Facile fabrication of mesoporous photoanodes for dye-sensitized solar cells by microwave sintering of binder-free TiO₂ paste

We report that microwave (MW) treatment of binder-free TiO₂ paste coating is a facile method that can replace energy- and time-consuming high-temperature sintering processes in the production of mesoporous electrodes in dye-sensitized solar cells. For example, 5 min of MW treatment at 110 W is sufficient to produce a device with ∼4% efficiency. Conventional sintering at 375 or 450 °C for ∼2 h is required to make devices with a comparable efficiency. Compatibility with common plastic substrates is another advantage of MW-treatment process. Substrate temperature remained below 205 °C after 5 min of MW treatment. Analysis of impedance spectra using equivalent circuit model showed a correlation between device performance and resistances. Specifically, the sum of charge-transfer resistances at TiO₂–TiO₂ and Pt-electrolyte junctions, the Warburg component, and contact and FTO sheet resistances was in good agreement with the series resistance deduced from the fitting of measured J–V curves to an imperfect diode with parasitic resistances. Moreover, the discrepancy in variations of short-circuit current and charge-transfer resistance in TiO₂ electrodes indicated that MW sintering can be effective in reducing charge-transfer resistance without sacrificing dye adsorption. (paper)