Transparent thin-film solar cell developed with flexible substrate

A research team led by Dr Jung-dae Kwon at the Korea Institute of Materials Science (KIMS) has developed a transparent thin-film solar cell on a flexible substrate that exhibits different reflective colours and does not significantly reduce the solar cell’s efficiency. This technology achieves reflective colour on a single material by periodically incorporating hydrogen into a zinc oxide material doped with aluminium, which is a transparent electrode, to induce a refractive index difference.

By designing a multi-layer thin film with a low refractive index difference of less than 5%, the reflection loss in the visible light region absorbed by the solar cell device was minimised. It can be applied to various absorbers for thin-film solar cells as it hardly reduces the solar cell efficiency due to colour implementation. It is also expected to serve as a benchmark for improving the aesthetics of flexible substrate transparent thin-film solar cells for BIPV (Building Integrated Photo Voltaic) and VIPV (Vehicle Integrated Photo Voltaic).

To date, multilayer thinning technology for materials with large refractive index differences, colour control thin-film coating technology for designing optical properties, and natural structure-mimicking structural colour technology have been used as colour application methods to improve the aesthetics of transparent thin-film solar cells. However, these technologies are not suitable for solar cells that absorb visible light due to a wide reflection band and high reflectivity.

The researchers formed multilayer thin films with different refractive indices through periodic hydrogen reactions while depositing zinc oxide thin films using the vacuum sputtering deposition method used in general semiconductor and solar cell manufacturing processes. They then obtained the three primary colours of light by adjusting the thickness of the multilayer thin film. At that time, the colour of the electrode was well implemented even when applied to a solar cell that absorbs light in the visible light range.

A multilayer transparent thin-film electrode based on a single material does not require additional processing. It is expected that various colours and high efficiency of thin-film solar cells can be realised at a low cost. Additionally, since the reflective colour is implemented as an optical filter, it can be applied to various fields such as image sensors, photolithography masks and infrared shielding.

“When commercialised, this technology will help to develop simple and process-free light filter technology and high-efficiency coloured flexible substrate transparent thin-film solar cells, as well as to realise BIPV systems for modern buildings and VIPV systems for vehicles with aesthetic features,” Kwon said.

The research results were published in the Chemical Engineering Journal.

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