The latest trend in solar cell technology is to develop photon managing processes that adapt the solar emission to the spectral range at which the devices show the largest intrinsic effi ciency. Triplet-triplet annihilationassisted photon upconversion (sTTA-UC) is currently the most promising process to blue-shift sub-bandgap photons at solar irradiance, even if the narrow absorption band of the employed chromophores limits its application. In this work, we demonstrate how to obtain broadband sTTA-UC at sub-solar irradiance, by enhancing the system's light-harvesting ability by way of an ad-hoc synthesized family of chromophores with complementary absorption properties. The overall absorptance is boosted, thus doubling the number of upconverted photons and signifi cantly reducing the irradiance required to achieve the maximum upconversion yield. An outstanding yield of ≈10% is obtained under broadband air mass (AM) 1.5 conditions, which allows a DSSC device to operate by exploiting exclusively sub-bandgap photons.

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A simple new heteroleptic copper dye, bearing one 2,9-dimesityl-1,10-phenanthroline and a 6,6′-dimethyl-2,2′-bipyridine-4,4′-dibenzoic acid anchoring ligand, was used as photosensitizer in dye-sensitized solar cells (DSSCs). High power conversion efficiencies are reached not only with conventional I–/I3 – electrolyte (40% relative conversion efficiency respect to N719) but, remarkably, also with a well-designed copper-based electrolyte. These proof-of-principle “full-copper” DSSCs open a fascinating route for environmentally friendly DSSCs.

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Two new heteroleptic copper(i) sensitizers with π-delocalized ancillary ligands for full copper DSSCs.