本研究利用Friedel–Craft醯化反應Stille偶合反應、Vilsmeier-Haack醛化反應及Knoevenagel縮合反應等化學方法,合成以benzodithiophene-4,8-dione (BDD)單元作為共軛骨架核心的D‒A‒π‒A型染料,BY1與BY2,並應用於染敏化太陽能電池。
在BDD單元兩邊各引入一個噻吩環後,三個噻吩環(terthiophene)基本上可以維持共面而有利於電子供體與受體間的電荷轉移,而BDD單元中的carbonyl group可以降低染料的能隙,透過BDD單元上之烷基鏈也可增加染料分子在溶劑中的溶解度,且有助於抑制暗電流。本研究因此利用BDD單元來建構敏化太陽能電池之光敏染料,並進行元件測試。
但由於高的平面性容易造成分子間的堆疊且與相當嚴重的電子捕獲(electron trapping)效應,導致電子注入TiO2薄膜的機會減少,造成染敏化電池的低效率(BY1 = 2.41%, BY2 = 1.23%)。其中的較高元件效率可歸諸於較高的染料吸附度,導致較高的光電流,以及較佳的暗電流抑制能力,導致交高的光電壓之故。
The new metal free organic dyes containing benzodithiophene-4,8-dione Core(BY1 and BY2) have been synthesized via Friedel-Crafts Acylation, Suzuki coupling, Stille coupling, Vilsmeier-Haack formylation and Knoevenagel condensation reactions. These dyes were used as sensitizers for dyesensitized solar cells (DSSCs).
Introducing a thiophene ring on each side of the BDD unit, the terthiophene can maintain coplanarity and facilitate charge transfer between the electron donor and the acceptor, and the carbonyl group in the BDD unit can reduce the dye energy band gap. Introducing the alkyl chain on the BDD unit can increases the solubility of the dye molecule in the solvent and helps to suppress dark current. In this paper, the BDD unit is used to construct the photosensitive dye for sensitized solar cells and to device performence testing.
However, due to the high planarity, it is easy to cause inter-molecular stacking and a relatively serious electron trapping effect, resulting in a reduced chance of electron injection into the TiO2 film, resulting in low efficiency of the dye-sensitized battery (BY1 = 2.41%, BY2 = 1.23%)