For the first time multiple exciton generation (MEG) is observed in all-inorganic perovskite nanocrystals (IP-NCs): we demonstrate this effect in a colloidal dispersion of CsPbI3 NCs with a bandgap energy of 1.78 eV. Due to the recent demonstration of a stable solar cell based on CsPbI3 NCs,  this material has suddenly changed its status from being a scientific curiosity to a highly-promising new alternative for perovskite-based applications. MEG is of interest because it can significantly enhance the efficiency of energy conversion processes in photo-detectors and solar cells. For solar cells in particular, an overall increased efficiency of 44% can be expected for devices that make use of MEG.  Previous investigations conducted larger bandgap Br-containing IP-NCs failed to reveal MEG, showing no specific increase in carrier generation rate when exciting with a photon energy (more than) twice the bandgap. Here, we explicitly demonstrate the MEG effect in CsPbI3 NCs by making use of ultrafast transient absorption spectroscopy. By comparing the photo-induced transients at different pump photon energies, typically below and above the threshold energy for CM, we observed the fingerprint of CM, in the form of a fast transient induced by Auger recombination. We confirm this observation by quantifying the fast decay as being induced by Auger interaction between multiple carriers co-localized in one IP-NC.
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