Fabrication and Characterization of High Efficiency Dye-sensitized Solar Cells

Autor: Hsuan-Fu Wang, 王炫富
Rok vydání: 2010
Druh dokumentu: 學位論文 ; thesis
Popis: 98
The objective of this thesis is to fabricate and characterize high efficiency Dye-Sensitized Solar Cells (DSSC) at low cost to fit commercial purpose. The nanoparticles of TiO2 used for DSSC were synthesized and characterized to be anatase structure with size distribution from 20 nm to 30 nm. These results were verified by Density Functional Theory (DFT) method. The doping effect of impurities on the as prepared TiO2 electrode has also been investigated. We have found that the doping effect of carbon increases the photocurrent while both the photocurrent and photo-voltage are increased by doping Sr ion. To understand the effect of solvent on the stability of electrolytes used in DSSC other than acetonitrile, we prepared the electrolyte with three different solvent systems. Although Ethylene carbonate (EC) mixed with diethyl carbonate (DEC) at ratio of 1:1, and propylene carbonate mixed with acetonitrile at ratio of 4:1 showed better stability than acetonitrile, among them 3-methoxypropionitrile showed the best stability with the highest conversion efficiency. To obtain a better counter electrode, four different material and composition were used to compare with platinum. Among those counter electrodes the one fabricated with 100% graphite showed 60% performance of platinum. Smooth thin film of platinum depositing on surface of porosity graphite electrode obtained by Cyclic Voltammetry (CV) showed very cost effective with high active area per unit mass of platinum as counter electrode. A novel architecture of polytetrafluoroethylene (PTFE)-framed TiO2 electrodes is developed for dye-sensitized solar cells. The PTFE-framed TiO2 electrodes with various thicknesses ranging from 20 to 160 µm with high surface area have been successfully fabricated. From the Electrochemical Impedance Spectroscopy (EIS) measurement, the PTFE-framed TiO2 electrodes showed low internal resistance compared to the Polyethylene glycol (PEG) TiO2 electrode. The quantity of dye adsorbed on the PTFE-framed TiO2 electrodes increases with increasing thickness of film. The optimal energy conversion efficiency of 9.04% is achieved at film thickness of 60 µm. The PTFE-framed structure provides not only tunable film thickness but also a cost-effective way for mass production of reliable photo-electrodes. The charge transfer between N3 dyes and TiO2 electrodes has been investigated by Raman spectroscopy. The red shift of Eg(3) mode of the TiO2 electrode increases with increasing synthesis temperature of TiO2 nanoparticles used in compact layer. The red shift is also associated with its structure change and conversion efficiency. The maximum charge transfer between N3 dyes and TiO2 electrodes have been obtained for TiO2 nanoparticles, synthesized at 190oC. In the EIS measurements of the DSSC, the internal resistance of the cell decreases with increasing synthesis temperature, suggesting that the electron transfer from N3 dyes into TiO2 electrodes was improved when the TiO2 nanoparticles of compact layer synthesized at higher temperature. Moreover, we have demonstrated that Raman technique is a convenient and useful tool to investigate the charge transfer between N3 dyes and TiO2 electrode and thus the impact on the performance of DSSC. To compare the conversion efficiency with N3 four cheaper organic dyes were synthesized, and characterterized with UV-vis spectrophotometry, Cyclic Voltametry, and performance test respectively. The energy levels of the dyes were calculated using the UV-vis and CV data. These new dyes were used in DSSC and compared with N3 dyes. Although one of the organic dyes shows an overall conversion efficiency of 2.84% which is only 45% of N3 dyes performance, its low cost and metal-free content make the dye a potential candidate in future application. Finally, the technique to fabricate PTFE-framed TiO2 electrode can be used as a platform for other researchers working on related areas such as organic and solid state solar cell.
Databáze: Networked Digital Library of Theses & Dissertations
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