Improvement of OLED performance by tuning of silver oxide buffer layer composition on silver grid surface using UV-ozone treatment

Abstract

In this study, silver grid/Ag2O and AgOx/MoO3 transparent conductive electrodes (TCEs) were fabricated and implemented in organic light-emitting diodes (OLEDs). The effects of ultraviolet (UV)-ozone treatment time on the silver grids are discussed. With a treatment duration of 15 s, the Ag2O thin films do not grow completely and current-voltage characteristics are poor. However, a 30 s UV-ozone treatment yielded good-quality Ag2O thin films. The Ag2O thin films were reconverted into the AgOx phase with further increases in UV-ozone exposure time. The Ag2O work function is nearly 5.0 eV, which decreases the injection barrier of the silver grids (∼4.7 eV) and MoO3 (∼5.3 eV). Nevertheless, excessive treatment time leads to the production of AgOx thin films and an increase in the work function to 5.3 eV, the same as the highest occupied molecular orbital energy of MoO3, which causes a work function mismatch. The work function mismatch between the Ag grids and the MoO3 layer results in a high injection barrier, decreasing OLED performance. The electrical properties of the electrodes and devices apparently depend on the composition of the silver oxide buffer layer, as determined using X-ray photoelectron spectroscopy. The surface and optical properties of the TCEs were also investigated. The results show that the OLED devices with the proposed TCEs have better roll off and current efficiency compared to traditional ITO-based devices.