| Summary: | 博士 === 國立成功大學 === 化學工程學系 === 105 === In this dissertation, the main purposes are to improve the preparation method of quantum dot (QD) sensitizers, and to develop highly efficient carbon black (CB)-related counter electrodes.
Quantum-dot-sensitized solar cells (QDSSCs) are often fabricated by the successive ionic layer adsorption and reaction (SILAR) process owing to this method’s simplicity and effectiveness; however, the distribution of QD sensitizers is usually inhomogeneous across the entire TiO2 film, thus affecting the penetration of electrolytes inside the mesoporous structure and the photovoltaic performance of relevant solar cells. In Chapter 3, a potential-assisted (PA) method is developed to fabricate CdSe-sensitized photoelectrodes. Applying a negative bias facilitates the penetration of cadmium ions directly into the TiO2 nanoparticulate structure, resulting in significant deposition of CdSe QDs. Compared to a CdSe thin film fabricated by the SILAR process, the PA-derived thin film exhibits strikingly improved QD distribution, and more importantly, the corresponding QDSSC reveals suppressed charge recombination and better cell performance. A strategy of combining the PA method and the SILAR process further increases the conversion efficiency, reaching 4.30%. In addition, the effect of sodium acetate (NaAc) additive in the SILAR process on the CdS deposition is carefully studied in Chapter 4. It is found that the CdS QD deposition is accelerated by introducing NaAc additives into the cationic precursors to adjust their apparent pH values; the dependence of the QD deposition rate on the pH value is therefore obtained. It is also observed that a more uniform QD distribution throughout the entire TiO2 film is attained for the CdS photoelectrode fabricated with fast QD deposition; the QDSSC assembled using this CdS electrode shows a conversion efficiency of 3.11%. By performing an ionic exchange to broaden the spectral region for light harvesting, the efficiency is further boosted to 4.51%.
A facile method is proposed in Chapter 5 to fabricate carbon black/copper sulfide (CB/CuxS) composite counter electrodes for QDSSCs. A simple combination of spin-coating and sulfidation creates mesoporous CB thin films with an accumulation of CuxS catalysts. The formation mechanism of CuxS catalysts during the sulfidation is thoroughly investigated in this chapter. Regarding the electrocatalytic activity, the CB/CuxS thin film fabricated by a single coating is comparable to the common copper sulfide prepared by chemical bath deposition. The electrocatalytic activity of the CB/CuxS composite is found to be directly related to the coating times employed. A conversion efficiency of 5.62% is achieved for the CdS/CdSe QDSSC using a CB/CuxS counter electrode fabricated with three coating times. Moreover, in Chapter 6, a commercial CB material is utilized to fabricate highly electrocatalytic yet low-cost counter electrodes for dye-sensitized solar cells (DSSCs), based on the cobalt complex electrolyte. Both the heat treatment and the amount of CB deposition dominate the electrochemical properties of CB thin films. The electrocatalytic activity of a well-prepared CB thin film is superior to that of the commonly used Pt. This CB material is also introduced to the fabrication of semitransparent catalytic thin films, to meet the demand of bifacial DSSC applications. When the Y123 dye sensitizer is employed, the DSSC equipped with a CB counter electrode shows a conversion efficiency of 8.81%. The feasibility of this carbon material as a highly efficient counter electrode catalyst in DSSCs is clearly demonstrated.
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