Ultrathin Oxide/Metal/Oxide Trilayer Transparent Conducting Electrodes for an All-Transparent Flexible UV Photodetecting Device

Amidst the rapid advancement of flexible and transparent optoelectronic devices, the oxide/metal/oxide (O/M/O) trilayer structure has been considered to be a potential transparent conducting electrode (TCE) because of its superior stability and better durability as compared to single-layered TCEs or metallic films. In this study, we report an ultrathin sputter-deposited SnO₂/Cu/SnO₂ trilayer TCE with excellent electrical and optical properties appropriate for flexible and transparent optoelectronic devices. All of the deposited TCE films are almost amorphous in nature with an excellent smooth surface texture, as evident from the X-ray diffraction and atomic force microscopy studies. The X-ray photoelectron spectroscopy study reveals that Cu remains in the elemental state, sandwiched between two oxide layers. The lowest resistivity value of 1.59 × 10^–4 Ω·cm along with the highest figure of merit value of around 1.37 × 10^–3 Ω^–1 have been obtained for a 23 nm (10/3/10) trilayer. The enhanced conductivity in the films primarily results from carrier injection from the Cu layer to the oxide layer. A ZnO-based flexible and all-transparent ultraviolet photodetecting device on polyethylene terephthalate substrates featuring optimized O/M/O (10/3/10) electrodes achieves responsivity and detectivity values of 0.33 mA/W and 3.06 × 10¹⁰ Jones, respectively. The device shows a remarkably stable photoresponse under flat as well as various bend conditions. Therefore, this study provides potential ways for fabricating high-quality O/M/O TCEs across a broader spectrum of flexible and transparent optoelectronic devices.