Polymer interlayers on flexible PET substrates enabling ultra-high performance, ITO-free dielectric/metal/dielectric transparent electrode

Highlights: • High performance transparent electrodes on flexible substrate with low temperature process, based on TiO_x/Ag/AZO • Polymer interlayers boost electrode's performance by altering the TiO_x growth. • Elucidation of mechanisms influencing the growth of reactively-sputtered TiO_x • Low roughness of electrode is advantageous for thin active-layer devices. -- Abstract: This work reports on the fabrication and properties of a dielectric/metal/dielectric (DMD) transparent electrode on polyethylene terephthalate (PET) flexible substrate with polymer interlayers. The sputtered TiO_x/Ag/AZO (AZO: Al-doped ZnO) DMD electrode yields performance beyond the current state-of-the-art for transparent electrodes on PET, with an average transmittance larger than 85% (including the substrate) in the range 400–700 nm and sheet resistance below 6 Ω/square. Within a broad visible spectral range, the transmittance of the flexible electrode surpasses the transmittance of the bare PET. This performance was enabled by the use of a polymer layer between the PET and the DMD electrode. The interlayer modifies the growth of the TiO_x on the flexible substrate, rendering it similar to its growth on glass. This markedly increases the transmittance of the DMD electrode and decreases its sheet resistance. The presented electrode has a large potential for photovoltaic and optoelectronic applications, outperforming the widely-used indium-tin-oxide (ITO) on flexible substrates.