Electrical and magnetic properties of LiPc and LiPcI

We studied the ac electrical (20 Hz ≤ v ≤ 1GHz) and magnetic properties of the molecular semiconductors lithium phthalocyanine (LiPc) and lithium phthalocyanine iodide (LiPcI) at temperatures 1.5 K ≤ T ≤ 300 K. The frequency and temperature dependence of the complex ac conductivity suggest polarons as the dominant species of charge carriers. The higher conductivity of the iodine salt can be attributed to an enhanced mobility of the polaronic charge carriers due to a better overlap of the π-orbitals along the stacking direction of the molecules. Up to 300 K the dc conductivity can be described by σdc α exp( −(T0/T)1/2), i. e. quasi one-dimensional tunneling of charge carriers is the dominant conduction process in both compounds. Preliminary electron spin resonance (ESR) experiments were performed on LiPc. A single narrow, lorentzian shaped line is observed. Below 30 K a significant decrease in linewidth appears which may indicate the onset of magnetic order or dimerization.