Visualizing Bulk-to-Surface Carrier Diffusion via Band-bending of Solar Cell Materials by 4D Electron Microscopy at Low Applied Potential

Utilizing four-dimensional scanning ultrafast electron microscopy (4D-SUEM) is a powerful tool to monitor charge dynamics at material surfaces and interfaces especially for the application in renewable energy field. Herein, we uncover unique physical features for 4D-SUEM upon reducing the acceleration of probed primary electrons to 1 keV, for wide range of materials including various single crystals, thin films and quantum dots upon the presence of oxidized and neat surfaces. Working at 1 keV helps to uncover the migration of photogenerated carriers originating from both sub-surface and bulk layers, under the influence of the carriers scattering and the band-bending phenomena. This approach provides a new avenue for the spatial and temporal access to the surface exclusive dynamics in renewable energy materials to unlock their interfacial behaviors at the nanoscale level.