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Theoretical and experimental study on the electronic and optical properties of K <sub/>0.5</sub> Rb <sub/>0.5</sub> Pb <sub/>2</sub> Br <sub/>5</sub> : a promising laser host material
摘要： The data on the electronic structure and optical properties of bromide K0.5Rb0.5Pb2Br5 achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported. The kinetic energy, the Coulomb potential induced by the exchange hole, spin-orbital effects, and Coulomb repulsion were taken into account by applying the Tran and Blaha modified Becke–Johnson function (TB-mBJ), Hubbard U parameter, and spin-orbital coupling effect (SOC) in the TB-mBJ + U + SOC technique. The band gap was for the first time defined to be 3.23 eV. The partial density of state (PDOS) curves of K0.5Rb0.5Pb2Br5 agree well with XES K Ll and Br Kb2, and XPS spectra. The valence band (VB) is characterized by the Pb-5d3/2 and Pb-5d5/2 sub-states locating in the vicinities of ~20 eV and ~18 eV, respectively. The VB middle part is mainly formed by K-3p, Rb-4p and Br-4s states, in which the separation of Rb-4p3/2 and Rb-4p1/2 was also observed. The strong hybridization of Br-p and Pb-s/p states near ~6.5 eV reveals a major covalent part in the Br–Pb bonding. With a large band gap of 3.23 eV, and the remarkably high possibility of inter-band transition in energy ranges of 4–7 eV, and 10–12 eV, the bromide K0.5Rb0.5Pb2Br5 is expected to be a very promising active host material for core valence luminescence and mid-infrared rare-earth doped laser materials. The anisotropy of optical properties in K0.5Rb0.5Pb2Br5 is not significant, and it occurs at the extrema in the optical spectra. The absorption coefficient a(u) is in the order of magnitude of 106 cm?1 for an energy range of 5–25 eV.
关键词： electronic structure,X-ray spectroscopy,optical properties,laser host material,first-principle calculations,K0.5Rb0.5Pb2Br5
更新于2025-09-23 15:19:57
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Structural isomers of 9-(pyridin-2-yl)-9H-carbazole in combination with 9a?2H-9,3':6a?2,9a?3-tercarbazole and their application to high efficiency solution processed green TADF OLEDs
摘要： Two host materials, CzPy2TCz and CzPy3TCz, were designed as structural isomers and synthesized to achieve high efficiency thermally activated delayed fluorescence-organic light emitting diodes (TADF-OLEDs). The design strategy involved introducing a pyridine group into the core structure as an electron-withdrawing unit and varying the substitution position of tercarbazole (TCz). To realize green TADF-OLED, the two host materials synthesized in this study have excellent thermal stability and high excited triplet energy (T1 ? 2.95–2.98 eV). The maximum external quantum efficiency and current efficiency values for CzPy2TCz were 23.81% and 80.2 cd/A, respectively and the respective values for CzPy3TCz were 20.27% and 70.1 cd/A, respectively. Structural isomers with carbazole (Cz) and TCz units at the 2,6-position of the pyridine core effectuate better device performance. Consequently, we found that the host materials introduced in this study play an important role in implementing high performing solution-processed green TADF-OLED.
关键词： Thermally activated delayed fluorescence,Organic light-emitting diode,Tercarbazole,Pyridine,Host material,Solution process
更新于2025-09-19 17:13:59
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High-performance hybrid white organic light-emitting diodes with bipolar host material and thermally activated delayed fluorescent emitter
摘要： Bipolar host material and thermally activated delayed fluorescent (TADF) emitter were used in hybrid white organic light-emitting diodes (OLEDs) with the aim to achieve high performance. First of all, the single color OLEDs was optimized by changing the thickness of hole transporting layer, electron transporting layer and the doping concentration of emission material. Then, white organic light-emitting diodes (WOLEDs) were fabricated on the basis of the former single color OLEDs by modifying the doping concentration of TADF emitter. Finally, an optimized white device shows the best results of 43.67 cd/A, 45.73 lm/W and 18.52% for current efficiency, power efficiency and external quantum efficiency, respectively. This research may supply a theoretical basis for the development of WOLEDs.
关键词： Thermally activated delayed fluorescent (TADF),Energy transfer,Hybrid white organic light-emitting diodes (WOLEDs),Bipolar host material,High performance
更新于2025-09-16 10:30:52
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Novel Carbazole/Fluorene-Based Host Material for Stable and Efficient Phosphorescent OLEDs
摘要： A novel host material of "M"-type carbazole/fluorene-based mDCzPF with a high triplet energy by utilizing meta-substituted phenyl groups as linkers was developed. It was demonstrated that the position of the substituents significantly affected the molecular configuration and dipole moment, which played a critical role in the device performances. Red phosphorescent OLED utilizing the "M"-type mDCzPF as the host represented a 10-fold operational lifetime improvement over the OLED using a "V"-type pDCzPF linked by para-substituted phenyl groups as the host because of the good charge transport ability of the mDCzPF. Additionally, the "M"-type mDCzPF host was also compatible with a blue emitting phosphorescent emitter PtNON. The PtNON-doped OLED using mDCzPF as the host exhibited a peak EQE of 18.3% with a small roll off, yet maintained an EQE of 13.3% at a high brightness of 5000 cd/m2. Thus, the novel "M"-type mDCzPF could be employed as stable host material for efficient OLED emitting across the whole visible spectrum. This study should provide a viable method for designing new host materials for the development of stable and efficient phosphorescent OLEDs.
关键词： operational lifetime,host material,blue device,OLED,high triplet energy
更新于2025-09-16 10:30:52
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Highly Efficient Solution-Processed TADF Bluish-Green and Hybrid White Organic Light-Emitting Diodes Using Novel Bipolar Host Materials
摘要： Two pyridine containing bipolar host materials with high triplet energy, 9,10-dihydro-9,9-dimethyl-10-(3-(6-(3-(9,9-dimethylacridin-10(9H)-yl)phenyl)pyridin-2-yl)phenyl acridin (DDMACPy) and N-(3-(6-(3-(diphenylamino)phenyl)pyridin-2-yl)phenyl)-N-phenylbenzenamine (DTPAPy), are synthesized from modifying the commonly adapted host material 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (DCzPPy). The HOMO levels of DDMACPy (5.50 eV) and DTPAPy (5.60 eV) are found to be shallower than that of DCzPPy (5.90 eV) that leads to the improvement in hole injection from the hole transport layer PEDOT:PSS (WF = 5.10 eV). These host materials are used in the emitting layer of bluish-green organic light-emitting diode (OLED) with the TADF emitter, 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DAMC-TRZ), as the guest. The DDMACPy-based device shows the highest performance among them with the maximum external quantum efficiency (EQEmax), current efficiency (CEmax) and power efficiency (PEmax) of 21.0%, 53.1 cd A-1 and 44.0 lm w-1 at CIE (0.17, 0.42), respectively. By further doping with the red emitting phosphor iridium(III) bis(2-phenylquinoline)(2,2,6,6-tetramethylheptane-3,5-ionate) [Ir(dpm)PQ2] and yellow emitting phosphor iridium(III) bis(4-(4-t-butyphenyl) thieno[3,2-c]pyridinato-N,C20)acetylacetonate (PO-01-TB) emitters into the bluish-green emitting layer, a TADF-phosphor hybrid white OLED (T-P WOLED) is obtained with excellent EQEmax, CEmax and PEmax of 17.4%, 48.7 cd A-1 and 44.5 lm w-1 at CIE (0.35, 0.44), respectively. Moreover, both the bluish-green and white OLED show the low efficiency roll-off with external quantum efficiencies at the brightness of 1000 cd m-2 (EQE1000) 18.7% and 16.2% respectively, and are the highest performance records among the solution-processed TADF bluish-green and T-P WOLEDs.
关键词： low efficiency roll-off,solution process,bipolar host material,TADF bluish-green organic light-emitting diode,hybrid white organic light emitting diode
更新于2025-09-12 10:27:22
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Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient full-color PhOLEDs
摘要： Many efforts have been focused on exploring highly efficient host materials that capable of function in phosphorescent organic light-emitting devices (PhOLEDs). However, superior hosts reported to date that are generally suitable to full-color devices are rare and the resultant device performances are far from satisfactory. A class of host compounds DCzPBI, POCzPBI, and DPOPBI, incorporating carbazole and diphenylphosphoryl oxide moieties as electron-donating and -accepting groups, respectively, are synthesized and successfully applied as universal hosts in the fabrication of full-color PhOLEDs. The effect of substituted groups on the photophysical, theoretical calculations, and electrochemical characters for host materials is systematically investigated. We adopt the same device architecture to fabricate the blue, green, yellow, and red PhOLEDs with the combination of the three hosts. As a result, DPOPBI and POCzPBI with good charge carrier transporting properties supported the devices with the impressive efficiencies. The best current efficiency (CE) are 23.2, 48.4, 45.7, 21.5 cd A?1 for blue, green, yellow, and red devices, respectively. Even at the brightnesses of 1000 cd m?2, the efficiency roll-offs are only 2% for green and 0.2% for yellow devices, indicating the promising applications as universal hosts for highly efficient PhOLEDs.
关键词： impressive efficiency,phosphorescent organic light-emitting device,good charge carrier transporting property,host material
更新于2025-09-11 14:15:04