Origin of the improved luminance-voltage characteristics and stability in organic light-emitting device using CsCl electron injection layer

The luminance-voltage characteristics and stability were highly improved by replacing LiF with CsCl in organic light-emitting devices. To investigate the origin of these improvements, ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy were used. The additional shifts of the vacuum, highest occupied molecular orbital, and lowest unoccupied molecular orbital levels due to the CsCl layer reduce the width and height of the electron injection barrier, resulting in the improved luminance-voltage characteristics of the devices. Additionally, the intervening CsCl layer between Al and Alq3 prevents N-Al reactions among Alq3 molecules and Al, which reduces distortion or breakdown of Alq3 molecules and slows the degradation of the device.