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Welsh scientists set highest efficiency record for printed solar cells

Image credit: Apisit Wilaijit/Dreamstime

A new study has reported the highest efficiency ever recorded for full roll-to-roll printed perovskite solar cells (PSCs). This marks a key step in creating cheaper and more efficient ways of generating solar energy.

A team at Swansea University’s 'SPECIFIC Innovation and Knowledge Centre', led by Professor Trystan Watson, said it used a roll-to-roll fabrication method for four layers of slot-die coated PSCs. 

The PSCs gave a stable power output of 12.2 per cent, which the teams said is the highest efficiency recorded for four layers of roll-to-roll printed PSCs to date.

A newcomer to the photovoltaic industry, PSCs have gained traction from researchers around the globe. With efficiency reaching similar levels to those of silicon photovoltaics (PV) - the current market leader - attention has been diverted towards upscaling PSCs.

Compared to silicon PV, which requires high temperature and high vacuum depositions, PSCs can be solution-processed at a low temperature, which significantly reduces the manufacturing cost, experts say.

Two-step roll to roll coating of perovskite thin films at Swansea University, where researchers from the SPECIFIC project have achieved record efficiency levels for printed solar cells.

Two-step roll to roll coating of perovskite thin films at Swansea University, where researchers from the SPECIFIC project have achieved record efficiency levels for printed solar cells.

Image credit: SPECIFIC/Swansea University

Low-temperature processing makes it possible to use plastic substrates to create flexible solar cells. 

The ability to solution-process provides the opportunity to apply various well-developed printing and coating techniques, such as screen printing; inkjet printing; gravure printing; slot-die coating and spray coating. Such benefits allowed the Swansea University researchers to use roll-to-roll manufacturing for four layers of PSCs.

“Perovskite solar cells aim to increase the efficiency and lower the cost of traditional solar energy generation,” said Rahul Patidar, lead researcher on the project. They have the potential to be highly efficient and relatively cheap to manufacture, so the aim is to improve fabrication methods for upscaling.”

According to the team, slot-die coating provides several advantages over the alternatives. It is a pre-metered technique, which means the wet film thickness can be controlled before coating. It is also highly efficient in material usage, with minimal loss of material compared with spray coating or screen printing.

Using the necessary toxic solvents at an industrial scale, however, requires a lot of air handling to stay under the safety limits, which can incur significant and unnecessary expenses. For this reason, an acetonitrile-based system was used, which has a rheological advantage due to low viscosity and low surface tension, which results in better coatings.

Thin flexible films with printed solar cells are a key step towards cheaper and more efficient solar energy - Swansea University researchers have demonstrated record efficiency levels for perovskite solar cells

Strip coating of perovskite thin films

Image credit: SPECIFIC/Swansea University

Along with this, a ternary blend of high workplace exposure limit solvents was introduced, replacing aromatic organic compound chlorobenzene for the deposition of hole transport material. This helped the PSCs achieve their record-high stable power output of 12.2 per cent.

A complete solar cell for a chosen architecture requires coating five layers. In this case, four layers were coated using slot-die coating and the top contact was put on using thermal evaporation. Slot-die coating the fifth (top) contact without destroying any layers underneath has not yet been achieved. Solving this, however, would enable the manufacture of a fully roll-to-roll printed PSC.

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