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

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 Omega/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. [GRAPHICS] .

Automated summary

Recently, a transparent electrode called dielectric/metal/dielectric (DMD) based on MoO3 has been applied in solar cells and organic light-emitting diodes (OLEDs). However, the MoO3 layer is easily dissolved in water, which hinders its processing with water-based solutions. In this study, a DMD electrode based on mixed molybdenum-titanium-oxide (MTO) was introduced to improve the stability in water. The addition of titanium greatly increased the stability in water while maintaining the desirable electronic properties of MoO3. The DMD electrodes with a silver (Ag) metal layer were fabricated on both glass and polyethylene terephthalate (PET) substrates, showing low sheet resistance and high transmittance. The MTO stability enabled processing with water-based solutions without electrode degradation. The DMDs were also successfully produced on a wide PET foil using a roll-to-roll process, demonstrating its compatibility for large-scale industrial production.