Solution-processed sodium hydroxide as the electron injection layer in inverted bottom-emission organic light-emitting diodes

Abstract

We present inverted bottom-emission organic light-emitting diodes (IBOLEDs), consisting of tris-(8-hydroxyquinoline)aluminum (Alq₃) as the emissive layer and an ultrathin layer of sodium hydroxide (NaOH) on top of indium tin oxide (ITO) as the electron injection layer. The devices with NaOH treated by water vapor and CO₂ and annealing show higher current efficiency than those with NaOH that are untreated. The current efficiency (6 cd A⁻¹) of the optimal devices with treated NaOH layer is improved. The enhancement is attributed to the reduction in barrier height for electron injection due to the dipole formation caused by the conversion of NaOH to sodium carbonate.