Singlet and triplet harvesting enable efficient NIR-II quantum-dot electroluminescence

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Colloidal quantum dots (CQDs) are key for near-infrared II (NIR-II) light-emitting diodes (LEDs) operating at 1000-1700 nm.
• Low external quantum efficiency (EQE) of CQD films hinders practical NIR-II LED applications.

Purpose of the Study:

• To enhance NIR-II emission in CQDs by incorporating photoactive fluorophores.
• To achieve high photoluminescence quantum efficiency (PLQE) and EQE for NIR-II LEDs.

Main Methods:

• A chemical strategy was employed to integrate diverse photoactive fluorophores (fluorescence, phosphorescence, thermally activated delayed fluorescence) into CQD films.
• Energy transfer mechanisms (singlet and triplet pathways) from fluorophores to CQDs were utilized.

Main Results:

• Achieved a PLQE of 85% for CQDs beyond 1000 nm through efficient energy transfer.
• Demonstrated record EQE of 25.3% for NIR-II LEDs emitting above 1000 nm.
• Successfully fabricated large-area (30 mm × 30 mm) NIR-II LEDs with uniform high performance, proving scalability.

Conclusions:

• The developed composite films significantly improve NIR-II emission efficiency.
• This approach offers a viable pathway for high-performance, large-area NIR-II LEDs.
• The strategy overcomes previous limitations in CQD film EQE for advanced optical applications.