Search

The research on new functional layer materials and optimization of fabrication in organic light-emitting diode (OLED) has been continuously concerned. In this work, phosphotungstic acid solution used as a precursor is spin-coated onto ITO anode, and then a phosphorus-tungsten oxide (WO 3 -P 2 O 5 ) film is obtained after annealing treatment. Various parameters which include film composition, surface morphology, work function and optical property are measured. It suggests that the film has the composition of 24 WO 3 ·P 2 O 5 annealed at 200 °C, which exhibits work function of 5.55 eV, surface root mean square (RMS) roughness value of 1.525 nm and optical transmittance of over 92%. The WO 3 -P 2 O 5 film is used as hole injection layer (HIL), and the OLED with the structure of [ITO/ WO 3 -P 2 O 5 / TPD/ Alq 3 / LiF/ Al] is fabricated. The performance of device shows turn-on voltage of 2.6 V, maximum luminance of 13553 cd/m 2 , maximum current efficiency of 5.87 cd/A and maximum power efficiency of 3.44 lm/W, respectively. The results provide a new way to deposit HIL based on solution-processed metal oxide in efficient OLED. [ABSTRACT FROM AUTHOR]

High performance with color stability and simplified device structure with uncomplicated fabrication processes are research focuses in white organic light-emitting diodes (WOLEDs). But it is not easy to simultaneously combine these characteristics into WOLEDs. Herein, efficient and color-stable WOLEDs with double light-emitting layer are constructed. The double light-emitting layer structure is composed of a red-green (RG) emitting light which originate from incomplete energy transfer from the host of tris-(8-hydroxyquinolinato)aluminum (Alq3) to guest of 4-(Dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)−4 H -pyran (DCJTB), and a blue-green emitting light from ( E )-9-(4-(2-(anthracen-9-yl)vinyl)phenyl)-10-(naphthalen-1-yl)anthracene (APEAn1N). In these WOLEDs, the different doping concentrations of DCJTB in Alq3 were optimized. Finally, a WOLEDs with relatively simple preparation was obtained with a maximum brightness of 9296 cd m −2 , maximum current efficiency (CE) of 10.17 cd A −1 , maximum power efficiency (PE) of 5.80 lm W −1 , maximum external quantum efficiency (EQE) of 4.09%, Commission Internationale de L'Eclairage (CIE) coordinate of (0.41, 0.46) and color rendering index (CRI) of 75 (85), respectively. And the chromaticity coordinate is stable at (0.41, 0.46) with increasing operation voltage. These results reveal that the fluorescent WOLEDs possess simplified fabrication, low cost, relatively high efficiency, acceptable CRI and stable color, simultaneously. [ABSTRACT FROM AUTHOR]

• A simple and efficient graphene patterned method has been demonstrated. • Patterned graphene possesses favorable graphic accuracy and optical/electrical properties. • The OLEDs array with patterned graphene electrode is fabricated. • Corresponding device exhibits bright and uniform light emission. A simple method for the preparation of patterned graphene electrodes by applying patterned copper film as the masking layer is demonstrated. As-prepared graphene pattern shows well-defined and straight boundary line. High-quality patterned graphene electrode possesses a low average sheet resistance of 556 Ω/sq meanwhile its transmittance exceeds 96% at 550 nm. The 4 × 2 organic light-emitting diodes array with patterned graphene electrode further proves the practical application of this simple patterned technology. Corresponding device exhibits a maximum luminance of 44 k cd/m2 at 15 V and current efficiency of 24 cd/A at 6 V. This patterned graphene electrodes also have great potential in application of flexible printed electronics and display. [ABSTRACT FROM AUTHOR]

Since the low work function of ITO, introducing hole injection layer (HIL) with controllable and efficient property is an effective way to improve the performance of organic light-emitting diodes (OLEDs). In this work, films, containing molybdenum oxide units by employing H 2 O 2 treated ammonium phosphomolybdate (AMP) as precursors, are fabricated through solution-processed procedure. The hole injection property of the HILs can be modulated by the gap-state density, which is negatively correlated with the molar ratio of AMP/H 2 O 2. Green fluorescent and phosphorescent OLEDs based on the HILs are endowed with reduced turn-on voltage from 3.4 to 2.5 V and 4.1 to 3.4 V, respectively. Furthermore, fluorescent OLEDs based on the HIL with AMP/H 2 O 2 of 1:14 show a maximum current efficiency of 6.82 cd/A, 1.2-flod higher than that of PEDOT:PSS based devices. This method opens up a new path to obtain HIL with adjustable property in mild prepare condition for various electroluminescent devices. Image 1 • Controllable HILs with MoO 3 units were fabricated by solution-processed procedure. • Hole injection property of HILs was modulated by gap-state density, negatively correlated with AMP/H 2 O 2 molar ratio. • Green fluorescent and phosphorescent OLEDs based on the HILs were endowed with low turn-on voltage and high efficiency. [ABSTRACT FROM AUTHOR]

Solution-processable hole transporting materials (HTMs) play a vital role in organic light emitting diodes (OLEDs) with the purpose of reducing costs and improving productivity. Herein, two twisted HTMs N 2 , N 2 , N 7 , N 7 -tetrakis(4-(3,6-di- tert -butyl-9 H - carbazol-9-yl)phenyl)-9,9-dimethyl-9 H -fluoren-2,7-diamine ( p -BCz-F) and N 2 , N 2 , N 7 , N 7 -tetrakis(4-(2,7-di- tert -butyl-9 H -carbazol-9-yl)phenyl)-9,9-dimethyl-9 H -fluoren-2,7-diamine ( m -BCz-F), have been successfully synthesized. The two compounds are endowed with superior solubility in common organic solvents, facilitating solution-processed OLEDs. By simply changing position of peripheral tert -butyl moiety, the material performance could be regulated. The HTMs p -BCz-F exhibits superior glass transition temperature (T g) of 168 °C. Particularly, in terms of mobility, 1.42-fold higher could be also found for p -BCz-F (4.35 × 10−4 cm2V–1S−1) than m -BCz-F (3.05 × 10−4 cm2V–1S−1). Similarly, the p -BCz-F-based blue devices with BCzVBi as the emitter show better performance with maximum current efficiency (CE) of 7.05 cd/A and luminance (L) of 23365 cd/m2, corresponding CE of 6.12 cd/A and L of 21055 cd/m2 for m -BCz-F-based devices. In short, the different position of peripheral tert -butyl on carbazolyl moiety will lead to different performance and it provided a simple strategy to design solution-processable HTMs for efficient OLEDs. Image 1 1. Two novel solution-processable HTMs with superior solubility, mobility and thermal stability were synthesized. 2. By only changing the positions of peripheral tert -butyl on carbazoyl group, material properties can be tuned simultaneously. 3. Applying the HTMs into BCzVBi doped blue fluorescence devices through solution-process method, high luminescence and current efficiency were obtained. [ABSTRACT FROM AUTHOR]

In this work, we designed and synthesized two novel bipolar deep-blue emitting materials, 2-(4'-(9 H -carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-1 (4(tri-fluoromethyl) phenyl)-1 H -phenanthro[9,10- d ] imidazole (CzB-FMPPI) and 9-(4'-(4,5-diphenyl-1 (4-(trifluoromethyl) phenyl)-1 H -imidazole-2-yl)-[1,1′-biphenyl]-4-yl)-9 H -carbazole (CzB-FMPIM). Among them, carbazole and phenanthroimidazole are bridged linkage by the biphenyl ring and act as electron-donating part. The CF 3 -substituted phenyl ring applies as strong electron-withdrawing moiety. The exhibit highly twisted molecular configuration of two compounds efficiently shorten π-conjugation and inhibit intermolecular interaction, resulting in superior thermal stability and deep blue emission. High decomposition temperature of 431 °C and 414 °C, glass transition temperature of 150 °C and 135 °C for CzB-FMPPI and CzB-FMPIM, respectively, had been achieved. As a consequence of breaking the conjugation of phenanthroimidazole chromophore, CzB-FMPIM achieves an 8 nm blue-shifted emission compared with CzB-FMPPI. CzB-FMPPI exhibits a higher relative fluorescence quantum yield of 92.5% than 83.3% of CzB-FMPIM. Moreover, bipolar property was observed in both compound and homogeneous amorphous films were deposited and applied in the non-doped deep-blue OLEDs. The devices based on two emitters showed maximum luminance of 6667 cd/m2 and 3084 cd/m2, maximum EQE of 4.10% and 3.17%, respectively. Commission International de l'Éclairage (CIE) coordinates of CzB-FMPIM based device achieved (0.15, 0.07) which is extremely close to the NTSC standard blue CIE (0.14, 0.08). Image 1 Two donor-acceptor type deep blue fluorescent materials were firstly designed and synthesized. Compounds exhibit high fluorescence quantum yield, good thermal stability and bipolar properties. Non-doped good-performance deep-blue OLED devices with CIE of (0.15, 0.07) were achieved. [ABSTRACT FROM AUTHOR]

Abstract It is still a matter of worldwide continuous concern about how to obtain efficient, stable, pure blue light emitting materials and apply them in industrialized OLED devices. Here, a novel deep blue fluorescent material 2-(4'-(9 H -carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-1-(4-methoxyphenyl)-1 H -phenanthro [9,10-d]imidazole(CzB-MOPPI) was firstly designed, synthesized and employed as emitters for deep-blue OLEDs. CzB-MOPPI, with carbazole as donor, twisted biphenyl bonded phenanthroimidazole which contains rigid plane structure as acceptor, exhibits high thermal stability with decomposition temperature (T d) of 480 °C. Weak donor carbazole unit and twist biphenyl both make the compound emit less red shift meanwhile maintain in deep blue region. The non-doped OLEDs based on the CzB-MOPPI as emitter show maximum emission at 435 nm, maximum luminance of 6450 cd/m2, maximum current efficiency (CE) of 3.34 cd/A. The chromaticity coordinate is (0.16, 0.08) which is extremely close to the NTSC standard blue. In Particular, the devices show an impressive external quantum efficiency (EQE) as high as 5.97%. Graphical abstract Image 1 Highlights • A donor-acceptor type deep blue fluorescent material was firstly designed and synthesized. • Compound exhibits high thermal stability and bipolar properties. • OLED devices were fabricated, showing deep blue emission and impressive high EQE of 5.97%. [ABSTRACT FROM AUTHOR]

Blue organic light-emitting diodes (OLEDs) are of great significance in the fields of flat-panel display and solid-state lighting. Herein, three carbazolyl-substituted blue emitters, namely SAF-CzB , SAF-2CzB , and F-2CzB , were designed and synthesized. Two compounds SAF-CzB and SAF-2CzB possess a rigid spiro[acridine-9,9′-fluorene] (SAF) central core. The counterpart F-2CzB , which contains 9,9-dimethylfluorene as core was, also researched for comparative purpose. The introduction of SAF into fluorene-based materials could simultaneously improve their thermal stability, hole injection and transport ability, as well as prevent the fluorenone defect. The compound SAF-2CzB shows a higher decomposition temperature ( T d ) of 534 °C compared to that of F-2CzB (488 °C). The hole-transporting property of SAF-2CzB is also better than that of F-2CzB demonstrated by single-carrier devices. The presence of a bulky spiro-annulated triphenylamine moiety at the C9 position of the fluorene might suppress the fluorenone defect. Non-doped OLED based on SAF-2CzB as the emitting layer shows the best performance with maximum current efficiency (CE) of 4.07 cd A −1 and power efficiency (PE) of 1.83 l m W −1 , compared with 3.03 cd A −1 and 1.08 l m W −1 for SAF-CzB , 3.14 cd A −1 and 1.23 l m W −1 for F-2CzB . In particular, both SAF-2CzB - and F-2CzB -based device exhibit good color stability with CIE coordinate of (0.16, 0.11) at the voltage of 7–12 V. [ABSTRACT FROM AUTHOR]

In this work, we report a systematic study of the properties of the thermal cross-linkable triarylamine based hole-transporting material (HTM) N,N ′-di- p -tolyl -N,N ′-bis(4-vinylphenyl)-[1,1′-biphenyl]-4,4′-diamine (V-p-TPD) and the distinctive nature of its cross-linked thin films fabricated by solution process under mild thermal polymerization without any initiator. The cross-linked V-p-TPD film exhibited remarkable solution resistance to common solute such as chlorobenzene, toluene, chloroform and tetrahydrofuran. The cross-linked V-p-TPD film showed better morphological stability than vacuum-deposited film of its monomer TPD. The space-charge-limited current (SCLC) measurements revealed that the cross-linked V-p-TPD film afforded comparable hole mobility with vacuum-deposited TPD film. Finally, we applied the cross-linked V-p-TPD film in organic light-emitting diodes (OLEDs) to evaluate its performance in all-solution-processed OLEDs. [ABSTRACT FROM AUTHOR]

Single layer structure is an ideal way to realize the low cost solution processed organic light-emitting diodes (OLEDs). Efficient electroluminescent material with hole and electron transport characters as well as suitable triplet energy levels is highly desired to realize single layer OLEDs with good performance. In this work, a bipolar compound with carbazole as electron donor and 4,5-diphenylimidazoleas as electron acceptor has been successfully synthesized and applied as emitting layer for both non-doped and doped single layer OLEDs fabricated by solution processing. A pure blue emission achieved in the non-doped single layer OLED with a current efficiency of 0.38 cd A −1 , luminance up to 672 cd m −2 . The single layer doped OLEDs with the bipolar compound as host achieved blue, green and red phosphorescence OLEDs with current efficiency of 0.083, 13.42, 2.58 cd A −1 and luminance up to 108, 17103, 1347 cd m −2 , respectively. The performance of single layer OLEDs has been greatly improved by bipolar emitting materials which show a great potential to simplify the configuration of OLEDs. [ABSTRACT FROM AUTHOR]

Three small molecular hole-transporting and emitting materials with naphthalene bridged triphenylamine or carbazole were synthesized. These compounds exhibited high absolute fluorescence quantum yields (70–88%) at the green light region (540–555 nm), suitable highest occupied molecular orbital levels (−5.26 ∼ −5.34 eV) and good hole mobilities (∼10 −4 cm 2 V −1 s −1 ). The hole-only organic light emitting diodes with as-synthesized hole-transporting and emitting materials showed a tune-on voltage and a maximum brightness of 2.6 V and 2010 cd m −2 , respectively. Three stages of voltage-dependent current were observed, which coincide with the characteristic of Ohmic current, Fowler-Nordheim current and space charge limited current. With analysis of above models, overlarge Fowler-Nordheim current and space charge limited current contribute to the low efficiency of the device. All these results indicated that the high hole mobility showed the negative effect on the device efficiency, especially at high operation voltage. [ABSTRACT FROM AUTHOR]

Film-forming property of organic semiconductors is one of crucial factors for the performance of flexible organic light-emitting diode. In this work, two hole transporting materials based on triphenylamine were synthesized, which showed an outstanding film-forming property and could form free-standing films with a diameter of 4 mm. The spin-coated films on the flexible substrates showed an unobvious mechanical failure bended with radius of curvature no less than 6 mm. Photoelectron yield spectroscopy show that the two compounds embody suitable highest occupied molecular orbital levels (−5.14 eV and −5.25 eV) for hole injection. The sandwiched organic light-emitting diodes use poly[2-(4-3′,7′-dimethyloctyloxy)-phenyl]- p -phenylenevinylene) as emitting and electron transporting layer showed higher stability with increasing operation current density, an maximum luminance level of 103,690 cd m −2 . It demonstrate that the as-synthesized hole transporting materials hold a promising in high brightness flexible organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Indium tin oxide was hybrid modified with MoO 3 and self-assembled monolayer. • Self-assembled monolayer was used to adjust oxygen vacancies in MoO 3. • Solution-processed hole transport layer-free OLED achieved EQE max of 18.18% Compared with current vacuum-deposited multilayer organic light-emitting diodes (OLEDs), solution-processed simplified-structured OLEDs are more appealing by merits of low costs and promising potentials in large-area OLEDs. Nevertheless, it remains challenging due to intermixing between adjacent organic layers. Herein, indium tin oxide (ITO) surface was deposited with molybdenum trioxide (MoO 3) and then modified with self-assembled monolayer (SAM) of pentafluorobenzyl phosphonic acid. The SAM modification process made the MoO x film rich in oxygen vacancies, which ensured effective hole injection from the hybrid modified ITO directly to the emitting layer. This strategy facilitates HTL-free OLEDs and then completely avoids interlayer intermixing. Using the hybrid modified ITO as anode, HTL-free solution-processed green phosphorescent OLED was prepared and achieved a maximum current efficiency of 63.24 cd A−1 and a maximum external quantum efficiency of 18.18%. Meanwhile, preferable operational stability than standard multilayer OLEDs was obtained. For red phosphorescent OLED, a maximum external quantum efficiency of 17.49% was achieved. This work proposed a new way of adjusting cation valence to improve hole injection, contributing to solution-processed OLED fabrication. [ABSTRACT FROM AUTHOR]

Since the inter-layer mutual solubility is an obstacle to the development of solution-processed OLED, cross-linking is considered to be the best method to obtain solvent resistance. Vinyl is the most widely reported crosslinking group, but a problem raised that crosslinking usually need a high temperature. Here, two vinyl-crosslinked hole transporting materials, 3,3'-(1,3,4-oxadiazole-2,5-diyl)bis (N -phenyl- N -(4-vinylphenyl)aniline) (OXZ-VPAN), 3,3'-(4-phenyl-4 H -1,2,4-triazole-3,5-diyl)bis (N -phenyl- N -(4-vinylphenyl)aniline) (TRZ-VPAN) were designed and synthesized. The introduction of pentaerythritol tetra(3-mercaptopropionate) (PETMP) and vinyl groups by thiol-ene reaction to reduce the crosslinking temperature. As a result, crosslinking can be achieved at 120 °C with the solvent resistance higher than 99%. The surface morphology of the films before and after crosslinking were characterized by atomic force microscope, and it was found that the roughness of the film was improved after dopped with PETMP. The solution-processed green phosphorescent OLEDs devices based on the obtained HTM exhibit excellent performance. Maximum current efficiency of 57.1 cd A−1 and external quantum efficiency of 16.0% (Ir (mppy) 3) are obtained when OXZ-VPAN served as HTL. This low temperature feasible cross-linking process to prepare HTLs promotes the development solution-processed OLEDs. [Display omitted] • Two cross-linked hole transport material of D-A-D structure was synthesized. •The cross-linking temperature was lowed to 120 °C by introducing PETMP. •The solution-processed PHOLED achieved CE max of 57.1 cd A−1. [ABSTRACT FROM AUTHOR]

• Two vinyl-based cross-linkable hole transporting materials are synthesized. • Cross-linking temperature is markedly lowered by doping photoinitiator. • Hole mobility is also enhanced by doping photoinitiator. • The highest external quantum efficiencies are 15.5% (green) and 15.0% (red). Recently, developing insoluble cross-linkable functional layers plays a vital role for solution-processed organic light emitting diodes (OLEDs). Here, two vinyl-based cross-linkable hole transporting materials V-TPAVTPD and V-TPAVCBP are designed and synthesized. Additionally, cationic photoinitiator 4-octyloxydiphenyliodonium hexafluoroantimonate (OPPI) is first introduced to chemically induce vinyl-based photo cross-linking process, aiming at lowering cross-linking temperature and enhancing hole mobility. As a result, cross-linking can occur at expressly low temperature of 120 °C with >95% solvent resistance. Moreover, hole mobility is markedly enhanced with the value higher than 10−3 cm2 V−1 s−1. When applying hole transporting layers (HTLs) to solution-processed green and red phosphorescent OLEDs, devices exhibit excellent properties. Particularly, the maximum current efficiency of 54.0 cd A−1 (green), 9.8 cd A−1 (red) and external quantum efficiency of 15.5% (green), 15.0% (red) are obtained when OPPI doped V-TPAVCBP serves as HTL. This low temperature feasible cross-linking process to prepare HTLs with preferable hole mobility promotes the development of OLEDs. [ABSTRACT FROM AUTHOR]