The dependence of the ideality factor on the charge density of a conjugated polymer (MEH-PPV) doped with some laser dyes

Blends made of poly[2-methyl-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) conducting polymer and cresyl violet 670 (CV) and coumarin 460 (C₄₆₀) have been utilized for preparation of organic Schottky diodes. The I–V characteristics of these diodes are then determined and interpreted in terms of thermoionic emission (TIE) conduction process. Upon blending MEH-PPV with CV and C₄₆₀ dyes, the conduction is seen to completely be through TIE conduction. The turn on voltage for MEH-PPV diode is found to be 2.0 V and decreases with CV blending in contrast to the blend of MEH-PPV-C₄₆₀. The Schottky parameters are determined where the potential barrier is found to be around 0.75 V which is consistent with reported values. The charge densities of the respective blends are calculated and found to reduce by in MEH-PPV-C₄₆₀ blends while it has been enhanced in the CV samples by an order of magnitude compared that of MEH-PPV. The correlation between the ideality factor with the dielectric constant and the charge density is inspected. It is found that the ratio between the charge density of the polymeric blend and the charge density of the Al-electrode is crucial for obtaining low ideality factor.