Charge transport in lithium phthalocyanine

The ac electrical properties of monoclinic lithium phthalocyanine (LiPc) and of the iodinated compound LiPcI have been investigated in the frequency and temperature regimes 20 Hz less than or equal to v less than or equal to 1 GHz and 1.5 K less than or equal to T less than or equal to 300 K, respectively. Both compounds are semiconductors with dielectric constants epsilon(infinity)approximate to 6 (LiPc) and 20 (LiPcI). Up to room temperature tunneling of charge carriers is the dominant conduction process in both compounds, yielding intrinsic de conductivities sigma(dc)approximate to 5.3x10(-4) Omega(-1) cm(-1) (LiPc) and 0.2 Omega(-1) cm(-1) (LiPcI). The frequency and temperature dependence of the complex ac conductivity suggests polarons as the dominant species of charge carriers. The higher conductivity of the iodinated compound can be attributed to an enhanced mobility of the polaronic charge carriers which is most probably due to a better overlap of the pi orbitals along the stacking direction of the molecules. (C) 1996 American Institute of Physics.