Validity of the concept of band edge in organic semiconductors

Because most organic semiconductors are disordered, the more appropriate function to describe their density of states (DOS) is the Gaussian distribution. A striking difference between the Gaussian DOS and the parabolic DOS found in conventional inorganic semiconductors is the fact that it does not allow for a simple and straightforward definition of the band edge. The most usual way found in the literature to define the band edge of a Gaussian DOS consists of extrapolating the tangent to the inflection point of the Gaussian curve. The aim of this paper is to discuss the validity of such a way of conduct. An analysis of data found in the literature shows that the width of the Gaussian distribution is significantly larger than what usually retained in transport models. It is also shown that the validity of the usual definition for the band edge is questioned by the fact that the density of charge carriers behave as a degenerate distribution, even at relatively low doping levels. (C) 2015 AIP Publishing LLC.