Commission Internationale De L'Eclairage Coordinates Research Articles

Photoluminescence and Stability of Dion–Jacobson Tin-Based Halide Perovskites with Different Spacer Cation Chain Length

Two-dimensional tin halide perovskites are of significant interest for light emitting applications. Here, we investigate the effect of organic cation A on the stability of different Dion–Jacobson tin-based halide perovskites. The ASnBr4 materials using diammonium cation A with shorter alkyl chains are found to exhibit improved stability, exhibiting dramatic stability difference between the most stable HDASnBr4, where HDA denotes 1,6-hexanediammonium, and two materials with 8- and 10-carbon alkyl chain ammonium cations. The HDASnBr4 powders were thermally stable at 100 °C in an argon environment but exhibited decreasing photoluminescence with time in ambient air at 100 °C. The sample degradation at 100 °C is accelerated compared to room temperature, but it proceeds along similar pathways, namely phase transformation followed by perovskite decomposition. Light emission from HDASnBr4 thin films could be further enhanced by methanol vapor treatment, and warm white emission with Commission Internationale de l’Eclairage (CIE) coordinates (0.37, 0.34) could be obtained by combining HDASnBr4 with a blue-emitting polymer film, while direct mixing of blue phosphor and HDASnBr4 powder yields white emission with CIE coordinates of (0.34, 0.32).

Dual‐Core Engineering for Efficient Deep‐Blue Multiple Resonance Thermally Activated Delayed Fluorescent Materials

AbstractDeveloping narrowband blue multiple resonance (MR) organic emitters with Commission Internationale de L'Eclairage (CIE) y coordinates <0.1 is essential for advanced display technologies. This study proposes a deep‐blue thermally activated delayed fluorescence (TADF) emitter, named 2BNO, which integrates two independent MR cores. Unlike many TADF materials with single‐bonded dual emitting cores, 2BNO utilizes a steric hindrance‐assisted fluorene bridge to achieve an orthorhombic molecular structure. The dual‐core MR‐TADF emitter shows enhanced light absorption and a high photoluminescence quantum yield. Notably, the emission of 2BNO is not significantly redshifted compared to single‐core compounds and maintains a narrow full width at half‐maximum (FWHM) of 24 nm with CIE coordinates of (0.147, 0.041) in 2Me‐THF solution, nearing the BT.2020 blue standard. Organic light‐emitting diodes (OLEDs) incorporating 2BNO as the emitter exhibit deep‐blue emission at 460 nm with a narrow FWHM of 29 nm and CIE coordinates of (0.14, 0.09). The dual emitting core design significantly improves device efficiency, achieving a high external quantum efficiency (EQE) of 19.8%. The dual‐core molecular design strategy in this work is demonstrated to be effective in promoting the efficiency of the TADF emitters while preserving deep‐blue color purity.

Single-Molecule White Circularly Polarized Photoluminescence and Electroluminescence from Dual-Emission Enantiomers.

The strategy of integrating conformational isomerization donors and chiral acceptors in a single molecule was proposed to construct white circularly polarized luminescence (WCPL) materials in this work. Consequently, a pair of dual-emission enantiomers, namely (R/S)-DO-PTZ, were designed and synthesized, which displayed white emission with blue and yellow dual-emission bands in solution and solid films with Commission Internationale de l'Eclairage (CIE) coordinates of (0.30, 0.33) and (0.33, 0.35), respectively. Meanwhile, (R/S)-DO-PTZ exhibited a high PLQY of up to 67 % in doped films and clear mirror-image WCPL signals with a |glum| value of 3.0×10-3. Moreover, white circularly polarized electroluminescence (WCPEL) based on organic light-emitting diodes (OLEDs) with (R/S)-DO-PTZ as emitters were also achieved with CIE coordinates of (0.32, 0.37) and EQEmax of 4.7 %, representing the state-of-the-art level of white OLEDs based on single-molecule purely organic emitters. By optimizing the device structure, warm WCPEL devices were further obtained with a |gEL| value of 2.8×10-3, CIE coordinates of (0.37, 0.48) and EQEmax of up to 15.6 %. To our knowledge, this is the first report of CP-WOLEDs based on single-molecule purely organic emitters.

High‐Efficiency Deep Red Fluorescent Material with Aggregation Induced Emission and the Application in Organic Light‐Emitting Diodes

AbstractThe development of highly efficient deep red materials with emission wavelength beyond 650 nm remains a big challenge due to the constraints imposed by the energy gap rule. In this work, a donor‐acceptor‐donor type emitter, 4,7‐bis (10‐(4‐(tert‐butyl) phenyl)‐10H‐phenothiazin‐3‐yl) benzo[c][1,2,5] thiadiazole (TBPPTZ) is designed and synthesized. Resulting from the slight twist angle between the donor and acceptor units, TBPPTZ exhibits nearly planar conformation and an extended conjugated structure. TBPPTZ shows a deep red emission peak at 687 nm and aggregation induced emission property with a high photoluminescence quantum yield of 45 % in neat thin film. The optimized organic light‐emitting diode (OLEDs) utilizing TBPPTZ as the non‐doped emissive layer obtains a high external quantum efficiency (EQE) up to 2.51 % with an electroluminescence (EL) peak at 676 nm, aligning with the Commission Internationale de L'Eclairage (CIE) coordinates (0.68, 0.31), which shows a small EQE roll‐off of only 5.6 % at 100 cd m−2. Additionally, the doped OLED achieves an EQE up to 5.09 %, with an EL peak at 656 nm and CIE coordinates of (0.65, 0.34). The findings of this research not only contribute to achieve highly efficient deep red OLEDs but also offer a novel and effective deep red molecular strategy to realize high‐quality OLEDs.

Investigation of red-emitting CaMoO4: Eu3+ phosphor by partitioning of substitutional PO4 3- ions via solid-state reaction method.

To investigate the impact of PO4 3- anionic groups, the trivalent europium ion-doped calcium molybdate (CaMoO3-PO4:xEu3+, where x = 0.5, 1.0, 1.5, 2.0, and 2.5mol%) phosphors were synthesized using the solid-state reaction method. The detailed study of the phosphor materials was carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), optical diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The XRD results indicate that the substitution of PO4 3- anion and Eu3+ dopant ion did not affect the crystal structures of the CaMoO4 phosphors. Ultraviolet-visible (UV-vis) absorption analysis revealed the change of absorption edge of both un-doped and Eu3+-doped CaMoO4-PO4 phosphors. Under the 394 nm UV-excitation, the recorded PL spectra showed an intense peak at 615 nm corresponding to the Eu3+: 5D0 → 7F2 transition. The results of the Commission Internationale de l'Eclairage (CIE) diagram reported that the color of the emissions lies in the red color zone and there is no change in the CIE coordinates of the overall emission for Eu3+-doped CaMoO4-PO4 as Eu concentration changes. Thus, these observations led to finding the best red components for white light-emitting diode applications.

Fine tuning of excited states by trifluoromethylphenyl for blue-shifted color and enhanced EQEs in thermally activated delayed fluorescence emitters

3,6-di-tert-butyl-9H-carbazole and 3,6-diphenyl-9H-carbazole have been widely used to construct blue thermally activated delayed fluorescence (TADF) emitters. However, it is difficult for related emitters to achieve maximum external quantum efficiency (EQEmax) above 20 % with the Commission Internationale de l'Eclairage (CIE) y ≤ 0.12. A new type of donor was developed to construct blue TADF molecules, namely CF3P-BuCz-TRZ and CF3P-PhCz-TRZ. The weak electron-withdrawing trifluoromethylphenyl (CF3P) with moderate steric hindrance was introduced into the 1-site of carbazole donor for improving the color purity for blue TADF emitters. More importantly, the introduction of CF3P tightly compacts the energy levels for the significant excited states in RISC process. The energy gap between the lowest singlet excited (S1) state and the lowest triplet (T1) state (Δ E(S1−T1)), as well as between T1 and the higher triplet (Tn, n ≥ 2) states (Δ E(Tn−T1)) were reduced, so that Tn (n ≥ 2) could be effectively harvested to further promote reverse intersystem crossing (RISC). As a result, the OLEDs based on CF3P-BuCz-TRZ and CF3P-PhCz-TRZ displayed blue electroluminescence with CIE coordinates of (0.156, 0.107) and (0.155, 0.115). In particular, the maximum EQEs of the CF3P-PhCz-TRZ device reached 20.43 % without employing any light out-coupling enhancement or TADF-sensitized structure. This strategy should be valuable for designing more pure-blue and deep-blue TADF emitters.

Enhancing Light-Emitting Efficiency of Blue Through-Space Charge Transfer Emitters via Fixing Configuration Induced by Intramolecular Hydrogen Bonding.

Closely aligned configuration of the donor (D) and acceptor (A) is crucial for the light-emitting efficiency of thermally activated delayed fluorescence (TADF) materials with through-space charge transfer (TSCT) characteristics. However, precisely controlling the D-A distance of blue TSCT-TADF emitters is still challenging. Herein, an extra donor (D*) located on the side of the primary donor (D) is introduced to construct the hydrogen bonding with A and thus modulate the distance of D and A units to prepare high-efficiency blue TSCT emitters. The obtained "V"-shaped TSCT emitter presents a minimal D-A distance of 2.890 Å with a highly parallel D-A configuration. As a result, a high rate of radiative decay (>107 s-1) and photoluminescence quantum yield (nearly 90%) are achieved. The corresponding blue organic light-emitting diodes show maximum external quantum efficiencies (EQEmax) of 27.9% with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.16, 0.21), which is the highest device efficiency of fluorene-based blue TSCT-TADF emitters. In addition, the TSCT-TADF emitter-sensitized OLEDs also achieve a high EQEmax of 29.3% with a CIE coordinate of (0.12, 0.16) and a narrow emission.

Constructing multifunctional deep-blue emitters with weak charge transfer excited state for high-performance non-doped blue OLEDs and single-emissive-layer hybrid white OLEDs

Deep-blue emitter with high photoluminescence efficiency (PLQY) is highly desirable in ultra-high definition displays and white solid-state lightings. In this work, two deep-blue phenanthro[9,10]imidazole derivatives, PPIS and PPPIS, with hot exciton property are successfully developed. Compared to PPIS, the embedded phenyl bridge in PPPIS is able to effectively increase the overlap of frontier molecular orbitals. In consequence, PPPIS shows higher oscillator strength and significantly enhanced PLQY. PPPIS also achieves better electroluminescence performance in non-doped device, showing deep-blue emission with Commission International de l'Eclairage (CIE) coordinates of (0.153, 0.087) and the maximum external quantum efficiency (EQEmax) of 8.5% with minuscule efficiency roll-off. Meanwhile, when PPPIS serves as the host for phosphor PO-01, high-efficiency orange phosphorescent device is obtained with high EQEmax of 29.8% and negligible efficiency roll-off at 1000 cd/m2. Further, efficient single-emissive-layer white device is assembled via utilizing PPPIS as a blue emitter as well as the host for PO-01 simultaneously, providing warm-white emission with CIE coordinates of (0.429, 0.433) at 1000 cd/m2, the forward-viewing EQEmax of 27.2% and maximum power efficiency (PEmax) of 80.1 lm/W, respectively. Our studies can establish a viable design strategy for deep-blue emitters in high-performance non-doped blue OLEDs and hybrid WOLEDs.

Elastic Organic Crystals Exhibiting Amplified Spontaneous Emission Waveguides with Standard Red Chromaticity of the Rec.2020 Gamut.

The use of mechanically flexible molecular crystals as optical transuding media is demonstrated for a plethora of applications; however, the spectral peaks of optical outputs located mainly in the range of 400-600nm are insufficient for practical telecommunication and full-color display applications. Herein, two elastically bendable organic crystals are reported that show red emission of the rec.709 gamut under 365nm UV light irradiation yet generate rec.2020 gamut red optical waveguides and amplified spontaneous emissions when irradiated by a 355nm laser. Capitalizing on the extended π-conjugation and donor-acceptor character, as well as mechanical elasticity, these organic crystals exhibit flexible optical waveguides with Commission Internationale de L'Eclairage (CIE) coordinates of (0.70, 0.29), nearly identical to the red chromaticity of the rec.2020 gamut required for ultrahigh-definition (UHD) displays. Notably, one of the elastic crystals functions as a soft resonance cavity, resulting in amplified spontaneous emission waveguides with CIE coordinates of (0.71, 0.29) and the standard red chromaticity of the rec.2020 gamut, both in straight and bent states. This study presents a new avenue for the development of high-purity red-emissive crystalline materials to create all-organic, lightweight, and mechanically compliant optical telecommunication and UHD display devices.

Donor engineering to regulate fluorescence of a symmetrical structure based on a fluorene bridge for white light emission.

A white organic light-emitting device (WOLED) obtained using blue and yellow complementary colors possesses extremely high optical efficiency. We designed and prepared a completely symmetric D-π-D type efficient blue light small molecule FFA based on octylfluorene as a π bridge, where the undoped device showed efficient blue organic light-emitting device (OLED) performance with a maximum emission wavelength of 428 nm, Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.11) and one of the narrowest full width at half maximum (FWHM) of 35 nm. To improve the matching measure of complementary color materials for achieving white light emission, a yellow light small molecule FCzA was prepared by adjusting the conjugation degree of peripheral electron-donating groups based on the same fluorene-based π bridge with FFA. Undoped devices based on FCzA demonstrated an electroluminescence (EL) emission peak at 576 nm with CIE coordinates of (0.43, 0.49) and a relatively wide FWHM of 130 nm. Ultimately, the white OLED device was modulated with CIE coordinates located at (0.33, 0.38) via proportional regulation with a mixture of FFA and FCzA in a ratio of 10 : 3 as the light-emitting layer.

A record-high EQE of 7.65%@3300 cd m-2 achieved in non-doped near-ultraviolet OLEDs based on novel D'-D-A type bipolar fluorophores upon molecular configuration engineering.

Developing a high-performance near-ultraviolet (NUV) material and its simple non-doped device with a small efficiency roll-off and good color purity is a promising but challenging task. Here, we proposed a novel donor'-donor-acceptor (D'-D-A) type molecular strategy to largely solve the intrinsic contradictions among wide-bandgap NUV emission, fluorescence efficiency, carrier injection and transport. An efficient NUV fluorophore, 3,6-mPPICNC3, exhibiting a hybridized local and charge-transfer state, is achieved through precise molecular configuration engineering, realizing similar hole and electron mobilities at both low and high electric fields. Moreover, the planarized intramolecular charge transfer excited state and steric hindrance effect endow 3,6-mPPICNC3 with a considerable luminous efficiency and good color purity in the aggregation state. Consequently, the non-doped device emitting stable NUV light with Commission Internationale de l'Eclairage (CIE) coordinates of (0.160, 0.032) and a narrow full width at half maximum of 44 nm exhibits a state-of-the-art external quantum efficiency (EQE) of 7.67% and negligible efficiency roll-off over a luminance range from 0 to 3300 cd m-2. This is a record-high efficiency among all the reported non-doped NUV devices. Amazingly, an EQE of 7.85% and CIE coordinates of (0.161, 0.025) are achieved in the doped device. This demonstrates that the D'-D-A-type molecular structure has great potential for developing high-performance organic light-emitting materials and their optoelectronic applications.

Synthesis, structure and optoelectronic properties of iridium(III) complexes bearing a four-membered Ir-N-C[sbnd]N chelate structure

Herein four novel iridium(III) complexes (tfpmd)2Ir(dpppy) (Ir1a, tfpmd = 2-(4-(trifluoromethyl) phenyl) pyrimidine, dpppy = P,P-diphenyl-N-(pyridin-2-yl)phosphinic amide), (tfpmd)2Ir(dppq) (Ir1b, dppq = P,P-diphenyl-N-(quinolin-2-yl)phosphinic amide), (tfpqz)2Ir(dpppy) (Ir2a, tfpzq = 4-(4-(trifluoromethyl) phenyl) quinazoline) and (tfpqz)2Ir(dppq) (Ir2b) were synthetized, and their structures, opto-physical, and electro-chemical properties were investigated in detail. The crystal structure shows that these complexes exhibit pseudo-octahedral geometry around iridium atom coordinated by C, N atoms from cyclometalated and ancillary ligands. Interestingly, two coordinated nitrogen atoms from the ancillary ligand form an unusual quaternary ring with the central iridium ion. Ir1a and Ir1b emit pure-green light with Commission Internationale de L'Eclairage (CIE) color coordinates of (0.25, 0.67) and (0.22, 0.67), respectively, in CH2Cl2 solution. With the increase of the degree of conjugation of the cyclometalated ligand from tfpmd to tfpqz, the luminescence of complexes Ir2a and Ir2b is greatly red-shifted, and pure-red emission with CIE coordinates of (0.66, 0.34) and (0.66, 0.34), respectively, is obtained. The photophysical behaviors were reasonably explained by quantum chemical calculations. The calculation results shows that their emission is ascribed to the mixed 3MLCT (metal-ligand charge transfer, dπ(Ir)→π*(cyclometalated ligand)) and 3LLCT (ligand-ligand charge transfer, π(ancillary ligand)→π*(cyclometalated ligand)) states. Owing to their good thermal and electrochemical stabilities, organic light emitting diode (OLED) devices with dual-emitting layer structure and a space interlayer were fabricated and exhibited high electroluminescent properties and mild efficiency roll-off (14%-21%).

Triphenylamine-phenylimidazole based hybridized local and charge-transfer molecular as blue-green/ white light emission emitter for light-emitting diode application

In this work, a new triphenylamine-phenylimidazole derivative named (E)-N,N-diphenyl-4-(2-(4'-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1′-biphenyl]-4-yl)vinyl)aniline (DPAvlBPI) with hybridized local and charge-transfer (HLCT) characteristics was successfully developed. The undoped organic light-emitting diode (OLED) based on DPAvlBPI (XF-OLED) is prepared with a maximum external quantum efficiency (EQE) of 1.23 %, and the exciton utilization efficiency (EUE) can reach 41 %. The Commission Internationale de L'Eclairage (CIE) color coordinate of XF-OLED is (0.1925, 0.3975), indicating that the device is in the blue-green light region. Since the photoluminescence quantum efficiency (PLQY) of DPAvlBPI in neat film is only 0.12, the maximum brightness of the device is 545 cd m−2. However, by dispersing DPAvlBPI in silica gel at a low concentration, the PLQY can approach 1. Therefore, the DPAvlBPI-based organic/inorganic hybrid LED XF-HBLED is prepared, and the device can achieve a luminous efficacy of 18.64 lm/W and EQE of 9.98 % at an operating current of 64.90 mA. To broaden the application scope of DPAvlBPI, a “Halochromism” white light emission system based on DPAvlBPI has been prepared, and the solution type (XF-SWLED) and solid-state(XF-W2) white light emission device based on this system have been successfully realized. The luminous efficacy of XF-W2 with a CIE coordinate of (0.3205, 0.4363) can reach 14.92 lm/W with an EQE of 8.23 % under the operating current of 64.90 mA. This provides a reference for expanding the multifunctional/multi-device applications of HLCT molecules.

Efficient deep blue fluorescent emitters based on bipolar phenanthroimidazole-carbazole hybrid for non-doped electroluminescent device with small CIEy

In this work, four bipolar deep-blue emitting materials of 2-(4-(9H-carbazol-9-yl)phenyl)-1-(4-methylphenyl)-1H-phenanthro[9,10-d]imidazole (MePPIM-Cz), 2-(4-(9H-carbazol-9-yl)phenyl)-1-(4-chlorophenyl)-1H-phenanthro [9,10-d]imidazole (ClPPIM-Cz), 2-(4-(9H-carbazol-9-yl)phenyl)-1-(4-tert-butyl phenyl)-1H-phenanthro[9,10-d]imidazole (BuPPIM-Cz) and 2-(4-(9H-carbazol-9-yl) phenyl)-1-(4-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazole (TFMPPIM-Cz) based on phenanthroimidazole and carbazole group have been designed and synthesized by introducing different electron active substitutions into the N1 position of phenanthroimidazole. The thermal, photophysical, electrochemical and computational properties of four compounds were investigated. All compounds exhibited the deep blue emission and good thermal stability with glass transition temperature (Tg) in range of 126°C–137 °C. Single carrier devices were also fabricated and demonstrated that the four compounds have bipolar transporting properties. The non-doped organic light emitting diodes (OLEDs) based on MePPIM-Cz, ClPPIM-Cz, BuPPIM-Cz and TFMPPIM-Cz showed deep blue emission with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.07), (0.16, 0.06), (0.16, 0.05) and (0.16, 0.10) and the maximum external quantum efficiencies (EQEmax) of 2.67%, 2.24%, 1.81% and 1.09%, respectively. The CIE coordinates of MePPIM-Cz, ClPPIM-Cz and BuPPIM-Cz is extremely close to the National Television System Committee (NTSC) standard blue CIE of (0.14, 0.08), which is very significant for high color purity full-color display.

Synthesis and luminescence characterization of Dy3+/Sm3+ Co-doped Y2MgTiO6 double-perovskite phosphors for warm WLED

Y2MgTiO6:Dy3+/Sm3+ double-perovskite phosphors were synthesized using the high-temperature solid-state reaction method, and their luminescence properties were examined through various techniques, including Rietveld refinement, excitation and emission spectra, Commission Internationale de l'Eclairage (CIE) analysis, and band gap simulation. Ab initio calculations were performed to analyze the band gap and density of states, allowing for the prediction of the effect of Dy3+ and Sm3+ doping on emission intensity. The emission spectra of Y2MgTiO6 (YMTO) doped with Sm3+ and Dy3+ exhibited maximum peaks at 602 nm and 575 nm, respectively, when excited at 325 nm. Both YMTO:Sm3+ and YMTO:Dy3+ demonstrated excellent thermal stability. The CIE coordinates of YMTO doped with 1 mol% Dy3+ were determined to be (0.3771, 0.3804), with a correlated color temperature (CCT) of 4115 K, confirming its suitability for warm white light applications. Introducing 1 mol% and 3 mol% of Sm3+ ions into the Dy3+/Sm3+ co-doped YMTO allowed for adjustable CCT values of 3719 K and 3302 K, respectively, further enhancing their potential for use in warm white light-emitting diodes (WLEDs).

Cyan luminescence from Bi ions-doped borosilicate glass induced by the gradual substitution of MO (M=Ca, Sr, Ba)

At present, amorphous glasses that can give blue light, green light, and yellow light emission upon ultraviolet excitation have achieved good commercial prospect, but lacking of the high-efficiency cyan luminescence is still a challenging problem. To fill the lack of cyan light emission in the current white light LED technology spectrum excited by ultraviolet light, the effect of the substitution of CaO for SrO and BaO, and that of SrO for BaO on the optical properties, structure, DSC, and CIE (Commission International de L'Eclairage) coordinates of Bi ions-doped borosilicate glasses were systematically studied in this work. The emission spectra results reveal that the emission position of Bi ions-doped borosilicated glasses is observed from 482 nm to 492 nm when CaO is gradually replaced by SrO, from 482 nm to 502 nm when CaO is gradually replaced by BaO. In one word, the luminescent peak position of the Bi ions-doped borosilicate glass can be easily tuned by altering the concentration of basicity-earth oxide modifier, and the cyan light emission can be finally achieved.

Spectrally Stable Deep‐Blue Perovskite Light‐Emitting Diodes Enabled by a Deep Eutectic Solvent

AbstractFull‐color LED display requires Commission Internationale de l'Eclairage (CIE) 1931 coordinates of (0.14, 0.08), based on the National Television Standards Committee (NTSC) blue standard. However, such deep‐blue perovskite light‐emitting diodes (PeLEDs) still lag far behind in terms of device efficiency. Moreover, spectral stability remains a big challenge. To settle these issues, a kind of deep eutectic solvent (DES) is introduced as the perovskite precursor solvent additive, which is formed from a hydrogen bond acceptor (HBA) choline chloride and a hydrogen bond donor (HBD) urea via the hydrogen bond interaction. The incorporation of DES has multiple advantages, shown as follows: 1) improves the solubility of CsCl to yield dense perovskite morphology, 2) inhibits the growth of the perovskite crystal to achieve low‐n phases with narrow distribution, and 3) stabilizes the halide anions in the lattice to ensure stable electroluminescence (EL) spectra. As a result, the as‐prepared PeLED shows the maximum external quantum efficiency (EQEmax) of 2.71% with a CIE coordinate of (0.134, 0.055). With the increase in the DES concentration, the spectra stability is also obviously enhanced.

Novel “hot-exciton” material with high hole mobility for highly efficient deep red OLEDs

Due to the limitation of the energy gap rule, the development of highly efficient deep red hot-exciton material (λEL ≥ 650 nm) remains a great challenge. Here, we designed and synthesized a novel D-A-D type deep red fluorescent molecule, 4,7-bis(10-phenyl-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazole (2PPOXBZ), which is not only efficient deep red emitter but also has high hole mobility (2.56 × 10−3 cm2 V−1 s−1). The excited-state characteristics were investigated through photophysical experiments and theoretical calculations, it had been demonstrated the hot-exciton properties. The optimized non-doped OLED using 2PPOXBZ simultaneously act as a light-emitting layer and the hole transport layer exhibits the maximum external quantum efficiency (EQE) as high as 3.38% with a deep red emission peak at 678 nm, corresponding to the Commission International de L'Eclairage (CIE) coordinates (0.70, 0.30). More importantly, the optimized doped deep red OLED based on 2PPOXBZ as dopant exhibits an EQE up to 7.52% with electroluminescence (EL) peak of 658 nm and CIE coordinates of (0.67, 0.33), which is among the best results based on “Hot-exciton” deep red fluorescent OLEDs at present. The results of this study not only realize highly efficient deep red OLEDs with high color purity but also provide an effective molecular strategy for efficient deep red EL emitters.

Intrinsically Flexible and Aging Resistant Fluorene‐Based Rod‐Coil Copolymer for Bendable Deep‐Blue PLEDs

AbstractIn the field of flexible light‐emitting display, goal‐oriented intelligent molecular design is used to control various behaviors of molecules, which provides potential for the development of flexible light‐emitting conjugated polymers (LCPs). The introduction of non‐conjugated units into polymer molecules is a key prerequisite for realizing the intrinsic flexibility, but its easy interchain slip will also lead to the formation of interchain excited states, which is detrimental to the efficiency of light‐emitting diodes. Herein, two kinds of fluorene‐based rod‐coil copolymer with stable deep blue emission characteristics is presented and with Commission Internationale de L'Eclairage (CIE) coordinates of (0.18, 0.14) and (0.15, 0.09), respectively. Surprisingly, the copolymer films show efficient blue emission even at 100% tension. Meanwhile, the rod‐coil copolymer possesses better aging resistance compared to rigid π‐conjugated counterparts. Finally, both rigid and flexible light‐emitting diodes based on rod‐coil copolymer exhibit stable deep blue emission, and the G2‐based PLED with CIE coordinates of (0.16, 0.08), which approach National Television System Committee standard blue specification. These results confirm the validity of rod‐coil copolymer design strategy in constructing inherently flexible polymers with deep blue emission, which have great application potential in flexible PLEDs.

Spectrally Stable Pure Red CsPbI3 Quantum Dots Light‐Emitting Diodes via Effective Low Temperature Gradient Centrifugation Separation and Surface Modification

AbstractDevelopment of high‐performance and stable pure red perovskite light‐emitting devices (LEDs) promotes commercialization of perovskite. Benefiting from the quantum confinement effect, pure red CsPbI3 quantum dots (QDs) can avoid the color drift issue for mixed halide systems. Herein, a facile temperature‐dependent hot‐injection method combined with low temperature gradient centrifugation is employed to prepare 5.60 ± 0.05 nm pure red QDs. The QDs exhibit 642 nm photoluminescence (PL) with 37 nm full width at half maximum, and their Commission Internationale de l'Eclairage (CIE) coordinates located at (0.708, 0.292) match well with standard pure red for Rec. 2020. The PL half‐lifetime for pure red QDs solution is 210 days under ambient conditions, and both the X and Y coordinates of CIE only fluctuate within (0.002, 0.002). Finally, a simple NH4I post‐treatment to decrease ligand length further boosts the QDs conductivity, and the pure red LED exhibits 9.4% maximum external quantum efficiency. The electroluminescence spectra exhibits a sharp peak at 645 nm, and their CIE coordinates are located at (0.707, 0.290). Furthermore, the pure red LED exhibits both good working and color stability. Its half‐lifetime is 25.1 min and color drifts are only (0.002, 0.002) after 30.0 min of continuous working at 60 cd m−2 with a constant current density of 3.5 mA cm−2.