Search

Aryl-substituted phenanthroimidazoles (PIs) have attracted tremendous attention in the field of organic light-emitting diodes (OLEDs), because they are simple to synthesize and have excellent thermal properties, high photoluminescence quantum yields (PLQYs), and bipolar properties. Herein, a novel blue-green emitting material, ( E)-2-{4′-[2-(anthracen-9-yl)vinyl]-[1,1′-biphenyl]-4-yl}-1-phenyl-1 H-phenanthro[9,10- d]imidazole (APE-PPI), containing a t-APE [1-(9-anthryl)-2-phenylethene] core and a PI moiety was designed and synthesized. Owing to the PI skeleton, APE-PPI possesses high thermal stability and a high PLQY, and the compound exhibits bipolar transporting characteristics, which were identified by single-carrier devices. Nondoped blue-green OLEDs with APE-PPI as the emitting layer show emission at λ=508 nm, a full width at half maximum of 82 nm, a maximum brightness of 9042 cd m−2, a maximum current efficiency of 2.14 cd A−1, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.55). Furthermore, a white OLED (WOLED) was fabricated by employing APE-PPI as the blue-green emitting layer and 4-(dicyanomethylene)-2- tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4 H-pyran (DCJTB) doped in tris-(8-hydroxyquinolinato)aluminum (Alq3) as the red-green emitting layer. This WOLED exhibited a maximum brightness of 10029 cd m−2, a maximum current efficiency of 16.05 cd A−1, CIE coordinates of (0.47, 0.47), and a color rendering index (CRI) of 85. The high performance of APE-PPI-based devices suggests that the t-APE and PI combination can potentially be used to synthesize efficient electroluminescent materials for WOLEDs. [ABSTRACT FROM AUTHOR]

1-(9-Anthryl)-2-phenylethene ( t -APE) is a blue-green material with high fluorescence quantum yield ( Ф f 0.44). However, it is easily crystallized. Herein, Two asymmetric blue-green emitting materials based on t -APE, ( E )-9-(4-(2-(anthracen-9-yl)vinyl)phenyl)-10-(naphthalen-1-yl)anthracene ( 6 ) and ( E )-9-(4-(2-(anthracen-9-yl)vinyl)phenyl)-10-(naphthalen-2-yl)anthracene ( 7 ) were firstly designed and synthesized. The two compounds possess high thermal stability, morphological durability, and bipolar characteristics. The non-doped blue-green organic light-emitting diodes (OLEDs) using 6 and 7 as emitting layers showed emission at 495 nm, full width at half maximum of 80 nm, maximum brightness of 13,814, 10,579 cd m −2 , maximum current efficiency of 3.62, 7.16 cd A −1 , and Commission Internationale de L'Eclairage (CIE) coordinate of (0.20, 0.43), respectively. Furthermore, when employing 6 and 7 as blue-green emitting layers and rubrene doped in tris-(8-hydroxyquinolinato)aluminum (Alq3) as the orange emitting layers to fabricate white OLEDs (WOLEDs), the WOLEDs exhibit a maximum brightness of 10,984, 14,652 cd m −2 , maximum current efficiency of 2.04, 2.70 cd A −1 , and CIE coordinate of (0.30, 0.40), (0.37, 0.47), Color Rendering Index (CRI) of 65, 60, stable EL spectra, respectively. This study demonstrates that the t -APE-type derivatives have the excellent properties for the emitting materials of OLEDs. [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]

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]

Typical π-π stacking and aggregation-caused quenching could be suppressed in the film-state by the spiro conformation molecular design in the field of organic light-emitting diodes (OLEDs). Herein, a novel deep-blue fluorescent material with spiro conformation, 1-(4-( tert-butyl)phenyl)-2-(4-(10-phenyl-10 H-spiro[acridine-9,9′-fluoren]-2-yl)phenyl)-1 H-phenanthro[9,10- d]imidazole ( SAF-BPI), was designed and synthesized. The compound consists of spiro-acridine-fluorene (SAF) as donor part and phenanthroimidazole (BPI) as acceptor part. Owing to the rigid SAF skeleton, this compound exhibits a high thermal stability with a glass transition temperature ( Tg) of 198 °C. The compound exhibits bipolar transporting characteristics demonstrated by the single-carrier devices. The non-doped OLEDs based on the SAF-BPI as the emitting layer shows maximum emission at 448 nm, maximum luminance of 2122 cd m−2, maximum current efficiency (CE) of 3.97 cd A−1, and a maximum power efficiency of 2.08 lm W−1. The chromaticity coordinate is stable at (0.15, 0.10) at the voltage of 7-11 V. The device shows a slow efficiency roll-off with CE of 3.35 and 2.85 cd A−1 at 100 and 1000 cd m−2, respectively. [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]