Surface and interface phenomena increasingly define the efficiency, stability, and scalability of next-generation photovoltaic (PV) and optoelectronic devices. As absorber layers become thinner, more defect-tolerant, and more solution-processable—exemplified by metal halide perovskites, organic semiconductors, and colloidal quantum dots—the influence of interfacial chemistry surpasses that of bulk transport in determining device performance. In parallel, advanced crystalline silicon architectures rely critically on ultrathin dielectric stacks and passivated contacts to minimize recombination losses. This review presents a comprehensive and cross-platform synthesis of surface functionalization strategies spanning silicon, perovskite, organic, and nanocrystal technologies. We classify interfacial engineering approaches into molecular monolayers, chemical passivators, inorganic ultrathin films, polymeric interlayers, ligand engineering strategies, and surface reconstruction treatments, and analyze their underlying mechanisms, including defect passivation, dipole-induced energy-level alignment, field-effect passivation, wettability and crystallization control, and environmental barrier formation. Particular emphasis is placed on self-assembled monolayers (SAMs) as ultrathin, multifunctional interlayers capable of simultaneously tuning work function, suppressing recombination, and directing film growth in inverted perovskite and organic architectures. In colloidal quantum dot devices, ligand exchange and surface shell engineering are examined as central determinants of trap density, carrier mobility, and radiative efficiency. Across material platforms, common physical principles emerge: reduction of nonradiative recombination, control of interfacial electrostatics, enhancement of selective carrier extraction, and stabilization against ion migration and environmental degradation. The review further addresses characterization methodologies linking surface chemistry to device physics, and evaluates manufacturability considerations including deposition compatibility, process tolerance, and long-term reliability. By integrating insights from diverse semiconductor systems, this work establishes transferable design rules and identifies research directions aimed at translating molecular- and nanoscale interface control into robust, scalable photovoltaic and optoelectronic technologies.