The ratio between mobility and diffusion parameters was derived for a Gaussian-like density of states. This steady-state analysis was expected to be applicable to a wide range of organic materials (polymers or small molecules) as it relies on the existence of quasi-equilibrium only. The present analysis showed that there was an inherent dependence of the transport in trap-free disordered organic materials upon the charge density. The implications for the contact phenomena and exciton generation rate in light emitting diodes as well as channel width in field-effect transistors were analyzed.

Generalized Einstein Relation for Disordered Semiconductors - Implications for Device Performance. Y.Roichman, N.Tessler: Applied Physics Letters, 2002, 80[11], 1948-50