Nanoscale interface engineering for enhanced performance in light-emitting-diode devices: ITO/Ag-SRCOOH

Abstract

In light-emitting diode (LED) devices, the hole-injection layer (HIL) reduces the hole injection barrier (HIB) between the anode and organic layers to obtain favorable conditions for hole transport, which considerably affects device efficiency and performance. However, the fabrication of ultrathin silver (Ag) films for electron and hole transport layers remains challenging. We demonstrated the design of a nanoscale HIL interface with chemisorption-bonded carboxylic acid-terminated alkanethiol self-assembled layers on ultrathin Ag. The device structure consisted of indium tin oxide (ITO)/Ag-mercaptan acid (Ag-SRCOOH)/N, Nj-Di (1-naphthyl)-N,Nj-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/ETL(LiF/Al. Notably, a chemical bond peak was not detected between ITO and ultrathin Ag. However, X-ray photoelectron spectroscopy (XPS) measurements confirmed Ag binding to the thiol group of 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) on the Ag island surface, which is evident from -S-Ag- and -RS-Ag- association peaks. Ultraviolet photoelectron spectroscopy analysis results revealed a reduction in the HIB of device from 0.68 to 0.19 eV. Consequently, the luminance and current density, and current density of the AgNP–MPA device increased by 63-fold, 5.8-fold, and 1.1-fold, respectively. Similarly, the AgNP-MUA device exhibited enhanced performance with a 61-fold increase in luminance, 43-fold increase in current density, and a 1.4-fold increase in current efficiency, respectively. The results of this study not only opened novel avenues for future applications, including operation requiring flexibility and transparency of LEDs, but also proposed the optimization of nanoscale interfaces to enhance LED performance.