High quantum efficiency above 18% and extended lifetime three times longer than that of phosphorescent organic light-emitting diodes (OLEDs) are demonstrated in blue thermally activated delayed fluorescent OLEDs.
Transistors On page 5875, J. H. Cho and co-workers demonstrate a new device architecture for flexible vertical Schottky barrier (SB) transistors and logic gates based on graphene-organic-semiconductor-metal heterostructures and ion gel gate dielectrics. The devices show well-behaved p-and n-type characteristics under low-voltage operation (<1 V), yielding high current densities (>100 mA cm-2) and on-off current ratios (>10 3). Biosensors On page 6034, P. K. Wong and co-workers demonstrate a nanorod-based biosensor for dynamic single-cell analysis in native tissue microenvironments. The biosensor is capable of monitoring spatiotemporal mRNA expression in primary human cells, capillary networks, and animal tissues, including the skin, retina, and cornea, challenged mechanically and biochemically. Conjugated Polymers M. Xue and co-workers describe an in situ polymerization method for yielding single-crystal-conjugated polymer (SCCP) arrays on page 5923. As-fabricated SCCP micro-arrays exhibit a smooth surface, excellent environmental stability, and enhanced electron sensitivity, which may bring high performances for CP-based devices, such as supercapacitors, organic solar cells, polymer super-conductors, organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), or some flexible electronics. Photocatalysts Well-designed hetero-nanostructural plasmonic photo-catalysts with a multichannel sensitization effect on the charge-carrier dynamics process are developed by B. Dong and co-workers, as described on page 5906. The rational combination of the semiconductor hetero-junction effect and a surface plasmon resonance (SPR) coupling effect of the plasmonic dimers, as well as the nanostructural property of electrospun nanofibers, results in a remarkable enhancement in the efficiency of sol ar to fuels conversion. Carbazole-and triazine-derived thermally activated delayed fl uorescent (TADF) emitters , with three donor units and an even distribution of the highest occupied molecular orbital, achieve high external quantum effi ciencies of above 25% in blue and green TADF devices.
Highly efficient green thermally activated delayed fluorescent organic light-emitting diodes with an external quantum efficiency of 31.2% were investigated by using 3-(3-(carbazole-9-yl)phenyl) pyrido[3',2':4,5]furo[2,3-b]pyridine (3CzPFP) derived from carbazole and pyrido[3',2':4,5]furo[2,3-b]pyridine. The host material showed well-matched photoluminescence emission with absorption of the green dopant material, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) and harvested all excitons of 4CzIPN. The 3CzPFP:4CzIPN film exhibited high photoluminescence quantum yield of 100%, and the green delayed fluorescence device employing the 3CzPFP host showed high maximum quantum efficiency of 31.2 ± 0.5% at 1% doping after optimization of the device structure.
The general concepts, design criteria, and physical parameters, such as component placement and electroluminescence, that relate to the construction of OLED devices are described, followed by a discussion of the current literature detailing the use of branched and dendritic materials as the key electroluminescent elements of single- and multi-layered fabricated devices. Their configurations, efficiencies, emission intensities, and molecular structural implications are also delineated and discussed. This critical review should appeal to researchers in the synthetic, material, and physical sciences (122 references).
High efficiency and color tuning of thermally activated delayed fluorescent emitters were achieved at the same time by designing emitters with a twin emitter molecular design. The control of the interconnect position between two emitters could manage the emission spectrum of the thermally activated delayed fluorescent emitters without affecting the quantum efficiency.
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