The Influence of Hydrogenation and Oxygen Vacancies on Molybdenum Oxides Work Function and Gap States for Application in Organic Optoelectronics

Molybdenum oxide is used as a low-resistance anode interfacial layer in applications such as organic light emitting diodes and organic photovoltaics. However, little is known about the correlation between its stoichiometry and electronic properties, such as work function and occupied gap states. In addition, despite the fact that the knowledge of the exact oxide stoichiometry is of paramount importance, few studies have appeared in the literature discussing how this stoichiometry can be controlled to permit the desirable modification of the oxide's electronic structure. This work aims to investigate the beneficial role of hydrogenation (the incorporation of hydrogen within the oxide lattice) versus oxygen vacancy formation in tuning the electronic structure of molybdenum oxides while maintaining their high work function. A large improvement in the operational characteristics of both polymer light emitting devices and bulk heterojunction solar cells incorporating hydrogenated Mo oxides as hole injection/extraction layers was achieved as a result of favorable energy level alignment at the metal oxide/organic interface and enhanced charge transport through the formation of a large density of gap states near the Fermi level.