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Darwish, M.; Boysan, H.; Liewald, C.; Nickel, B.; Gagliardi, A. (2018): A resistor network simulation model for laser-scanning photo-current microscopy to quantify low conductance regions in organic thin films. In: Organic Electronics, Vol. 62: pp. 474-480
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Organic field effect transistors (OFETs) show considerable variation from device to device and batch to batch. For the basic understanding of the microscopic origins of these variations, it is crucial to develop both experimental and theoretical methods that allow to localize ineffective regions in a device. Raster techniques, which manipulate conductivity locally, combined with global current readout may provide this information, e.g. it has been suggested that diffraction limited illumination of OFETs by laser scanning photo-current microscopy provides trap density distribution maps. However, the question arises whether local variation of conductivity is indeed suited for localization of such defects given that the detected photo-current passes through the whole network of conductance in the thin film device. In this study, we present a simulation model based on resistor networks to investigate the effect of defective regions in organic thin films. We show that varying conductances locally allows indeed to reconstruct the spatial distributions of ineffective areas. We also demonstrate how such simulations can be applied to interpret photo-current microscopy maps in terms of trap densities.