Recent advances in the application triplet–triplet annihilation-based photon upconversion systems to solar technologies

Upconversion (UC) of low-energy photons into high-energy light can in principle increase the efficiency of solar devices by converting photons with energies below the energy absorption threshold into radiation that can be utilized. Among UC mechanisms, the sensitized triplet-triplet annihilation-based upconversion (sTTA-UC) is the most recent that would be applied in solar technologies. sTTA-UC was demonstrated using sunlight in 2006, and due to its high efficiency at low excitation intensities with noncoherent light, it is considered a promising strategy for the recovering of subbandgap photons. Here, we describe briefly the working principle of the sTTA-UC, and we review the most recent advances of its use in solar applications