Photon upconversion via triplet-triplet annihilation bears promise in advancing e.g., photovoltaics, photocatalysis, biomedical imaging and optogenetics. In photon upconversion, two low energy photons are combined to generate one high energy photon. To comply with energy conservation laws, this occurs by combining two or more low energy photons through triplet states. Since triplet states are ‘spin-forbidden’, so-called sensitizers are required to indirectly populate the triplet state. Triplet sensitizers span a broad range of material classes including from metal-organic complexes, nanomaterials, and bulk films. Understanding the differences in energy transfer mechanisms is crucial for the advancement of optoelectronic devices based on triplet generation at the organic/inorganic hybrid interface. <br/>The exact triplet sensitization mechanism varies depending on several factors including: (i) the absolute alignments of the sensitizer and acceptor energy levels. (ii) The exciton binding energy in the sensitizer, resulting in excited states in form of excitons or free carriers. (iii) Energetic polydispersity of a sample, which varies the energetic driving force for triplet transfer. <br/>I will present the current understanding of the triplet sensitization mechanism based on inorganic sensitizer materials with different dimensionalities spanning from zero-dimensional quantum dots to 3D bulk lead halide perovskites and highlight the differences of each upconversion system.

Triplet generation at the hybrid organic/inorganic interface for photon upconversion

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ACS Fall 2022

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