Direct measurement of internal potential distribution in organic electroluminescent diodes during operation

Direct measurement of the internal potential distribution in an organic electroluminescent (EL) diode under operating conditions was carried out by inserting a third gold electrode in the bulk of the organic thin film to monitor the potential. This electrode was sandwiched between two driving metal electrodes. During the operation of the organic EL diode, consisting of hole transporting and emitter layers, the applied voltage was distributed mainly across the emitter layer. The present technique provides a useful method for elucidating the operating mechanism of various types of organic thin-film devices.