Spectral, electrical and morphological properties of spin coated MEH-PPV and cresyl violet blended thin films for a light emitting diode.

In this work, the spectral, and morphological properties of a conjugated polymer poly [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with Cresyl Violet (CV) in thin films have been studied. First, MEH-PPV was dissolved in benzene for different concentrations. The solutions were then deposited on glass substrates as thin films using spin coating with thicknesses ranging from 0.85 to 1.40 μm. The photoluminescence (PL) spectrum for the thickness 0.85 μm showed dominated peak at 572 nm and at 615 nm as shoulder peak. By increasing the thickness, the intensity of the peak at 572 nm decreased and the intensity of the peak at 611 nm increased. At a thickness of 1.40 μm there was only one peak at 615 nm and the peak at 572 nm was almost vanished. In general, absorption spectra indicate no aggregation in these films as no new peaks appears by changing the thickness. The morphology of the spin coated conjugated polymer MEH-PPV thin films was measured using Atomic Force Microscopy (AFM). All films examined by AFM, showed a dense structure with average roughness of 7–14 nm. Finally, we reported results of a single layer structure LED with MEH-PPV: CV blend as an active organic layer. The current–voltage ( I – V ) characteristics of these diodes were determined. By blending MEH-PPV with CV dye, we found that the turn on voltage for MEH-PPV diode is 2.0 V and decreases with CV blending. [ABSTRACT FROM AUTHOR]