Ion agent mitigates efficiency roll-off in near-infrared electroluminescence for practical bioimaging and information encryption

Perovskite quantum dots (PQDs) have emerged as promising emitters for next-generation light-emitting diodes (LEDs). However, PQD-based near-infrared (NIR) LEDs still suffer from relatively low external quantum efficiencies (EQEs) and severe efficiency roll-off, which largely originate from the long-standing trade-off between enhancing carrier transport with conductive ligands and preserving PQD surface integrity during ligand exchange.

 

In a new paper published in Light: Science & Applications, a research team led by Professor Liang-Sheng Liao from the Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, and the State Key Laboratory of Bioinspired Interfacial Materials Science, Soochow University, China, and co-workers developed an ionic liquid-mediated surface reconstruction strategy to overcome this trade-off.

 

Researchers introduced a multifunctional ionic liquid 1‑methyl‑3‑propylimidazolium iodide (MPII) into the antisolvent during purification process. This strategy simultaneously suppresses defect formation and forms an in situ protective layer on the PQD surface, thereby preserving lattice integrity while significantly enhancing film conductivity. The treated PQD films exhibit significantly improved phase stability with nearly twofold lower trap densities and an order-of-magnitude higher conductivity than control films, enabling balanced carrier injection and efficient radiative recombination. As a result, the fabricated PQD-based NIR-LEDs achieved a record EQE of 24.8% with the lowest efficiency roll-off reported to date: the EQE remains approximately 20% even at a high radiance of 10 W sr^-1 m^-2. Furthermore, the researchers demonstrated large-area (900 mm²) devices with EQEs up to 20%, together with practical applications in biomedical imaging and information encryption, highlighting the considerable potential of this approach for advancing high-performance NIR optoelectronics.

 

The findings highlight a promising pathway toward next-generation NIR-LEDs and other PQD-based optoelectronic technologies. By simultaneously suppressing surface defects and enhancing film conductivity through ionic liquid-mediated ligand engineering, this strategy opens new opportunities for the integration of PQDs into advanced applications such as sensing, displays, biomedical imaging, and health monitoring devices.

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