Upconversion at Solid/Liquid Interfaces Using Perovskite Single Crystal Triplet Sensitizers

Perovskite-sensitized photon upconversion (UC) has the potential to improve a wide range of technologies including photocatalysis and photovoltaics, by converting two low energy photons into a single photon of higher energy. To date, perovskite-sensitized UC has been studied by using nanocrystals in solution and solid-state thin film bilayers using polycrystalline perovskite films. While efficient UC has been achieved in thin film bilayers, surface inhomogeneities and defects due to individual perovskite crystal grains and grain boundaries may limit the overall performance. However, one of the main issues in solid-state UC is a limited number of viable triplet annihilators in the solid-state due to unfavorable intermolecular interactions and competing relaxation pathways. Here, we investigate the properties of mixed cation methylammonium formamidinium lead triiodide perovskite single crystals using X-ray diffraction and optical spectroscopy and their subsequent incorporation and performance as triplet sensitizers for triplet-triplet annihilation in solution-based rubrene. With the hybrid solid-state/solution approach presented here, a wide number of potential annihilators can be rapidly be screened. In addition, the higher surface homogeneity and orders of magnitude lower defect densities and higher stability of perovskite single crystals allow for potential improvements to interfacial charge transfer processes and increases in UC performance due to reduced carrier trapping.