Improvement of device efficiency by cross-linkable interlayer in blue polymer light-emitting diodes

We report that high efficiency blue polymer light-emitting diodes obtained by adding a thin interlayer between a poly(3,4-ethylene dioxythiophene)- poly(styrene sulfonic acid) (PEDT:PSS) hole transporter and emissive polymer. The one of OLED hole transporters, N,N'-bis(4-methylphenyl)-N,N'-diphenyl-1,4'- phenylenediamine (PDA), was modified with cross-linkable trichlorosilyl groups and used for the interlayer material. The devices, with configuration of indium tin oxide (ITO)/PEDT:PSS (65nm)/interlayer (10-20nm)/emitting polymer layer (70nm)/BaF2 (2nm)/Ca (50nm)/Al (300nm), were fabricated by spin coating and thermal evaporation. In this device structure, the cross-linkable interlayer is more adherent and mechanically robust as well as impervious to spin coating of next emitting polymer layer and shows a better stability. In addition, the devices with the interlayer exhibit a higher luminescence and current efficiency than those in devices without the interlayer.