Flexible transparent layered metal oxides for organic devices

Abstract

In this manuscript we report that an ultra-thin (∼10 nm thick) molybdenum oxide/aluminum oxide layered-metal-oxide (LMO) exhibits sufficient electrical conductance as a contacting electrode for organic light-emitting diodes (OLEDs). Owing to its high optical transparency, the LMO device performance is found to be superior to that of devices made with today's industrial staple material, indium tin oxide (ITO). The transmittances of the ITO and LMO electrodes at 520 nm wavelength are 81.8% and 86.7%, respectively. Its excellent optical characteristics and facile fabrication make LMO attractive for future flexible OLEDs and other optoelectronic devices. Analysis using photoemission measurements revealed defect states near the Fermi level in the LMO films. Variable temperature current–voltage measurements show that the electron conduction process follows well the Mott variable-range hopping theory. These findings demonstrate that the gap states in the LMO are Anderson–Mott localized quantum states, which establish an efficient conduction pathway for electron conduction in the LMO electrodes. It is noted that the simplicity of fabricating the LMO electrodes makes this material system extremely attractive for other optoelectronic applications such as in solar cells.