開發高效能光敏劑應用於染料敏化太陽能電池

我們有系統地設計並合成四個系列的鋅紫質光敏劑及一個系列的有機分子光敏劑，並應用於染料敏化太陽能電池的研究上。第一個系列為修飾不同多環芳香族碳氫化合物之紫質染料，代號為 LD1~LD4。隨著取代基之共軛系統的延伸，紫質染料之電子吸收光譜會有明顯變寬且紅移，在螢光放射光譜中也可觀察到一致的趨勢。電化學實驗顯示 LD1~LD4 之氧化電位沒有明顯的差異；而還原電位則會隨著取代基的共軛長度的延伸而降低。LD1~LD4 DSSC 元件之光電總轉換效率的趨勢為 LD4 (10.06%) > LD3p (8.26 %) > LD2 (7.83 %) > LD3a (6.62 %) > LD1 (5.11 %)。第二，為了改善紫質染料的溶解度及抑制分子之堆疊現象，我們在紫質分子的結構中導入了烷氧鍊，合成出 LD11~ LD16 紫質光敏劑，並探討於不同位置修飾之烷氧長鍊對於紫質染料光伏性質之影響。在光學性質方面，於不同位置修飾之烷氧長鍊並不會對其電子吸收光譜造成明顯的影響，由染料吸附在 TiO2 薄膜上之電子吸收光譜可以觀察到，修飾有烷氧鍊的紫質染料吸附在 TiO2 薄膜上時，較不容易產生分子堆疊的現象。電化學實驗顯示，烷氧鍊修飾的位置對於紫質分子之電化學性質會造成部分的影響。Molecular dynamics simulations 的結果顯示，適當長度的烷氧鍊可有效抑制染料分子產生堆疊。LD11~LD16 DSSC 元件之光電總轉換效率的趨勢為 LD12 (7.43 %) > LD11 (4.78 %) 及 LD16 (10.24 %) > LD14 (10.05 %) > LD14-C4 (8.94 %) > LD15 (8.92 %) > LD13 (8.37 %) > LD14-C4 (5.91 %)，由光電效能量測的結果可得知，於紫質苯環 ortho-位置修飾適當長度之烷氧鍊，可以有效改善紫質染料之光電效能。第三，我們合成了修飾有不同高共軛性蔥或芘取代基的紫質光敏劑，命名為LD31~LD34，希望藉由分子共軛系統的擴張，造成吸收光譜紅移及吸收範圍變寬，藉此改善紫質染料之吸光能力。在光學性質方面，LD31~LD34 之電子吸收光譜都有明顯變寬且紅位移，其中以 LD31 與 LD32 之光譜紅移與變寬的程度最為顯著；在螢光放射光譜中也可觀察到一致性的光譜紅移的趨勢。電化學實驗顯示 LD31~LD34 之氧化電位並沒有明顯的差異；還原電位則會受到取代基的不同而改變。LD31~LD34 DSSC 元件之光電總轉換效率的趨勢為 LD33 (9.25 %) > LD31 (8.82 %) > LD34 (8.65 %) > LD32 (7.58 %)。第四，我們合成修飾有具胺類稠環烴取代基之紫質光敏劑 LWP11~LWP15，希望藉由紫質分子的吸收光譜紅移及吸收範圍變寬，來改善典型紫質染料在 Soret bands 與 Q bands 之間吸光能力較弱的問題，並搭配不同的推電子基團，希望可提升電子注入能力與改善染料的溶解度。在光學性質方面，LWP11 紫質分子之電子吸收光譜與 LD14 相當類似；而 LWP12~ LWP15 之吸收光譜則都有明顯變寬且紅移的現象，在螢光放射光譜也可觀察到一致性的光譜紅移的趨勢。電化學實驗顯示 LWP11~LWP15 之氧化電位會隨著取代基的不同而明顯變化，還原電位則會隨著取代基之共軛系統擴張而往正電位方向移動。由染料的能階相對位置可得知，此系列染料之 S* 能階高度都具有足夠的驅動力使激發態電子注入 TiO2 的導帶，表示 LWP11~LWP15 適合作為 DSSC 元件中之光敏劑的部分。第五，我們合成出一系列 anthracene based 有機分子染料 LWO1~LWO8。在光學性質方面，LWO1~LWO8 會因分子的共軛系統延伸或取代基的不同，導致電子吸收光譜有不同的紅移程度。電化學實驗顯示，LWO1~LWO8 之氧化電位都相當接近，而還原電位的則會受到取代基之影響。 LWO1~LWO8 DSSC 元件之光電性質量測的結果顯示，LWO1~LWO8 元件總轉換效率的趨勢為 LWO3 (5.39 %) > LWO4 (4.96 %) > LWO1 (3.59 %) > LWO2 (2.94 %) 以及 LWO8 (5.80 %) > LWO5 (5.22 %) > LWO6 (4.51 %) > LWO7 (1.58 %)。

關鍵字

染料敏化太陽能電池；紫質分子；有機分子染料

並列摘要

We have systematically designed and synthesized four series of porphyrin sensitizers and a series of organic sensitizers for dye-sensitized solar cell applications. Firstly, five novel zinc porphyrins bearing a polycyclic aromatic hydrocarbon substituent (denoted as LD1, LD2, LD3a, LD3p and LD4) were prepared as photosensitizers for dye-sensitized solar cells. LD3a and LD4 yielded the most red-shifted and broadened UV-visible absorption and fluorescence bands in the series. Electrochemical tests show that LD4 is the easiest to reduce in this series. As for the photovoltaic performance of LD1~ LD4-sensitized solar cells, we observed a systematic trend of LD4 (10.06 %) > LD3p (8.26 %) > LD2 (7.83 %) > LD3a (6.62 %) > LD1 (5.11 %). Secondly, a series of porphyrins bearing alkoxyl and/or alkyl chains (LD11~ LD16) were prepared to investigate the relationship between alkoxyl/alkyl chains and the enhanced photovoltaic performance of the dyes. The alkoxyl/alkyl chains have little effect on the porphyrin UV-visible absorption and fluorescent emissiom spectra, but singnificantly affect the electrochemical properties of these porphyrin dyes. Based on the experimental results and the molecular simulations, we demonstrated that suitable long alkoxyl chains are capable of wrapping the porphyrin core, thus resulting in decreased dye aggregation, elevated excited states and LUMOs, and improved photovoltaic performance. The LD16-sensitized solar cells outperform other dyes in this series with an overall efficiency of 10.24 %. Thirdly, four novel zinc porphyrins substituted with an anthracene or pyrene (denoted as LD31, LD32, LD33 and LD34) were prepared as photosensitizers for dye-sensitized solar cells. The UV-visible absorption spectra of LD31~LD34 show thelarge red-shifted and broadening of absorption bands. The oxidation potentials of these porphyrins are very similar. The preliminary results of PCE value measurement of LD31~ LD34-sensitized solar cells show a trend of LD33 (9.25 %) > LD31 (8.82 %) > LD34 (8.65 %) > LD32 (7.58 %). Fourthly, a series of porphyrins bearing different amino-modified acene substituents (LWP11~LWP15) were prepared as photosensitizers for dye-sensitized solar cells. The UV-visible absorption spectrum and fluorescence spectra of LWP11 is very similar to that of LD14, whereas LWP12~LWP15 exhibit large red-shifted and broadened UV-visible absorption and fluorescence bands. Electrochemical experiments show that the amino-modified acene substituents have a significant effect on the oxidation potential of these porphyrins. The energy level diagram suggests that LWP11~LWP15 porphyrins should be capable of injecting electrons to the CB of TiO2 upon excitation. Finally, we successfully synthesized a series of anthracene-based organic sensitizers, (LWO1~LWO8). The elongation of the conjugation system or changing the substituents near the anchoring groups resulted in red-shifted absorption bands. The oxidation potential of LWO1~LWO8 are very similar to each other. The preliminary results of PCE value measurement of LWO1~LWO8-sensitized solar cells showed a trend of LWO3 (5.39 %) > LWO4 (4.96 %) > LWO1 (3.59 %) > LWO2 (2.94 %) and LWO8 (5.80 %) > LWO5 (5.22 %) > LWO6 (4.51 %) > LWO7 (1.58 %).