CHARGE-TRANSPORT IN LITHIUM PHTHALOCYANINE

The ac electrical properties of monoclinic lithium phthalocyanine (LiP c) and of the iodinated compound LiPcI have been investigated in the f requency and temperature regimes 20 Hz less than or equal to v less th an or equal to 1 GHz and 1.5 K less than or equal to T less than or eq ual to 300 K, respectively. Both compounds are semiconductors with die lectric constants epsilon(infinity)approximate to 6 (LiPc) and 20 (LiP cI). Up to room temperature tunneling of charge carriers is the domina nt conduction process in both compounds, yielding intrinsic de conduct ivities sigma(dc)approximate to 5.3x10(-4) Omega(-1) cm(-1) (LiPc) and 0.2 Omega(-1) cm(-1) (LiPcI). The frequency and temperature dependenc e of the complex ac conductivity suggests polarons as the dominant spe cies of charge carriers. The higher conductivity of the iodinated comp ound can be attributed to an enhanced mobility of the polaronic charge carriers which is most probably due to a better overlap of the pi orb itals along the stacking direction of the molecules. (C) 1996 American Institute of Physics.