Trap Free Space Charge Limited Conduction and High Mobility in Cobalt Phthalocyanine - Iron Phthalocyanine Composite Thin Films

Charge transport of pure and composite thin films (20 nm thickness) of cobalt phthalocyanine (CoPc) and iron phthalocyanine (FePc) grown by molecular beam epitaxy has been investigated in the temperature range of 300 K-25 K. Composite films with optimum composition showed very high mobility of 110 cm2V-1s-1 at room temperature. X-ray diffraction and UV-Vis studies showed that the films were well oriented with planar co-facial structure. The current density-voltage (J-V) characteristics of composite films showed trap free space charge limited conduction (SCLC) while individual phthalocyanine films showed SCLC with exponential distribution of traps. Several factors such as effect of substrate, very small thickness and effect of mixing two phthalocyanines are responsible for the very high mobility observed in present study.