Electron transportation and optical properties of micro-structure TiO₂ films: applied in dye-sensitized solar cells

Abstract

Micro-structure of TiO₂ films in dye-sensitized solar cells (DSSCs) can affect light absorption and electron transportation that impact on the characteristics of current-voltage (J-V). In this paper, films with different surface area, pore size and porosity were obtained by adding different ratio of ethyl cellulose (Ec-S) to pastes, and a photo-electric conversion efficiency (η) of 7.55% with a short-circuit current density (J_sc) of 16.81 mA·cm^-2 was obtained when the ratio of Ec-S was 10∶5. BET results showed that film with this optimum ratio had the most suitable pore size and surface area for good properties of photovoltaic, which had a low reflectivity and high transmission rate, and the efficiency of light utilization was improved. Moreover, measurements by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) implied that the electron transport time (τ_d) increased as the content of Ec-S increased, which was related to the larger surface area. Results of steady-state cyclic voltammetry indicated that diffusion-limited current density (J_lim) of I_3^{-} in TiO₂ film increased with its porosity, which revealed that the transportation of redox mediators in the electrolyte was speeded up.

Keywords

micro-structure / porosity / optical property / electron transport / dye-sensitized solar cell (DSSC)

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Acknowledgements

This work was financially supported by the National Basic Research Program of China (No. 2011CBA00700), the National High Technology Research and Development Program of China (No. 2009AA050603), funds of the Chinese Academy of Sciences for Key Topics in Innovation Engineering (No. KGCX2-YW-326), and the National Natural Science Foundation of China (Grant No. 20703046).

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg