The main limit to the efficiency of a solar cell is its ability to harvest with equal efficacy all of the Sun spectrum. The down-shifting technique tries to overcome this problem by employing fluorescent molecules to tune the spectrum that reaches the cell, shifting higher energy photons to wavelengths where the cell absorption reaches a maximum. For this purpose we have synthesized a series of substituted 1-phenylimidazo[1,5-a]pyridine trough the reaction of various aromatic aldehydes with phenyl(pyridin-2-yl)methanone and ammonium acetate in hot acetic acid. The photophysical properties of these easily and economically obtained compounds were studied by means of absorption and emission spectra, quantum yields and solvatochromism in order to show their differences depending on the side group (R) attached to the main fluorophor. Intense absorption maxima were noted at ca. 310-350 nm and emission maxima were noted at ca. 470-550 nm with quantum yield from 6,4% to 38,5 % and Stokes shifts from 97 nm to 186 nm. It is demonstrated that this class of fluorophores can collect UV/violet photons and shift them into the visible, therefore they are suitable for down-shifting applications.
1-phenylimidazo[1,5-a]pyridine: synthesis and characterisation of compounds with large Stokes shift for solar applications
VOLPI, GIORGIO;SACCONE, DAVIDE;I. Benesperi;BAROLO, CLAUDIA;VISCARDI, Guido
2013-01-01
Abstract
The main limit to the efficiency of a solar cell is its ability to harvest with equal efficacy all of the Sun spectrum. The down-shifting technique tries to overcome this problem by employing fluorescent molecules to tune the spectrum that reaches the cell, shifting higher energy photons to wavelengths where the cell absorption reaches a maximum. For this purpose we have synthesized a series of substituted 1-phenylimidazo[1,5-a]pyridine trough the reaction of various aromatic aldehydes with phenyl(pyridin-2-yl)methanone and ammonium acetate in hot acetic acid. The photophysical properties of these easily and economically obtained compounds were studied by means of absorption and emission spectra, quantum yields and solvatochromism in order to show their differences depending on the side group (R) attached to the main fluorophor. Intense absorption maxima were noted at ca. 310-350 nm and emission maxima were noted at ca. 470-550 nm with quantum yield from 6,4% to 38,5 % and Stokes shifts from 97 nm to 186 nm. It is demonstrated that this class of fluorophores can collect UV/violet photons and shift them into the visible, therefore they are suitable for down-shifting applications.
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