Sun-light upconversion in multi-component organic systems: development towards application for solar cells outcome enhancement

The specific application of photon upconversion (UC) in photovoltaics is only possible when the following requirements are fulfilled: First, the excitation intensity necessary for effective UC needs to be small (as low as 1Wcm-2) − comparable with light intensities obtainable from the moderate concentrated sunlight. Second, the excitation spectral power density required for effective UC needs to be comparable with those of the terrestrial sun irradiation (in order of 100μWnm-1). Third, efficient UC must be obtained by non-coherent light excitation (sunlight). And last but not least – compatibility between the UC device and the photovoltaic device, including good optical coupling has to be realized. Up to now the triplet-triplet annihilation-supported upconversion (TTA – UC) is the only upconversion process excited with moderate concentrated sunlight. Our group demonstrates UCd based on various UCmolecular systems efficiently transforming the NIR and IR-A part of the sun spectrum into the VIS-range, operating at moderate sunlight concentrations (10-50 suns, AM1.5). The next important accomplished requirement is the transfer of the hydrophobic UC-molecular system from an organic solvent to the aqueous environment. These new aqueous UC systems with high efficiencies ensure good sealing of the UC device and in this way its compatibility with different solar cells.