Hot electrons in cool nanocrystals

In this thesis, the main focus is on all-inorganic perovskite nanocrystals (IP-NCs) that are studied from a microscopy and spectroscopy point of view. Due to a direct band gap and high photoluminescence efficiencies, the IP-NCs lend themselves very well for these various techniques. Moreover, their outstanding characteristics are the major reason why the IP-NCs recently have attracted a lot of attention.
One of the subjects discussed in this thesis is the process of carrier multiplication. In semiconductor NCs this counteracts the loss of energy through thermalization of hot carriers created upon high-energy photo-excitation. As such, carrier multiplication in all-inorganic CsPbI₃ NCs is revealed and described.
The IP-NCs also lend themselves very well for microscopy. Transmission electron imaging allows for direct visualization of NCs, with the high resolution microscopy providing information about their composition, crystal structure, size and shape, aggregation, and ordering when in an ensemble. In addition, the electron energy loss spectroscopy technique can give important insights into the energy structure of individual IP-NCs. In this way, it has been revealed that the energy structure of a (single) IP-NC is different when isolated and in an ensemble, which means that neighboring NCs interact with each other.
This technique has also allowed for distinguishing between different polymorphs of perovskite which typically are simultaneously produced during the synthesis. The characteristics of green-emitting CsPbBr₃ and insulating Cs₄PbBr₆ NCs were investigated at a single object level. It is shown that the two materials co-exist and inevitably hybridize forming nanoparticles with a spherical shape.