Efficiency Roll-Off Free Electroluminescence from Monolayer WSe₂

Area of Science:

• Materials Science
• Optoelectronics
• Solid State Physics

Background:

• Exciton-exciton annihilation (EEA) is a key factor limiting luminescence efficiency in excitonic materials at high densities.
• This efficiency roll-off is a major challenge for light-emitting devices.
• Transition metal dichalcogenides (TMDCs) offer potential for high quantum yields, but practical device applications remain difficult.

Purpose of the Study:

• To demonstrate a strain-tunable, roll-off free electroluminescence (EL) device based on TMDC monolayers.
• To investigate the impact of strain on EL enhancement and quantum efficiency in WSe2.
• To explore the potential for low turn-on voltages in these devices.

Main Methods:

• Fabrication of an electroluminescence device using strain-tunable TMDC monolayers.
• Application of a small strain (0.5%) to a WSe2 monolayer to modify its band structure.
• Measurement of electroluminescence enhancement, internal quantum efficiency, and transient EL turn-on voltages.

Main Results:

• Achieved a 2 orders of magnitude enhancement in EL from a WSe2 monolayer with minimal strain.
• Attained a stable internal quantum efficiency of 8% across all injection rates, demonstrating roll-off free operation.
• Demonstrated transient EL turn-on voltages as low as the material's band gap.

Conclusions:

• Strain engineering is an effective strategy to overcome exciton-exciton annihilation and achieve roll-off free electroluminescence in TMDCs.
• The developed strain-tunable WSe2 device shows significant promise for high-performance optoelectronic applications.
• This approach contributes to the advancement of roll-off free devices utilizing excitonic materials.