Mixed bipolar fluorescent small molecules for solution processable white light-emitting devices with excellent efficiency roll-off

Abstract

The efficiency roll-off is a key issue in organic light-emitting diodes. We report here the device performance of a white light-emitting device based on the mixture of solution processable bipolar small-molecules. On the basis of spectral analysis, charge trapping is found to be the dominating mechanism of the present white device of bipolar small-molecules. The host materials, which are contributing to the blue spectrum and charge transport, play a key role in device performance especially for efficiency roll-off. We show that devices based on the bipolar host material (TCSoC) exhibited fairly stable color and efficiency when operated at different current densities, which are improved significantly as compared to the device based on a hole dominating host material (TCPC). We propose that at high current density, the carrier balancing properties of host materials affect efficiency roll-off, and ratiocinatively balanced charge injection and transport can result in effective carrier recombination in the emissive region in a device.