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Jeremy Dunklin1 Hanyu Zhang1 Ye Yang1 Jao van de Lagemaat1

1, National Renewable Energy Laboratory, Golden, Colorado, United States

Two-dimensional transition metal dichalcogenides (TMDs) have garnered significant recent interest due to their efficient visible light absorption, emission, and photocatalytic activity. While the electronic structure and excitonic transitions governing their optoelectronic properties are becoming well-understood, less is known about the photophysics and carrier dynamics following light excitation. This work monitors relaxation dynamics of single-layer chemical vapor deposited MoS2 and few-layer liquid exfoliated samples with femtosecond to nanosecond transient absorption spectroscopy featuring tunable pumping and broadband visible probing. Femto to picosecond dynamics exhibit a simultaneous bleaching of excitonic states as well as a red-shifted absorption spectrum attributed to both bandgap renormalization and dielectric effects. Long-lived, nanosecond scale features exceeding reported PL lifetimes and spectral differences at ca. 100-fold variation in nanosheet length could be critically important in understanding edge and carrier trap sites for device optimization. Studying the transient absorption behavior under redox-active conditions provides insight into dynamic charge transfer and chemical reactions catalyzed by both substrate-supported and liquid-phase 2D TMDs. Overall, these results provide an important step forward for understanding and implementing these emerging materials into photocatalytic and optoelectronic applications.

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