Investigating Morphology and Stability of Fac-tris (2-phenylpyridyl)iridium(III) Films for OLEDs

TitleInvestigating Morphology and Stability of Fac-tris (2-phenylpyridyl)iridium(III) Films for OLEDs
Publication TypeJournal Article
Year of Publication2011
AuthorsSmith, Arthur R. G., Ruggles Jeremy L., Cavaye Hamish, Shaw Paul E., Darwish Tamim A., James Michael, Gentle Ian R., and Burn P. L.
JournalAdvanced Functional Materials
Volume21
Issue12
Pagination2225–2231
Date Published06/2011
Keywordsmorphology, neutron reflectometry, optoelectronics, organic light emitting diodes, stability
AbstractAbstract Stable film morphology is critical for long-term high performance organic light-emitting diodes (OLEDs). Neutron reflectometry (NR) is used to study the out-of-plane structure of blended thin films and multilayer structures comprising evaporated small molecules. It is found that as-prepared blended films of fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)3] in 4,4′-bis(N-carbazolyl)biphenyl (CBP) are uniformly mixed, but the occurrence of phase separation upon thermal annealing is dependent on the blend ratio. Films comprised of the ratio of 6 wt% of Ir(ppy)3 in CBP typically used in OLEDs are found to phase separate with moderate heating while a higher weight percent mixture (12 wt%) is found to be stable. Furthermore, it is found that thermal annealing of a multilayer film comprised of typical layers found in efficient devices ([tris(4-carbazoyl-9-ylphenyl)amine (TCTA)/Ir(ppy)3:CBP/bathocuproine (BCP)]) causes the BCP layer to become mixed with the emissive blend layer, whereas the TCTA interface remains unchanged. This significant structural change causes no appreciable difference in the photo­luminescence of the stack although such a change would have a dramatic effect on the charge transport through the device, leading to changes in performance. These results demonstrate the effect of thermal stress on the delicate interplay between the chemical composition and morphology of OLED films.
URLhttp://dx.doi.org/10.1002/adfm.201002365
DOI10.1002/adfm.201002365