Fabrication and characterization of high efficiency dye-sensitized solar cell based on TiO₂nanofiber photoanode

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Fabrication and characterization of high efficiency dye-sensitized solar cell based on TiO₂nanofiber photoanode


Author: Yang, Lijun
Title: Fabrication and characterization of high efficiency dye-sensitized solar cell based on TiO₂nanofiber photoanode
Degree: Ph.D.
Year: 2013
Subject: Dye-sensitized solar cells.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xxi, 150 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2681813
URI: http://theses.lib.polyu.edu.hk/handle/200/7372
Abstract: Dye sensitized solar cell (DSSC) offers the advantages of low-cost, high-efficiency, and large flexibility in color, shape and transparency. However, the highest power conversion efficiency to-date is 15% for a small size device, which is still too low to be considered as a commercially viable technology. The power conversion efficiency of the photovoltaic device can be expressed as the product of three factors -the light absorption efficiency, the charge injection efficiency, and the charge collection efficiency. Improvement in any of these factors alone, or in combination, could certainly improve the performance of the DSSC device. In this study, the one-dimensional nanostructure made out of TiO₂ nanofibers has been adopted as the photoanode of the DSSC, which provides several advantages. The one-dimensional nanofiber configuration provides a direct path for transport and collection of electrons. In addition, a large surface-to-volume ratio that favors dye adsorption can be attained as the TiO₂ nanofiber is composed of closely packed anatase single crystallites with sizes less than 10 nm. In consequence, a high efficiency of 7.14% has been obtained in our DSSC device using a TiO₂ nanofiber photoanode. To further improve the efficiency of the DSSC based on TiO₂ nanofiber photoanode, two different novel scattering configurations have been introduced, in the photoanode to improve the light harvesting efficiency. A high efficiency of 8.71% and 9.28% has been achieved, respectively, with the polydispersed-size TiO₂ nanoparticles and the large-diameter TiO₂ nanofibers as the scattering layer. Other than trapping the incident light, another improvement has been made on light harvesting by adopting the dye cocktail approach. A novel design of core-shell photoanode where a thin-shell of infrared dye is deposited on the core of sensitized TiO₂ nanofiber has been developed. Specifically, the ruthenium-based dye (N719) sensitized TiO₂ nanofibers are wrapped by thin-shell of copper phthalocyanine (CuPc). In this architecture, photons are absorbed by the infrared dye and undergo charge transfer to the sensitizing dye, and subsequently to the TiO₂. This approach not only broadens the absorption spectrum, it also further suppresses the recombination of electrons and the electrolytes, which is a common limiting factor on performance of DSSC using TiO₂. The highest efficiency attained is 9.48%. Finally, to enhance the charge transport and collection efficiency, multiwall carbon nanotube is incorporated in the TiO₂ nanorods, which make up the photoanode. The multiwall carbon nanotubes inside the nanorods can effectively transport and collect photogenerated electrons and reduce the recombination, both of which improve the efficiency of the device. The maximum efficiency achieved is 10.24% accompanied with a high fill factor of 74%.

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