Transparent conductive oxides (TCOs) play important roles in information and energy technologies. In the photovoltaic (PV) community, they are normally required to provide sufficient lateral carrier transport towards metal electrodes at the illumination side. Thus, a trade­off between optical and electrical properties is of critical importance in relevant device fabrications. So far, within the PVMD group, the investigation on TCOs has been mainly focused from an experimental perspective. In this thesis, a firstprinciples approach based on DFT software is investigated to obtain the self­consistent opto­-electrical properties of TCOs. A comprehensive study is carried out to understand the fundamentals of DFT software, as this is crucial to get reliable results from it. Within the PVMD group, the DFT method is applied on the indium­oxide (IO) host material. It was found that referable results for the (partial) density of states and band structure could be obtained for this structure using the PBE exchange­correlation (XC) functional. The dielectric function could be obtained by combining the PBE and HSE06 XC functional through the PHSmethod. Based on a preliminary validation of IO, two case studies are carried out. In these case studies, it is investigated if DFT can be used to compare the opto­-electrical properties of different doping types and ratios. This is done for post­transition metals (Sn), transition metals (W and Mo) and anionic doping (F). By observing the partial density of states of each element, it was found that significant hybridization of dopant states with the CBM of the IO host states occurs for the cases of Sn­ and F­doping. Such disturbance in the host conduction band may lead to detrimental influences to the opto­-electrical properties of corresponding TCOs. However, in the cases of W­ and Mo­doped TCOs at commonly used doping concentrations, no hybridization between dopant states and the host conduction band was observed. Furthermore, physical parameters of different TCOs at different doping levels are extracted and compared, such as band gap, effective electron mass, work function and dielectric functions. These results may provide supportive and indicative information for the experimental work. This thesis work has successfully introduced DFT calculation into TCO investigations within our research group. Although the preliminary results were not sufficiently accurate to predict the opto­-electrical properties of the TCOs in a quantitative way, the qualitative trend can still be used as guidance and support for explaining experimental results. However, many challenges still remain, especially for determining some optical properties like the band gap and dielectric function. Further research is still needed to improve the proposed method.

Metal–organic frameworks (MOFs) are a class of hybrid materials with metal-based inorganic nodes connected by organic linkers via strong coordination bonds. These building blocks can be arranged in 3-D crystalline lattices to synthesize structures with varying pore sizes and a variety of structures (tuneability). These hybrid materials possess exceptional porosity and large surface areas, making them suitable for applications in gas separation and storage, catalysis, and biomedical fields. MOFs also exhibit remarkable flexibility, which is determined by the topology of the framework and the degrees of freedom between bond angles in the organic linkers or coordination bonds between the organic linkers and inorganic nodes. One among the major categories of flexibility in MOFs is the rotational dynamics of organic linkers. The structural dynamics can have a pronounced influence on gas adsorption, diffusion and optical properties. Chapter 4 and Chapter 5 study the rotational dynamics of terephthalate linkers in functionalized MIL-53 MOFs by varying the steric interactions between the linkers using computational methods like ab initio molecular dynamics and classical molecular dynamics. Using the remarkable porosity, structural flexibility, and tuneability features of MOFs as central handles, in this thesis, we aim to study the (a) Piezoelectric properties in MOFs for their application as energy harvesters and (b) Rotational dynamics of linkers in MOFs. It is well-known that MOFs possess a high degree of flexibility and permanent porosity. High porosity of MOFs leads to low dielectric constants. This, together with higher flexibility of MOFs, makes them promising candidates for piezoelectric energy harvesting. Although all non-centrosymmetric MOFs are piezoelectric, their piezoresponse has hardly been studied thoroughly. Chapter 2 and Chapter 3 of this thesis will investigate the structure-property relationships of piezoelectric properties in MOFs through computational methods, and provide design guidelines that can contribute to the development of high-performing piezoelectrics. @en

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.@en

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. @en

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...@en

Many drugs cannot be made without homogeneous catalysis. To increase the yield of drug synthesis, the search for new catalysts continues. Computational catalysis is becoming a more prominent tool since it en- ables to screen many catalysts without performing (m)any laboratory experiments. In this research a com- putational workflow has been created to calculate both electronic (e.g. dipole, ionisation potential, nucle- ophilicity, etc.) and steric (bite angle, buried volume, cone angle, etc.) molecular descriptors. The structures were automatically created starting from the metal centre, some bidentate phosphorus ligands, auxiliary lig- ands, and the substrate. An in-house computational workflow, MACE, is used for for high-throughput gen- eration of structures from the starting bidentate phosphorus ligands, by generating stereo-isomers around to metal centre. Afterwards small substituents (H, CH3, Ph, etc.) are changed by ChemSpaX increasing the number of structures combinatorically. To reduce the computational cost of this workflow, it has been re- searched whether properties of the octahedral geometry could be predicted using properties from a simple model structure containing only the metal centre and the bidentate phosphorus ligand. This model structure did not show a correlation except for the electronic energy and the solvent accessible surface area, which are both primarily influenced by the number of electrons. Other correlations may be found if some other descriptors were calculated which where excluded now, like the HOMO-LUMO gap and the substrate bind- ing energy. The workflow could be extended to machine learning and improved by including symmetry and optical isomerism.