Recent advances of triplet–triplet annihilation upconversion in solvent-free solid materials

Abstract

Triplet–triplet annihilation upconversion that converts low-energy photons to high-energy photons with an incoherent exciting light source is attracting considerable attention due to the wide applicating potential in improving the efficiencies of solar-powered devices by recovering the wasted sub-bandgap photons. For real-world applications, TTA-UC in the solvent-free solid state is highly demanded but challenging to realize due to the poor exciton diffusion in the solid matrix, which hinders exciton encounter and the TTET and TTA processes. Many endeavors have been devoted to achieving efficient solid-state UC emission, and a quantum yield of 23.8% has been achieved recently. In this review, we will mainly focus on the recent research progress of UC emission in the solid state and will especially summarize the efficient strategies for achieving UC emission in solvent-free solid materials.