Fast sputter deposition of MoO_x/metal/MoO_x transparent electrodes on glass and PET substrates

Dielectric/metal/dielectric (DMD) transparent electrodes emerged as a compelling alternative to the widely used indium-tin-oxide (ITO) for solar cells and optoelectronic devices. DMD electrodes are especially attractive for flexible substrates, as, in contrast to ITO, they retain their low electrical resistance upon substrate bending and they do not require deposition at elevated temperatures. In a DMD, the choice of the dielectric is mainly dictated by the device architecture. Owing to its high work function, MoO₃ is a commonly used hole-selective dielectric layer. The present work investigates MoO_x/metal/MoO_x (with 2 < x < 3) DMD electrodes, with Ag and Au as metals, fabricated by direct current, magnetron sputtering, at industry-relevant, high deposition rates. This was possible with a properly engineered MoO_x target, providing high electrical conductivity and compactness. The sputtered electrodes on polyethylene terephthalate (PET) substrates show higher figure-of-merit than similar, evaporated electrodes in the literature. It is shown that the DMD electrodes with amorphous MoO_x layers have low stability in water, but they are stable to other solvents, such as toluene, dimethylsulfoxide (DMSO), dimethylformamide (DMF), chlorobenzene or chloroform, allowing their implementation in devices like organic light-emitting diodes or perovskite solar cells. Further, it is shown that the electrodes show dramatically enhanced mechanical stability compared to ITO, when subjected to tensile bending tests.