電化學沉積法製備不同形貌奈米鉑電極於染料敏化太陽能電池之應用

Abstract

在本論文中，我們使用電化學沉積法(CED-Pt)在無燒結製程中製備鉑對電極應用於染料敏化太陽能電池(DSSC)。藉著 (1)無機鹽類的添加，(2)前驅物濃度以及(3)沉積圈數的調整，來改變鉑對電極的表面形貌，從奈米團簇、奈米片、奈米草乃至於奈米花，我們皆可藉實驗條件的控制成長出均一的奈米形貌，並製備在導電玻璃上，其中尤以奈米草(Nano-grass)鉑對電極有著立於基材上的二維片狀結構最為特殊。利用電化學交流阻抗分析法，我們發現奈米草對電極有著優異的電荷轉移阻抗(Rct= 0.3 Ω)；利用循環伏安法量測其催化效能，我們發現CED-Pt比起傳統的熱還原鉑電極(TD-Pt)及真空濺鍍鉑電極(SD-Pt)可以得到較大的I3-還原波峰電流: CED-Pt(Ipc2 = 1.43 mA cm-2) > TD-Pt ( Ipc2 = 1.16 mA cm-2 ) > SD-Pt (Ipc2 = 1.14 mA cm-2)，以及較小的氧化還原峰電位差(|ΔE | = 0.31V)。此外，其片狀結構除了具高催化效能外同時亦具有高反射率(reflectivity ~50%)，可以有效散射入射光，增加光捕捉率。我們可以知道鉑奈米草電極有著優異的電催化活性及高反射率，利用所述此電極進行元件光電轉換效率的量測，可以發現其效率可以達到9.61 %，比起傳統TD-Pt元件 (η = 8.55 %) 提升12 %，尤以光電流及填充因子的提升最為明顯。最後搭配高效率的陽極材料與Z907染料製備成高效率的DSSC元件進行效率最佳化的測試，更將效率提升至10.6 % 的新里程碑。

Cyclic electro-deposition (CED) is a cost-effective tool to synthesize nanostructures with a solution process, controllable morphology and high purity. In this thesis we report novel platinum nanostructures fabricated according to CED in solution containing H2PtCl6 precursor and NaNO3. Remarkable Pt nanostructures – from nanocluster, nanosheet , nanograss to nanoflower – were produced through morphological control via variation of either period of CED scans or concentration of the precursor. Pt films with uniform nanograss structure have great electro-catalytic performance (electron-transfer resistance = 0.3 Ω) and intrinsic light-scattering (reflectivity~50%), perfectly suitable for use as counter electrodes for dye-sensitized solar cells (DSSC). According to the electro-catalytic activity determined by cyclic voltammetry , the CED-Pt has larger I3□□reduction peak current (Ipc2 = 1.43 mA cm-2) compared to the Pt electrodes fabricated by vacuum sputtering deposition (Ipc2 = 1.14 mA cm-2) and conventional thermal decomposition (Ipc2 = 1.16 mA cm-2) method. The large cathodic peak current of CED-Pt and the small potential difference, (|ΔE| =0.31V) between Epc2 and Epa1 indicates its superior electro-catalytic performance. The DSSC device made with the Pt-nanograss counter electrode attained efficiency η = 9.61 % of power conversion, which is 12% enhanced from that fabricated according to a conventional thermal decomposition method (η = 8.55 %) under similar experimental conditions. The best performance of the DSSC device made with the Pt-nanograss counter electrode was achieved at the TiO2 active layer with thickness of 22 □m, giving JSC = 19.431 mA cm-2, VOC = 0.754 V, FF = 0.70, and eff = 10.6 %.