DEFECT-DRIVEN TRANSPORT PHENOMENA IN ENERGY AND FUNCTIONAL MATERIALS: A COMPREHENSIVE REVIEW

Abstract

Defect-driven transport, involving ionic, electronic, and thermal carriers, is fundamental to the performance of many energy and functional materials. Intrinsic and extrinsic defects (vacancies, interstitials, substitutions) create pathways for ion migration and tune carrier concentrations, thereby controlling conductivity and reactivity. In complex oxides (e.g. perovskites) and solid electrolytes, oxygen or lithium vacancies greatly enhance ionic conduction. In thermoelectric materials (e.g. Bi–Te, Pb–Se alloys), controlled doping introduces charged defects that optimize carrier mobility and Seebeck coefficient. Two-dimensional materials (graphene, MoS₂, h-BN) can have their electronic band structure and conductivity tailored via atomic vacancies or substitutional dopants. This review surveys recent theoretical, computational, and experimental studies (primarily 2015–2025) across these classes and identifies common mechanisms by which defects modulate transport. We discuss key findings in perovskite oxides, halide perovskites, solid electrolytes, thermoelectrics, and 2D materials. We emphasise the correlation between defect structure (type, concentration, and mobility) and transport properties, along with emerging design strategies. The review also identifies open questions and future directions for defect engineering to optimize performance in energy devices.