Different surface treatments of hydrothermally synthesized titania nanotubes for the improvement of the dye-sensitized solar cells
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Date
2015
Authors
Akilavasan, J.
Journal Title
Journal ISSN
Volume Title
Publisher
University of Peradeniya
Abstract
Dye-sensitized Solar Cells (DSCs) are considered as a promising alternative system for con ventional silicon based solar cells with economically viable cost. One of the major factors limiting the power conversion efficiency (TJ) of the DSC is the charge carrier recombination which is mainl y due to the random orientation of the nanocrystalline Ti0 2 particles. Therefore, the main objective of this stud y is to introduce one-dimensional Ti0 2 nanotubes as the electron transport medium in the fabricat ion of DSCs to reduce the charge carrier recombination. For th is purpose, Ti02 nanotubes with diameter of ~ 10 nm and length 'of ~ 250 nm were successfully synthesized via hydrothermal treatment ofTi02 nanoparticles and different surface treatment methods were investigated for the improvement of the DSCs.
DSCs fabricated using hydrothermally synthesized Ti02 nanotubes treated with 0.5 M TiCl 4 and sensitized with N7l9 dye showed the '1 of 7.6 % at AM 1.5 G illumination w ith iodide/tri-iodide electrolyte. In this work, the effect of different TiCI 4 concentration treatment on both Ti02 nanotubes and Ti02 nanoparticles were investigated. The effect of TiCl4 treatment is more significant for Ti02 nanotubes than Ti02 nanoparticles and the TiCI 4 surface treatment step is crucial for the enhancement of the solar cell performance. The electron transport resistance, electron life-time and charge recombination properties of bare and TiCl4 treated Ti02 nanotubes were investigated by electrochemical impedance method (EIS) .
Further surface treatment of the Ti02 nanotubes was done with the MgO coating. The DSC s fabricated using Ti02 nanotube electrode treated with 0.02 M Mg2+ solution showed the highest TJ of 8.9 % while the bare electrode showed the TJ of 5.4 %. Drop and Imm erse treatment methods were inve stigated to optimise the MgO coating on Ti0 2 nanotubes. Drop method showed the better passivation on T i02-nanotubes to suppress the charge carrier recombination than the immerse method .
Finally, a composite electrode consists of both Ti02 nanotubes and nanoparticle film s were fabricated on a conductive glass substrate using electrophoretic deposition and doctor-blade methods respectively. DSC fabricated using the composite photoelectrode show ed the '1 of 9.2 %. The efficiency enhancement was mainly due to the enhancement of charge collection efficiency and better Iight scattering effects which were confirmed by charge tran sport parameters measured by EIS and the diffuse reflectance spectra. EIS ana lyses also revealed that the composite incur smaller charge transport resistances when compared with those in the Ti0 2 nanotubes and Ti0 2 nanoparticle films.
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Keywords
Dye-sensitized solar cells , Solar cells , Titanium dioxide , Titania nanotubes