How to Find Out the Density of States in Disordered Organic Semiconductors

We suggest a recipe on how to determine the density of states (DOS) in disordered organic semiconductors from the measured dependence of the charge carrier mobility on the concentration of carriers n. The recipe is based on a theory for the concentration-dependent mobility. As an example, we apply our theoretical results to experimental data obtained on two polymers and show that from the class of trial DOS functions g(epsilon) proportional to exp{-(epsilon/sigma)(p)}, only those with p > 1.8 can explain the experimental results. In particular, we claim that the concentration-independent mobility at low n evidences that the DOS cannot be purely exponential, which is in contrast to numerous recent assumptions in the literature.