An experimental and theoretical study of exciplex-forming compounds containing trifluorobiphenyl and 3,6-di-tert-butylcarbazole units and their performances in OLEDs

Derivatives of trifluorobiphenyl and 3,6-di-tert-butylcarbazole were synthesised as potential components of emitting layers of OLEDs. Molecular design of the compounds was performed taking into consideration the hydrogen bonding ability of the fluorine atom and electron-donating ability of the carbazole moiety. Their toluene solutions exhibited very high triplet-energy values of 3.03 eV and 3.06 eV. Ionisation energies of the compounds in the solid-state were found to be in the range from 5.98 to 6.17 eV. Density functional theory (DFT) calculations using the ωB97XD functional, with the ω parameter tuned in the presence of the solvent, uncovered singlet–triplet energy splitting in good agreement with the experimental results. The materials were tested in the emissive layers of OLEDs, showing the ability to form exciplexes with complementary electron-accepting 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine. Using the synthesised compounds as exciplex-forming materials, highly efficient exciplex emission-based OLEDs were developed. In the best case, a high maximum current efficiency of 24.8 cd A−1, and power and external quantum efficiencies of 12.2 lm W−1 and 7.8%, respectively, were achieved

Carbazole based polymers as hosts for blue iridium emitters: synthesis, photophysics and high efficiency PLEDs

This article reports the synthesis of new carbazole based polymers and their application as hosts in sky-blue polymer light emitting devices (PLEDs) with a solution-processed emitting layer doped with a cyclometalated Ir(III) complex. We systematically investigate their effect on the PLED performance. A current efficiency of 19.7 cd A(-1) and a brightness of 1850 cd m(-2) were achieved with these polymers. The roll-off in electrophosphorescent quantum efficiency in PLEDs was shown to arise mainly from triplet-triplet annihilation between dopants in the hosts with tert-butyl groups. It has been shown that in the devices with hosts without tert-butyl groups the efficiency roll-off is additionally affected by electric field quenching. In these carbazole based polymers, triplet dimers are formed and tert-butyl groups do not limit the intermolecular interactions to prevent triplet dimer formation, nevertheless tert-butyl groups reduce charge transport

Energy Structure and Electro-Optical Properties of Organic Layers with Carbazole Derivative

Phosphorescent organic light emitting diodes are perspective in lighting technologies due to high efficient electroluminescence. Not only phosphorescent dyes but also host materials are important aspect to be considered in the devices where they are a problem for blue light emitting phosphorescent molecules. Carbazole derivative 3,6-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole (TCz1) is a good candidate and has shown excellent results in thermally evaporated films. This paper presents the studies of electrical properties and energy structure in thin films of spin-coated TCz1 and thermally evaporated tris[2-(2,4-difluorophenyl)pyridine]iridium(III) (Ir(Fppy)3). The 0.46 eV difference of electron conduction level between TCz1 and Ir(Fppy)3 compounds was obtained from the cyclic voltammetry and photoconductivity measurements. Temperature modulated space charge limited current (TM-SCLC) method is used to measure the local trapping states for charge carrier in the energy gap. The TM-SCLC measurements for the system TCz1 + 8 wt.% Ir(Fppy)3 show a trapping state with the value of 0.4 eV which is comparable to the conduction level difference of these materials. It allows to conclude that Ir(Fppy)3 molecules act as electron traps in the TCz1 matrix and the TM-SCLC method is applicable to investigate dopants as trapping states. To show the trap effect, an organic light emitting diode was made where the electroluminescent layer was a spin-coated host-guest system of TCz1 with incorporated 8 wt.% Ir(Fppy)3

Blue organic light-emitting diodes based on pyrazoline phenyl derivative

The results of an experimental study of the electroluminescent device made of ITO/CuI/2,6-di-tert.-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)- phenol (HPhP)/3,6-Di(9-carbazolyl)-9-(2-ethylhexyl) carbazole (TCz1)/Ca:Al with efficacy up to 10.63 cd/A are presented. HPhP provides blue emission with a peak wavelength at 445 nm. The layer of TCz1 acts as an electron-transporting layer. In the framework of density functional theory (DFT) approach the geometry configuration and energy levels of HPhP are found being in a good agreement with spectral and cyclic voltammogram data. © 2011 Elsevier B.V

Blue organic light-emitting diodes based on pyrazoline phenyl derivative

The results of an experimental study of the electroluminescent device made of ITO/CuI/2,6-di-tert.-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)-phenol (HPhP)/3,6-Di(9-carbazolyl)-9-(2-ethylhexyl) carbazole (TCz1)/Ca:Al with efficacy up to 10.63 cd/A are presented. HPhP provides blue emission with a peak wavelength at 445 nm. The layer of TCz1 acts as an electron-transporting layer. In the framework of density functional theory (DFT) approach the geometry configuration and energy levels of HPhP are found being in a good agreement with spectral and cyclic voltammogram data