[14p-B5-1~12] 12.2 Characterization and Materials Physics

▲ [14p-B5-2] Thermal and Field Dependence of the Conductivity of Terbium(III)-Phthalocyaninato Double-Decker Complex (TbPc₂) Terbium Bisphthalocyanine Thin Films

〇Richard Murdey¹, Keiichi Kato² (1.Kyoto Univ., 2.Tohoku Univ.)

Keywords:organic radical, hopping transport, conductivity

Narrow gap, highly conductive semiconductors such as stable organic radical phthalocyanines and bisphthalocyanine have the thermal activation energies of conductance around 0.1 eV - 0.2 eV. Such a low value makes the physical interpretation of the activation energy in such systems ambiguous. The activation energy may represent the dissociation energy of intrinsically-generated electron-hole pairs, an energy barrier associated with shallow trap level or dopant site and the mobility edge, or it may be partially or wholly due to a thermally activated carrier mobility arisign from hopping transport.
Terbium bisphthalocyanine thin films were found to exhibit exceptional electrical stability, enabling the present precise study of the ohmic and space charge limited currents over a range of temperature between 203 K and 423 K, and fields up to 5 MV m^-1. While both were found to be thermally activated, the Arrhenius plot of the Ohmic currents revealed a slight curvature consistent with the pre-factor having a linear temperature dependence while the activation energy remains temperature-independent.
The energetics of the measured conductivity do not conform to the expected behavior for hopping transport, leading to the conclusion that the thermal dependence of the conductivity in terbium bisphthalocyanine has two contributing factors, a thermally activated charge dissociation and a charge carrier mobility which varies linearly with temperature.