Sometimes it can be good to loose focus! In our latest paper in Nature Communications, Francisco shows how defocused orientation and position imaging can be used to map the orientation of individual emitter molecules in a state-of-the-art thermally evaporated OLED host film and thereby obtain complete orientation distributions of OLED emitters. The work opens the door to attaining unprecedented information on the factors that determine emitter orientation in current and future material systems for organic light-emitting devices. 

Horizontal alignment of the transition dipole moment (TDM) of emitter molecules is a popular strategy to achieve improve the optical efficiency of OLEDs without needing to add a dedicated outcoupling structure. However, our understanding of TDM alignment is limited by the amount of information we can obtain using current measurement techniques. Here, we adapted and developed DOPI to measure the complete orientation distribution of the TDM of emitter molecules in state-of-the-art vacuum-deposited OLEDs. To achieve this, we made several modificatoins and improvements, including optimized, thorough purification of a state-of-the-art OLED host material and careful management of the excitation and imaging conditions. These allowed us to attain sufficient signal-to-noise and signal-to-background ratios to experimentally measure the orientation distribution of thousands of single molecules of the hyperfluorescence-terminal emitter Coumarin 545T.

Find our paper here: https://www.nature.com/articles/s41467-023-41841-2