Journal
NANO LETTERS
Volume 22, Issue 3, Pages 1067-1074Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.1c03941
Keywords
nanoscale charge carrier transport; diffusion; ultrafast photoelectron spectroscopy; electronic structure; semiconductors; lead halide perovskites
Categories
Funding
- European Research Council [2020 695197 DYNAMOX]
- Swiss National Science Foundation through the NCCR MUST [R'EQUIP 206021_182994]
- Max Planck-EPFL Center for Molecular Nanoscience and Technology
- Swiss National Science Foundation [186406, SPP219]
- ETH Zurich through ETH + Project SynMatLab
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Describing the nanoscale charge carrier transport at surfaces and interfaces is crucial for designing high-performance optoelectronic devices. In this study, time- and angle-resolved photoelectron spectroscopy was used to investigate the ultrafast decay of carrier population associated with surface-to-bulk transport. The study achieved sub-nanometer spatial resolution normal to the surface and femtosecond time scale tracking.
Describing the nanoscale charge carrier transport at surfaces and interfaces is fundamental for designing high-performance optoelectronic devices. To achieve this, we employ time- and angle-resolved photoelectron spectroscopy with ultraviolet pump and extreme ultraviolet probe pulses. The resulting high surface sensitivity reveals an ultrafast carrier population decay associated with surface-to-bulk transport, which was tracked with a sub-nanometer spatial resolution normal to the surface, and on a femtosecond time scale, in the case of the inorganic CsPbBr3 lead halide perovskite. The decay time exhibits a pronounced carrier density dependence, which is attributed via modeling to enhanced diffusive transport and concurrent recombination. The transport is found to approach an ordinary diffusive regime, limited by electron-hole scattering, at the highest excitation fluences. This approach constitutes an important milestone in our capability to probe hot-carrier transport at solid interfaces with sub-nanometer resolution in a theoretically and experimentally challenging, yet technologically relevant, high-carrier-density regime.
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