Plasmons Enable Ultralow Threshold Solid-State Triplet Fusion Upconversion with a 2D Sensitizer.

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Solid-state triplet-triplet annihilation (TTA) upconversion is promising for light harvesting and bioimaging.
• High optical power requirements currently limit TTA upconversion efficiency.
• 2D transition-metal dichalcogenides (TMDs) show potential as sensitizers but suffer from low absorption.

Purpose of the Study:

• To demonstrate plasmon-enhanced near-infrared (NIR)-to-blue TTA upconversion in a monolayer WSe2/organic heterojunction.
• To investigate the role of plasmon excitation in overcoming low far-field absorption of 2D TMDs.
• To optimize device performance through material transfer process improvements.

Main Methods:

• Fabrication of a monolayer WSe2/organic heterojunction.
• Utilizing surface plasmon polariton (SPP) excitation for enhanced light absorption.
• Characterizing upconversion efficiency, threshold power, and external quantum efficiency (EQE).

Main Results:

• Achieved NIR-to-blue TTA upconversion with a threshold of 19 mW/cm2 and EQE of 0.17% under far-field excitation.
• Plasmon excitation reduced the threshold to 0.9 mW/cm2 and increased EQE to 3.6%.
• Attributed enhancement to SPP near-field effects and dark-exciton absorption, with WSe2 transfer optimization being crucial.

Conclusions:

• Plasmon excitation significantly enhances TTA upconversion in monolayer TMDs, overcoming their inherent low absorption.
• This approach enables high-performance solid-state upconversion, comparable to the best reported results.
• Demonstrated potential for advanced optoelectronic devices and light-harvesting applications.