• organic light emitting diodes;
  • neutron reflectometry;
  • morphology;
  • optoelectronics;
  • stability
Thumbnail image of graphical abstract

Stable film morphology is critical for durable, high-performance organic light-emitting diodes. On page 2225, Ian R. Gentle, Paul L. Burn, and co-workers use neutron reflectometry to study the out-of-plane structure of blended thin films and multilayer structures. Uniformly blended films of fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)3] in 4,4'-bis(N-carbazolyl)biphenyl (CBP) can be formed by evaporation, while 6 wt% films of Ir(ppy)3 in CBP, typically used in OLEDs, were found to phase-separate with moderate heating. Luminescence microscopy shows that phase separation leads to fiber-like structures of CBP (blue) and Ir(ppy)3 (green).