Optical-cavity-driven photogenerated charge separation revealed by spatiotemporal imaging

Photogenerated charge separation across micro- to nanometer scales is essential for photoelectric and photocatalytic conversion. However, identifying microstructures that sustain efficient charge separation and elucidating the underlying mechanisms remain challenging. Here, by combining surface photovoltage microscopy with optical imaging, we show that optically resonant cavity structures generate highly non-uniform light-field distributions that subsequently drive efficient charge separation through asymmetric electron and hole diffusivities. Spatiotemporal imaging of carrier dynamics from femtoseconds to seconds reveals that this charge separation originates from the combined contributions of ultrafast hot-electron diffusion (∼3 ps) and long-lived trap-limited transport (∼5 ms). Leveraging these effects, we demonstrate control over both the magnitude and direction of charge separation via optical structure engineering. These findings deepen the fundamental understanding of diffusion-driven charge separation in semiconductors and establish optical-architecture engineering as a viable approach for manipulating this process, providing a blueprint for advancing solar energy conversion and optoelectronic technologies.