1-4hit |
Hisahiro SASABE Masatoshi ISHIBA Yong-Jin PU Junji KIDO
We designed and synthesized alkoxyphenyl group containing starburst host materials 1. Using 1 as a host material, efficient phosphorescent OLEDs with the power efficiencies of 32 lm W-1 for blue, and 85 lm W-1 for green at 100 cd m-2 were developed.
Toshinari OGIWARA Jun-ichi TAKAHASHI Hitoshi KUMA Yuichiro KAWAMURA Toshihiro IWAKUMA Chishio HOSOKAWA
We carried out degradation analysis of a blue phosphorescent organic light emitting diode by both impedance spectroscopy and transient electroluminescence (EL) spectroscopy. The number of semicircles observed in the Cole-Cole plot of the modulus became three to two after the device was operated for 567 hours. Considering the effective layer thickness of the initial and degraded devices did not change by degradation and combining the analysis of the Bode-plot of the imaginary part of the modulus, the relaxation times of emission layer and hole-blocking with electron transport layers changed to nearly the same value by the increase of the resistance of emission layer. Decay time of transient EL of the initial device was coincident with that of the degraded one. These phenomena suggest that no phosphorescence quenching sites are generated in the degraded device, but the number of the emission sites decrease by degradation.
Tatsunari HAMASAKI Taichiro MORIMUNE Hirotake KAJII Yutaka OHMORI
The characteristics of violet-sensitive organic photodetectors (OPDs) utilizing polyalkylfluorene and triplet materials have been studied as a host and a dopant material, respectively. For the photo absorption layer, poly(9,9-dioctylfluorene) [PFO] and a phosphorescent iridium complex (Iridium (III) bis(2-(4,6-difluorophenyl)pyridinato-N,C2) [FIrpic] or Iridium (III) bis(2-(2'-benzothienyl)pyridinato-N,C3')(acetyl-acetonate) [(btp)2Ir(acac)]) were used as a host and a dopant material, respectively. PFO: (btp)2Ir(acac) device showed less photocurrent than PFO device because (btp)2Ir(acac) enhances recombination of the photo generated carriers in the photo absorption layer. On the other hand, PFO : FIrpic device showed larger photocurrent than PFO device due to triplet energy transfer from FIrpic to PFO. A cutoff frequency of 20 MHz was observed using a sinusoidal modulated violet laser light illumination under the reverse bias of 8 V.
Yuichi HINO Hirotake KAJII Yutaka OHMORI
We have demonstrated improvement in the efficiency of TDAPB-based OLEDs. The external quantum efficiency of 8.2% and a power efficiency of 17.3 lm/W were achieved. The results suggest that using the starburst small-molecule TDAPB allows for easy fabrication and is effective for achieving high efficiencies in simple device structures.