Narrowband, angle-stable, and highly efficient polariton organic light emitting diodes employing thermally activated delayed fluorescence

Narrowband emission is crucial for next generation optoelectronic devices to satisfy demands for high color brilliance. Microcavities can narrow emission spectra of organic light-emitting diodes (OLEDs) through the creation of resonant standing waves, independent of emitter material, enabling flexibility in molecular and device design. However, they induce a strong angle-dependence of the perceived emission color. Utilizing strong light-matter coupling of cavity photons with the virtually angle-independent exciton, leads to exciton-polariton emission showing reduced linewidths and suppressed angular dispersion if tuned correctly. Creating polaritons in highly efficient materials such as thermally activated delayed fluorescence (TADF) molecules is however difficult as their low oscillator strengths intrinsically disfavor light-matter interaction. Here, we present the successful combination of a highly efficient but intrinsically broadband TADF emitter with a strongly absorbing assistant strong coupling material in a modified microcavity structure. Through optimizing the assistant strong coupling layer architecture, we demonstrate polariton OLEDs with exceptionally narrowband, angle stable emission at external quantum efficiencies above 20% for both bottom- and top-emitting designs, more than doubling the performance of previous record devices. The results pave the way for utilizing polaritonic emission at practical device efficiencies for display applications.