Investigation into the polymer-small molecule blends film morphology on electroluminescence

POLY 520

Ting Zhang, and Gao Liu. Lawrence Berkeley National Laboratory, 1 Cyclotron Rd.,MS 70R108B, Berkeley, CA 94720
Polymer based OLED device is produced via solvent based processing techniques, such as printing and spin coating. Morphology of the film varies depending on the processing condition. Polymer matrix can host small molecules by blending to tune its conductivity and emitting properties. It is therefore crucial to achieve understanding of the effect film morphology has on the device performance, and, ultimately, to achieve control over the phase separation in a blend, so that structures can be designed that yield the desired device performance. In our work, electron-transport material 2,5-Diphenyl-1,3,4-oxadiazole, hole-transport material Triphenylamine, and Tris(2-phenylpyridine) iridium (III) (Ir(ppy)3) emitter were blend with polystyrene host polymer. The film morphology was controlled by different annealing techniques. The film morphologies at different blending ratio were studied with optical microscopy, TEM, and AFM techniques. OLED devices were built and tested with corresponding morphologies. We attempted to link the film morphology to the electronic performance of electroluminescent devices.