Synergistic effect between anatase and rutile TiO2 nanoparticles in dye-sensitized solar cells.
ABSTRACT A synergistic effect between anatase and rutile TiO2 is known, in which the addition of rutile can remarkably enhance the photocatalytic activity of anatase in the degradation of organic contaminants. In this study, mixed-phase TiO2 nanocomposites consisting of anatase and rutile nanoparticles (NPs) were prepared for use as photoanodes in dye-sensitized solar cells (DSSCs) and were characterized by using UV-vis spectroscopy, powder X-ray diffraction and scanning electron microscopy. The addition of 10-15% rutile significantly improved light harvesting and the overall solar conversion efficiency of anatase NPs in DSSCs. The underlying mechanism for the synergistic effect in DSSCs is now explored by using time-resolved terahertz spectroscopy. It is clearly demonstrated that photo-excited electrons injected into the rutile NPs can migrate to the conduction band of anatase NPs, enhancing the photocurrent and efficiency. Interfacial electron transfer from rutile to anatase, similar to that in heterogeneous photocatalysis, is proposed to account for the synergistic effect in DSSCs. Our results further suggest that the synergistic effect can be used to explain the beneficial effect of TiCl4 treatment on DSSC efficiency.
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ABSTRACT: In order to enhance the electron transport on the photoelectrodes of dye-sensitized solar cells, one-dimensional rutile nanorods were prepared using electrospun TiO2 nanofibers. The grain size of the nanorods increased with increasing temperature. Electrochemical impedance spectroscopy measurements revealed reduced interface resistance of the cells with the one-dimensional rutile nanorods due to the improved electron transport and the enhanced electrolyte penetration. Intensity-modulated photocurrent/photovoltage spectroscopy showed that the one-dimensional rutile nanorods provided the electrons with a moving pathway and suppressed the recombination of photogenerated electrons. However, an excessive quantity of rutile nanorods created an obstacle to the electrons moving in the TiO2 thin film. The photoelectrode with 7 wt.% rutile nanorods optimized the performance of the dye-sensitized solar cells.Nanoscale Research Letters 01/2013; 8(1):37. · 2.52 Impact Factor
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ABSTRACT: High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO2 nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO2 DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO2 electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO2 nanofibers are achieved by increasing sintering temperature above 500 [degree sign]C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-mum-thick mixed-phase (approximately 15.6 wt.% rutile) TiO2 nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01 % and 17.3 mA cm-2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO2 nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.Nanoscale Research Letters 01/2013; 8(1):9. · 2.52 Impact Factor
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ABSTRACT: The photoexcited electron injection dynamics of free-base and metallo-derivatives of tris(pentafluorophenyl)porphyrins bound to TiO2 and SnO2 nanoparticle surfaces have been investigated using Time-Resolved Terahertz Spectroscopy (TRTS). The metallo-derivatives include Zn(II), Cu(II), Ni(II), and Pd(II). For the TiO2-porphyrin assemblies, electron injection from the photoexcited dye to the semiconductor occurs only when using the zinc derivative as the sensitizer because it is the only dye studied in this report with long-lived excited states higher in energy than the TiO2 conduction band edge. All of the dyes, however, have excited-state energies above the SnO2 conduction band edge, and the electron injection rates vary widely from 0.4 – 200 ps depending on the sensitizer. For the SnO2-porphyrin assemblies, electron injection is strongly influenced by competition with alternate deactivation routes that are accessible following Soret band excitation. These results offer thermodynamic and kinetic considerations for designing improved high-potential porphyrin photoanodes with applications to solar-powered water oxidation.The Journal of Physical Chemistry C 09/2013; · 4.81 Impact Factor