Highly Efficient and Stable Electron Injection Layer for Inverted Organic Light-Emitting Diodes

Abstract

A highly efficient and stable electron injection layer (EIL) for inverted organic light-emitting diodes (OLEDs) is developed. A 1 nm-thick Al is deposited between indium tin oxide cathode and commonly used Cs2CO3 EIL, which can significantly improve the stability. The Al may react with evaporated Cs2CO3 and form a much stabler Al-O-Cs complex, avoiding Cs oxidization by air according to X-ray photoemission spectroscopy measurement. When the Al is evaporated after Cs2CO3 layer, although such a Al-O-Cs complex also forms, the inferior electron injection at Al/4,7-diphenyl-1,10-phenanthroline interface leads to a joule heat-induced resistance that adversely affects the air stability of the device. It is expected that the developed Al/Cs2CO3 EIL promotes high efficiency and stable active-matrix OLEDs based on n-type thin film transistor.

Interface Engineering for Controlling Device Properties of Organic Antiambipolar Transistors

“…Cs 2 CO 3 has been already known to be decomposed during thermal evaporation to produce metallic Cs. Then, the metallic Cs reduces the contact resistance to enhance electron injection due to its low work function. − The I D – V G curve (purple) in Figure a shows an n-type operation obtained from a device with a Cs 2 CO 3 interlayer at a PTCDI-C8/source interface. The I D – V G curve of the pristine device (red) is also shown for comparison.…”

Solution-Processed Hybrid Light-Emitting Devices Comprising TiO2 Nanorods and WO3 Layers as Carrier-Transporting Layers

“…The lifetime of the device is defined as the time when the luminance is decreased to a half of its initial luminance, which is determined about 40 h. The stability test of inverted OLEDs is seldom reported in the literature. G. He et al reported the inverted OLEDs with the configuration of ITO/Cs 2 CO 3 /Bphen/Alq3/NPB/MoO 3 /Au [35]. The device lifetime was only 20 h when using Cs 2 CO 3 as the EIL.…”

Facilely Solution‐Processed Lithium Carbonate for Tailoring Electron Injection in High‐Performance Inverted Near‐UV Organic Light‐Emitting Diodes

“…Active metals (Al [ 14 ] and Mg [ 15 ] ), metal compounds (LiF, [ 16 ] Cs 2 CO 3 , [ 17 ] Li 2 CO 3 , [ 18 ] MgO, [ 19 ] ZnO, [ 20 ] TiO 2 , [ 21 ] and MoS 2 [ 22 ] ), and organic polymers (PEO, [ 23 ] PEIE, [ 24 ] and PEI [ 25 ] ) are common EILs in OLEDs. n‐type dopants (e.g., Li, [ 26 ] Cs 2 CO 3 , [ 22 ] Rb 2 CO 3 , [ 3 ] and Li 2 CO 3 [ 27 ] ) incorporating into electron transport material or introducing multilayer‐stacked EILs [ 22,28 ] provides an alternative approach for constructing efficient inverted OLEDs, although such a composite EIL complicates device fabrication process. Lithium carbonate (Li 2 CO 3 ) is an effective electron injection material and n‐type dopant due to its suitable work function, facile solution processability, and easy handling by thermal evaporation.…”