Peel-and-stick process boosts potential of thin-film solar cells

Unlike standard thin-film solar cells, the peel-and-stick version from Stanford does not require any direct fabrication on the final carrier substrate. The breakthrough is described in a paper in the 20 December issue of Scientific Reports.

According to a statement, all the challenges associated with putting solar cells on unconventional materials are avoided with the new process, thereby expanding the potential applications of solar technology.

Thin-film photovoltaic cells are traditionally fixed on rigid silicon and glass substrates, greatly limiting their uses, said Chi Hwan Lee, lead author of the paper and a PhD candidate in mechanical engineering.

While the development of thin-film solar cells promised to inject some flexibility into the technology, scientists found that the use of alternative substrates was problematic, said Xiaolin Zheng, a Stanford assistant professor of mechanical engineering and senior author of the paper.

‘Non-conventional or “universal” substrates are difficult to use for photovoltaics because they typically have irregular surfaces and they don’t do well with the thermal and chemical processing necessary to produce today’s solar cells,’ Zheng said. ‘We got around these problems by developing this peel-and-stick process, which gives thin-film solar cells flexibility and attachment potential we’ve never seen before and also reduces their general cost and weight.’

Utilising the process, researchers attached their solar cells to paper, plastic and window glass among other materials.

‘It’s significant that we didn’t lose any of the original cell efficiency,’ Zheng said.

The new process involves a unique silicon, silicon dioxide and metal sandwich.

First, a 300nm film of nickel is deposited on a silicon/silicon dioxide wafer.

Thin-film solar cells are then deposited on the nickel layer utilising standard fabrication techniques and covered with a layer of protective polymer.

A thermal release tape is then attached to the top of the thin-film solar cells to augment their transfer off of the production wafer and onto a new substrate.

To remove the solar cell from the wafer, the wafer is submerged in water at room temperature and the edge of the thermal release tape is peeled back slightly, allowing water to seep into and penetrate between the nickel and silicon dioxide interface.

The solar cell is freed from the hard substrate but still attached to the thermal release tape.

Zheng’s team heat the tape and solar cell to 90°C for several seconds and then the cell can be applied to virtually any surface using double-sided tape or other adhesive. Finally, the thermal release tape is removed, leaving the solar cell attached to the chosen substrate.

Tests have demonstrated that the peel-and-stick process reliably leaves the thin-film solar cells wholly intact and functional, Zheng said.

‘There’s also no waste. The silicon wafer is typically undamaged and clean after removal of the solar cells and can be reused.’