染料敏化太陽能電池(Dye Sensitized Solar Cell，DSCs)具有低成本、高產量的優勢，目前相當地受到矚目。白金(Platinum，Pt)被廣泛利用在DSCs的對電極；但是，Pt為稀有金屬之一，價格也是目前最昂貴的金屬。然而，若要使DSCs大面積製作或普及化，使用Pt當對電極將會提高其製作成本。現今已找到替代材料當作DSCs的對電極，主要被廣泛應用的材料為碳基材料。本論文使用的碳基材料是將奈米碳管紙(Buckypaper，BP)利用在染料敏化太陽能電池對電極，並探討其在不同光強度下與Pt染敏電池的差異性，以及探討DSCs內部載子傳輸的行為。由於BP具有高表面積，因此可提升電荷還原電解液的速率。因此，本研究希望透過BP來取代對電極材料(Pt)於DSCs。實驗結果得知，DSCs從電化學阻抗頻譜(Electrical impedance spectrum，EIS)分析中發現，BP-CE 的DSC (BP-DSC)於對電極處的電子轉移頻率(Charge transfer of frequency，fct)為9357 Hz，而Pt-CE的DSC (Pt-DSC)的fct為698 Hz；在光電極與電解液界面，BP-DSC的電子電洞對再結合的頻率(Recombination of frequency，frec)為1.1 Hz，而Pt-DSC的frec為1.7 Hz；由於BP-DSC中的BP與 離子的電子轉移頻率較高(對應到對電極與 離子有較高的還原速率)，使得其電子電洞對再結合的程度較低。從循環伏安法(Cyclic Voltammetry，CV)分析中發現，BP作為電極的還原電流為-0.956 mA，而Pt電極的還原電流為-0.083 mA。從EIS與CV的結果，BP有較高的還原速率及還原電流，原因在於BP具有高表面積的特性，使得DSCs電解液中的 離子能有效地被還原成 離子。由於BP-DSCs有較高的還原速率，其在漏電程度相較Pt-DSCs低，BP-DSC在Voc及FF的表現也較Pt-DSC高。因此，隨著照光強度增加，BP-DSCs的能量轉換效率(PCE)相較於Pt-DSCs的PCE高，指出BP-DSCs適用於高照度環境。本實驗成功地將BP應用在DSCs的對電極上，達到100 %取代傳統Pt對電極的目的。 Photoelectrochemical dye-sensitized solar cells (DSCs) have attracted much interest in the field of sustainable green energy. However, their counter electrodes (CEs) usually fabricated by the noble metal Pt. To obtain the alternative Pt-Free CEs for DSCs is desirable for the wide deployment of DSCs.Buckypapers (BPs) are prepared in the random and highly interpenetrative configuration of multi-walled carbon nanotubes (MWCNTs), and it has high porosity and conductivity. In this study, BPs are unitized as the CEs for DSCs. From the results of electrochemical impedance spectroscopy (EIS) analysis, the charge transfer rate (fct) of BP-DSC (9357 Hz) is greater than that of Pt-DSC (698 Hz) and the recombination rate (frec) of BP-DSC (1.1 Hz) is lower than that of Pt-DSC (1.7 Hz), indicating the BP-CE provides an efficient reduction and suppresses the recombination in DSC. For the results of cyclic voltammetry (CV), the reduction current [I(Red1)] of BP electrode (-0.956 mA) is greater than that of Pt electrode (-0.083 mA). The results of EIS and CV measurement reveal that the reduction reaction of BP electrode is improved because of its extreme electroactive surface area, and this improvement suppresses the recombination rate in DSCs. Accordingly, BP-DSCs show a high open-circuit voltage (Voc) and fill factor (FF) in power-dependent J-V characterization. As the results, BP-DSCs exhibit a higher enhancement in PCE than that of Pt-DSCs and show the PCE comparable to Pt-DSCs under 100 mW/cm2 illumination.
