Organic light-emitting transistors optimized by self-assembled monolayers

Abstract

Light-emitting transistors based on organic semiconductors have a range of potential advantages incl. tunability, flexibility, and high energy efficiency. A remaining challenge is the required high driving voltages that are caused by energy barriers at the interfaces between the metal electrodes and the organic material that hinder efficient charge carrier injection. In this work, we study the influence of two different self-assembled monolayers based on polar molecules deposited on the metal electrodes in terms of electrical and light-emitting properties of such organic transistors. The dipoles of the two monolayers are in opposite directions, so one monolayer is expected to lower the electrode work function while the other is expected to increase the work function. From an energy barrier perspective, it is thus expected that one monolayer should increase charge carrier injection while the other should reduce it. We find, however, that both types of monolayers improve both the electrical conductance and the emitted light intensity significantly. This is attributed to a change in interfacial microstructure due to the change in surface energy that results from the monolayer. This strategy is therefore a promising route to achieve higher device efficiencies in organic light-emitting transistors.