Understanding negative capacitance effect using an equivalent resistor‐capacitor circuit

Abstract Negative capacitance effect has been observed in disordered solids and is shown to be linked to the presence of traps. Thus far, few theories have been applied rigorously to the reported (negative capacitance) data in the literature. This work continues an earlier effort to study negative capacitance effect using the Drude model. We have extended the model and have correlated it with an equivalent circuit model consisting of a resistor and a capacitor. With this model, we have derived an equation for the negative capacitance and have shown that it exists when the real and the imaginary components of the complex conductance are roughly equal and have opposite signs. We have also computed the frequency at the negative capacitance peak and have shown that it is proportional to the complex conductance and hence the complex carrier mobility. It confirms our earlier hypothesis on the “universality of photocurrent transients” in disordered organic solids when the capacitance‐frequency curves are normalized with respect to bias and temperature. Based on our results, we confirm that the negative capacitance effect arises from time delay in the current flow related to the trapped carriers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)