Role of molybdenum oxide for organic electronics: Surface analytical studies

Extensive studies have been conducted on molybdenum oxide since it has outstanding properties as an insertion layer for efficient charge injection and extraction in organic semiconductor devices. Efficient charge transfer at semiconductor and electrode interface is one of the most crucial issues for the performance of organic electronic device. A lot of efforts have been spent to address this issue, but there are still many unclarified issues to understand the physical mechanisms. In this review, the authors summarize surface analytical investigations on the mechanisms that govern the effectiveness of the insertion layer. Measurement results on the electronic structure, composition, and morphology are presented. It is found that the high work function of MoOx is the dominant factor for the device performance improvement. Compromising environmental effects and methods to recover or prevent such effects are described. Finally, the criteria for MoOx insertion layer to be effective are provided by comparing the work function of MoOx and the ionization potential of organic semiconductors.