奈米管染料敏化太陽能電池的製備與鑑識及其交流阻抗圖譜的研究

Abstract

在本論文中我們提出利用電化學交流阻抗圖譜(EIS)之等效電路模型來探究元件特性。其中包括了傳統的Transmission Line (TL) model、簡化之S model、以及將二氧化鈦/染料/電解液界面以不完美電容來描述之S-CPE model。我們發現，S-CPE model模擬的結果其不論於相位角或阻抗百翻偏差值均最小。而元件於不同強度之AM 1.5模擬光源照射下，其短路電流(Jsc)與開路電壓(Voc)值皆隨光照度減弱增加，但其填充因子(FF)值則隨光照度減弱而增加，因為FF值隨光減弱而增加的幅度大於Voc，因此使得NT-DSSC元件隨光照度減弱，而呈現出較佳之光電轉換效能。 此外，我們於NT-DSSC元件未照光但施加與Voc值相當之偏壓，使元件TiO2層維持與太陽光照下相同之費米能階(EF)，再進行交流阻抗的量測，此時的量測結果可以將二氧化鈦/染料/電解液界面複雜的電子傳遞路徑排除，則其相對應的阻抗會與電子由傳至電解液的攔截有比較直接的關聯性。此法將DSSC中最複雜的界面簡單化，而使我們可以較容易地分析不同染料之間元件效能的差異性。

In this case, we report three equivalent circuit models- Transmission Line (TL) model, simplified(S) model, and S-CPE model- to simulate the data obtained from the electrochemical impedance spectroscopy (EIS) experiments of a NT-DSSC device. We found that the new established S-CPE model gave the best results among others in terms of the phase difference and the impedance percentage deviations. With the device under AM1.5 one-sun irradiation of varied intensities, we found that the short-circuit (Jsc) and open-circuit voltage (Voc) decrease upon decreasing the irradiation intensity, but the fill factor (FF) an opposite trend. Because the effect of the FF increasing is larger than Voc decreasing that of the overall efficiency of a NT-DSSC device slightly increases under low-intensity condition. On the other hand, we performed EIS measurements equivalent to Voc under dark condition to the TiO2 layer with the same Fermi level (EF) as one-sun irradiation. This approach excludes complex electron transfer processes in the TiO2/dye/electrolyte interface so that the corresponding impedance is related to only the electron III interception from TiO2 to electrolyte. This method simplifies the interfacial problem so that we can easily analyze the difference of the cell performance resulting from different photosensitizers.