Effects of energetic disorder on the low-frequency differential capacitance of organic light emitting diodes

Abstract

It has recently been shown how the injection barriers at the electrode interfaces and the built-in voltage (Vbi) of organic light emitting diodes can be obtained from measurements of the differential capacitance at low frequencies, using the voltage and height of a distinct peak in the capacitance-voltages curves. In this paper, we investigate the effects of Gaussian energetic disorder on the analysis, for single-carrier and double-carrier devices. We show how the disorder affects the peak position and height, and how from combined capacitance-voltage measurements and device modeling the injection barriers and Vbi can be determined. As examples, hole-only and double-carrier devices are investigated based on a blue-emitting polyfluorene-triarylamine copolymer.