2-Methyl-9,10-bis(naphthalen-2-yl)anthracene Doped Lithium Carbonate as an Effective Electron Injecting Layer for Both Inverted and Conventional Organic Light-Emitting Diode Structures

High driving voltage, low power efficiency, and insufficient device stability are the most critical complications for organic light-emitting diodes (OLEDs) on their way to practical applications. Particularly in the case of active-matrix organic light emitting device (AMOLED) displays, inferior electron injection from commonly-used ITO electrodes is a critical issue. In this work, 2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate (MADN:Li2CO3) is used as an effective electron injecting layer for both inverted and normal bottom-emission organic light-emitting diodes. When the concentration of Li2CO3-doped MADN is optimized, the device exhibits improved characteristics, including improvements in turn-on voltage, luminance, and efficiency. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses reveal an energy level shift in MADN:Li2CO3, which indicates the Fermi level of MADN is moving close to its lowest unoccupied molecular orbital (LUMO) and therefore facilitating electron injection from ITO. In addition, the AFM measurement showed the morphology of the Li2CO3-doped MADN films, revealing good thermal stability in the material related to enhanced lifetime. The results unveiled in this work indicate that Li2CO3:MADN is a promising electron injecting layer for OLEDs with different device structures and provide a vision of the mechanisms behind this phenomenon.