Maria Antonietta Loi1

1, University of Groningen, Groningen, , Netherlands

In this presentation, the optical properties of the newly developed near-infrared emitting formamidinium lead triiodide (FAPbI3) nanocrystals (NCs) and their polycrystalline thin film counterpart are comparatively discussed. The excitonic emission is dominant in NC ensemble because of the localization of electron-hole pairs. A promisingly high quantum yield above 70 %, and a large absorption cross-section (5.2×10-13 cm-2) were measured. At high pump fluence, biexcitonic recombination was observed, featuring a slow recombination lifetime of 0.4 ns. In polycrystalline thin films, the quantum efficiency is limited by nonradiative trap-assisted recombination that turns to bimolecular at high pump fluences. From the temperature-dependent photoluminescence (PL) spectra, a phase transition is clearly observed in both NC ensemble and polycrystalline thin film. It is interesting to note that NC ensemble show PL temperature anti-quenching, in contrast to the strong PL quenching displayed by polycrystalline thin films. This difference is explained in terms of thermal activation of trapped carriers at the nanocrystal’s surface, as opposed to the exciton thermal dissociation and trap-mediated recombination, which occur in thin films at higher temperatures.