Surface morphology, optical and electrical characterization of poly (p-phenylenevinylene) multilayer films

In this work we report the topology characterization of poly(p-phenylenevinylene) - PPV multilayer films using statistical analysis of atomic force microscopy (AFM) images. PPV spin-coating multilayers were deposited on glass covered with indium thin oxide (ITO) anode using the precursor polymer route thermal converted at 200 °C and under vacuum. On the top of the PPV films, aluminum thin film was evaporated and used as cathode to obtain a typical polymer light emitting diode structure. The AFM images were used to analyze the height distribution; the results show clearly the interaction with the substrate for low number of layers. In the case of thick films (5 layers) the polymer surface is more close to a random surface, indicating the loose of the interaction with the substrate. The physical parameters that characterizes the quality of the polymer diode, where also analyzed. The current vs. voltage curves display an increase in the operating voltage with the increment of the polymer layers. However, the probability of short curt decrease substantially for thick devices. The photoluminescence spectra present a decrease in the vibronic region associated with film disorder and/or intrinsic structural defects. The mean conjugation length seams to be similar for all thickness.