Nozomu Tamoto

Molecular design of hole transport materials for obtaining high durability in organic electroluminescent diodes

The molecular design of hole transport materials (HTMs) for producing high durability in organic layered electroluminescent (EL) diodes was elucidated. The durability tests were examined using fourteen hole transport materials in the cell structure of an anode/hole transport layer (HTL)/emitter layer (EML)/cathode. The ionization potential (Ip) of HTLs was found to be the dominant factor for obtaining high durability in organic EL devices. The formation of the small energy barrier at the interface of a HTL/anode was required for high durability. Moreover, no straightforward relations between melting point, glass transition temperature of the HTMs, and durability of the EL devices were observed. The EL device using the HTM having a low Ip (5.08 eV) showed an especially remarkable stability. In this case, the half‐life period of the initial luminance was beyond 500 h.

Durability characteristics of aminopyrene dimer molecules as an emitter in organic multilayered electroluminescent diodes

We report the structure design of emitter molecules using aminopyrene dimers for obtaining durable organic electroluminescent (EL) diodes. Using eighteen kinds of emitter molecules having a variety of substituents and linking groups, we investigated the durability of the cell structure of the anode/hole transport layer/emitter layer/electron transport layer 2/electron transport layer 1/cathode. We observed that the chemical structures of the emitter molecules strongly influenced the durability of the EL devices under continuous DC operation. We observed no direct relationships between melting point (T m), glass transition temperature (T g), ionization potential (I p), electron affinity (E a) of emitter layers and EL device durabilities. The effect of the substituent groups of emitter molecules on EL device durability suggests that the chemical stability of the emitter molecules largely influences EL device durability.

Promotion of High-Tc Phase in Te-Doped (Bi, Pb)2Sr2Ca2Cu3Oy Superconductors Prepared by the Melt-Quenching Method

We prepared superconducting Bi1.6Pb0.4-xTexSr2Ca2Cu3Oy (x=0.1~0.4) ceramics by the melt-quenching method and examined the effect of Te addition on the formation of the high-Tc phase. It was found that the onset temperature of partial melting for the glass sample with x=0.1 was the lowest, and the formation of the high-Tc phase was greatly promoted. The bulk ceramics with x=0.1 and 0.2 exhibited superconductivity with a critical temperature of 101~103 K and a critical current density (77 K, zero magnetic field) of around 200 A/cm2. The main superconducting phase in the ceramics with x=0.4 was the low-Tc phase.

On the Formation of High-Tc Phase in Mo-Doped (Bi, Pb)2Sr2Ca2Cu3Oy Superconductors

We prepared superconducting Bi1.6-xPb0.4MoxSr2Ca2Cu3Oy (x=0.05 and 0.1) and Bi1.6Pb0.4-xMoxSr2Ca2Cu3Oy (x=0.1, 0.2, 0.3 and 0.4) ceramics by the melt-quenching method and examind the effect of Mo addition on the superconducting properties. It was found that the formation of the high-Tc phase was largely enhanced by the coexistence of Pb and Mo elements. It was concluded that the lowering of the partial melting temperature at around 870°C caused by the addition of Mo element was very important for the formation of the high-Tc phase.

Glass-forming ability and superconductivity in Bi2−xPbxSr2CaCu2Oy glass-ceramics

The glass-forming ability and superconducting properties in the Bi2−xPbxSr2CaCu2Oy glass-ceramics were examined by using a conventional melt-quenching method. The complete glassy samples were obtained in the composition range of x=0−1.0. The glass transition and crystallization temperatures of the glasses decreased monotonically with increasing Pb content. It was found from the ac complex susceptibility measurements that the onset temperature of superconducting transition decreased with increasing Pb content but the superconducting weak links at grain boundaries among the low-Tc phases were greatly improved due to the Pb doping. The significant grain growth of the low-Tc phase was observed in the Pb-doped glass-ceramics.