Achieving the hypsochromic electroluminescence of ultraviolet OLED by tuning excitons relaxation

Abstract

Organic light emitting diode (OLED) has huge impact on display-related fields. Due to potential applications in information storage and backlight sources for full color display, ultraviolet OLED has attracted widespread attention. In this paper, we present an inverted UV OLED device with electroluminescence (EL) peak of 369 nm. The device employs zinc oxide (ZnO) as electron injection layer (EIL), revealing a relationship between the exciton diffusion and emitting peaks. The organic-inorganic interface in the device reduces the diffusion length of excitons and that can lead to a hampered relaxation of higher energy states, resulting in a hypsochromic shift of the EL spectrum. The existence of buffer layer will affect the relaxation process. Additionally, the emission peak of the UV-OLED can be adjusted from 369 nm to 384 nm by varying kinds and thickness of the organic functional layers.