels and its light harvest ability of the sensitizers in solution. Theoretical computations were also carried out on these dye molecules. The dyes with two anchors have more efficient interfacial charge generation and transport, as well as better light harvesting capacity compared with their congeners with only single anchor. Incorporation of hexyl chains into the π-conjugated spacer of these double-anchoring dyes can efficiently suppress dye aggregation and reduce charge recombination. Furthermore the 2,6-bis(hexyloxy)phen-1-yl substituent at the nitrogen atom of the phenothiazine entity not only led to more red shift of the absorption spectra, but also better suppressed the π-π stacking of the molecules and the dark current. Among them, the best conversion efficiency reaches 8.32%, which exceeds the N719-based (7.35%) DSSCs fabricated and measured under the similar conditions.