Measurements of the Einstein relation in doped and undoped molecular thin films

We present the Kelvin probe force microscopy measurements of the Einstein relation, i.e., the relation between the diffusion coefficient of charge carriers and their mobility, in undoped and doped disordered organic thin films. The theoretical prediction of a large deviation of the Einstein relation from its classical value is verified and attributed to the energy distribution of the density of states. The results are explained in the context of degeneracy effects on the transport in disordered organic thin films, and their implications for organic-based devices are discussed.