Transparent electrodes based on molybdenum–titanium–oxide with increased water stability for use as hole-transport/hole-injection components

Abstract

Recently, dielectric/metal/dielectric (DMD) transparent electrodes based on MoO₃ have been applied in solar cells and organic light emitting diodes, by virtue of the favourable properties of MoO₃ as hole-transport/hole-injection material. However, amorphous MoO₃ layers are easily dissolved in water, thus inhibiting device processing with water-based solutions. To improve the stability in water, the present study introduces DMD electrodes based on mixed molybdenum–titanium–oxide (MTO), fabricated by DC magnetron sputtering from a conductive oxide target. It is demonstrated that the addition of Ti strongly increases the stability in water, while the desirable electronic properties of MoO₃, specifically the high work function and wide bandgap, are maintained. The DMD electrodes, with Ag as metal layer, were fabricated on both rigid and flexible substrates, namely glass and polyethylene terephthalate (PET). The obtained electrodes have low sheet resistance around 5 Ω/sq and high average visible transmittance well above 0.7 (including the substrate). As a result of the MTO stability, processing with water-based solutions takes place without electrode degradation. To demonstrate the process compatibility for large-scale, industrial production, the DMDs were sputter-deposited by a roll-to-roll process on a 300 mm-wide PET foil, achieving similar electrode properties with the laboratory-scale samples. Graphical abstract: [Figure not available: see fulltext.]