Enhancing the hole injection ability of indium tin oxide viaammonium salts in polymer light-emitting diodes

The enhancement of the hole injection ability of indium tin oxide (ITO) by spin-coating ammonium salts onto it is investigated. The work function of the ITO is increased via spin-coating an NH4Br aqueous solution onto it, which is observed using ultra-violet photoelectron spectroscopy. The formation of H-bonds at the interface between the ITO and the NH4Br is corroborated by utilising the surface sensitivity of synchrotron X-ray photoelectron spectroscopy at low photoelectron take-off angles. We illustrate the increase in the work function of the ITO with a possible scheme involving H-bonding between NH4+ and the ITO. Polymer light-emitting diodes (PLEDs) with ITO/NH4Br showed significantly enhanced performances compared to those with ITO only, with higher current density (924 mA cm−2vs. 903 mA cm−2) and brightness (44 224 cd m−2vs. 1987 cd m−2) at a bias voltage of 7.0 V. To confirm the advantages of general ammonium salts for enhancing device performance, PLEDs with ITO coated by NH4Cl, NH4H2PO4, and (NH4)2SO4 were fabricated and their performances were verified.