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

Abstract Perovskite quantum dots (PQDs) are promising emitters for next-generation light-emitting diodes (LEDs), yet PQD-based near-infrared (NIR) LEDs still suffer from low external quantum efficiencies (EQEs) and severe efficiency roll-off. This limitation arises from the trade-off between enhancing carrier transport with conductive ligands and preserving PQD surface integrity during ligand exchange. Here, we report an ionic liquid-mediated surface reconstruction strategy that simultaneously stabilizes PQD surface and enhances charge transport. Incorporating the multifunctional ionic liquid 1-methyl-3-propylimidazolium iodide (MPII) into the antisolvent suppresses defect formation while forming an in situ protective layer, effectively reducing surface traps and preserving PQD structural integrity. The treated PQD films exhibit a twofold reduction in trap density and a tenfold increase in conductivity, ensuring balanced carrier injection and efficient radiative recombination. As a result, the fabricated NIR LEDs achieve a record EQE of 24.8%, maintaining ~20% EQE at a radiance of 10 W sr - ¹ m - ²—representing the lowest efficiency roll-off for PQD-based NIR LEDs reported to date. Furthermore, large-area devices (900 mm²) reach EQEs of up to 20% and demonstrate practical applications in biomedical imaging and information encryption, underscoring the broad potential of this strategy for high-performance NIR optoelectronics.