Universal Host Materials Research Articles

Benzophenones as Generic Host Materials for Phosphorescent Organic Light-Emitting Diodes.

Despite the fact that benzophenone has traditionally served as a prototype molecular system for establishing triplet state chemistry, materials based on molecular systems containing the benzophenone moiety as an integral part have not been exploited as generic host materials in phosphorescent organic light-emitting diodes (PhOLEDs). We have designed and synthesized three novel host materials, i.e., BP2-BP4, which contain benzophenone as the active triplet sensitizing molecular component. It is shown that their high band gap (3.91-3.93 eV) as well as triplet energies (2.95-2.97 eV) permit their applicability as universal host materials for blue, green, yellow, and red phosphors. While they serve reasonably well for all types of dopants, excellent performance characteristics observed for yellow and green devices are indeed the hallmark of benzophenone-based host materials. For example, maximum external quantum efficiencies of the order of 19.2% and 17.0% were obtained from the devices fabricated with yellow and green phosphors using BP2 as the host material. White light emission, albeit with rather poor efficiencies, has been demonstrated as a proof-of-concept by fabrication of co-doped and stacked devices with blue and yellow phosphors using BP2 as the host material.

Benzophenone-imbedded benzoyltriptycene with high triplet energy for application as a universal host material in phosphorescent organic light-emitting diodes (PhOLEDs)

Benzoyltriptycene functions as a very good host material for blue, green, yellow and red dopants in PhOLED devices.

Universal Host Materials for High-Efficiency Phosphorescent and Delayed-Fluorescence OLEDs.

A series of bipolar hosts, namely, 5-(2-(9H-carbazol-9-yl)-phenyl)-1,3-dipyrazolbenzene (o-CzDPz), 5-(3-(9H-carbazol-9-yl)-phenyl)-1,3-dipyrazolbenzene (m-CzDPz), 5-(9-phenyl-9H-carbazol-3-yl)-1,3-dipyrazolbenzene (3-CzDPz), and 5-(3,5-di(9H-carbazol-9-yl)-phenyl)-1,3-dipyrazolbenzene (mCPDPz), are developed for phosphorescent and thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). They are designed by selecting pyrazole as n-type unit and carbazole as p-type one. The triplet energy (E(T)), the frontier molecular orbital level, and charge transporting abilities, are adjusted by varying the molar ratio of pyrazole to carbazole and the linking mode between them. They have high E(T) values of 2.76-3.02 eV. Their electroluminescence performance is evaluated by fabricating both phosphorescent and TADF devices with blue or green emitters. The m-CzDPz hosted blue phosphorescent OLEDs achieves high efficiency of 48.3 cd A(-1) (26.8%), the 3-CzDPz hosted green phosphorescent device exhibits 91.2 cd A(-1) (29.0%). The blue and green TADF devices with 3-CzDPz host also reach high efficiencies of 26.2 cd A(-1) (15.8%) and 41.1 cd A(-1) (13.3%), respectively. The excellent performance of all these OLEDs verifies that these pyrazole-based bipolar compounds are capable of being universal host materials for OLED application. The influence of molar ratio of n-type unit to p-type one and the molecular conformation of these hosts on their device performance is discussed and interpreted.

M‐Indolocarbazole Derivative as a Universal Host Material for RGB and White Phosphorescent OLEDs

The host materials designed for highly efficient white phosphorescent organic light‐emitting diodes (PhOLEDs) with power efficiency (PE) >50 lm W‐1 and low efficiency roll‐off are very rare. In this work, three new indolocarbazole‐based materials (ICDP, 4ICPPy, and 4ICDPy) are presented composed of 6,7‐dimethylindolo[3,2‐a]carbazole and phenyl or 4‐pyridyl group for hosting blue, green, and red phosphors. Among this three host materials, 4ICDPy‐based devices reveal the best electroluminescent performance with maximum external quantum efficiencies (EQEs) of 22.1%, 27.0%, and 25.3% for blue (FIrpic), green (fac‐Ir(ppy)3), and red ((piq)2Ir(acac)) PhOLEDs. A two‐color and single‐emitting‐layer white organic light‐emitting diode hosted by 4ICDPy with FIrpic and Ir(pq)3 as dopants achieves high EQE of 20.3% and PE of 50.9 lm W−1 with good color stability; this performance is among the best for a single‐emitting‐layer white PhOLEDs. All 4ICDPy‐based devices show low efficiency roll‐off probably due to the excellent balanced carrier transport arisen from the bipolar character of 4ICDPy.

(Invited) Reversible Co-Intercalation of Sodium and Solvent in Graphite

Graphite is a universal host materials that can accommodate various guest species in its galleries. Its capability of reversible lithium de/intercalation facilitates graphite as a standard anode for lithium ion batteries, while the thermodynamic instability of sodium intercalation made it not suitable for sodium ion batteries. We recently discovered that reversible solvated-Na ion intercalation enables graphite to become a promising anode for sodium ion batteries. As a continuous effort to exploit the graphite as an anode in sodium ion batteries, here we investigate the solvated-Na intercalation mechanism through in operando X-ray diffraction analysis, electrochemical titration, real-time observation of graphite expansion and density functional theory-based calculations. This work demonstrates the formation of first-stage graphite intercalation compound where the solvated-Na ions are doubly stacked in parallel with graphene layers. We further provide insights on tuning energy storage potentials of solvated ion intercalation electrodes by introducing various solvents.

螺芴氧杂蒽(SFX)类有机半导体及其OLEDs

One-pot protocol to spiro-based organic semiconductors has several advantages such as low-cost stuffs available, pot-atom-step economic (PASE) procedures, and others over the conventional o -halobiaryl method, representing the paradigm of green organic semiconductors (GOS) with the application of information technology. Herein, this review traces back to the history of spiro-compounds, including synthesis, structures and the application of electronics, followed by the discovery on one-pot synthesis of spirocyclic arenes with the merit of tandem mechanism that involves three bonding at once. We demonstrated the SFX-based molecular design platform under the four-element theory to organic semiconductors, affording a chance to get insight into structure-parameter relationship. Finally, we highlighted the SFX-based electroluminescent materials, including various fluorescent materials, RGB phosphorescent host and guest materials as well as printable OLEDs materials. Among them, the best deep-blue fluorescent OLED exhibits the maximum current efficiency (CE), the maximum power efficiency (PE) and external quantum efficiency (EQE) of 7.4 cd/A, 4.1 lm/W, 4.6%, respectively; the obtained green phosphorescent OLED with the CE of 70.0 cd/A, PE of 77.0 lm/W, EQE of 19.2%, as well as universal host materials for phosphorescent OLEDs. Finally, we outlook the spiro-based GOSs, including the obstacle of synthetic methodology to spiro-arenes, application bottleneck for OLEDs display and lighting source, potential explorations in other electronics, molecular circuits as well as smart devices.

Arylfluorene based universal hosts for solution-processed RGB and white phosphorescent organic light-emitting devices

A series of easily synthesized arylfluorenes (AFs)/carbazole universal host materials have been demonstrated for efficient solution-processable phosphorescent OLEDs.

Novel diarylborane–phenanthroimidazole hybrid bipolar host materials for high-performance red, yellow and green electrophosphorescent devices

In this work, two novel bipolar host materials p-BPPI and m-BPPI containing phenanthroimidazole/dimesitylborane (Mes2B) with para- and meta-linkage have been designed, synthesized and characterized. The appending Mes2B moiety improves the thermal stability, electrochemical stability and carrier injection/transport ability of both target compounds. The test results of time-of-flight (TOF) and single-carrier devices show that both the new hosts possess bipolar charge-transporting characteristics. As a result, series of highly efficient green (66.3cdA−1, 63.1lmW−1, 18.2%), yellow (55.2cdA−1, 66.6lmW−1, 14.5%) and red (20.1cdA−1, 20.4lmW−1, 13.5%) PhOLEDs are achieved by using them as the universal host materials. The results indicate that bipolar host p-BPPI and m-BPPI have high potential in fabricating various color OLEDs for displays and lighting applications. Our study further enriches the selection of D and A group for phosphorescent host materials. The relationship between molecular structures and optoelectronic properties is discussed experimentally and theoretically.

New universal bipolar host materials with fluorene as non-conjugated bridge for multi-color electrophosphorescent devices

Two novel bipolar hosts (CzFCN2 and CzDFCN) comprising a hole-transport carbazole donor and electron-transport cyano-substituted fluorene acceptor have been synthesized, and their thermal, photophysical, and electrochemical properties were characterized. The non-conjugated linkage between the carbazole donor and the cyano-substituted fluorene acceptor provides excellent thermal/morphological properties and high triplet energies (ET=2.86 eV) for both CzFCN2 and CzDFCN. These bipolar hosts also exhibited reversible redox behavior, which makes them good candidates for the host material in efficient phosphorescent organic light-emitting diode (PhOLED) devices. Multi-color PhOLED devices incorporating CzFCN2 and CzDFCN as the universal host achieved maximum external quantum efficiencies (ηext) as high as 10.7, 17.0, 17.2, and 17.6% for blue, green, yellow, and red devices, respectively. In addition, three-component white PhOLEDs (WOLEDs) based on CzFCN2 and CzDFCN as host materials exhibited high color stabilities with ηext as high as 10.5 and 12.4% and power efficiencies (ηp) of 20.5 and 26.7 lm W−1, respectively.

A Universal Host Material for High External Quantum Efficiency Close to 25% and Long Lifetime in Green Fluorescent and Phosphorescent OLEDs

High quantum efficiency close to 25% and long lifetime in green thermally activated delayed fluorescent and phosphorescent organic light emitting diodes are achieved using universal 3',5'-di(carbazol-9-yl)-[1,1'-biphenyl]-3,5-dicarbonitrile host material.

Manipulation of connecting topology in carbazole/benzimidazole universal bipolar host materials for RGB and White PhOLEDs

Two isomeric bipolar molecules (o-CPhBzIm and m-CPhBzIm) composed of a carbazole as central donor and two benzimidazoles as peripheral acceptors bridged by phenylene groups with different connection topology are reported. The molecular π-conjugation is only limitedly extended with a meta-conjugation in m-CPhBzIm and a highly twisted conformation in o-CPhBzIm, giving blue-shifted UV-vis and PL spectra and higher triplet energies as compared to those of their para-counterpart (p-CPhBzIm). o-CPhBzIm exhibited interesting photophysical and electrochemical behaviors due to significant intramolecular donor–acceptor interactions, which were confirmed by the results of theoretical analyses and the observation of its X-ray structure. The physical properties are subtly governed by the linkage topology, giving o-CPhBzIm and m-CPhBzIm promising properties for serving as universal bipolar PhOLEDs with a common device configuration. Especially, the high triplet energies of o-CPhBzIm and m-CPhBzIm assure efficient confinement of blue phosphor emission, rendering the realizations of high efficiency blue and white PhOLEDs feasible. Monochromatic low roll-off PhOLEDs using m-CPhBzIm as universal host gave high efficiencies of 16.7% for red, 21.4% for green, 11.9% for blue, and 19.3% for yellow. PhOLEDs hosted by o-CPhBzIm performed with excellent efficiencies of 19.4% for red, 18.9% for green, 15.6% for blue, and 14.8% for yellow. In addition, three-color-based single-host WOLEDs hosted by o-CPhBzIm with high efficiency (18.5%, 32.6 cd A−1, 34.1 lm W−1) and CRI (up to 79) were successfully achieved.

A diarylborane-substituted carbazole as a universal bipolar host material for highly efficient electrophosphorescence devices

Recently bipolar phosphorescent host materials have attracted wide attention since they can achieve better charge balance and hence better device performance. In this work, we report the synthesis and physical properties of a novel bipolar host material containing the dimesityl borane/carbazole hybrid, CMesB. With a high triplet energy, CMesB is considered a promising universal host material and has been applied to phosphorescent OLEDs of various colors. Red/green/blue/white (RGBW) OLEDs based on CMesB all show high external quantum efficiencies (20.7% for red, 20.0% for green, 16.5% for blue, and 15.7% for white) at practical brightnesses. The results indicate that the bipolar host CMesB with high triplet energy has high potential in manufacturing RGBW OLEDs for display or lighting applications.

Carbazole-based coplanar molecule (CmInF) as a universal host for multi-color electrophosphorescent devices

The synthesis, isomerism, photophysics and electrophosphorescent characterization of some functional cyclometallated iridium(III) complexes containing 2-[2-(N-phenylcarbazolyl)]pyridine and 2-[3-(N-phenylcarbazolyl)]pyridine molecular frameworks are described. A carbazole-based coplanar molecule (CmInF) obtained through the intramolecular ring closure of aryl substitutions at the C3 and C6 positions exhibits a high triplet energy (ET = 2.77 eV), morphological stability (Tg = 195 °C) and hole mobility in the range of up to 5 × 10−3 cm2 V−1 s−1. Highly efficient multi-color electrophosphorescent devices have been successfully achieved employing CmInF as the universal host material doped with phosphorescent dopants of various colors under the same device configuration of ITO/PEDOT:PSS (300 A)/TCTA (250 A)/CmInF: dopant (250 A)/TAZ (500 A)/LiF/Al (PEDOT:PSS = poly(ethylene dioxythiophene):polystyrene sulfonate; TCTA = 4,4′,4′′-tri(N-carbazolyl)triphenylamine; TAZ = 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole). Through the mixing of two phosphorescent dopants of complementary colors, we also fabricated a two-color white organic light-emitting device (WOLED) with the same device structure consisting of 12 wt% FIrpic and 0.3 wt% (Mpg)22Ir(acac) co-doped into CmInF as a single-emitting-layer, which exhibits peak WOLED efficiency of 13.4% (23.4 cd A−1) and 11.2 lm W−1 with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.37). In addition, the use of such device structure in full-color OLEDs has the advantages of simplifying manufacturing process and reducing production cost that are the critical issues of commercialization.