Ultra-low efficiency roll-off high color purity blue perovskite QLEDs with exceeding 20% efficiency

Recent breakthroughs in device engineering have propelled the external quantum efficiency (EQE) of blue perovskite LEDs beyond 20%, rivaling cadmium-based QLEDs. However, this performance is typically accompanied by poor color purity—most efficient devices exhibit a CIEy > 0.1, far below the Rec. 2020 standard for blue. Moreover, devices tuned toward high color purity blue (CIEy < 0.1) often suffer from severe efficiency roll-off under high luminance (> 4,000 cd m^-2) and short operational lifetimes (T₅₀ < 100 minutes at 100 cd m^-2) due to surface defects, Auger recombination, and charge-injection imbalance. Therefore, achieving simultaneously high color purity, low roll-off, and long lifetime remains an unresolved bottleneck toward commercial viability.

 

In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Silu Tao from School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, and co-workers have developed a multifunctional molecule passivation strategy utilizing 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF₆). The [PF₆]⁻ anions coordinate with lead dangling bonds, cesium sites, reduce surface defects and weaken coupling, while [EMIM]⁺ cations suppress bromine-related defects, inhibit Auger recombination and tune the band alignment. Crucially, the resulting devices deliver a record-high EQE exceeding 20% at 6,441 cd m^-2 and maintain 18.47% EQE at 9,587 cd m^-2 with nearly eliminated roll-off, representing the best performance to date for blue perovskite QLEDs (CIEy < 0.1). Moreover, the operational lifetime improves by an order of magnitude compared with previous reports using the thermal evaporation process to fabricate devices, which reach 692 minutes at an initial brightness of 106 cd m^-2.

 

These scientists confirmed the improvement of the optical performance of QDs by the multifunctional molecule through time-resolved photoluminescence (TRPL) spectroscopy and photoluminescence quantum yield (PLQY); and demonstrated the enhanced stability of QDs after the introduction of the multifunctional molecule through illumination and high-temperature tests; also discovered that the 1-ethyl-3-methylImidazolium cations with a large permittivity can significantly inhibit the Auger recombination of QDs by enhancing the dielectric screening effect.

 

These scientists also used X-ray diffraction (XRD) spectra to confirm that the multifunctional molecule did not enter the interior of the lattice; and utilized Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) to illustrate the interaction between the multifunctional molecule and the QD surface; and discovered through scanning transmission electron microscopy (STEM) that the multifunctional molecule enhanced the degree of order of QD arrangement and weakened the coupling between QDs.

 

These scientists summarized: “We demonstrate that a multifunctional molecule effectively stabilizes perovskite QD surfaces, simultaneously addressing carrier trapping, interdot coupling, and Auger recombination—key challenges limiting blue perovskite QLED performance. These advances enable blue perovskite QLEDs that combine high color purity (CIEy = 0.091) with outstanding EQE (20.02%) at high luminance (6,441 cd m^-2) and exhibit markedly suppressed efficiency roll-off. Importantly, the devices also achieve extended operational lifetimes with stable emission spectra throughout.”

 

“Our findings provide a promising pathway toward robust, high-performance blue perovskite QLEDs suitable for demanding display applications.” they added.

 

“This work provides a solution to the problem of 'low efficiency at high luminance' that high color purity blue perovskite QLEDs may face in practical applications, and it should stimulate the interest of researchers in lowering the efficiency roll-off, and then promoting high color purity perovskite QLEDs to the market.” the scientists forecast.

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