ABSTRACT
We report the construction of an organic crystal multiplexer using three chemically and optically different acicular, flexible organic crystals for a broadband, visible light signal transportation. The mechanical integration of a highly flexible crystal waveguide of (Z)-2-(3,5-bis(trifluoromethyl)phenyl)-3-(7-methoxybenzo[c][1,2,5]thiadiazol-4-yl)acrylonitrile (BTD2CF3 ) displaying bright yellow (λ1 ) fluorescence with blue-emitting (λ2 ) BPP and cyan emitting (λ3 ) DBA crystals using AFM-tip provides a composite organic crystal multiplexer. The constructed hybrid single crystal multiplexer effectively transduces three optical signals (λ1 +λ2 +λ3 ) covering the 420-750â nm region as a composite output signal. The presented proof-of-principle experiment demonstrates the real potential of organic flexible crystal waveguides for visible light communication technologies.
ABSTRACT
Organic polymers that exhibit features pertinent to functioning as host materials for thermally activated delayed fluorescence (TADF) emitters have considerable potential in solution-processable organic light-emitting diodes (OLEDs), allowing simple, low-cost, and large-area applications. In particular, polymer hosts have superior characteristics, including facile functionality to introduce various electron donor and acceptor entities, the ability to uniformly disperse and contain small molecular dopants, and the ability to produce more smooth and homogeneous films, compared to those of their small-molecule counterparts. This manuscript describes the design and development of three new styrene-based copolymers (ABP91, ABP73, and ABP55) bearing diphenylacridine as the electron donor and 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene as the electron acceptor. In particular, ABP91, ABP73, and ABP55 were synthesized via variations in the ratio of donor to acceptor monomers to substantiate their influence in OLED applications. With the ability of the styrene backbone of interrupting the direct electronic coupling between the adjacent electron donor and acceptor entities through non-conjugated linkages, high triplet energy can be inherited by the resulting polymers (>2.70 eV). Furthermore, these materials manifest thermal robustness through high decomposition temperatures (between 348 and 366 °C) and high glass transition temperatures (between 234 and 277 °C). Consequently, solution-processable OLEDs fabricated using the newly synthesized copolymers as host materials and the familiar t4CzIPN as a green-emissive TADF dopant deliver state-of-the-art performance with maximum external quantum efficiencies of 21.8, 22.2, and 19.7% for ABP91, ABP73, and ABP55, respectively. To our knowledge, this is, to date, the best performance reported when organic polymers are used as host materials in solution-processable TADF OLEDs. The pragmatic outcomes obtained in this study can provide useful insights into the structure-property relationship to the OLED community for the further development of efficient polymer hosts for use in solution-processable TADF OLEDs.
ABSTRACT
Organic entities that can transport electrons are seldom available to develop adequate bipolar host materials applicable for solution-processable thermally activated delayed fluorescence (TADF)-organic light-emitting diodes (OLEDs). Therefore, the introduction of new electron-affine entities that plausibly demonstrate high triplet energy (E T) is of urgent need. In this contribution, we introduced benzimidazo[1,2-a][3,1]benzothiazine (BBIT) as a novel electron-affine entity and developed two new bipolar host materials, CzBBIT and 2CzBBIT. Both host materials exhibit high E T of 3.0 eV, superior thermal robustness with the thermal decomposition temperature of up to 392°C, a glass transition temperature of up to 161°C, and high solubility in common organic solvents. Consequently, the solution-processable OLEDs fabricated using a recognized IAcTr-out as the green TADF emitter doped into CzBBIT as the host, realized a maximum external quantum efficiency (EQE) of 23.3%, while the 2CzBBIT:IAcTr-out blend film-based device displayed an EQE of 18.7%. These outcomes corroborated that this work could shed light on the scientific community on the design of new electron-affine entities to establish the effective use of bipolar host materials toward proficient solution-processable TADF-OLEDs.
ABSTRACT
This study reports the design, synthesis, and characterization of two new bipolar host materials, DCzCP and TCzCP. Both materials were implemented as hosts by doping a known green thermally activated delayed fluorescent (TADF) emitter (t4CzIPN) in solution-processable OLEDs. DCzCP-based devices afford the best performance with the maximum external quantum efficiency (EQE) of 21.2%. Notably, the EQE was maintained at 20.7% and 19.7% at a practical luminance of 500 cd m-2 and 1000 cd m-2, respectively, demonstrating very small roll-off.
ABSTRACT
A light-emitting molecular triad (BPCP-2CPC) with dual functionality was successfully synthesized and applied to solution-processed non-doped organic light-emitting diodes. The BPCP-2CPC triad contains 9-phenyl-9H-carbazole units as a host moiety tethered to a green-emitting core (BPCP) through a cyclohexane unit and exhibits thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) characteristics simultaneously. The BPCP-2CPC-based non-doped TADF-OLED devices showed a high external quantum efficiency (EQE) of 13.4%.
ABSTRACT
A new side-chain polymer (X-TPACz) bearing hole-transporting pendant groups accompanying a thermally crosslinkable entity was synthesized using N-([1,1'-biphenyl]-4-yl)- N-(4-(9-(4-vinylbenzyl)-9 H-carbazol-3-yl)phenyl)bicyclo[4.2.0]octa-1(6),2,4-trien-3-amine (6) via addition polymerization. The X-TPACz could be spontaneously crosslinked without using any further reagents and showed a good film-forming property upon low-temperature thermal treatment. The thermal curing temperature for the X-TPACz film was optimized to be 180 °C based on a differential scanning calorimetry thermogram. Moreover, the thermal degradation temperature of X-TPACz measured to be over 467 °C using thermogravimetric analysis demonstrated that it shows excellent thermal stability. In particular, X-TPACz exhibits the highest occupied molecular orbital (HOMO) energy level to be -5.26 eV, which is beneficial for facile hole injection and transportation. Consequently, the thermally activated delayed fluorescence organic light-emitting diodes fabricated using X-TPACz as the hole-transporting material showed state-of-the-art performances with a low turn-on voltage ( Von) of only 2.7 V and a high external quantum efficiency (EQE) of 19.18% with a high current efficiency (CE) of 66.88 cd/A and a high power efficiency (PE) of 60.03 lm/W, which are highly superior to those of the familiar poly(9-vinylcarbazole) (PVK)-based devices ( Von = 3.9 V, EQE of 17.42%, with CE of 58.33 cd/A and PE of 33.32 lm/W). The extremely low turn-on voltage and high EQE were found to be due to the higher-lying highest occupied molecular orbital energy level ( EHOMO = -5.23 eV) and better hole-transporting property of X-TPACz than those of PVK.
