Pure Blue Organic Light-emitting Diodes Research Articles

Stepwise Toward Pure Blue Organic Light-Emitting Diodes by Synergetically Locking and Shielding Carbonyl/Nitrogen-Based MR-TADF Emitters.

Deep-blue multi-resonance (MR) emitters with stable and narrow full-width-at-half-maximum (FWHM) are of great importance for widening the color gamut of organic light-emitting diodes (OLEDs). However, most planar MR emitters are vulnerable to intermolecular interactions from both the host and guest, causing spectral broadening and exciton quenching in thin films. Their emission in the solid state is environmentally sensitive, and the color purity is often inferior to that in solutions. Herein, a molecular design strategy is presented that simultaneously narrows the FWHM and suppresses intermolecular interactions by combining intramolecular locking and peripheral shielding within a carbonyl/nitrogen-based MR core. Intramolecularly locking carbonyl/nitrogen-based bears narrower emission of 2,10-dimethyl-12,12-diphenyl-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione in solution and further with peripheral-shielding groups, deep-blue emitter (12,12-diphenyl-2,10-bis(9-phenyl-9H-fluoren-9-yl)-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione, DPQAO-F) exhibits ultra-pure emission with narrow FWHM (c.a., 24nm) with minimal variations (∆FWHM ≤ 3nm) from solution to thin films over a wide doping range. An OLED based onDPQAO-F presents a maximum external quantum efficiency (EQEmax) of 19.9% and color index of (0.134, 0.118). Furthermore, the hyper-device of DPQAO-F exhibits a record-high EQEmax of 32.7% in the deep-blue region, representing the first example of carbonyl/nitrogen-based OLED that can concurrently achieve narrow bandwidth in the deep-blue region and a high electroluminescent efficiency surpassing 30%.

Imide-modified thermally activated delayed fluorescent materials for pure blue organic light-emitting diodes with low efficiency roll-off

Imide-modified thermally activated delayed fluorescent materials for pure blue organic light-emitting diodes with low efficiency roll-off

Carbazole-based thermally activated delayed fluorescent emitters for efficient pure blue organic light-emitting diodes

Carbazole-based thermally activated delayed fluorescent emitters for efficient pure blue organic light-emitting diodes

Pure blue emitters based on benzo[4,5]thieno-S,S-dioxide-[3,2-b]benzofuran with high thermal stability

Molecules with hybrid local charge transfer (HLCT) state can theoretically realize 100% exciton utilization by using high energy level triplet excitons to generate singlet excitons through reverse intersystem crossing, and thus has attracted attention. Because it is difficult to obtain HLCT molecules with both short-wavelength emission and high exciton utilization, it is challenging to develop high-performance pure blue organic light-emitting diodes (OLEDs). In this study, a series of novel D-π-A blue emitters (CZ-Ph-BTOBF, DCZ-Ph-BTOBF and SAF-Ph-BTOBF) with carbazolyl or acridinyl group as a donor, benzo [4,5]thieno-S,S-dioxide-[3,2-b]benzofuran (BTOBF) as an acceptor, and phenyl group as a π bridge are designed and synthesized. These emitters exhibit good thermal, morphological stability and HLCT excited-state characteristics. OLEDs using CZ-Ph-BTOBF efficiently emits pure blue light (472 nm, CIEx,y = 0.15, 0.17) with full width at half maximum (FWHM) of 65 nm and maximum external quantum efficiency (EQE) of 6.85%. The visible bright blue emission is corroborated by the remarkably high photoluminescent quantum yield up to 92% in doped thin films. OLEDs of DCZ-Ph-BTOBF also exhibit pure blue emission with enhanced color purity (CIEx,y = 0.15, 0.11) and narrow emission peaks (FWHM = 64 nm). In conclusion, by adding a phenyl π bridge between the donor and acceptor groups, triplet excitons can be utilized through HLCT excited states and thus the electroluminescence efficiency can be improved. These results suggest that the rationally designed BTOBF based emitters have great potential for achieving solution-processible, high-performance and stable blue OLEDs.

Boron‐Based Multi‐Resonance TADF Emitter with Suppressed Intermolecular Interaction and Isomer Formation for Efficient Pure Blue OLEDs (Small 19/2022)

Pure Blue Organic Light-Emitting Diodes In article number 2107574, Jeong-Hwan Lee, Yun-Hi Kim, and co-workers use a strategic substitution of the bulky groups to effectively suppress the intermolecular interaction and the formation of isomers in mBP-DABNA-Me. Therefore, the mBP-DABNA-Me–based organic light-emitting diode exhibits an efficiency of 24.3% with a pure blue emission, color-coordinate of (0.124, 0.140). Notably, the substituents hinder the bathochromic shift, keeping the pure blue emission even at a high concentration of 25%.

Multiple charge transfer disk-like emitters with fast fluorescence radiation rate and high horizontal dipole orientation for pure blue organic light-emitting diodes

• Multiple CT channels and 3 LE states contribute to the speedy k r and RISC processes. • High Θ and small FWHM are realized due to the rigid disk-like structure. • η r and η out above 30% are achieved owing to triplet exciton utilization and high Θ . • EQE above 10% was realized for the standard blue device based on BO3N. The efficiency of pure blue Organic light-emitting diodes (OLEDs) still needs to be improved, which is limited by the utilization of the forbidden transition triplet excitons and low light-out-coupling efficiency in devices. Herein, two blue emitters were developed through combining multiple diphenylamine (DPA) donors with an oxygen-bridged boron (DBA) or triphenyl triazine (TRZ) acceptor. Notably, a narrow-band deep blue emission with a peak of 423 nm and a Full-width at half-maximum (FWHM) of 34 nm is realized for the boron-based emitter in toluene solution. Thanks to their multiple Charge transfer (CT) channels and high orientated disk-like structure, high radiative transition rates ( k r > 10 8 s −1 ) and high horizontal emitting dipole ratios ( Θ > 80%) can be realized simultaneously. Meanwhile, the introduction of the peripheral DPA units can also provide multiple localized triplet ( 3 LE) states for spin up-conversion of forbidden transition triplet excitons. Owing to the effective up-conversion of triplet excitons and high light-out-coupling efficiency, maximum external quantum efficiency of more than 10% is achieved for the boron emitter-based pure blue OLEDs with a Commission Internationale de l’Eclairage (CIE) coordinates of (0.14, 0.08).

Long-lasting and efficient inverted pure blue organic light-emitting diodes by inserting an ultrathin aluminum interlayer

Blue organic light-emitting diodes (OLEDs) play an important role in OLED display and lighting applications, but short lifetime and low efficiency are still their two key issues in the commercialization. Here, we manage to address the two issues at the same time by simply inserting an ultrathin aluminum (Al) interlayer between the indium tin oxide (ITO) cathode and the electron injection layer of an inverted pure blue OLED. Current efficiency (CE) and external quantum efficiency were improved by optimizing the thickness of the Al interlayer. It has been approved from current-voltage characteristics, impedance spectra and an ultraviolet photoelectron spectrum that 1 nm thick Al interlayer is an effective work function modifier for the ITO cathode and can help to enhance electron injection from the ITO cathode to the electron transporting layer. The Al interlayer contributed also to extend dramatically the lifetime of the inverted pure blue OLED. A long operation lifetime (T80 > 83 h) with the maximum CE of 7.9 cd A−1 was achieved after adding 1 nm Al interlayer.

Photophysical Identification of Three Kinds of Low-Energy Green Band Defects in Wide-Bandgap Polyfluorenes.

Blue-light-emitting semiconductors based on polyfluorenes often exhibit an undesired green emission band. In this report, three well-defined oligofluorenes corresponding to three types of "defects" attributed to aggregation, keto formation, and chain entanglement, respectively, are systemically investigated to unveil the origins of the green emission band in fluorene-based materials. First, the optical properties of defect molecules in different states are studied. The defect associated with aggregation is absent in dilute solutions and in films doped at 0.01 wt % with poly(methyl methacrylate). Second, the dependence of the emission spectra on the solvent was monitored to compare the effects of the "keto-" and "chain-entanglement defect" molecules. The green emission of keto defects exhibited a strong dependence on solvent polarity, whereas this cannot be observed in case of chain-entanglement defect. Third, energy transfer between poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]- co-[5-(octyloxy)-9,9-diphenyl-fluoren-2,7-diyl] and the keto or chain-entanglement defect molecules is illustrated. Compared to those of the chain-entanglement defect, the spectra of the keto defect molecule (1:10-3) show signs of defect emission at lower proportions. These investigations not only provide insight into the photophysics of oligofluorenes but also supply a new strategy to explore defects in semiconductor polymers, which will aid in the development of effective approaches to obtain stable, pure blue organic light-emitting diodes based on polyfluorenes.

Efficient non-doped pure blue organic light-emitting diodes based on an asymmetric phenylenevinylene with cis double bond

We reported an asymmetric phenylenevinylene with a cis double bond 2-(4-( p-tolyl)styryl)-1,4-dip-tolylbenzene ( cis-TSDTB) and its use as efficient deep-blue emitter for organic light-emitting diodes (OLEDs) applications. The crystal structure of cis-TSDTB showed torsion configuration and asymmetric geometry, which make it packing in a reduced intermolecular interaction arrangement. And its single crystals showed excellent fluorescence owing to this unique molecular configuration. Typical OLEDs using cis-TSDTB as non-doped emitters exhibited saturated blue light with the CIE 1931 coordinates of (0.15, 0.10), which is quite close to the National Television Standards Committee (NTSC) blue standard. High luminescence efficiency (3.4 cd A −1) and high brightness (9855 cd m −2) have been realized in the device. All of these outstanding results indicated that cis-phenylenevinylene will be a promising candidate as blue light-emitting materials.