Electro-thermal modeling of organic semiconductors describing negative differential resistance induced by self-heating

We discuss self-heating of organic semiconductor devices based on Arrhenius-like conductivity laws. The self-consistent calculation of charge and heat transport explains thermal switching, bistability, and hysteresis resulting from S-shaped current-voltage curves with regions of negative differential resistance (NDR). For large area thin film organic devices we study the appearance of a spatially localized NDR region and the spatial evolution of this NDR region in dependence on the total current. We propose that in organic light emitting diodes (OLEDs) these effects are responsible for spatially inhomogeneous current flow and inhomogeneous luminance at high power.