Electrical conductivity, dielectric properties and optical absorption of organic based nanocrystalline sodium copper chlorophyllin for photodiode application

Sodium copper chlorophyllin (SCC) thin films were successfully prepared, using dip coating technique. Thermal gravimetric analysis (TGA) was performed for studying the thermal stability of SCC film. The surface morphology of thin films was studied by using scanning electron microscopy (SEM). The crystalline structural characteristics were undertaken with the aim of determining the lattice parameters together with a complete list of the Miller indices and interplanar spacing for SCC. The molecular structure and electronic transitions of SCC were investigated by Fourier-transform infrared (FTIR) and absorption spectrum, respectively. Temperature dependence of the DC electrical conductivity, (sigma(DC)) was investigated in the temperature range 289-373 K. Measurements revealed that the sigma(DC) behavior of the films can be described by Mott's one-dimensional variable range hopping (VRH) model in the entire temperature range. The AC conductivity, (sigma(AC)(omega)) results were discussed in terms of the correlated barrier hopping (CBH) mechanism for charge carrier transport. The maximum barrier height and the hopping length were estimated. The temperature dependence of the sigma(AC)(omega) shows Arrhenius type with one thermal activation energy for each frequency. The behavior of the real and imaginary parts of the dielectric constant as a function of both temperature and frequency were discussed. The energy band model was applied and the type of the optical transitions responsible for optical absorption was found to be direct allowed transition. Position dependent for SCC thin film photo-detector was studied by using laser diode source. (C) 2011 Elsevier B. V. All rights reserved.