Perovskite LED - Page 2

Researchers from Hanyang University, Ajou University and POSTECH have developed a hydrolysis-assisted ligand-exchange strategy that significantly improves charge transport and efficiency in metal halide perovskite nanocrystal (MHP NC) LEDs, achieving a record external quantum efficiency (EQE) of 31.7% for green-emitting devices.

Schematic illustration of the ligand-exchange and surface-functionalization process of MHP NCs. Image from: Advanced Materials

MHP nanocrystals are widely considered promising candidates for next-generation light-emitting diodes due to their excellent color purity and high radiative efficiency. However, their performance has been limited by the presence of long-chain native ligands on the nanocrystal surface. These ligands are weakly bound and electrically insulating, which hinders charge injection and transport, introduces trap states, and ultimately leads to energy losses in devices. To address these challenges, the researchers introduced a multifunctional π-conjugated pyridine carboxamide (PCA) ligand via a hydrolysis-assisted, one-step ligand-exchange process. This approach removes the original insulating ligands under mild conditions and replaces them with PCA, which provides multidentate, multisite surface coordination. The ligand acts as a strong anchoring group while simultaneously enabling enhanced electronic coupling between nanocrystals and inducing n-type surface functionalization.

Researchers from the University of Science and Technology of China and the University of Colorado Boulder have demonstrated a perovskite diode that acts as both an efficient solar cell and a high‑efficiency LED using the same 800 nm thick absorber layer.

The device embeds porous micrometer‑scale alumina (Al₂O₃) “sponge” islands (∼5 μm wide, 0.5 μm tall) inside the perovskite, allowing a layer thick enough for photovoltaics to also extract light efficiently like an LED. In conventional devices, perovskite LEDs rely on ultrathin, discontinuous layers of about 50 nm, whereas efficient solar cells need layers roughly sixteen times thicker; this architecture reconciles those opposing thickness requirements in a single stack. Surface‑functionalized alumina nanoparticles assemble electrostatically into these islands: one population is coated with negatively charged Me‑4PACz, the other with positively charged ODA, giving a porous, low‑index network the perovskite can grow through without disrupting charge transport.

A recent University at Buffalo (SUNY) study has shown that a fluorinated multifunctional ligand can dramatically improve both efficiency and stability in deep-blue CsPb(Br/Cl)₃ perovskite nanocrystal LEDs by suppressing defect formation and halide ion migration.

Deep-blue PeLEDs require emission in the 460-470 nm range, which can be realized either with mixed-halide CsPb(Br/Cl)₃ nanocrystals or with strongly quantum-confined CsPbBr₃ nanoplatelets. Quantum-confined CsPbBr₃ NPLs have demonstrated 461 nm emission with a 13 nm FWHM and 96% PLQY, enabling REC.2020-compliant deep blue (CIE (0.135, 0.046)), but EQE remains below 7%. Mixed-halide CsPb(Br/Cl)₃ offers a more direct compositional route, yet is prone to halide vacancies and instability, as seen in formamidinium-doped CsPb(Cl₀.₅Br₀.₅)₃ PeNCs that reach 1452 cd m⁻² but only 5% EQE and a peak at 474 nm, slightly red of the target window. In the new work, HFPA-engineered CsPb(Br/Cl)₃ emitters are tuned specifically for operation in the 460-470 nm pure-blue range, directly targeting display-relevant color coordinates.

Researchers from Shaanxi University of Science & Technology, Henan Academy of Sciences and North China Electric Power University have developed a dual-active-site ligand strategy to address one of the most persistent challenges in mixed-halide perovskite nanocrystal LEDs: halide ion migration and the resulting spectral instability.

Mixed Br/I CsPbI₃₋ₓBrₓ nanocrystals are widely considered the most viable route to achieving pure-red emission in the 620-650 nm range required by the Rec. 2020 display standard (CIE coordinates ~0.708, 0.292). However, under an applied electric field, mobile halide ions (Br⁻ and I⁻) readily migrate through vacancy-mediated hopping pathways. This leads to phase segregation into bromide-rich and iodide-rich domains, causing irreversible spectral shifts, efficiency loss, and device degradation. While external quantum efficiencies (EQEs) of pure-red perovskite LEDs have exceeded 20% in recent years, operational spectral stability remains a key bottleneck.

Researchers from the University of Electronic Science and Technology of China, Harbin Engineering University, Peking University and Soochow University have reported an advance in blue perovskite quantum dot light-emitting diodes (QLEDs), achieving record-high efficiency with minimal roll-off and excellent spectral stability. By introducing a multifunctional molecule passivation strategy based on 1‑ethyl‑3‑methylimidazolium hexafluorophosphate (EMIMPF₆), the team effectively suppressed multiple non-radiative decay pathways that have long limited blue perovskite QLED performance.

The [PF₆]⁻ anions in EMIMPF₆ coordinate strongly with lead dangling bonds and cesium sites, substantially reducing defect-assisted carrier loss and mitigating inter-dot electronic coupling. Complementarily, the [EMIM]⁺ cations interact with bromine vacancies and modulate band alignment, optimizing hole injection and improving charge balance under operating bias. This synergistic dual-ion passivation also increases the dielectric constant of the active layer, which suppresses Auger recombination - a major contributor to efficiency roll-off in high-brightness operation.

Researchers at CEA-Leti (Université Grenoble Alpes) have developed green and red-emitting thin-film perovskite color conversion layers (CCLs) using pulsed laser deposition (PLD), targeting GaN-based microLED displays for AR/MR applications.

GaN-based microLEDs offer a superior image quality with high dynamic range and saturated colors for AR/MR glasses, smartwatches, and more. However, achieving full-color pixels remains difficult since conventional InGaN/GaN multi-quantum wells (MQWs) emit a single color based on indium content - blue (~10% In), green (~25% In with lower efficiency), or red requiring separate InGaP materials. Mass-transfer works for larger displays but fails for microdisplays needing sub-1μm pixel pitches, where growing all three colors adjacently is still years from production.

Researchers from Nankai University, Hebei University and King Saud University have developed a new strategy for fabricating all‑perovskite triple‑junction light‑emitting diodes (LEDs) that simultaneously emit red, green, and blue light. This breakthrough could mark a step toward high‑efficiency, full‑color back‑lighting for next‑generation ultrahigh‑definition (UHD) displays.

Triple‑junction tandem LEDs are widely seen as the ideal architecture for compact, energy‑efficient white light sources. However, stacking multiple metal halide perovskite layers through conventional solution processing often causes severe interlayer damage and carrier losses, making it difficult to maintain high efficiency across the junctions. To address this, the team introduced a manufacturing‑compatible transfer‑printing approach for seamless monolithic integration of the three emissive layers. 

Researchers from Tsinghua University and Beijing Institute of Technology have developed an ion-pair pinning strategy that enables the fabrication of high-performance perovskite quantum dot light-emitting diodes (QLEDs) under ambient air conditions - an important step toward cost-effective, large-scale production of next-generation display and lighting technologies.

a Schematic structure, b cross-sectional SEM image, and c energy diagram of the device. Image from: Light: Science & Applications

Traditionally, the emissive perovskite quantum dot (QD) layers used in QLEDs must be processed in inert gas atmospheres to avoid degradation from moisture and oxygen. This requirement hinders manufacturing scalability and increases costs. To overcome this, the team introduced tetraalkylammonium triflate (NR₄OTf) into the precursor solution to stabilize and passivate formamidinium lead bromide (FAPbBr₃) QD films during air processing.

Sungkyunkwan University (SKKU) researchers have developed an indium-free transparent electrode technology for perovskite light-emitting diodes (PeLEDs), achieving high performance, chemical robustness, and improved device stability. The work, led by Professors Han-Ki Kim and Bo Ram Lee, introduces nitrogen-doped tin oxide (NTO) as a cost-effective, sustainable alternative to conventional indium tin oxide (ITO).

Image from: Materials Today

Perovskite LEDs are recognized for their exceptional color purity and processing flexibility, but the reliance on ITO remains a bottleneck due to indium’s rarity, high cost, and poor chemical compatibility with acidic hole transport layers such as PEDOT:PSS. Over time, indium diffusion and electrode corrosion can degrade device performance and shorten operational lifetime.

Researchers from Jilin University, Fudan University, the Chinese Academy of Sciences (CAS), Beijing Jiaotong University, and Southeast University have developed a new design strategy for metal halide perovskite light-emitting diodes (PeLEDs) that improves their performance while simplifying fabrication. Their work introduces a spontaneously formed 3D/2D vertically oriented perovskite heterojunction, created via a simple one-step spin-coating process that simultaneously improves charge confinement, light extraction, and operational stability.

PeLEDs hold great promise for next-generation displays and lighting due to their tunable colors, high brightness, and low manufacturing costs. However, their efficiency has traditionally fallen short of organic LEDs (OLEDs) - which can reach ~40% external quantum efficiency (EQE) - because of insufficient charge confinement and non-radiative recombination losses at defect-rich surfaces.