This symposium invites contributions on innovative semiconductor materials and device concepts for photo-assisted electrochemical (PV-EC), photoelectrochemical (PEC), and photocatalytic (PC) systems. The focus is on establishing clear structure-property-function relationships that connect fundamental materials design to application-driven performance metrics. The symposium will consider advances in materials synthesis and compositional engineering, semiconductor optimization and defect control, device architectures, and system-level engineering strategies. Particular emphasis will be placed on advanced experimental and computational characterization approaches that provide mechanistic insight into charge generation, transport, interfacial transfer, and reaction pathways under operating conditions. Various materials will be of interest: oxides, nitrides, chalcogenides, (halide) perovskites, organic and hybrid semiconductors for the production of solar fuels and renewable chemicals or the degradation of contaminants. Related topics include scalable fabrication strategies, operando and multimodal characterization, theory-guided materials discovery, and sustainability-driven design principles, aiming to accelerate the development of efficient, stable, and environmentally responsible photo-driven energy conversion systems.