Dispersion of graphene in organic solvents and their use for improving efficiency of dye- and quantum dot-sensitized solar cells

• Direct exfoliation of graphite in organic solvents.
• Dispersion of pristine graphene in organic solvents.
• Characterization by microscopy, XPS and Raman spectroscopy.
• Incorporation in sensitized solar cells of three different types.
• Enhancement of solar cell efficiency by tiny quantities of pristine graphene.

Pristine graphene was directly suspended in a variety of organic media, which are used either as electrolyte solvents or deposition media in sensitized solar cells. Dispersion occurred directly through sonication-assisted exfoliation of graphite powder, without adopting the oxidative approach involving intermediate formation of graphene oxide and its subsequent reduction. The concentration of the thus dispersed graphene was relatively low, in the order of a few tens of micrograms per ml, but it was very effective in increasing the efficiency of sensitized solar cells. Dispersed graphene was first deposited on solid substrates and was extensively characterized by TEM, SEM, XPS and Raman spectroscopy. Also dispersed graphene has been introduced in liquid-electrolyte and gel-electrolyte dye-sensitized solar cells by means of sulfolane/3-methoxypropionitrile mixtures and in quantum dot sensitized solid-state solar cells by means of chlorobenzene-based suspensions. Increase of cell efficiency in the presence of the above tiny quantities of graphene was very large, particularly in the case of solid state cells where more than 3-fold increase of efficiency was observed.

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