Professor Choi Doo-ho's Team at Dong-Eui University Develops Ultra-Thin Copper-Based Transparent Electrode

The research team led by Professor Dooho Choi from the Department of Electrical and Electronic Materials Engineering, School of Materials Science and Engineering at Dong-Eui University, developed a transparent electrode technology based on ultrathin copper (Cu) with the world’s highest performance by controlling the interface characteristics of zinc oxide (ZnO) thin films.

Professor Choi’s team recently published their paper titled “Smooth, Chemically Altered Nucleating Platform for Abrupt Performance Enhancement of Ultrathin Cu-Layer-Based Transparent Electrodes” in the July issue of the nanotechnology journal Nano Letters (impact factor: 12.262).

According to the research results, the newly developed copper-based transparent electrode offers many economic advantages compared to previously studied silver (Ag)-based transparent electrodes and also possesses flexibility.

Additionally, it has the advantage of maintaining its properties even under repeated exposure to very high thermal, electrical, and mechanical stresses simultaneously, making it applicable in various fields.

A transparent electrode refers to a functional thin-film electrode that simultaneously exhibits high optical transmittance in the visible light range and electrical conductivity, and it is used as a key material in displays, touchscreens, and next-generation solar cells.

For transparent electrodes to be effective, they must have both low electrical resistance and high visible light transmittance. Therefore, recent research on transparent electrodes with a ‘metal oxide-metal-metal oxide’ structure to prevent light reflection and oxidation of ultrathin metal layers has been active.

In the case of the metal layer copper, as the thickness of the thin film increases, transmittance decreases, so it is important to form a continuous thin film with the highest optical transmittance at the thinnest possible thickness.

Schematic diagram of ultra-thin copper-based transparent electrode technology.

To solve this issue, Professor Choi’s team applied an argon (Ar) plasma process to the surface of the underlying oxide to control the oxygen vacancy concentration and utilized this as a nucleation site for copper, developing a technology to form a fully continuous copper thin film at an ultrathin thickness of 6 nm.

This technology forms a very flat oxide-metal interface, reducing interface scattering of photons and electrons.

The research team achieved a maximum transmittance of 94% and a sheet resistance of 9.1 Ωsq-1 with this technology, reaching a Haacke Figure of Merit of 0.063 Ω-1 for the transparent electrode. This value is the highest performance index reported for copper-based transparent electrodes in the literature, representing a world record.

This research was supported by the Korea Research Foundation’s Mid-career Researcher Support Program, the Ministry of Education’s Basic Science Research Capacity Enhancement Project, and the Ministry of Trade, Industry and Energy’s Industrial Innovation Talent Support Project.

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