Noriyuki Matsusue

Microwave Synthesis of Iridium(III) Complexes: Synthesis of Highly Efficient Orange Emitters in Organic Light-Emitting Devices

Microwave synthesis of tris-ortho-metalated Ir(III) complexes was performed and resulted complexes were applied to the electrophosphorescent devices. For synthesis of Ir(ppy)3, the product was obtained by 30 min. microwave irradiation. That is microwave irradiation reduced the reaction time to 1/20 of that under conventional heating. Furthermore, we succeeded the rapid microwave synthesis of tris(2-phenyl-1-quinoline)iridium(III), Ir(phq)3, which is hard to synthesis by conventional method. An electrophosphorescent device with Ir(phq)3 as a dopant in emitting layer was developed. It demonstrated a high-efficient orange emission with maximum luminous efficiency of 33.4 cd/A and a power efficiency of 11.7 lm/W at 800 cd/m2. The color of emission corresponds to CIE coordinates x=0.56, y=0.43. The device showed a projected operational lifetime, namely T1/2, of 6500 h at an initial brightness of 1500 cd/m2 under constant dc drive.

Temperature Dependence of Photoluminescence Lifetime and Quantum Efficiency in Neat fac-Ir(ppy)3 Thin Films

Temperature dependences of lifetime and intensity of photoluminescence have been investigated in neat fac-Ir(ppy)3 thin films, which have a nonradiative decay channel due to aggregate quenching. Both temperature dependences can be well understood by a model which consists of three substates of the triplet metal-to-ligand-charge-transfer (3MLCT) state and a nonemissive state. Good agreement between the experimental results and the calculations based on the model suggests that nonradiative decay occurs through a higher lying excited state in fac-Ir(ppy)3 molecules, and that the nonemissive excited state has a decay rate of 3.1×109 s-1 and is located at 0.12 eV above the lowest substate of the 3MLCT state.

Developments in OLEDs with a co-dopant system for improved efficiency and stability

Development of RGB material has already reached the level of commercial products for full color displays devices such as digital cameras. However, the key challenges that still remain are improving luminance efficiency for lower power consumption and better stability. Applying a co-dopant into the EML is an effective way to adjust device performance. A large proportion of power is consumed in red sub-pixels in full-color displays with RGB sub-pixels. Previously we found that rubrene doping of red emitting layer improved the luminance efficiency and operational stability by enhancing the energy transfer from host material to emitting dopant. To increase the efficiency, a phosphorescent material as a red emitter was studied. We review the requirements for and characteristics of RGB OLEDs and the impact of co-doping systems on the performance of full-color displays.