Achieving high efficiency by high temperature annealing of hole transporting polymer layer in solution-processed organic light-emitting devices

•We developed highly efficient solution-processed OLEDs.•Poly-TPD was used as hole transporting polymer layer.•Annealing of poly-TPD at about glass transition temperature was critical.•Maximum current efficiency of 61.5 cd/A was achieved.•Maximum external quantum efficiency of 17.5% was achieved.

We developed highly efficient solution-processed phosphorescent organic light-emitting device by annealing of hole transporting polymer layer at about glass transition temperature. Poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine) (poly-TPD) was used as a hole transporting polymer layer and tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] doped N,N'-dicarbazolyl-3,5-benzene (mCP) was used as a solution-processed emission layer. The annealing temperature was critical to the well-defined interface between the poly-TPD and mCP:Ir(ppy)3 layers. In addition, the carrier recombination was significantly enhanced by high temperature annealing of poly-TPD layer. A current efficiency of 61.5 cd/A and an external quantum efficiency of 17.5% were achieved by annealing of poly-TPD layer at about glass transition temperature.