Bulk Metal Halide Perovskites as Triplet Sensitizers: Taking Charge of Upconversion

Photon upconversion via triplet–triplet annihilation has the potential to improve the performance of photovoltaics, as additional sub-bandgap photons can be harnessed. Recently, bulk metal halide perovskite materials have been introduced as triplet sensitizers, resulting in near-infrared-to-visible upconversion when coupled to the triplet annihilator rubrene. Perhaps most excitingly, the perovskite layer can absorb up to 60% of the incident light at wavelengths up to 780 nm, a feat not possible with previously examined PbS nanocrystalline sensitizers. However, the exact nature of the triplet sensitization process, which is thought to occur through a free charge mechanism, is not completely elucidated, in large part due to the complexity of this upconversion system. Perovskite-sensitized upconversion systems, while still in their infancy, have the potential to revolutionize the field of photon upconversion, eventually resulting in industrial relevance, once the rich photophysics of this system are fully understood.