Estimation of the Occupied Density of States Using Capacitance–Voltage Measurement in the NPB System

Abstract

The determination of trap density of states remains a challenging problem in organic semiconductors. In this paper we have demonstrated estimation of occupied density of defect states acting as traps located in the HOMO level in the model small molecular system of NPB using C–V characteristics. A Gaussian distribution of occupied density within the band is observed. Its occupation is sensitive to the temperature and the frequency of measurement. The density of defect states is obtained to be 4.47 × 1014 cm−3 with an energetic distribution of 54–48 meV in the temperature range of 297–257 K. The energetic disorder of the full HOMO level is also calculated to be 126 meV from the occupied density of states.