Solar cells can play a key role in the transition towards a sustainable future. This transition is one of the major challenges our society faces during the coming decades. Development of high-efficiency photovoltaic solutions at reasonable costs will help accelerating the transformation of our energy system. In this respect, perovskite solar cells are very promising due to their outstanding opto-electronical properties and low-cost fabrication. Obtaining a complete understanding of the device physics and charge transfer mechanisms inside perovskites is crucial for further device improvements. This thesis focuses on the notorious hysteresis in the current-voltage characteristics of perovskite solar cells. So far, this remarkable phenomenon has usually been explained using ion migration, despite the lack of clear experimental evidence. We implement a simulation platform of perovskite solar cells to analyse the charge transfer mechanisms among energy states including those with energy within the forbidden bandgap. We evaluate transient behaviour and identify the limiting physical mechanisms. To explain anomalous hysteresis in perovskite solar cells we use a novel approach in which charge accumulates near the material interfaces due to defects with relatively low capture cross-sections. Defects in lead halide perovskites create shallow sub-gap energy states, that act as charge carrier traps. Near the interfaces, this leads to accumulation of trapped charge carriers, effectively screening the electric field inside the perovskite layer. This reduces the device performance. A slow release of trapped charge due to low capture cross-sections results in hysteresis in the current-voltage curve at commonly used scan rates. TCAD Sentaurus is used as a platform to simulate J-V scans of a planar non-inverted architecture based on the archetypal perovskite MAPbI3, with TiO2 as electron transport layer and spiro-OMeTAD as hole transport layer. This thesis presents a systematic study of different trap distributions, both in the spatial and energetic domain. The capture cross-sections, densities, energy levels and locations of traps are varied and also the effect of scan rate is analysed. This work analyses both tail state defects and deep defects, based on reported values in literature. It is found that defects near the ETL/perovskite interface potentially cause anomalous hysteresis in the current-voltage curve. These defects have their transition energy around 0.25 eV and are possibly attributed to iodine interstitials. ... Read more

Quantum networks play an important role in the fields of quantum information and quantum computation. One of the current problems for these networks concerns nonlocality. Characterizing and detecting nonlocality is relevant to the implementation of quantum networks and quantum repeaters, where Bell inequalities can be used to test if configurations are prepared correctly.
This report contains an overview of an iterative method to find Bell inequalities for networks. Starting from a given network, this method constructs a new Bell inequality for a network containing one additional source and one additional party. We use this procedure to find new Bell inequalities for specific network structures and analyse how these can be used to detect nonlocality within a network.
In the first part the Bell inequalities are considered from a more theoretical point of view. We focus on star-shaped networks and discuss violations predicted by quantum mechanics. We look for quantitative bounds describing a set of states that lead to violation, giving an indication of the required quality of the sources.
Finally this method is applied to a setup similar to the one described by Bernien et al. We consider a network consisting of three parties and two sources. The effect of errors during preparation of an entangled pair of photons on the ability to detect nonlocality is evaluated. The same is done for the effect of measurement errors. Using numerical computations we show that violation of the Bell inequality can be improved by choosing different measurement angles. ... Read more