Broadband energy transfer to sensitizing dyes by mobile quantum dot mediators in solar cells.

The efficiency of solar cells depends on absorption intensity of the photon collectors. Herein, mobile quantum dots (QDs) functionalized with thiol ligands in electrolyte are utilized into dye-sensitized solar cells. The QDs serve as mediators to receive and re-transmit energy to sensitized dyes, thus amplifying photon collection of sensitizing dyes in the visible range and enabling up-conversion of low-energy photons to higher-energy photons for dye absorption. The cell efficiency is boosted by dispersing QDs in electrolyte, thereby obviating the need for light scattering or plasmonic structures. Furthermore, optical spectroscopy and external quantum efficiency data reveal that resonance energy transfer due to the overlap between QD emission and dye absorption spectra becomes dominant when the QD bandgap is higher than the first excitonic peak of the dye, while co-sensitization resulting in a fast reduction of oxidized dyes is pronounced in the case of lower QD band gaps.