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Highlights: [•] Two host materials for solution-processed green PhOLEDs were synthesized. [•] The hosts exhibit high triplet energy, excellent thermal and morphological stability. [•] The solution-processed single-layer green device shows the LE of 10.1cd/A. [ABSTRACT FROM AUTHOR]

Abstract: A dendritic host material 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl for solution-processed blue phosphorescent organic light-emitting devices was designed and synthesized. Owing to the decrease of the π conjugation length of biphenyl moiety in molecule structure, this carbazole derived derivative shows high triplet energy. Furthermore, the thermal, photophysical and electrochemical properties of 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl were investigated. The high triplet energy of 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl ensures efficient energy transfer from the host to the triplet emitter iridium(III) bis(4,6-difluorophenylpyridinato)picolinate. The single layer device using the carbazole derivatives as the host for iridium(III) bis(4,6-difluorophenylpyridinato)picolinate showed the maximum luminance efficiencies of 5.8 cd A−1, and a maximum external quantum efficiency 2.8%. The efficiency of the carbazole derivative based device was almost 3 times higher than the corresponding 1,3-bis(9-carbazolyl)benzene based device. [Copyright &y& Elsevier]

Abstract: This paper reports the synthesis and physical properties of a series of bipolar host materials, using of a hole-transporting triphenylamine (TPA) monomer as a core incorporated with different numbers of diphenylphosphine oxide (PO) as electron-transporting moieties, 4-(diphenylphosphoryl)-N,N-diphenylaniline (DDPA), 4-(diphenylphosphoryl)-N-(4-(diphenylphosphoryl)phenyl)-N-phenylaniline (DDPP), and tris(4-(diphenylphosphoryl)phenyl)amine (TDPA), for solution-processed deep-blue phosphorescent organic light-emitting devices (PhOLEDs). With the increasing numbers of PO units, the glass-transition temperature of those compounds rise gradually. Moreover, the newly synthesized compounds all possess high triplet energies, which can prevent back energy transfer between the host and dopant molecules, and are expected to serve as appropriate hosts for iridium(III) tris(3,5-difluoro-4-cyanophenyl)pyridinato-N,C′ (FCNIrpic). The solution-processed devices using DDPP and TDPA as the hosts for the phosphorescence emitter FCNIrpic showed the maximum luminance efficiencies of 9.7 and 6.6cdA−1, respectively. The efficiency of TDPA based device shows nearly three times higher than the value of commonly used host material 1,3-bis(9-carbazolyl)benzene (mCP) with the same structure, which is outstanding with respect to other works related to the solution-processed deep-blue PhOLEDs based on small-molecule hosts. [Copyright &y& Elsevier]

Abstract: This paper reports the synthesis and physical properties of two novel carbazole-based dendritic host materials Cz-CCP and Cz-mCP for solution-processed blue phosphorescent organic light-emitting devices (PhOLEDs). These dendritic hosts exhibit high triplet energy (≥2.85 eV), excellent film-forming ability (with low root-mean-square (rms) values less than 0.2 nm), high glass-transition temperatures in the range of 242–248 °C, and the appropriate HOMO energy levels (−5.33–−5.35 eV) facilitating the transfer of holes from Poly(3,4-ethylenedioxythiophene):Poly(styrene-4-sulfonate) (PEDOT:PSS) to the emitting layer. The single-layer device using Cz-CCP and Cz-mCP as the host for the phosphorescence emitter iridium(III) bis(4,6-difluorophenylpyridinato)-picolinate (FIrpic) showed the maximum luminance efficiencies of 9.6 and 10.8 cd A−1, respectively. By introducing a thin 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI) electron-transporting and exciton-confining layer, the maximum efficiency of the solution-processed double-layer device based on Cz-CCP and Cz-mCP can be further improved to 20.5 and 22.7 cd A−1, and maximum external quantum efficiencies as high as 10.2% and 11.5%, respectively. These results demonstrated that the newly synthesized, carbazole-based dendritic host materials are advantageous for fabrication of highly efficient blue PhOLEDs. [Copyright &y& Elsevier]