Application of Anion-Physisorbed Multi-walled Carbon Nanotubes on Photoelectrode for Dye-sensitized Solar Cells
Date Issued
2012
Date
2012
Author(s)
Yeh, Chia-Wen
Abstract
In this thesis, multi-walled carbon nanotubes(MWCNTs) physisorbing anionic and nonionic dispersing agent for surface modification were dispersed in TiO2 thin film utilizing as a photoelectrode for dye-sensitized solar cells (DSSCs). Anionic dispersing agents such as sodium dodecylbenzenesulfonate(SDBS) and poly (sodium4-styrenesulfonate) (NaPSS) with molecular weight of 9350, 20800 and 70000 were used to disperse MWCNTs. We also chose amphiphilic triblocks of PEG-PPG-PEG as nonionic surface modifying agents, such as P123、F68、and F108. The procedure for surface treatment MWCNTs is as following. Surface modifying agents and MWCNTs were dispersed and adsorbed in water by sonication. After fully adsorption, the solution was filtrated to remove the extra dispersing agents. After drying, the surface-modified MWCNTs were obtained. From the results of UV-vis spectroscopy, zeta potential and dynamic light scattering measurements, anionic surface modifying agents have better dispersing power than nonionic surface modifying agents because anionic agents have benzene ring to physisorb onto CNTs via π-π stacking. Furthermore, the electrostatic repulsion from the SO3- groups leads to the charge stabilization of MWCNTs compared to the nonionic agents. Then we dispersed anion-physisorbed MWCNTs onto the TiO2 system. From the XRD results, we found that TiO2 can crystallize into more anatase structures in the presence of MWCNTs. The resulting materials also had higher light transmittance. For the performance of DSSCs with MWCNT-TiO2 photoelectrode, the addition of 0.03wt% CNT to the TiO2 film could enhance the Jsc of DSSC from 18.65mA/cm2 to 19.26 mA/cm2. And the increase of Jsc resulted in higher power conversion efficiency and better charge collection efficiency because of good conductivity of MWCNTs, more anatase TiO2 crystal structures and higher light transmittance of the MWCNT-TiO2 films. The best Jsc and power conversion efficiency of 20.68mA/cm2 and 8.42% were achieved with MWCNT(70000) dispersing in TiO2. In addition, in order to enhance the light harvesting efficiency, the larger size of TiO2 scattering layer was deposited on the outer layer of MWCNT-TiO2 thin films. After addition of the scattering layer, the Jsc and power conversion efficiency were both increased to 21.44mA/cm2 and 8.84%.
Subjects
Multi-walled carbon nanotube
Physical adsorption
Dye-sensitized solar cells
TiO2 thin films
Type
thesis
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