Highly efficient photon upconversion based on triplet-triplet annihilation from bichromophoric annihilators

Owing to its unique ability to efficiently convert low-energy photons into high-energy photons, triplet-triplet annihilation (TTA) based photon upconversion is a promising strategy for harvesting the low-energy tail of the solar spectrum for photovoltaic technologies. However, breaking through the upconversion quantum efficiency is not easy due to the few examples of existing annihilators that maximize the efficiency of singlet generation by TTA. Here, we present a new bichromophoric annihilator (PCP) that is paired with a metallic porphyrin as a sensitizer in low viscosity solution, and the system shows a record red-to-green external upconversion yield of 42%. This value can be achieved thanks to the photophysical properties of PCP that allow achieving a unitary triplet-to-singlet conversion efficiency and to its structural features that enable high fluorescence yields even at high concentrations.