Optical and electrical properties of poly(4-vinyl pyridine)/NiPc composite doped with iodine

Optical and electrical properties of homogeneously dispersed Ni-phthalocyanine (NiPc) microparticles in poly(4-vinyl pyridine) (P4VP) films have been studied. Optical micrograph of these composites reveal homodispersion of NiPc in P4VP at lower composition(5–10%). But for higher composition, aggregation of NiPc/P4VP clusters is found. In the UV–VIS spectrum, a change in broad peak is observed which may be due to weak binding of NiPc units to basic groups of P4VP. The conductivity increases by 3–4 orders of magnitude depending on the percentage of NiPc. I–V study shows that there is weak dependence of current at low field but turns to ohmic behavior at moderate and high field region. With increasing temperature, thermally generated carriers cause ohmic conduction even at low field. On further doping with I2, the conductivity is found to increase by 5–6 orders of magnitude. The UV–VIS spectrum shows substantial decrease in broad peak intensity in the 600–700 nm region of pure NiPc revealing the complete absorption of Pc moieties by I2. From the I–V characteristics, it is found that the conduction is ohmic in both regions for moderate temperature. At high temperature, thermal activation of large number of carriers gives large increase in current conduction.