Functional Atomic Force Microscopy for Energy Device Interfaces: Evolution from In Situ to In Operando

Rational interface design is of paramount importance for advancing energy devices. However, molecular-scale interfacial engineering faces two fundamental challenges: first, the intrinsic nanoscale heterogeneity in interfacial morphology, structure, and composition impedes the seamless upscaling from molecular-level insights to macroscopic device behavior; second, static molecular characteristics alone are insufficient to capture the dynamic evolution of these nanoscale interfacial features under operating conditions. Atomic force microscopy (AFM), with its high spatial resolution, versatile functional imaging modes, and exceptional capability for dynamic characterization, provides an ideal platform for interrogating nanoscale interfacial phenomena and holds the potential to bridge molecular design with device performance. This review focuses on the application of functional AFM in the study of interfaces in thin-film solar cells and all-solid-state lithium batteries, tracing the development from in situ to in operando characterization. We discuss the associated challenges and corresponding strategies, highlight the critical role of nanoscale interfacial characterization under operando scenarios, and conclude with an outlook on future directions for the development of the in operando AFM fields.