Tailoring Oxidation State of Solution‐Processed MoO3–x Layer Using Laser‐Irradiation and Its Application in Organic Solar Cells

Abstract

AbstractSolution‐processed molybdenum oxide (MoO3–x) is a promising material for charge transport layer in optoelectronic devices. However, no clear relationship between oxidation state and electrical properties has been experimentally derived to guide the optimization of MoO3–x. Here, oxidation state of solution‐processed MoO3–x is controlled by both a photoassisted reduction and a spontaneous reduction. The photoassisted reduction proceeds by absorbing the incoming high flux photons, resulting in oxygen vacancies. Moreover, the spontaneous reduction occurs when MoO3–x layer is in contact with indium‐tin oxide (ITO) electrode and affects for several nanometers away from the interface. Thus, both the photon flux and the thickness of MoO3–x layer play a key role in determining the oxidation state. Synchrotron radiation photoelectron spectroscopy confirms a relationship that the oxidation state gradually decreases with increasing the photon flux and thinning the MoO3–x layer. As a result, at an optimized photon flux and thickness of MoO3–x layer, both high work function (>4.7 eV) and high electrical conductivity (29.1 µS cm‐1) could be simultaneously obtained. These beneficial electronic properties make the solution‐processed MoO3–x thin films to be an efficient hole transport layers in organic solar cells.