Structural and transport properties of thermally evaporated nickel phthalocyanine thin films

Abstract

X-ray diffraction patterns of NiPc in powder form show that it has a β-form with monoclinic structure. The thermal evaporation of NiPc led to α-polycrystalline films orientated preferentially to the (001) plane with an amorphous background. After annealing at 573 K for 2 h, a mixture of α- and β-phases was formed, while the conversion into β-NiPc is completed at 623 K. The dark electrical resistivity has been measured on NiPc films in the temperature range 298–423 K. Two activation energies ΔE1 = 0.12 eV and ΔE2 = 0.76 eV were obtained. The thermal activation energy ΔE1 is associated with impurity conduction and ΔE2 is associated with intrinsic conduction. Thermoelectric power measurement proved that NiPc films are p-type. The thermoelectric power curves also exhibit two different regions corresponding to extrinsic and intrinsic conductions. Room temperature J–V measurements show a linear ohmic dependence at low voltages, followed by SCLC at higher voltage levels, dominated by an exponential distribution of traps with total trap concentration of 2.79 × 1022 m−3.