Perovskite solar cells (PSCs) are gaining increasing importance and attention in the last decade. Even though high conversion efficiencies have been reached, one of the major bottlenecks for the commercialization of PSCs is their stability. Issues at the interfaces in the multilayered PSC architecture are suspected to be the significant contributor in causing low stability. This doctoral thesis focusses on the analysis of various interfaces present in PSCs and traces methods to improve them. The investigation of individual interfaces is performed by developing suitable sub-cells, i.e., comprising only the particular interface of interest. Various optical and structural characterization methods are used to determine layer and interface properties. After this step, complete devices are manufactured from the sub-cells, and their final performance is investigated to conclude the role and optimization of the interfaces. The thesis accounts for the analysis of the interfacial quality of different in-room ambient processed n-i-p perovskite solar cells configurations, being based on hole-transport-layer (HTL)/Au or HTL-free/carbon-graphite (CG) electrodes. The findings show that developing suitable sub-cells allows to investigate the quality of the various interfaces of PSCs individually. Results from the sub-cell analysis are compared with the performance of complete devices to verify their significance. Thereby, methods to improve the interfaces can be found to achieve higher device efficiencies without compromising its stability.

With time-resolved microscopy this work reveals the physical processes on to the femtosecond to nanosecond scale, which are induced by intense pulses in silicon. To tailor a laser process towards applications in photovoltaics, such as pulsed laser annealing and laser ablation, a detailed knowledge of those mechanisms is required. Combining measurements and simulations, this work demonstrates how they determine the outcome and potential damage.

A set of 15 thermomechanical design rules is derrived to support and accelerate PV module developments. Three methods are developed and applied: 1. Thermomechanical FEM-simulations of PV module designs. 2. µ-Raman spectroscopy of laminated solar cells. 3. Solar cell integrated stress sensors (SenSoCell®). The concept of specific thermal expansion stiffness E ̂_α is introduced as a measure of how much thermal strain one material induces in another.

Silicon solar cells are one piece in the puzzle of a successful energy transition towards renewable energies. Unfortunately, many outdoor parameters such as high temperatures have a detrimental impact on solar cells' energy output. To enhance the understanding of silicon as a semiconductor used in photovoltaics, this thesis investigates the temperature dependence of silicon and silicon solar cells. Measurement approaches for spatially-resolved temperature-dependent characterization of silicon wafers and solar cells were developed being based e.g. on photoluminescence imaging or lock-in thermography at realistic operation temperatures. The temperature dependence of three different regions of silicon solar cells is investigated in detail: the bulk, surfaces and diffused regions. The acquired knowledge is employed in a sensitivity analysis to demonstrate how new findings about temperature sensitivity of silicon solar cells influence numerical simulations of silicon solar cell devices. Finally, all developed approaches of this work are combined to predict silicon solar modules' energy yield in spatial resolution via measurements at wafer level before metallization.