2, Technische Universiteit Eindhoven, Eindhoven, , Netherlands
3, Weizmann Institute of Science, Rehovot, , Israel
We demonstrate a facile route to obtain strong and broad-band circular polarization of electro-luminescence in single-layer polymer OLEDs. As light-emitting material we use a donor-acceptor polyfluorene with enantiomerically pure chiral side-chains. We show that the polymer self-assembles into a multi-domain cholesteric film, simply requiring thermal annealing. We achieve high levels of circular polarization of electro-luminescence (up to 40% excess of right-handed polarization), which are between the highest reported for polymer OLEDs. We model the surprisingly strong and broad-band polarization by taking into account circular selective scattering of electro-luminescence in the emitting cholesteric layer. These results indicate an easily accessible route to develop full circular polarization in OLEDs. More generally, our work demonstrates that chiral supramolecular self-assembly can be used to combine photonic and semiconducting properties for advanced control of light in organic optoelectronic devices.