Defect profiling in organic semiconductor multilayers

Defect depth profile study has been carried out in organic semiconductor (OSC) multilayers to characterize the buried interfaces and layers using beam based positron annihilation spectroscopy. The bilayer and trilayer heterostructures (p-n, p-p and n-p-n) comprise of organic-organic and organic-inorganic (substrate) interfaces. Our study reveals the presence of defects at the interfaces whose concentration is seen to vary with the layer thickness. The S-W correlation has been used to examine the effect of organic materials as well as thickness of the layers on the defect microstructure in multilayers. The nature and type of defects in p-p bilayer are seen to be different as compared to p-n and n-p-n multilayers. Positron mobility in OSC layers has been calculated from the fitted diffusion length which is seen to be of the same order as the effective mobility of charge carrier obtained from the measured current density-voltage (J-V) characteristics. The role of structural defects and the intrinsic electric field at the interfaces on positron systematics is also examined. Positron diffusion modeling together with experimental data suggests that the defect at the interfaces has a stronger influence on the positron systematics than the intrinsic electric field across organic-organic interfaces. (C) 2012 Elsevier B.V. All rights reserved.