Studies of morphological optical and electrical properties of the MEH-PPV/azo-calix[4]arene composite layers

Thin films of poly[2-methoxy-5-(20-ethylhexyloxy)-1,4 phenylenevinylene] (MEH-PPV), 5,17-bis(4-nitrophenylazo)-26,28-dihydroxy-25,27-di(ethoxycarbonylmethoxy)-calix[4]arene (azo-calix[4]arene) and MEH-PPV doped azo-calix[4]arene, with 30 wt% and 70 wt% doping ratios, were prepared from chloroform solution by spin coating technique on quartz and ITO substrates. Morphological and optical properties of the samples were investigated by scanning electron microscopy (SEM) and UV–visible spectrophotometry techniques, respectively. Further, the charge carrier transport properties and conduction mechanism of the composite MEH-PPV:azo-calix[4]arene thin films based junction were studied by using current–voltage (I–V) characteristics and dielectric spectroscopy technique. I–V characteristic of ITO/MEH-PPV:azo-calix[4]arene/Al devices showed that the space charge limited conduction (SCLC) dominates in the high voltage region. Moreover, frequency dependence of ac conductivity obeys Jonscher's universal power law. Finally, dielectric constant (ε′), dielectric loss (ε″) and loss tangent (tan δ) were investigated as function of amount of azo-calix[4]arene in the MEH-PPV polymer matrix.