Researchers at the Karlsruhe Institute of Technology (KIT) have produced perovskite solar modules with greatly reduced loss of efficiency due to scaling. The team reported an efficiency of 18% for a perovskite solar module with an area of ​​4cm2 - a world record for vacuum-processed perovskite solar modules. To this end, they combined the series connection by laser with the vacuum processing of all layers of the solar cell.

Interconnecting cells into modules with almost no losses is achieved with an innovative combination of processes image

"One of the main challenges is to transfer the efficiencies achieved on areas of a few square millimeters to typical solar module surfaces of a few hundred square centimeters," says Dr. Tobias Abzieher, who heads the development of perovskite solar cells deposited from a vacuum at the Light Technology Institute (LTI) of the KIT. Perovskite solar cells are often joined together to form large-area solar modules using the so-called monolithic series connection. For this purpose, structuring lines are introduced during the deposition of the individual layers of the solar cell, which causes the solar cell strips to be connected in series.

In the case of perovskite solar modules, the upscaling has so far resulted in significant efficiency losses. Firstly, the greater the surface area, the more difficult it is to deposit the individual solar cell layers, and secondly, when connected in series, so-called dead areas arise between the active solar cell strips. These are areas that cannot later contribute to the generation of electricity, but are required for series connection.

The Karlsruhe team has now succeeded in minimizing the influence of both loss mechanisms by evaporating all layers of the solar modules in a vacuum. "Great advantages of the deposition from the vacuum with regard to the production of efficient solar modules are the simple controllability of the processes, the small number of process parameters and, in particular, the independence of the deposition mechanism from the coating surface”, explains Abzieher.

The researchers combined this innovative process with high-precision structuring and series connection by engraving lines using a laser (monolithic series connection). This is the first time they have produced a large-scale perovskite solar module with almost no loss of scaling - an important step from the laboratory into industry.

With the combination of vacuum processing and laser ablation, the researchers at LTI achieved efficiencies of up to 16.6% on a component area of ​​over 50 square centimeters and even 18% on an area of ​​four square centimeters. “Despite the enlargement of the component area by a factor of over 500, almost no loss of efficiency can be observed,” reports David Ritzer from LTI, who developed the high-precision laser circuit. With this approach, the Karlsruhe team succeeded in reducing the scaling losses in perovskite solar modules to values

In the future, the researchers will work on optimizing the pure solar cell layer stack and on further reducing the dead areas. "If we fully exploit the potential of the technology, the production of perovskite solar modules with efficiencies of well over 20%, even on even larger areas, is a realizable goal in a timely manner," says tenure-track professor Ulrich W. Paetzold, head of the cross-institute "Taskforce Perovskite Photovoltaics“ at KIT.