Fraunhofer IAO building in Stuttgart fitted with 'efficient design' solar facade

Colour-adding technology for solar cells

Not only efficiency but also design presents limitations to solar panel utilisation. German researchers are now developing a technology that could add more colour to the solar cells.

Nanostructured solar cells, suitable for mass production, are being developed by a team of researchers from the Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) in Jena.

“Not enough work has been done so far on combining photovoltaics and design elements to really do the term ‘customized photovoltaics’ justice,” said the project’s manager Kevin Füchsel.

The team’s goal is to create coloured solar cells from paper-thin silicon wafers comprising of three layers. Only a few micrometres thick, silicon semiconductor material in the core of the panel absorbs light and turns it into electricity. Above the silicon substrate, two additional layers are created – the transparent protective insulating layer and a hundred-millimetre thick conductive oxide (TCO) layer, which actively channels the light particles toward the semiconductor in the core of the panel, increasing its efficiency

Such semiconductor-insulator-semiconductor (SIS) structure could provide up to 20 per cent higher energy yields, depending on the actual design of the panel and whether the building faces the sun directly or not.

The upper oxide layer could come in different colours, without compromising the efficiency. With the exception of certain shades of red, blue and green, mostly all colours are possible. “The colour comes from changing the physical thickness of the transparent conductive oxide layer, or modifying its refractive index,” Füchsel said. It also allows for greater flexibility when it comes to shapes of the panels.

As existing solar panels are currently delivered only in black, the team believes the colourful panels could easily find their niche in the market. They could offer entirely new options, for example, for decorative facades, roofs or even energy self-sustaining billboards. “This opens up numerous possibilities to use a building to communicate information, displaying the name of a company or even artistic pictures,” Füchsel said.

To simplify and speed up the manufacturing process, the researchers are developing an inkjet printer capable of spreading the conductive TCO on the silicon wafer.

In the future, the team hopes to be able to substitute the currently most common coating material - the indium tin oxide – with a cheaper alternative. They are currently researching the properties of the zinc oxide, reinforced with aluminium.

The research is funded by Germany’s Federal Ministry for Education and Research (BMBF).

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