Prolonging blue TADF-OLED lifetime through ytterbium doping of electron transport layer

Abstract

Balanced charge carrier transport and broad carrier recombination zone are essential features for reducing triplet exciton concentration and suppressing triplet-mediated annihilation processes, which affect the performance and stability of blue-emitting organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) phenomenon. Doping of organic layers is among the most effective methods to control these features. Herein, the impact of ytterbium (Yb) doping of electron transport layer on the TADF-OLED performance, and particularly the lifetime, was thoroughly assessed. It was found that the lower doping concentrations of Yb (<10wt%) cause electron trapping and reduced current density, whereas higher Yb concentrations facilitate electron transport in the device. Although the introduction of Yb somewhat deteriorated device efficiency, it extended operational lifetime of blue-emitting device by 2 orders of magnitude (up to 46 hours at 1000 cd/m2). This was shown to occur as a result of Yb-assisted non-radiative triplet exciton quenching at the electron transport and emission layer interface, thus diminishing detrimental exciton annihilation processes.