Large polaron hopping under high electric fields

Current voltage characteristics of organic light emitting diodes cannot be understood without the knowledge of the field dependent mobility in the organic material. This issue is addressed in the present paper within the framework of a large polaron hopping theory under high electric fields. We find that the hopping rate is very sensitive to the conjugation length. At short conjugation lengths the mobility is essentially activated as a function of the temperature and the field , like in small polaron hopping. At long conjugation lengths, it exhibits a Fowler Nordheim like dependence with the field, and a very weak temperature dependence at high fields.