Improvement of Device Efficiency by Cross-Linkable Interlayer in Blue Polymer Light-Emitting Diodes

Abstract

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.