White vertical organic permeable-base light-emitting transistors obtained by mixing of blue exciton and orange interface exciplex emissions

Abstract

In contrast to passive organic devices, such as organic light-emitting diodes and organic solar cells, which require a transistor in electrical circuits to modulate in/out-put signals and/or to reduce parasite resistivity, organic light-emitting transistors expectedly have the highest market potential of all organic electronic devices, including for high-density logic applications and novel multifunctional photonic circuits. In this work, we aimed to develop white organic light-emitting transistors exploiting a vertical device structure on a permeable base. Before the fabrication of white vertical organic permeable-base light-emitting transistors (OPB-LETs), orange and blue exciplex-based OPB-LETs were studied using known exciplex emitters. Due to electron injection problems, these emitters did not show white electroluminescence in OPB-LETs. When a newly synthesised blue emitter 4,6-bis(4-(9H-carbazol-9-yl)phenyl)pyrimidine-5-carbonitrile (CzPm) with orange exciplex forming ability was used, white electroluminescence from OPB-LETs was achieved by mixing of the blue exciton and orange exciplex emissions. Orange exciplex CzPm:TAPC with the photoluminescence spectrum peaking at 558 nm was characterized by thermally activated delayed fluorescence. The white OPB-LETs demonstrated a maximum external quantum efficiency of 2.4%, CIE colour coordinates in the range of (0.31, 0.38)–(0.34, 0.36), and colour rendering index in the range from 77 to 93.