Extremely-low-voltage, high-efficiency and stability-enhanced inverted bottom OLEDs enabled via a p-type/ultra-thin metal/n-doped electron injection layer

Abstract

The enhancement of charge injection is significant to lower the voltage, reduce the power consumption, improve the efficiency, and prolong the lifetime of organic light-emitting diodes (OLEDs). However, effective strategies to enhance the electron injection for inverted bottom OLEDs (IBOLEDs) are still rarely reported. Herein, a novel p-type/ultra-thin metal/n-doped electron injection layer (EIL) has been proposed to remarkably enhance the electron injection of IBOLEDs. Specifically, the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ)/Al/4,7-diphenyl-1,10-phenanthroline (BPhen):Li EIL based IBOLEDs exhibit an extremely low voltage of 2.97 V and a high power efficiency of 84.9 lm W⁻¹ at 100 cd m⁻², and are among the best IBOLEDs. Additionally, an enhanced device stability is obtained. The electron dynamics are investigated by both experimental characterization and simulation, showing that the low work function of Al and its self-doping effect increase the electron density and reduce the interfacial energy barrier effectively. Furthermore, the better film-forming properties of Al decrease the film roughness and improve device stability. The results not only indicate that the enhancement of electron injection enables high-performance IBOLEDs and can be further applied to other kinds of LEDs, but also provide guidelines for the development of IBOLED-based display technology and related optoelectronic applications.