螢光子之螢光共振能量轉移應用於染料敏化太陽能電池

Application of Fluorophore-Induced Förster Resonance Energy Transfer in Dye-Sensitized Solar Cells

何妤安(Yu-An Ho) ； 林裕傑(Yu-Jie Lin) ； 吳致中(Chih-Chung Wu) ； 張健忠(Cheng-Chung Chang) ； 陳志銘(Chih-Ming Chen)

《興大工程學刊》 26卷1期 (2015/03) Pp. 25-33

https://doi.org/10.6287/JENCHU.2015.2601.03

摘要

染料敏化太陽能電池（dye-sensitized solar cell, DSSC）中的敏化染料（sensitizing dye）吸收光子後激發產生電子，若能大幅度增加敏化染料激發所產生的電子，則能顯著提升電池之光電轉化效率（power conversion efficiency, PCE）。一般常用的敏化染料N719與TiO_2光電極所組成的染敏電池，其入射單色光子─電子轉換效率（Incident Photon to Current conversion Efficiency, IPCE）峰落於可見光波長500~600 nm處。本研究將螢光共振能量轉移（Förster resonance energy transfer, FRET）概念引入染料敏化太陽能電池的運作機制中，加入一種naphthalimide衍生物N-OH（6-(6-(4-methylpiperazin-1-yl)-1, 3-dioxo-1Hbenzo[ de]isoquinolin-2(3H)-yl) hexanol）於N719/TiO_2系統中，N-OH吸收原本N719之IPCE響應較低波長的光（397 nm）並放出N719之IPCE響應較高波長的光（約513 nm），經由FRET效應將能量傳遞給N719，使N719激發出更多電子，進而提升光電轉換效率。本研究觀察加入螢光N-OH後，在不同的浸泡時間、濃度及方法下，探討太陽能電池之短路電流密度（J_SC）、開路電壓（V_OC）、填充因子（Fill Factor）、光電轉化效率（PCE）、電化學阻抗分析（Electrochemical impedance spectroscopy, EIS）及IPCE之變化及影響。此外，使用醋酸酸化螢光N-OH後，螢光發光強度會顯著提升，但醋酸與敏化染料皆有能與TiO_2產生化學吸附的官能基（-COOH），故研究亦探討添加醋酸對染料敏化太陽能電池之影響。當光電池浸泡於10^(-5) M N-OH（溶劑體積比為乙醇：醋酸20,000:1）4小時，可使DSSC光電流由15.4上升至16.8 mA/cm^2，而效率可由8.40提升至9.07%。

關鍵字

螢光共振能量轉移 ； 螢光子 ； 吸收

並列摘要

The power conversion efficiency (PCE) of the dye-sensitized solar cells (DSSCs) strongly depends upon the electron generation efficiency from the dye molecules excited by photons. One useful method in enhancing the PCE of DSSC is to generate more electrons by enhancing the light harvesting of the dye molecules. Typically, the DSSC uses N719 dye molecules as the sensitizing material and the best incident photon to current conversion efficiency (IPCE) locates in the 500 ~ 600 nm wavelength range. The rest spectrum range, for example, the ultra-violet (UV) and infrared (IR) spectra, is regrettably not efficiently utilized. To extend the sensitizer molar extinction performance to wider range spectrum, numerous efforts are made on the synthesis of new dyes, structural modification of existing dyes, and co-sensitization by couples of various dyes. However, the foregoing methods may come up against some problems, for example, the compatible property with the existing working components in DSSC such as organic solvents and TiO_2 nanoparticles. In this study, we proposed a facile method which efficiently enhanced the PCE of DSSC through the Förster resonance energy transfer (FRET) effect without changing the existing operation mechanism of commercial N719 dye. A naphthalimide derivative 6-(6-(4-methylpiperazin-1-yl)-1,3-dioxo- 1H-benzo[de]isoquinolin-2(3H)-yl) hexanol, called N-OH which was a pH sensor commonly used in the biomedical field, was synthesized and added into the TiO_2 mesoporous film together with the N719 dye molecules by a two-step soaking process. The N-OH fluorophore absorbed the UV light around the 397 nm wavelength and emitted the green light around the 513 nm wavelength. The emitted green spectrum was absorbed by the neighboring dye molecules through the FRET effect. Because the N719 dye molecules exhibited better IPCE response in the green spectrum range than in the UV spectrum range, the FRET effect enhanced the light harvesting of the N719 dye molecules. In other words, the FRET effect converted the UV light into more useful green light for the N719 dye absorption and accordingly enhanced the PCE of DSSC. Electrochemical impedance spectroscopy (EIS) analysis was performed to understand the charge transfer behaviors in the DSSC. The EIS results indicated that the N-OH fluorophore doping together with the N719 dye molecules inside the TiO_2 mesoporous film did not affect the charge transfer at the TiO_2/ N719 dye/electrolyte interface. The effect of the addition of acetic acid into the N-OH solution was also investigated, and the results indicated the acetic acid addition generally enhanced the fluorescent intensity of the N-OH fluorophore and therefore the PCE of DSSC. However, the concentration of acetic acid needed to be carefully controlled because too much acetic acid might occupy the TiO_2 sites through its carboxyl group which affected the N719 dye adsorption. By optimizing the experimental parameters including the N-OH concentration, the N-OH soaking time, and the acetic acid concentration, the best PCE of DSSC reached 9.07 % with a short-circuit current density of 16.8 mA/cm^2, an open-circuit voltage of 0.743 V, and a fill factor of 0.725, which was better than the typical DSSC without the N-OH fluorophore doping (8.4%).

並列關鍵字

Förster resonance energy transfer ； fluorophore ； absorption