Dependence of porosity, charge recombination kinetics and photovoltaic performance on annealing condition of TiO₂ films

Abstract

Effect of annealing temperature, time of nanocrystalline TiO₂ film on porosity, electron transport/recombination and photovoltaic performance on dye-sensitized solar cell (DSSC) had been investigated in this article. Photocurrent density was slightly higher as annealing at 550°C compared to those of annealing at 450°C and 500°C under the given annealing time of 60€min, which was correlated with the amount of adsorbed dye. Thermogravimetric analysis showed there was a more weight loss between 500°C and 550°C, which revealed there were more sites for dye adsorption. Given the annealing temperature of 550°C, as annealing time varied from 60 to 90 and 120 min, results showed that the average size of pore and surface area decreased with longer annealing time, which deteriorated photocurrent density due to less dye loading. Electron diffusion rate remained almost unchanged regardless of annealing condition. However, electron recombination was influenced by annealing condition, it became slower with the increase of the annealing temperature under the given annealing time. In the contray, the electron recombination developed faster for the longer annealing time at a given annealing temperature. These results suggested that heat treatment of TiO₂ film at 550°C for 60 min in air would be the optimal annealing condition to achieve high efficiency DSSC.

Keywords

dye-sensitized solar cell (DSSC) / annealing conditions / surface area / porosity / electron life time

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Acknowledgements

This work was supported by the National Research Foundation of Korea grant funded by the Ministry of Education, Science and Technology of Korea (No. 2010-0014992), R31-2008-000-10029-0 (WCU Program), and the Korea Institute of Energy Technology Evaluation and Planning grant funded by the Ministry of Knowledge Economy (No. 20103020010010).

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