Sustainable components for solar panels

Scientists from Daegu Gyeongbuk Institute of Science and Technology (DGIST) have identified a novel method to create efficient alloy-based solar panels free of toxic metals, publishing their results in the journal Advanced Energy Materials.

Most common thin-film solar panels consist of expensive rare-earth elements like indium and gallium, or highly toxic metals like cadmium. Environmentally friendly solar panels consisting of more abundant materials offer attractive alternatives, but are hindered by their low practical efficiency compared to their theoretical potential. DGIST researchers, led by Dr Jin-Kyu Kang and Dr Dae-Hwan Kim, have now discovered a solution to this problem.

“Thin-film solar cells using bronze (Cu-Sn) and brass (Cu-Zn) as base materials are composed of non-toxic earth-abundant materials, and have been studied worldwide because of their low cost, high durability and sustainability,” said Dr Kang. However, using these alloys in thin film technology has its own drawbacks.

While the theoretical efficiency of these panels matches the efficiencies of top-market products, they tend to underperform drastically in practice. This is because of the formation of various defects in the materials, such as point defects, surface defects and volume defects, during the annealing (heating and cooling) process. These defects undermine the current flow, resulting in loss of electricity generated.

The scientists wanted to find a way to synthesise the best-quality CZTSSe (copper, zinc, tin, sulfur and selenium) thin films. They played around with the annealing profile, which has a strong effect on the grain size of CZTSSe thin film: the longer the annealing time and higher annealing temperature, the larger the grains and the lesser the electricity loss. However, as the annealing temperature and time increase, there is a change in the properties of the CZTSSe thin film due to decomposition.

To bypass this issue, the team used a special ‘liquid-assisted method’, which allowed the grains of CZTSSe to grow at a faster rate. This meant that the grains could grow large even at low temperatures, preventing the change in the properties of the CZTSSe thin film. The scientists thus managed to overcome a significant hurdle in the search for low-cost, environmentally friendly solar energy, with one of their CZTSSe solar cells exhibiting an impressive 12.6% conversion efficiency.

“Our technology has diverse applications, including in electronic devices, household goods, buildings and vehicles,” Dr Kim said. “The best part is that CZTS solar cells are free of the current drawbacks of toxic and rare metals. We can install everywhere we want!”

Image caption: The DGIST team prepared lab-scale CZTSSe solar cells. Image ©DGIST.

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