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 ( 65 nm)= interlayer ( 10 - 20 nm)= emitting polymer layer ( 70 nm)= BaF2 ( 2 nm)= Ca ( 50 nm)= Al ( 300 nm), 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.