Clean energy infrastructures of the future depend on efficient, low-cost, long-lasting systems for the conversion and storage of solar energy. This is currently limited by the durability and economic viability of today’s solar energy systems which arise from a variety of technical challenges; primarily, a need remains for the development of stable solar absorber catalyst interfaces and improved understanding of their mechanisms. Although thin film oxides formed via atomic layer deposition have been widely employed between the solar absorber-catalyst interface to improve the stability of photoelectrochemical devices, few stabilization strategies have focused on improving the intrinsic durability of the semiconductor. The work in this Thesis aims to provide a framework for designing inexpensive stable light absorber for solar energy generation, particularly water splitting, CO2 reduction, and waste treatment. This Thesis will therefore be divided into three parts: (1) The first project investigates the effects of subsurface nanomorphology in nanostructured silicon photocathodes. Here, we demonstrate a sinuous black silicon photocathode (s-bSi) with intrinsically improved stability compared to the common columnar analogue owing to the twisted nanostructure. (2) The second project studies fine control of the subsurface morphology of b-Si interfaces using magnetically guided nanoparticles. Results from Chapter 2 indicate a twisted morphology is superior, thus, a method for producing an organized sinuous structure is devised using magnetic control of the silicon etchant. These results open the door for further sub-surface morphology control and improved performance. (3) Access to clean water is equally as important to our growing society as generating clean energy and combatting climate change, therefore, the final project focuses on the design of photocatalytic materials for pharmaceutical organic waste treatment coupled with CO2 reduction (CO2RR) and/or hydrogen evolution (HER). Composites of 1T-MoS2, an HER catalyst, and graphitic carbon nitride show excellent activity in breaking down pharmaceutical waste while producing hydrogen and carbon monoxide. The work in this Thesis provides a groundwork for the design of photoelectrochemical and photocatalytic materials for high performance reactions with long lifetimes, where the methods presented can be applied to the design of many other photoabsorber and electronic systems.