Fuzhou University researchers have developed a multifunctional ligand engineering strategy that enables efficient and stable near-infrared perovskite quantum-dot LEDs (NIR-PQLEDs) fabricated entirely under ambient air conditions.
Metal halide perovskite quantum dots (PQDs), particularly formamidinium lead iodide (FAPbI₃), are attractive for NIR emission above 750 nm due to their tunable bandgaps, high color purity, and solution processability. These properties make them promising for applications such as biomedical imaging, night vision, and optical communication. However, despite rapid efficiency improvements in recent years - reaching EQEs above 20% in optimized systems - high-performance NIR-PQLED fabrication still typically relies on inert environments due to the extreme air sensitivity of PQDs.
The instability originates from both surface chemistry and lattice fragility. Conventional ligands such as oleic acid (OA) and oleylamine (OAm) bind weakly and can desorb during film formation, leaving behind defects such as uncoordinated Pb²⁺ ions and halide vacancies. These defects act as non-radiative recombination centers, severely limiting device efficiency. At the same time, moisture and oxygen accelerate degradation: water disrupts the FAPbI₃ lattice via hydrogen bonding with FA⁺, while oxygen induces photooxidation processes that further destabilize the structure.
To address these challenges, the researchers introduced 1-naphthylmethylammonium iodide (NMAI) as a multifunctional ligand for surface modification of PQDs. Unlike conventional ligands, NMAI simultaneously targets stability, defect passivation, and charge transport through three coordinated mechanisms.
First, the hydrophobic aromatic naphthalene group significantly enhances surface hydrophobicity. This promotes the formation of a dense and compact ligand shell that effectively blocks the ingress of water and oxygen, improving environmental stability under ambient conditions. The rigid molecular structure also contributes to a more tightly packed surface, suppressing ion migration and reinforcing structural integrity.
Second, the combined action of NMA⁺ cations and I⁻ anions enables efficient defect passivation. The cations provide electrostatic anchoring to the PQD surface, while iodide ions help fill halide vacancies. This synergistic interaction reduces trap-state density and suppresses non-radiative recombination pathways.
Third, the intrinsic dipole moment of NMAI induces surface reconstruction and modifies interfacial energetics. This dipole effect improves energy-level alignment between layers, enhances carrier injection, and promotes balanced electron and hole transport, ultimately facilitating efficient radiative recombination.
These combined effects lead to substantial improvements in both optical and device performance. The photoluminescence quantum yield (PLQY) of PQD films increases from 74.4% to 87.9%, indicating a significant reduction in non-radiative losses. Devices fabricated under ambient air conditions achieve a peak external quantum efficiency (EQE) of 16.15%, representing more than a threefold enhancement compared to untreated devices.
In addition to efficiency gains, operational stability is markedly improved. The device half-lifetime (T50) exceeds 140 minutes under a constant current density of 3 mA·cm⁻², corresponding to more than a fourfold increase. This demonstrates that the NMAI ligand effectively mitigates environmental degradation pathways while maintaining efficient charge transport.
Overall, this work highlights the importance of multifunctional ligand design in overcoming the longstanding trade-offs between passivation, environmental protection, and carrier dynamics. By enabling high-performance NIR-PQLEDs processed in air, the approach provides a practical pathway toward scalable, low-cost manufacturing of perovskite-based optoelectronic devices.
