Field induced reorientation of emitter molecules
The emitter molecules in luminescent thin-film devices can be imagined as light-
emitting antennas. In this picture, the axis of such an antenna corresponds to the
transition dipole moment (TDM) of the molecule. Most efficient devices are achieved
when the TDM is aligned parallel to the substrate plane because in this way optical
losses like total internal reflection are reduced.
There exist several approaches how to manipulate the orientation of the molecules,
for instance chemically by changing their size, shape, and components, or physically
by applying different processing conditions like evaporation rate and substrate
temperature. However, a method that is able to modify the emitter orientation in an
already finished device is missing so far.
In this work, the interaction of electric fields with the permanent dipole moment of
emitter molecules at different temperatures will be investigated. Angle-resolved
photoluminescence spectroscopy will be used to measure and track orientation
changes. A successful reorientation should be directly reflected in the transport
characteristics and/or efficiency of the device.
The work will include theoretical parts (e.g. optical modelling, device planning) and
experimental tasks (e.g. measurement of IVL-curves, efficiencies, and angle-resolved
emission spectra).