(346g) Differences in the Performance Characteristics of Dye-Sensitized Solar Cells Using Aqueous and Organic Electrolytes: Insights from Atomistic and Molecular Simulations

Visible-light-absorbing dyes adsorbed on broad-band gap oxide semiconductors such as titania have shown remarkable power conversion efficiencies when used as photoanodes in dye-sensitized solar cells (DSSCs). The dye molecules oxidize upon illumination, transferring the electrons to the titania particles. A redox electrolyte, such as an acetonitrile solution of iodide and triiodide, is required to regenerate the oxidized dye and maintain continuity in the photovoltaic activity. DSSC-based photoelectrochemical cells are being explored to desalinate brackish water and produce potable water [1]. Applications such as these preclude the use of toxic and volatile solvents in the preparation of the redox electrolyte. Water is the preferred solvent. However, DSSCs show a significant performance loss when water is used instead of acetonitrile as the electrolyte solvent.

This work used atomistic and molecular simulations of selected dyes (known to exhibit photovoltaic activity in experiments) to gain fundamental insights into the differences between the aqueous and organic electrolyte interfaces. Critical optical and electronic properties of the dyes were predicted using density functional theory (DFT) calculations. Also, a molecular dynamics (MD) model was developed to study the behavior of the dye/titania interface in water and acetonitrile. Based on the DFT calculations, the absorption spectra and electronic properties of the implicitly solvated dyes were similar in the two solvents. However, MD simulations presented some fundamental differences between the dye exposed to water vs. acetonitrile interfaces. These include differences in the structural re-orientation of the dye moieties, the solvation behavior of the dye functional groups, and the transport properties of the electrolyte ions. The computational framework described in this work would be helpful in identifying ideal materials for the DSSC and rationally designing the electrode-electrolyte interface using molecular predictions.

Reference:

[1] Mohandass, G.; Kim, T.; Krishnan, S. Continuous Solar Desalination of Brackish Water via a Monolithically Integrated Redox Flow Device. ACS ES&T Engineering 2021, 1, 1678−1687. https://doi.org/10.1021/acsestengg.1c00266