The following research proposal is aimed at providing a fundamental understanding of how dopants and defects (including their respective energetic and structural disorder) can modify the electronic structure and charge transport properties of main group metal oxide perovskites, such as oxygen-deficient BaSnO3-x, which possess optically active valent ns2 lone pair states. This project offers an exceptional combination of fundament energy materials theory, advanced spectroscopic characterization, and device demonstrations. One of the main goals of the project is to resolve certain controversies in the current understanding of charge transport in engineered metal oxide semiconductors, which often deviate from the typical band-like models applied to classical crystalline absorber materials. Adding specific dopants and/or defects into oxide perovskites, at relatively high concentrations (1-10 mol %) can lead to increased peak charge carrier mobilities, moderate carrier concentrations (via compensation), and simultaneously generate mid-band gap states with relatively strong optical transitions. This engineering process has the potential to substantially enhance the optoelectronic performance of the oxide semiconductors. A combination of state-of-the-art experimental and theoretical approaches will be used, including advanced chemical deposition and device fabrication, in-depth materials characterization, photo-electrochemical/catalytic analysis, and energy and time dependant spectroscopy. A unique aspect of this research is the characterization of temperature-dependent charge carrier dynamics to provide an accurate mechanistic understanding of thermally activated charge transport in oxide materials by considering dynamic disorder models. Subsequently, we aim to demonstrate how solar thermal integration can act as an innovative strategy to enhance the performance of oxide based photocatalytic and photovoltaic (PV) systems for efficient solar energy conversion up to 10%.