am7b15542_si_001.pdf (1.57 MB)
Morphology of OLED Film Stacks Containing Solution-Processed Phosphorescent Dendrimers
journal contribution
posted on 2018-01-22, 21:06 authored by Jake A. McEwan, Andrew J. Clulow, Andrew Nelson, Ross D. Jansen-van Vuuren, Paul L. Burn, Ian R. GentleOrganic
light-emitting devices containing solution-processed emissive dendrimers
can be highly efficient. The most efficient devices contain a blend
of the light-emitting dendrimer in a host and one or more charge-transporting
layers. Using neutron reflectometry measurements with in situ photoluminescence,
we have investigated the structure of the as-formed film as well as
the changes in film structure and dendrimer emission under thermal
stress. It was found that the as-formed film stacks comprising poly(3,4-ethylenedioxythiophene):polystyrene
sulfonate/host:dendrimer/1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene
(where the host was deuterated 4,4′-N,N′-di(carbazolyl)biphenyl or tris(4-carbazol-9-ylphenyl)amine,
the host:dendrimer layer was solution-processed, and the 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene evaporated) had well-defined
interfaces, indicating good wetting of each of the layers by the subsequently
deposited layer. Upon thermal annealing, there was no change in the
poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/host:dendrimer
interface, but once the temperature reached above the Tg of the host:dendrimer layer, it became a supercooled
liquid into which 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene
dissolved. When the film stacks were held at a temperature just above
the onset of the diffusion process, they underwent an initial relatively
fast diffusion process before reaching a quasi-stable state at that
temperature.