在本文中設計合成了一系列以pyridomethene-BF2 complex與phenothiazine混成，以thiophene做為π-spacer之有機敏化材料。以phenothiazine的基本架構上引入pyridomethene-BF2 complex於數據上顯示會有很高的莫耳消光係數，對於製作一個染料敏化材料來說，有利捕光效應的產生。在本文以pyridomethene-BF2對合成出之Ｋ系列染料所影響之DSSC元件之效果進行探討，其中以K3染料，於pyridomethene-BF2 complex與phenothiazine之間引入一thiophene的結構呈現出最好的光電性能(Jsc=15.43 mA cm-2，Voc=0.69 mV，FF=0.62，轉換效率為 6.58%，光源為AM 1.5 illumination 100 mW cm-2)。
並且於K3結構中再引入另一個pyridomethene-BF2 complex，設計出K6、K7目的在於提高染料之吸光係數，實驗結果顯示其吸光係數達138000 ¬M-1cm-1。另外，於K3之thiophene之不同取代位置引入烷基鏈觀察其碳鏈位置效應，設計出K4、K5。
結果顯示與參考化合物R1、R2相比，於phenothiazine結構中引入pyridomethene-BF2 complex能夠進一步提升染料之穩定性，並大幅提升元件之光電轉換效應。另外，在K3的π-bridge位置添加烷基鏈可進一步提高開路電壓(Voc)，並且會對分子的電子傳導路徑與光電轉換效率(IPCE)會有不同的影響。
A series of new pyridomethene-BF2/Phenothiazine-hybrid metal-free organic sensitizers K containing different π-spacers were synthesized and applied in dye-sensitized solar cells (DSSC). The introduction of the pyridomethene-BF2 complex unit in the phenothiazine showed a high molar extinction coefficient which is favorable to the light-harvesting.
Moreover, the incorporated unit of pyridomethene-BF2 complex in dyes K weakens the deprotonation effect in solution and on TiO2 film. Quantum chemical calculations were performed by using the density functional theory (DFT) at the B3LYP/6-31G(d,p) level to investigate the structural properties and density distributions of the dyes. Compared to the typical phenothiazine dyes R, the introduction of the pyridomethene-BF2 complex moieties in the phenothiazine significantly increases the photostability.
The effect of the pyridomethene-BF2 complex in dyes K on the performance of DSSC was investigated systematically. With deoxycholic acid coadsorption, insertion of the thiophene unit between the phenothiazine and pyridomethene-BF2 complex in K3 exhibits the best photovoltaic performance, with a short-circuit current density (Jsc) of 15.43 mA cm-2, an open-circuit voltage (Voc) of 0.69 V, and a fill factor (FF) of 0.62, corresponding to a power-conversion efficiency (η) of 6.58% under AM 1.5G irradiation (100 mW•cm-2) condition. The grated additional alkyl chain on the π-bridge thiophene segment in K3 could further improve the Voc.
Additionally, it was found that the substitution position of n-hexyl chain on the thienyl unit has a crucial effect on the molecular electronic structure as well as photovoltaic performance. The introduction of the phenyl pyridomethene-BF2 complex at the N(10) atom of phenothiazine has a good influence on preventing the molecular π-π aggregation. These results suggest that the DSSC based on pyridomethene-BF2 complex dyes could achieve both high performance and photostability.
