Enhancing the Hole Injection and Transporting of Organic Light-Emitting Diodes by Utilizing Gradient Doping

Abstract

We demonstrate significant improvement of hole injection and transporting in organic light-emitting diodes (OLEDs) by utilizing gradient doping in hole transporting layer (HTL). An ultrahigh doping concentration at the anode side to enhance the hole injection, whereas low doping concentration close to emission layer to avoid possible quenching of excitons. A plural HTL with concentration step are introduced in between to smooth the hole transporting. Compared to conventional hole injection technologies, the gradient doping significantly enhances the current density and luminance of the OLED.

High‐efficiency organic light‐emitting diodes based on the gradient doping and nonlinear cross‐fading doping in transporting layers

“…The current density–voltage–luminance characteristics of the devices are measured using a computer‐controlled Keithley 2400 and Topcon BM‐7A measurement system. All the measurements are carried out at room temperature under ambient atmosphere …”

“…All the measurements are carried out at room temperature under ambient atmosphere. 6 3 Gradient doping in electron transporting layer is greatly higher than that of doped devices, which is due to a large energy barrier between Al and VOM1973. When the doping ratio in ETL increases up to 30 wt.%, the current density grows to the highest level, indicating that better electron injection has been realized with reduced energy barrier.…”