In this dissertation, we investigate charge transport in magnetic nano-objects. We use the mechanically-controlled break junction (MCBJ) technique to contact single molecules and use three different device geometries to optimize the process of contacting nanoparticles. We focus in particular on magnetic signatures in the quantum transport of these structures.

Due to their size-dependent properties, high photoluminescence quantum yield and relatively cheap solution-based processing, colloidal quantum dots (QDs) are of great interest for application in optoelectronic devices. However, the efficiency of these devices is often limited by the presence of trap states: localized electronic states that lead to energy levels in the bandgap. Although much research has been geared to passivating (i.e., removing) these trap states, our understanding of the atomic configurations that lead to traps remains limited. Therefore, the work presented in this thesis is aimed at investigating trap states and the QD surface on an atomistic scale. We use a combination of experimental and computational techniques to show that reduced metal sites can lead to trap-formation, and that these trap states can be dynamic in nature. In addition, we find suggestions that the QD surface is more complex than often assumed and that surface reconstructions may play a pivotal role in the delocalization of the wavefunction. Lastly, we study the formation of deep traps in CsPbBr3 perovskite nanocrystals. We find that the traditional picture of defect tolerance in these materials is incomplete and should also include the local electrostatic potential in order to explain deep traps.

In this dissertation, we analyse the charge transport of nanoscale molecular junctions in mechanically controllable break junction (MCBJ) experiments. In particular, we focus on the characterization of molecular features going beyond the "single-peak" picture, that is, considering features in the measurements in addition to themost prominent one. To achieve this goal, we use a combination of improved experimental techniques and data analysis...

For centuries we have relied on fossil fuels to produce energy for our needs, causing significant damage to the environment and our own health. To make an energy transition possible, technology has to step up, providing solutions for cleaner and cheaper energy production. In the field of solar energy, perovskite-based devices can offer a feasible alternative to conventional technologies, involving less energy intensive and cheaper manufacturing processes. Despite the great technological advancements of the past years, open circuit voltage losses and especially poor long-term stability are two of the main bottlenecks that still have to be overcome in order to bring the technology to market. In this thesis we have addressed such issues by investigating the origin and impact of electronic trap states on charge carrier dynamics in perovskite thin films of different composition...

Hybrid halide perovskites are currently the most studied optoelectronic materials. They have been successfully employed as the active material in solar cells. Despite the achieved success of these materials, the properties of these hybrid frameworks of an inorganic lattice that includes organic cations are not fully understood. This is because of the multiple complex processes that are operative in these materials and it is very hard to unravel them just on basis of experiments. Therefore, computational studies of these materials are important to gain insight in the material structure, the electronic structure and the processes dictated by these properties. An additional advantage of computational studies is that properties can be predicted without actually making the materials in the lab. Such computational study thus give insights in the functioning of hybrid perovskite materials and gives directions to their further development. Of particular interest in this thesis is the role of the organic cation. In some earlier studies it has been pointed out that he role and presence of the organic cations is just limited to stabilizing the structure of hybrid perovskites without influencing the electronic energy states. In this thesis we examine the role of the organic cation in detail, demonstrating that the organic cation has a distinct effect on the electronic structure of hybrid halide perovskites.