Nanotechnology Technology

Electrodes Based on Leaf Veins Result in Highly Efficient Solar Cells

leaf vein

Prof. Michael Giersig from Helmholtz-Zentrum Berlin (HZB) recently led an international team that showed that current metallic networks are surpassed in utility by networks of metallic mesh possessing fractal like nano features.

The new technology uses quasi fractal nano features that are similar to the hierarchical networks of veins in leaves. The team demonstrated that metallic networks with these features improve performance of electrodes for various applications. The new networks combine ultra-low total resistance and minimized surface coverage while uniform current density is maintained. It was also shown that the networks that are inspired by nature could surpass the performance of conventional layers manufactured from indium tin oxide (ITO).

A model of a metallic nano-network with periodic arrangement (left) and visual representation of a fractal pattern (right). Image credit: HZB/M. Giersig
A model of a metallic nano-network with periodic arrangement (left) and visual representation of a fractal pattern (right). Image credit: HZB/M. Giersig

The scientists conducted experiments on different topologies of artificially constructed electrode networks. They found that non-periodic hierarchical organization exhibited excellent optical transmittance when compared to periodic organization, as well as a lower resistance. The output power for photovoltaic components was found to be elevated as a result.

Giersig noted that they were able to develop an economical transparent metal electrode based on the results of these studies. This was achieved by integrating two silver networks. The first is applied with a broad mesh spacing between the micron diameter main conductors and serves as the “highway” for electrons that transport electrical current over macroscopic distances. The second layer consists of additional nano wire networks distributed randomly. This serves as local conductors to cover the surface between the large mesh elements. The smaller networks can be seen as regional roadways beside the highways and they randomize the strengths and directions of the local currents. Their secondary purpose is to create refraction effects that improve transparency above that of conventional shadow limited performance. Exceptional high efficiencies were achieved with solar cells based upon these electrodes.

Study has been published in Nature Communications.

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