Influence of source/drain electrodes on external quantum efficiency of ambipolar organic light-emitting transistors

Abstract

The influence of source/drain (S/D) electrodes on the external quantum efficiency (EQE) of ambipolar organic light-emitting transistors (OLETs) based on fluorene-type polymer films is investigated. The electrical properties and the maximum EQE value of the device with indium tin oxide (ITO) S/D electrodes are almost the same as those of the device with Ag S/D electrodes. A relatively high EQE of 1% is achieved regardless of the emission site for the OLET with ITO. In contrast, the EQE of the OLET with Ag is low when the emission occurs close to the S/D electrodes. The maximum EQE of the device with Ag is obtained when the emission is observed in the middle of the channel. It is found that the exciton quenching by Ag electrodes significantly influences the low EQE of the OLET with Ag electrodes. The achievement of high EQE regardless of the emission site is attributable to both better carrier injection and lower exciton quenching at the interface of S/D electrodes for the OLET with ITO.