| Summary: | 碩士 === 大葉大學 === 醫療器材設計與材料碩士學位學程 === 105 === In the present study, research work can be divided into two parts.Firstly, Graphene oxides (GrO) were synthesized by modified Hummers method with natural graphite as the raw materials, following by chemical analysis and materials characterization for the as-synthesized samples by Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Inductive Couple Plasma Optical Emission Spectroscopy (ICP-OES) and FE-SEM, etc.. In the second part, The GrO dispersion was prepared to deposit on ITO substrate by asymmetric AC electrophoretic deposition, designated as GrO(AAC-EPD/ITO), as the counter electrode (CE) for the dye-sensitized solar cells (DSSC).The electrochemical properties of the electrodes were explored by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) whereas thephotovoltaic characteristics of the as-fabricated DSSCs were recorded, accordingly.To explore the platinum (Pt) deposits as the electro-catalysts for the CE of DSSCs, three different approaches were employed to prepare Pt-based CE on ITO substrates: by sputtering of Pt thin film, Pt(sputtering)/ITO; by impregnationwith Pt precursor solution, Pt(impregnation)/ITO; and by asymmetric AC electrodeposition, Pt(AAC-ED)/ITO. Similarly, both the electrochemical properties of the electrodes and the photovoltaic characteristics of the as-fabricated DSSCs were examined.
Under standard illumination (AM 1.5), the highest energy conversion efficiency of the as-fabricated cell by applying rGO(AAC-EPD/ITO) as CE was only 1.20% with VOC = 0.701 volt, JSC = 5.20 mA/cm2, FF = 0.330. Equivalent circuit analysis (EQC) results reveal that the charge transfer resistance at the electrolyte/GrO interface was exceedingly large, indicating that the catalytic activity of GrO(AAC-EPD)/ITO is insufficient. In contrast, all Pt-based CEs in the present study exhibits substantial high catalytic activity for the iodide/triiodide redox system.Under AM 1.5 illumination, the conversion efficiency of DSSCs with the Pt-based CEs is, from high to low, 4.7% (Pt(AAC-ED)/ITO), 3.87% (Pt(impregnation)/ITO) and 3.25% (Pt(sputtering)/ITO). EQC results reveals that by Pt(impregnation)/ITO, the charge transfer resistance at the electrolyte/GrO interface was smallest, while those made by asymmetric AC electrodeposition exhibits largest charge transfer resistance at counter electrode. It is noteworthy that, by cyclic voltammetry, the latter (Pt(AAC-ED)/ITO) shows best electro-catalytic activity. It could be reasoned that although the CEs made with AAC-ED had large charge transfer resistance owing to the low Pt content, as confirmed by ICP-OES analysis, the sub-nano Pt clusters as exhibited by the SEM photographs render high catalytic surface area at the electrode, leading to high electro-catalytic activity which compromise the adverse effect of the high impedance.
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