Highly Efficient Hole Injection Using Polymeric Anode Materials for Small‐Molecule Organic Light‐Emitting Diodes

Abstract

A novel, highly efficient hole injection material based on a conducting polymer polythienothiophene (PTT) doped with poly(perfluoroethylene‐perfluoroethersulfonic acid) (PFFSA) in organic light‐emitting diodes (OLEDs) is demonstrated. Both current–voltage and dark‐injection‐current transient data of hole‐only devices demonstrate high hole‐injection efficiency employing PTT:PFFSA polymers with different organic charge‐transporting materials used in fluorescent and phosphorescent organic light‐emitting diodes. It is further demonstrated that PTT:PFFSA polymer formulations applied as the hole injection layer (HIL) in OLEDs reduce operating voltages and increase brightness significantly. Hole injection from PTT:PFFSA is found to be much more efficient than from typical small molecule HILs such as copper phthalocyanine (CuPc) or polymer HILs such as polyethylene dioxythiophene: polystyrene sulfonate (PEDOT‐PSS). OLED devices employing PTT:PFFSA polymer also demonstrate significantly longer lifetime and more stable operating voltages compared to devices using CuPc.

Red organic light emitting device with improved performance using a novel fluorescent dye codoped with phosphor-sensitizer

“…Moreover, when at a current density of 4 mA/cm 2 (100 cd/m 2 ) and 52 mA/cm 2 (1000 cd/m 2 ), the η p percentages are about 160% and 143% higher than that of device D. A slow decrease of η p between 0.1 mA/cm 2 to 200 mA/cm 2 is shown in device A. The low η p roll-off at high current density of the phosphor-sensitized device precedes that of Ir(ppy) 3 :CBP device, indicating that T-T annihilation in Ir(ppy) 3 is reduced by the presence of DCDDC [5]. This reduced annihilation is probably due to rapid Förster transfer of the radiative Ir(ppy) 3 triplet to the singlet manifold of DCDDC [18,19].…”

“…Two peaks at 385 and 412 nm in long-wavelength region are due to the transition from ground state to singlet and triplet MLCT excited state [9]. There is a good overlap between the PL spectra of CBP and the MLCT absorption of Ir(ppy) 3 . Also, it can be calculated that the triplet energy levels of CBP is 2.6 eV [10], which is higher than that of Ir(ppy) 3 with a 2.3 eV [11].…”

Origin of Enhanced Hole Injection in Inverted Organic Devices with Electron Accepting Interlayer

“…The position of the maximum in time, τ DI , is related to the transient time by τ DI ≈ 0.8 τ tr . The shift in τ DI to shorter times with increasing applied bias indicates that the hole mobility in NPB is field dependent 7. Larger current density values can be observed in the inverted hole‐only devices compared to normal devices with the same film thickness.…”

Improving the lifetime of a polymer light-emitting diode by introducing solution processed tungsten-oxide

“…11,12 Efficient hole-injection through WO x is possible because of its high work-function and ability to form a good interface with ITO. 4,19 Devices C and D show higher efficiencies compared to devices A and B because of hole injection improvement by higher conductivity of PEDOT:PSS with WO x . 11 Device characteristics at 1000 cd m À2 are listed in Table 1.…”