Tsunenori Suzuki

Highly efficient long-life blue fluorescent organic light-emitting diode exhibiting triplet–triplet annihilation effects enhanced by a novel hole-transporting material

A novel hole-transporting material with high singlet and triplet excitation energy levels was developed. Quantum efficiency of a fluorescent organic light-emitting diode (OLED) using this material as a hole-transporting layer can be increased because of facilitated triplet–triplet annihilation (TTA) due to exciton confinement in an emission layer. Furthermore, this material has a deep highest occupied molecular orbital level because of the absence of triarylamine structure. This feature also contributes to the increase in the quantum efficiency, owing to inhibition of a low-energy exciplex formed between the material and a host in the emission layer. Achieved consequently was a blue fluorescent OLED exhibiting a high external quantum efficiency of 11.9% and a long half-decay time of 8,000 h at 1,000 cd/m2. By the device analysis including time-resolved electroluminescence measurements, it was confirmed that TTA contributes to the high efficiency.

69.3: Polymer/Metal‐Oxide Composite: A Novel Buffer Layer for Solution‐Processible OLEDs

We developed a novel polymer-metal oxide composite which is suitable as a buffer layer for solution-processible OLEDs. The composite, which consists of vanadium oxide and an amine-containing polymer, was fabricated by a sol-gel technique. It is possible to create Ohmic contact between the composite and electrodes, and this enabled the production of OLEDs with low driving voltage and high current efficiency.

Effect of halogenated impurities on lifetime of organic light emitting diode

We investigated a correlation between lifetime and the halogen element concentration in an organic light-emitting diode (OLED) and conducted experiments and simulations to discuss degradation mechanisms due to the halogen. OELD is generally formed of high-purity materials. Since the synthesis of high-purity materials takes time and cost, quantitative understanding of the kind, amount, and influence of impurities in OLED devices is expected. The results of combustion ion chromatography show that, if the chlorine concentration in the host material is more than several parts per million, the lifetime of the device is drastically reduced. The chlorine element, which is derived from the chlorinated by-product of the host material, is found to be transferred from the chloride to other materials (e.g., an emissive dopant) according to the results of LC-MS analysis. In addition, the electron transport layer including such impurities is also found to adversely affect the lifetime. The results of TOF-SIMS analysis suggest that the dissociated chlorine element diffuse to the light-emitting layer side when the device is driven. The results of simulations (Gaussian 09) and electrochemical analyses (cyclic voltammetry and electrolysis) reveal that the halogen element is easy to dissociate from halide by excitation or reduction. The halogen element can repeat reactions with the peripheral materials by excitation or reduction and cause damages, e.g., generate radicals or further reaction products due to the radicals. The results of simulation suggest that, such compounds have low energy level and become quenchers.

P‐157: Highly Efficient Long‐Lived Blue Fluorescent OLED Achieving External Quantum Efficiency over 8% and Its Application to OLED Lightings

We succeed in achieving both a long lifetime of 12,000 hours and a high power efficiency of 13 lm/W at a luminance of 1,000 cd/m2 in a pure-blue fluorescent OLED. In addition, we have also developed a high-performance warm-white OLED achieving 100 lm/W by incorporating the blue fluorescent OLED into a tandem structure, which is applicable to OLED lightings.