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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]

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]

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]