Researchers in Wales have demonstrated the world's highest efficiency for full roll-to-roll printed perovskite solar cells (PSCs), marking a key step on the way to cheaper and more efficient ways of generating solar energy.
The team at Swansea University's SPECIFIC Innovation and Knowledge Centre, led by Professor Trystan Watson, used a four layer roll-to-roll fabrication method to produce perovskite cells with a stable power output conversion of 12.2 percent. This is the highest efficiency recorded for four layers of roll-to-roll printed PSCs to date.
In contrast to silicon photovoltaic cells which require high temperature and high vacuum deposition, perovskite solar cells can be solution-processed at a low temperature, which significantly reduces the manufacturing cost. The 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, spray coating and slot-die coating. The last technique has several advantages over the alternatives: it is a pre-metred 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 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. This system has a rheological advantage due to low viscosity and low surface tension, which results in better coatings. This also allowed the team to use a new blend of solvents, replacing chlorobenzene for the deposition of hole transport material.
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