Long-lasting and efficient inverted pure blue organic light-emitting diodes by inserting an ultrathin aluminum interlayer

Abstract

Blue organic light-emitting diodes (OLEDs) play an important role in OLED display and lighting applications, but short lifetime and low efficiency are still their two key issues in the commercialization. Here, we manage to address the two issues at the same time by simply inserting an ultrathin aluminum (Al) interlayer between the indium tin oxide (ITO) cathode and the electron injection layer of an inverted pure blue OLED. Current efficiency (CE) and external quantum efficiency were improved by optimizing the thickness of the Al interlayer. It has been approved from current-voltage characteristics, impedance spectra and an ultraviolet photoelectron spectrum that 1 nm thick Al interlayer is an effective work function modifier for the ITO cathode and can help to enhance electron injection from the ITO cathode to the electron transporting layer. The Al interlayer contributed also to extend dramatically the lifetime of the inverted pure blue OLED. A long operation lifetime (T80 > 83 h) with the maximum CE of 7.9 cd A−1 was achieved after adding 1 nm Al interlayer.