Universal imaging of material functionality through nanoscale tracking of energy flow

The ability of energy carriers to move within and between atoms and molecules underlies virtually all biochemical and material function. Understanding and controlling energy flow, however, requires observing it on ultrasmall and ultrafast spatiotemporal scales, where energetic and structural roadblocks dictate the fate of energy carriers. We therefore developed a universal, non-invasive optical scheme that leverages interferometric scattering to track energy transport in four dimensions of spacetime with fewnanometer precision and directly correlate it to material morphology. We visualize exciton, charge, and heat transport in polyacene, silicon and perovskite semiconductors and elucidate, in particular, how grain boundaries impact energy flow through their lateraland depth-dependent resistivities. We reveal new strategies to interpret energy transport in disordered environments that will direct the design of defecttolerant materials for the semiconductor industry of tomorrow. Text Energy flow is a ubiquitous phenomenon, central to the function of all biological, chemical and material systems. Elucidating how distinct macroscopic system functions emerge from different structural arrangements of atoms and molecules is a longstanding goal of scientific research, and one that necessarily relies on understanding how energy is transduced and transported between the system’s building blocks (1). Materials science, for example, is undergoing a revolution with a recent burst of new high-performing semiconductors made from a vast diversity of molecular building blocks that can be readily tuned for specific functions (2–4). Nevertheless, a fundamental understanding of why some semiconductors perform better than others remains elusive (5), inhibiting the rational design of future materials. The difficulty in gaining such predictive power is compounded by often-encountered nanoscale spatio-energetic disorder, manifested in defects, impurities, and grain boundaries (GBs), that give rise to complex and spatiotemporally heterogeneous energy transport behavior. Elucidating how the microscopic details of a material relate to its emergent optoelectronic function will therefore require the ability to individually, systematically, and easily correlate nanoscale structure to energy flow across a wide range of systems. Resolving how energy flow is impacted by material structure and spatio-energetic disorder requires tracking energy carriers over a wide spatiotemporal range, typically nanometers to microns and picoseconds to milliseconds, and directly correlating the measurement to material morphology. This correlation notwithstanding, powerful spatiotemporally resolved approaches have recently been developed to visualize nanoscale energy flow using photoluminescence (6–8), transient absorption (9–12), or electron scattering (13) as contrast mechanisms. They achieve femtosecond time resolution (11, 13), large dynamic range (6), chemical specificity (6–8, 11), and excellent spatial sensitivity (6–8). Nevertheless, in their current implementations, most of these methods track only a subset of energy carrier types, and rely on samples having specific optical or electronic properties, such as being absorbing yet low optical density (11), having