Research brings ‘breakthrough’ solar cells closer to production

A new kind of solar cell that is exciting energy researchers could be manufactured much faster thanks to research in the US.

Perovskite cells, made from crystalline material with a specific molecular structure, have recently shown a rapid improvement in their ability to convert sunlight into electricity and so have been touted as a replacement for conventional silicon cells.

Scientists at Brown University in Rhode Island have developed a way to make perovskite films much faster and on a wider range of substrates than is currently possible, using a room-temperature solvent bath rather than the blast of heat used in existing crystallisation methods.

The new process can produce very thin but high-quality perovskite films.

“We think this could be a significant step toward a variety of commercially available perovskite cell products,” said Nitin Padture, professor of engineering at Brown and director of the Institute for Molecular and Nanoscale Innovation.

Perovskite cells, named for the crystalline structure of their light-absorbing material that mirrors the molecular shape of the mineral perovskite, were invented in 2009 but have already shown efficiencies of over 20 per cent – a level it took traditional silicon cells decades to reach.

As silicon cells are still only a few percentage points more efficient than this – and more expensive to make – some researchers believe perovskite has the potential to become the leading solar technology, although questions have been raised over the stability and durability of perovskite cells.

Perovskite films are usually made by coating a substrate with a solution of chemicals and then removing the unwanted solvent by applying temperatures of 100-150°C.

However, this can cause the crystals to form unevenly and reduce efficiency, as well as limiting the kinds of substrates it is possible to use. Plastic, for example, would be damaged by the heat.

The new solvent-solvent extraction (SSE) method, developed by Brown PhD student Yuanyuan Zhou, uses a second solvent instead of heat to remove the first solvent, leaving an ultra-smooth film of perovskite crystals.

The process produces very thin but high-quality films with efficiencies of over 15 per cent and takes less than two minutes, compared to an hour or more for heat-treating, making it more amenable to mass production.

The research was published in the Royal Society of Chemistry’s Journal of Materials Chemistry A.