Effects of Local Environment on the Ultra-Fast Carrier Dynamics of Photo-Excited 2D Transition Metal Dichalcogenides
Layered transition metal dichalcogenides (TMDs) represent a diverse, emerging source of two-dimensional (2D) nanostructures with broad application in optoelectronics and energy. In particular, tungsten disulfide (WS2) is an efficient visible light absorber with relatively high carrier mobilities and catalytic activity towards hydrogen evolution. While explanation of the quantum confinement and excitonic effects governing TMD optoelectronic properties has progressed in recent years, less is known about the ultra-fast photoresponse and carrier dynamics following light excitation. This work utilizes transient absorption spectroscopy, with pump tunability and broadband visible probing, to monitor the carrier dynamics of both CVD-grown monolayer and solution exfoliated WS2. Picosecond-scale features include simultaneous bleaching of excitonic states and a red-shifted absorption spectrum attributed to bandgap renormalization, while free carriers, defect trapped carriers, and recombination signatures are apparent at increasing pico- to nanosecond lifetimes. Features associated with excitons, trions, and photo-excited carriers exhibit strong dependence on local environmental factors. Moisture, oxygen, chemical dopants, and dielectric environment strongly affect the strength and decay lifetimes of these photo-excited species. These results highlight the importance of understanding and controlling these local environmental factors to the rational design and implementation of 2D TMDs optoelectronic device platforms.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22), Solar Photochemistry Program
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1482496
- Report Number(s):
- NREL/CP-5900-72379
- Resource Relation:
- Conference: Presented at SPIE Nanoscience + Engineering, 19-23 August 2018, San Diego, California
- Country of Publication:
- United States
- Language:
- English
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