We have carried out comparative studies on transparent conductive thin films made with two kinds of commercial carbon nanotubes: HiPCO and arc-discharge nanotubes. These films have been further exploited as hole-injection electrodes for organic light-emitting diodes (OLEDs) on both rigid glass and flexible substrates. Our experiments reveal that films based on arc-discharge nanotubes are overwhelmingly better than HiPCO-nanotube-based films in all of the critical aspects, including surface roughness, sheet resistance, and transparency. Further improvement in arc-discharge nanotube films has been achieved by using PEDOT passivation for better surface smoothness and using SOCl2 doping for lower sheet resistance. The optimized films show a typical sheet resistance of approximately 160 Omega/ square at 87% transparency and have been used successfully to make OLEDs with high stabilities and long lifetimes.

No abstract

No abstract

Conductivity dopants are used in organic light-emitting devices (OLEDs) to reduce the operating voltage and consequently improve the power efficiency. Here, we report the synthesis, as well as photophysical and electroluminescent properties, of an organic molecular p-type conductivity dopant: 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TNAP). F6-TNAP was obtained in a three-step two-pot synthesis from commercially available octafluoronaphthalene. When 1%-5% of F6-TNAP was coevaporated with N,N 0 -di-1-naphthyl-N,N 0 -diphenyl-1,1 0 -biphenyl-4,4 0 diamine (R-NPD) an absorption band at 950 nm was formed, which is attributed to charge transfer and assigned to the F6-TNAP radical anion. Single-carrier (hole-only) devices fabricated with F6-TNAP doped into R-NPD as the hole transport layer (HTL) show a >2 V decrease in operating voltage, compared to the undoped device. A decrease in operating voltage was also demonstrated in blue OLED devices using a F6-TNAP-doped HTL, with only a slight decrease in external quantum efficiency, thus resulting in a net improvement in power efficiency. These results demonstrate that F6-TNAP may be useful in generating high-efficiency OLEDs.

We report high efficiency and low roll-off for blue electrophosphorescent organic light emitting devices based on a mixed host layer architecture. The devices were fabricated using a mixed layer of di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, a hole transport material, and 2,8-bis(diphenylphosphoryl)dibenzothiophene, an electron transport material, as the host layer doped with the blue phosphor iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate. Using a mixed layer as the host allowed us to achieve high power efficiency (59 lm/W at 100 cd/m2), low turn-on voltage (2.7 V for >10 cd/m2), and low roll-off in these devices.