Themed collection FOCUS: Recent progress on Light-emitting Technologies

This work describes recent developments in near-infrared (NIR) organic light-emitting diode (OLED) emitters. We discuss applications of NIR OLEDs as well as various groups of highly luminescent materials used in the OLED emissive layer.

Thermally activated delayed fluorescent (TADF) materials shown great attention in Organic light-emitting diodes (OLEDs). Herein, we have systematically reviewed the Acceptor–Donor–Acceptor based TADF materials with electroluminescent characteristics.

We herein briefly review the recent advances in transition metal ion-doped cesium lead halide perovskite nanocrystals including the typical strategies for effective doping and optical properties manipulation.

To avoid the interlayer erosion challenge in the IJP process and direct patterning process of the QD emissive layer (EML), cross-linking strategies have been introduced to construct solvent-resistant films (hole transport layers or QD EMLs) upon exposure to heat or light.

Several methods are summarized for controlling the excited states of TADF conjugated polymers, covering: (a) maintaining suitable ΔE_ST; (b) localized triplet excited state assisted reverse intersystem crossing; (c) hyperfine coupling facilitates reverse intersystem crossing.

In this article, we overview the latest advancements in organic near-infrared (NIR) materials, light-emitting devices and their applications. Moreover, we discuss the current limitations and future prospects for the NIR technology.

This review focuses on fused-ring carbazole derivatives, their molecular design, electronic and photophysical properties, and their applications as the emitter and/or the host material in organic light emitting diodes (OLEDs).

The recent research progress of organic boron-containing thermally activated delayed fluorescence (TADF) materials is reviewed systematically with a focus on the molecular design, photophysical properties and performance of the corresponding OLEDs.

To summarize the achievements of organic micro/nanocrystals in the field of solid-state lasers, we herein briefly review their recent progress from the perspective of organic molecules, morphology modulation, laser applications in photonic devices.

The engineering of the refractive index, transition dipole moments, the integration of photonic structures, and the photon-recycling process are the representative strategies to improve the outcoupling in perovskite light-emitting diodes (PeLEDs).

This review summarizes the mechanisms and development of sensitized OLEDs, with phosphorescent, TADF, and exciplex materials as sensitizers.

Recent advances in solution-processed organic light-emitting diodes toward printing displays are reviewed in terms of light-emitting materials, devices, printing techniques and applications.

The synthesis and structural design of I–III–VI quantum dots are summarized and WLED applications are highlighted. The routes to improve the performance of WLED devices and the challenges of design optimization and practical application are discussed.

The decreased energy difference between ⁴T₂ and ²E states leads to tunable and abnormal thermal quenching performance of Lu_3−xCa_xGa_5−xSi_xO₁₂:Cr³⁺ phosphors.

Multiple-site functionalization of fluorene-based molecules can not only obtain robust deep-blue electroluminescent behavior but also enhance the film-forming ability to manufacture large-area film via solution processing technology.

Due to their rigid and plane conjugated skeletons, small molecular semiconductors always present irreversible brittle properties in the nano-film state, which is not conducive to deformation and operation stability in flexible optoelectronic devices.

We developed a facile synthesis for preparation of stable CsPbBr₃/Cs₂PbBr₅ heterostructures at room temperature, which could be used to scale up production of perovskite phosphors without compromising their performance. This process used SiO₂ nanospheres to avoid using hazardous organic solvents.

Constructing regioisomeric red TADF emitters via managing donor connecting patterns. A DPDPZ-PXZPh-based OLED affords an improved EQE of 28.0%, peaking at 600 nm.

Linearly expanded rigid TADF emitters, composed of a tri-spiral acridine donor and a spiro-fluorenyl-B-heterotriangulene acceptor, exhibit very high horizontal dipole orientation ratios, thereby achieving high efficiencies in deep-blue OLEDs.

Deep-red (DR)/near-infrared (NIR) emitters have extensive applications in bioimaging and flexible optoelectronics.

Two green Ir(III) complexes based on the ligands containing indolo[3,2,1-jk]carbazole and pyrimidine units show high PLQYs and small FWHMs. The OLEDs show good performances with an EQE_max of 31.3% and extremely low efficiency roll-offs.

Phenoxazine–phenazine exhibits variable emission by suppressing and utilizing Kasha's rule and demonstrates both dual emission and near-infrared emission. This significant mechanism related to Kasha's rule would be advantageous in various fields.

The origin of the reorganization energy can be elucidated from the perspective of molecular orbital (MO). Furthermore, the reorganization energy variations can be rationalized by MO distribution.

Pt(II) dicarbene pincer complexes served as a promising dopant sensitizer to an MR-TADF terminal emitter.

Energy transfer and charge transport in the thermally activated delayed fluorescence polymer doped quantum-dots were investigated. A high EQE of 18.1% was demonstrated for the first time in the quantum-dot red LEDs without any hole transport layers.

White light-emitting diodes (WLEDs) are gradually replacing traditional lighting devices and are becoming a mainstream photosource, as they have advantages of low energy consumption and high efficiency.

The introduction of different donors at the para-carbon position of the BNCz core modulates the predominance of locally excited (LE)/charger transfer (CT) states of the TADF materials to achieve full-color emission.

Blue emitters with various electron-donors attached to the 9-phenyl-9-phosphafluorene oxide (PhFIOP) moiety and their thermally activated delayed fluorescence (TADF) behavior.

The regioisomeric effect of cyano substituents on the photoluminescence and electroluminescence properties of thermally activated delayed fluorescence molecules is studied.

A super-efficient hybrid WOLED was achieved by blending the HLCT-based blue fluorescent molecule (TPACFOXZ) with a yellow phosphorescent molecule.

Benefitting from the concurrent intramolecular TBCT and TSCT of ortho-linked TADF materials, high k_F and k_RISC are achieved simultaneously and the devices using o-DCz-TRZ and BN-DMAc as emitters achieved high EQEs of 20.3% and 24.2%.

High-performance red and NIR organic light-emitting diodes (OLEDs) have been achieved using highly robust and phosphorescent diplatinum(II) complexes featuring strong intramolecular Pt–Pt and π–π interactions.

High band exciton is easily trapped and quenched by the defect structure in wide bandgap light-emitting conjugated materials (LCMs), which is harmful to the performance and stability of deep-blue organic light-emitting diodes (OLEDs).

Highly emissive organic semiconductor that supports the combination of balanced ambipolar charge transport, weakened light waveguiding, and strongly polarized surface electroluminescence in organic light-emitting transistors is reported.

High external quantum efficiencies of 7.08% and 27.30% and low efficiency roll-off are achieved simultaneously based on HLCT-sensitized fluorescent and phosphorescent OLEDs.

A facile EuCl₃-based route to CsAgCl₂ nanocrystals with tunable particle size was proposed. LEDs fabricated exhibit favorable warm white-light emission, which opens up new avenues to develop single-component warm white LEDs.

TADF dendrimers with a D–A–D structure, with multi-carbazole as the donor and di(pyridine-3-yl)methanone as the acceptor, are synthesized and their solution-processed OLEDs achieved a CE_max of 52.6 vs. 27.0 cd A⁻¹ and an EQE_max of 20.4% vs. 9.2%.

A donor–π-acceptor-type TADF emitter (BzITz) was designed and synthesized using 5H-benzo[d]benzo[4,5]imidazo[1,2-a]imidazole as a fused rigid electron donor and a benzonitrile merged triazine unit as an electron acceptor.

A solution-processable HLCT fluorescent molecule realizes a highly efficient non-doped OLED with a high brightness of 30 800 cd m⁻², a maximum external quantum efficiency (EQE_max) of 6.74% and a maximum current efficiency (CE_max) of 14.38 cd A⁻¹.

XTaO₄:Cr³⁺ presents a high internal/external quantum efficiency and good thermal stability.

Formation of secondary phase polytypes through incorporation of copper into MAPbBr₃ perovskite yields bandgap reduction with generation of near-IR photocarriers.

A deep-blue HLCT emitter PTPC achieved a high EQE of 6.78% in a non-doped OLED as well as a low ASE threshold of 1.18 μJ cm⁻².

Utilization of a purely organic based room-temperature phosphorescent (RTPH) emitter as a sensitizer was studied by employing it in yellow fluorescent organic light-emitting diodes (OLEDs).

Deep blue electroluminescence is highly required for organic light-emitting diode (OLED) technology. We report, in this work, blue emitting fluorophores for OLED with  low CIEy.

The blue-emissive Cs₃Cu₂I₅, yellow-emissive CsCu₂I₃, and white-emissive Cs₃Cu₂I₅@CsCu₂I₃ composites have been obtained by a one-step microwave method. The three UV-pumped WLEDs are fabricated by using the composites, and a CRI of 92 is achieved.

We report a current efficiency of 99.7 cd A⁻¹ for a red OLED with an electroluminescence (EL) peak at 604 nm (full width at half maximum of 32 nm).

The color purity of the pixels is an essential indicator in organic light-emitting diode (OLED) commercial displays.

New aggregation-induced delayed fluorescence luminogens are developed, which exhibit high electroluminescence efficiencies, very small efficiency roll-offs and high emission color stability.

The development of high-performance host materials for blue thermally activated delayed fluorescence (TADF) emitters is crucial for realizing efficient blue organic light-emitting diodes (OLEDs).

Spirobifluorene modified materials developed as electron transport layers lowered device driving voltage, enhanced quantum efficiency, and more than doubled the lifetime of green phosphorescent organic light-emitting diodes.

The emission mechanism and origin of the host and Cr³⁺/Yb³⁺ co-doped Ca₄ZrGe₃O₁₂.

Metal halide perovskites are emerging as promising candidates for next-generation display and lighting technologies.

Recent advancements in solution-processable AIO hybrid semiconductors. The formation of ionic and coordinate bonds at the organic/inorganic interface leads to desirable properties for the fabrication of thin-film based optoelectronic devices.

This Chemistry Frontiers deals with a new generation of host materials for phosphorescent OLEDs only constituted with carbon and hydrogen atoms, which can be beneficial for the future development of the OLED industry.