Enhance the Optical Absorptivity of Nanocrystalline TiO₂ Film with High Molar Extinction Coefficient Ruthenium Sensitizers for High Performance Dye-Sensitized Solar Cells

Abstract

We report two new heteroleptic polypyridyl ruthenium complexes, coded C101 and C102, with high molar extinction coefficients by extending the π-conjugation of spectator ligands, with a motivation to enhance the optical absorptivity of mesoporous titania film and charge collection yield in a dye-sensitized solar cell. On the basis of this C101 sensitizer, several DSC benchmarks measured under the air mass 1.5 global sunlight have been reached. Along with an acetonitrile-based electrolyte, the C101 sensitizer has already achieved a strikingly high efficiency of 11.0−11.3%, even under a preliminary testing. More importantly, based on a low volatility 3-methoxypropionitrile electrolyte and a solvent-free ionic liquid electrolyte, cells have corresponding >9.0% and ∼7.4% efficiencies retained over 95% of their initial performances after 1000 h full sunlight soaking at 60 °C. With the aid of electrical impedance measurements, we further disclose that, compared to the cell with an acetonitrile-based electrolyte, a dye-sensitized solar cell with an ionic liquid electrolyte shows a feature of much shorter effective electron diffusion lengths due to the lower electron diffusion coefficients and shorter electron lifetimes in the mesoporous titania film, explaining the photocurrent difference between these two type devices. This highlights the next necessary efforts to further improve the efficiency of cells with ionic liquid electrolytes, facilitating the large-scale production and application of flexible thin film mesoscopic solar cells.