GaN-Based Solar Cells and Silicon Photovoltaic Modules Advanced Characterization and Modeling

This work presents and analyzes InGaN/GaN multi-quantum wells (MQWs) GaN-based solar cells, which exhibit outstanding efficiency in the blue and near-UV regions. These solar cells are promising for applications in space environments, concentrator solar systems, wireless power transmission and they can also be integrated into multi-junction (MJ) solar cells, potentially increasing the efficiency of MJ cells from the current record of ~47% to over 50%. In Chapter 4, a model is proposed to describe the quantum efficiency of these devices, taking into account factors such as layer thickness, temperature, and quantum confinement effects. The model accurately predicts the spectral response of the cells, showing that photogenerated carriers in the p-GaN region do not significantly contribute to the current. Chapter 5 focuses on the degradation of MQW solar cells subjected to high-temperature, high-intensity optical power stress. It was found that thinner p-GaN layers shown greater degradation, likely due to impurity diffusion (e.g., hydrogen), which increases Shockley-Read-Hall (SRH) recombination in the quantum wells. A thicker p-GaN layer canreduce the amount of defects reaching the active region. Chapter 6 investigates the electrical characteristics of these devices under dark conditions using numerical simulations by means of TCAD Sentaurus suite from Synopsys. It introduces two nonlocal models: one for intra-barrier tunneling and another for trap-assisted tunneling. However, for devices with thin p-GaN layers, the simulations needed to account for defects such as V-pits, as discussed in Chapter 7. In Chapter 8, the optical properties of V-pits and their agglomerates, surrounded by trench-like defects, are studied. These defects cause redshifted emission wavelengths, with the effect being more pronounced in devices with thinner p-GaN layers due to increased carrier localization near defects. Chapter 9 explores GaN-based devices with only two quantum wells, highlighting the importance of proper device design for carrier collection efficiency. Degradation under optical stress was observed, affecting parameters like short-circuit current and open-circuit voltage, primarily due to increased trap density. Finally, Chapter 10 examines the effects of a severe hailstorm on a residential photovoltaic system, emphasizing the importance of testing beyond current standards, the detection of latent damage, and the risks posed by cracks, even when protective glass remains intact. This study highlights the need for thorough inspections after severe weather events to ensure the long-term reliability of PV systems.