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Abstract: By simple modification of the functional groups on the donor unit, the thermally activated delayed fluorescence (TADF) properties of emitters can easily be manipulated. A series of deep blue to blue emissive TADF derivatives is developed, capable of deep‐blue emissions from 403 to 460 nm in toluene. Deep‐blue organic light‐emitting diodes (OLEDs) based on this series of TADF emitters are fabricated, resulting in an electroluminescence peak at 428 nm and a high external quantum efficiency of up to 10.3%. One deep‐blue OLED has achieved the commission internationale de l'eclairage (CIE) coordinates of (0.156, 0.063), which is among the best reported TADF performances for deep‐blue OLEDs with CIEy < 0.07. [ABSTRACT FROM AUTHOR]

A family of organic emitters with a donor-σ-acceptor (D-σ-A) motif is presented. Owing to the weakly coupled D-σ-A intramolecular charge-transfer state, a transition from the localized excited triplet state (3LE) and charge-transfer triplet state (3CT) to the charge-transfer singlet state (1CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200-400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-σ-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes. [ABSTRACT FROM AUTHOR]

The development of efficient metal-free organic emitters with thermally activated delayed fluorescence (TADF) properties for deep-blue emission is still challenging. A new family of deep-blue TADF emitters based on a donor-acceptor architecture has been developed. The electronic interaction between donor and acceptor plays a key role in the TADF mechanism. Deep-blue OLEDs fabricated with these TADF emitters achieved high external quantum efficiencies over 19.2 % with CIE coordinates of (0.148, 0.098). [ABSTRACT FROM AUTHOR]

Much effort has been devoted to developing highly efficient organic light-emitting diodes (OLEDs) that function through phosphorescence or thermally activated delayed fluorescence (TADF). However, efficient host materials for blue TADF and phosphorescent guest emitters are limited because of their requirement of high triplet energy levels. Herein, we report the rigid acceptor unit benzimidazobenzothiazole (BID-BT), which is suitable for use in bipolar hosts in blue OLEDs. The designed host materials, based on BID-BT, possess high triplet energy and bipolar carrier transport ability. Both blue TADF and phosphorescent OLEDs containing BID-BT-based derivatives exhibit external quantum efficiencies as high as 20 %, indicating that these hosts allow efficient triplet exciton confinement appropriate for blue TADF and phosphorescent guest emitters. [ABSTRACT FROM AUTHOR]

Two new 10-phenyl-9,10-dihydroacridine derivatives attached by dibenzothiophene (DBT) and dibenzofuran (DBF) were synthesized. The influence of the substituents of these materials was studied by theoretical calculations (DFT calculation) and experimental measurements. Owing to the twisted N-phenyl ring, both molecules possess sufficiently high triplet energies and are suitable as hosts for phosphorescent organic light-emitting diodes. To evaluate the electroluminescent (EL) performance of these materials, FIrpic-based blue PHOLEDs and two-color white PHOLEDs (FIrpic and PO-01 as the dopants) were fabricated using the common device structures. High external quantum efficiencies (EQE) of 21.1 % and 20.9 % for FIrpic-based blue PHOLEDs were achieved by FPhAc and TPhAc, respectively. The white device based on the host FPhAc achieved a higher performance, with a maximum EQE of 24.7 % than the device with TPhAc as host material. [ABSTRACT FROM AUTHOR]

Highlights: [•] The HOMO energy levels of carbazole-based host materials can be independently turned with simple spacers. [•] A blue PHOLED device incorporating PBCz host achieved a maximum EQE of 19.5%. [•] Two-color, all-phosphor WOLEDs was achieved with an EQE of 24.6%. [•] The three colors WOLEDs was demonstrated a high EQE of 19.1%. [Copyright &y& Elsevier]

Theintrinsic asymmetry of 1,2,4-oxadiazole was utilized to synthesizethree isomers, DCzmOXD-1, DCzmOXD-2, and mCzmOXD, and high tripletenergies over 2.80 eV made them good candidates for host materialsin blue OLEDs. The best efficiencies of 23.0 cd A–1/20.5 lm W1–/11.2% in CE/PE/EQE were achieved byDCzmOXD-1 with derivation at the β-carbon position of 1,2,4-oxadiazole. [ABSTRACT FROM AUTHOR]

Abstract: Two novel bipolar host materials, namely 3,5-bis(4-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (pCzmOXD) and 3,5-bis(3-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (mCzmOXD) were designed and synthesized, by incorporating a new block 1,2,4-oxadiazole as the n-type moiety and changing its linking pattern with carbazole. As expected, high triplet energy (over 2.81 eV) for mCzmOXD was achieved due to the intrinsic meta-linkage of 1,2,4-oxadiazole. When both materials were applied in blue phosphorescent organic light-emitting diodes, good performance of 13.0 cd A−1/16.0 cd A−1 were achieved for pCzmOXD and mCzmOXD in iridium(III) picolinate (FIrpic)-based devices, respectively. [Copyright &y& Elsevier]

A novel silicon-based compound, 10-phenyl-2′-(triphenylsilyl)-10 H-spiro[acridine-9,9′-fluorene] (SSTF), with spiro structure has been designed, synthesized, and characterized. Its thermal, electronic absorption, and photoluminescence properties were studied. Its energy levels make it suitable as a host material or exciton-blocking material in blue phosphorescent organic light-emitting diodes (PhOLEDs). Accordingly, blue-emitting devices with iridium(III) bis[(4,6-difluorophenyl)-pyridinato- N, C2′]picolinate (FIrpic) as phosphorescent dopant have been fabricated and show high efficiency with low roll-off. In particular, 44.0 cd A−1 (41.3 lm W−1) at 100 cd m−2 and 41.9 cd A−1 (32.9 lm W−1) at 1000 cd m−2 were achieved when SSTF was used as host material; 28.1 lm W−1 at 100 cd m−2 and 20.6 lm W−1 at 1000 cd m−2 were achieved when SSTF was used as exciton-blocking layer. All of the results are superior to those of the reference devices and show the potential applicability and versatility of SSTF in blue PhOLEDs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Novel phosphine-oxide based host materials were facile synthesized and used in organic light-emitting diodes. [•] The substituted position is meta-position, which is rarely developed in the previous work. [•] As expected, the higher triplet energy and good thermal stability were obtained. [•] The better performance with deep blue phosphorescence was achieved as compared to its well-known isomer. [ABSTRACT FROM AUTHOR]

Two luminescent dibenzo[ b,d ]thiophene 5,5-dioxide derivatives combined with 9,9-dimethyl-9,10-dihydroacridine were synthesized and the appearance of thermally activated delayed fluorescence was confirmed. Both 3,7- and 2,8-bis(9,9-dimethyl-9,10-dihydroacridine)dibenzo[ b,d ]thiophene 5,5-dioxide ( 3ASOA ) and ( 4ASOA ) showed prompt and delayed fluorescence with high total photoluminescence (PL) quantum efficiencies of 72% and 88% in their doped films, respectively. The maximum external electroluminescence (EL) efficiencies of 13.8% in 4ASOA and 10.4% in 3ASOA were obtained. Further, 4ASOA showed slightly relaxed rolloff behavior, indicating that 2,8-substitution of the donors appreciably improved both PL and EL characteristics. [ABSTRACT FROM AUTHOR]

Two novel spiro-based host materials, namely 3-(9,9′-spirobi[fluoren]-6-yl)-9-phenyl-9 H -carbazole ( SF3Cz1) and 9-(3-(9,9′-spirobi[fluoren]-6-yl)phenyl)-9 H -carbazole ( SF3Cz2) were designed and synthesized. Due to the meta -linkage of spirobifluorene backbone, both SF3Cz1 and SF3Cz2 possess triplet energies over 2.70 eV, indicating they could serve as suitable hosts for blue and even white phosphorescent organic light-emitting diodes (PHOLEDs). The fabricated bis (4,6-(difluorophenyl)-pyridinato -N,C′)picolinate (FIrpic) based PHOLEDs hosted by SF3Cz1 and SF3Cz2 exhibited excellent performance with maximum external quantum efficiencies (EQEs) of 18.1% and 19.7%, respectively. Two-color warm white PHOLEDs fabricated by utilizing SF3Cz1 and SF3Cz2 as hosts also achieved high EQEs and low efficiency roll-offs. The results demonstrate that SF3Cz1 and SF3Cz2 are promising hosts for blue and white PHOLEDs. [ABSTRACT FROM AUTHOR]

A new bipolar host material (PBCz-PO) consisting a phosphinic amide is developed to show a resonance effect. It possesses quite high triplet energy (2.76 eV), and this high triplet energy make it suitable to be blue host in phosphorescent organic light-emitting diodes (PHOLEDs). The device with PBCz-PO as a host and FIrpic as a dopant achieved a maximum current efficiency ( η c ) of 31.5 cd/A, a maximum power efficiency ( η p ) of 31.0 lm/W and a maximum external quantum efficiency (EQE) of 13.4% as well as low driving voltage. [ABSTRACT FROM AUTHOR]

Solution-processed organic light-emitting diodes (OLEDs) are currently attracting a lot of attention for their simple fabrication process. However, most laboratory-scale solution-processed devices are fabricated by spin-coating method which is not the optimum method for fabricating devices with a larger area as much of the material is wasted. Herein, a dip-coating method is introduced for its advantages for producing large-sized devices. The method is a more reliable and material saving fabrication process. In the present study, both the hole-transporting layer (HTL) and emitting layer (EML) were prepared by dip coating, and solution-processed green thermally activated delayed fluorescence (TADF) based OLEDs with high efficiencies were fabricated. [ABSTRACT FROM AUTHOR]

Abstract: A novel multifunctional spiro-annulated fluorene/triarylamine based compound (STNPB) has been designed, synthesized and characterized. It exhibits a high glass transition temperature of 140 °C, due to the rigid spiro-configuration molecular structure. According to its suitable energy level and triplet energy (2.34 eV), improved performances, such as lower driving voltage, enhanced device power efficiency, and longer stability, are shown in organic light-emitting diodes with STNPB as the hole-transport material, compared with the ones with the widely used arylamine derivative N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB). Through further studies, it has been demonstrated that the enhanced stability is attributed to suppressed crystallization process as a result of employing STNPB instead of NPB as the hole-transport material. [Copyright &y& Elsevier]

Abstract: Two host materials, DBTSF2 and DBTSF4, were designed and synthesized, incorporating dibenzothiophene (DBT) and spirobifluorene (SF) blocks. Their thermal, electrochemical and photo-physical properties were fully characterized. DBTSF4, which adopted an ortho-linkage between DBT and SF moieties, showed a significantly higher T 1 energy of 2.82eV as compared to its para-linkage analogue DBTSF2 (2.49eV). Their applications as host for green, blue and white phosphorescent organic light-emitting diodes (PHOLEDs) were explored. The DBTSF4 based blue PHOLED has a highest current efficiency of 23.5cdA−1. And using DBTSF4 as a single host, two-color based white PHOLEDs were achieved from cold white emission with CIE coordinate of (0.31, 0.43) to yellowish warm white emission (0.44, 0.49) with maximum current efficiencies varying from 35.8 to 52.3cdA−1 and maximum external quantum efficiencies from 13.1% to 16.9% respectively. The white PHOLED devices also showed a low efficiency roll-off even at 10,000cdm−2. [Copyright &y& Elsevier]