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

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.