Controlling dye aggregation, injection energetics and catalytic recombination in organic sensitizer based dye cells using a single electrolyte additive

Abstract

Organic dyes have been used extensively in recent years as sensitizers for Dye Sensitized Solar Cells (DSSCs) due to their high molar extinction coefficients, straightforward synthetic routes and readily available synthetic precursors. Though widely used, these dyes have some drawbacks, such as a tendency to aggregate and to catalyze electron recombination, thereby compromising both photovoltage and photocurrent. To circumvent the above-mentioned shortcomings of organic dyes, we adopt a novel strategy based on the addition of substituted benzene co-solvents to the electrolyte. This approach has several advantageous features which enhance cell performance: first, the substituted benzene molecules penetrate the dye layer to form stable complexes, thereby screening the excited state quenching and increasing the charge separation efficiency in the cell. Second, the benzene additive inhibits the catalytic recombination processes between electrons in TiO₂ and the oxidized electrolyte, which increases the device V_oc. Finally, despite not being adsorbed to the surface, the benzene derivatives shift the TiO₂ conduction band positively, which improves the J_sc. SQ-1 sensitized DSSCs obtained using this strategy show a J_sc of 10.7 mA cm⁻², a V_oc of 657 mV and a total efficiency of 4.7% which is the best efficiency reported so far for such dyes in DSSCs.