Photon recycling can play an important role to increase solar cell efficiency: by repeated absorption and emission of photons in a material, it keeps the photons within the active layer so that they’re not lost. The repeated absorption and emission is typically related to a small Stokes shift, leading to overlap of absorption and emission wave lengths, high absorption and high PL quantum yield.
By combined experimental and computational study, we identify strong photon recycling in perovskite nanocrystal suspensions. We observe a pronounced red shift, prolonged PL lifetimes, and concomitant decrease of the PL quantum yield with increasing nanocrystal concentration, all pointing towards repeated absorption and re-emission of photons. Simulations of photon diffusion through the suspension account very well for all observed trends, and identify up to 5 absorption and re-emission cycles underlying the experimentally observed trends. This surprisingly efficient recycling of photons boosts the already very beneficial properties of inorganic perovskite nanocrystals for photovoltaic applications.