This image shows the 2D periodic array that is patterned into the upper gold layer of the metasurface by focused ion beam etching. Image: University of Bristol.Researchers from the universities of Bristol and Exeter in the UK are one step closer to developing a new generation of low-cost, high-efficiency solar cells, through the creation of one of the world's first examples of a tri-layer metasurface absorber with a carbon interlayer.
Developed by Chenglong Wang, a PhD student in Martin Cryan's research group at the University of Bristol, and described in a paper in Nano Energy, the metasurface comprises a layer of amorphous carbon sandwiched between thin gold films. Using focused ion beam etching, the researchers also pattern the upper gold film with a two-dimensional (2D) periodic array.
This trilayer gold-carbon-gold metasurface is able to absorb light strongly across the solar spectrum while minimizing emission of thermal radiation. As a result, it has the potential to reach much higher temperatures than simple black surfaces, making it ideal for solar thermal energy applications. This work is still at an early stage, though. Eventually, the researchers want to replace the gold with other refractory metals such as tungsten or chrome and to replace the amorphous carbon with diamond.
The researchers developed this metasurface as part of a joint project between the Department of Electrical and Electronic Engineering and the Schools of Physics and Chemistry at the University of Bristol. The aim of the project is to develop diamond-based solar thermionic devices, which are heated by sunlight until they get sufficiently hot to emit electrons directly into a vacuum. If these electrons are collected at a cooled anode, electrical energy can be produced with efficiencies that are predicted to be much higher than can be achieved with conventional silicon solar cells.
"Integrating diamond within metasurfaces is very challenging, and this paper is a first step in that direction using amorphous carbon, " said Cryan, professor of applied electromagnetics and photonics in the Department of Electrical and Electronic Engineering. "The next stage is to carry out high temperature testing on the structures and to attempt to reach the ~700°C required to obtain efficient thermionic emission."
The Bristol team are working with Tapas Mallick at the University of Exeter to develop these low-cost solar thermionic devices.
This story is adapted from material from the University of Bristol, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.