Perovskite solar modules break a world record

From cell to module without loss of efficiency: this is one of the main challenges of perovskite photovoltaics. Researchers at Karlsruhe Institute of Technology (KIT) have now managed to produce perovskite solar modules with minimal scaling loss, combining laser-based series interconnections with vacuum processing of all layers of the solar cell — and achieving a world record for vacuum-processed perovskite solar modules in the process.

In photovoltaics, perovskite semiconductors are regarded as particularly promising materials thanks to their low-cost availability, ease of manufacture and enormous potential with regard to efficiency, ie, how much of the irradiated light energy is converted into electrical energy. The task now is to move perovskite photovoltaics from the lab — where they have achieved efficiency levels of more than 25% — to industry.

“A key challenge is to transfer the efficiency levels achieved on areas of a few square millimetres to typical solar module surfaces of several hundred square centimetres,” said Dr Tobias Abzieher, head of development of vacuum-deposited perovskite solar cells at the Light Technology Institute (LTI) of KIT.

Perovskite solar cells are thin-film solar cells that are assembled into large-area solar modules using a so-called monolithic series interconnection. For this purpose, structuring lines are introduced into the solar cell during the deposition of each individual layer, which interconnect the resulting solar cell strips in series. But due to upscaling, perovskite solar modules have so far suffered significant efficiency losses.

On the one hand, the difficulties in depositing the individual solar cell layers increase with their surface area; on the other hand, series interconnection produces so-called dead zones between the active solar cell strips. These zones are useless for later power generation, but indispensable for series interconnection. The KIT team succeeded in minimising the impact of these two loss mechanisms by using a vapour-deposition process for all layers of the solar modules in a vacuum.

“Major advantages of vacuum-based deposition with regard to the production of efficient solar modules are the good controllability of the processes, the limited number of process parameters and, in particular, the fact that the deposition mechanism is independent of the surface to be coated,” Dr Abzieher noted.

The researchers combined this innovative process with high-precision structuring and series interconnection by engraving lines with a laser (monolithic series interconnection). This is believed to be the first time that a large-area perovskite solar module has been produced with nearly no scaling loss — an important step in transferring this technology from lab to industry.

Thanks to the combination of vacuum processing and laser ablation, the LTI researchers achieved efficiency levels of up to 16.6% on a component area of over 50 cm² and 18% on an area of 4 cm² — a world record with vacuum-processed perovskite solar modules. The scientists presented their results at this year’s spring meeting of the Materials Research Society (MRS).

“Despite the increase in component area by a factor of more than 500, we observed nearly no loss of efficiency,” said LTI’s David Ritzer, who designed the high-precision laser-based interconnection.

With their approach, the KIT team succeeded in reducing the scaling losses of perovskite solar modules to levels that have been achieved for photovoltaic technologies already established in the industry, such as cadmium telluride (CdTe) or copper indium gallium diselenide (CIGS). The researchers’ future activities will focus on optimising the actual solar cell layer stack as well as further reducing the size of dead zones.

“If we can leverage the full potential of the technology, the production of perovskite solar modules with efficiency levels of significantly more than 20%, indeed on even larger surfaces, is an achievable goal for the near future,” said KIT Professor Ulrich W Paetzold.

Image caption: An innovative combination of processes enables the interconnection of cells to form modules with nearly no losses. Image credit: Amadeus Bramsiepe, KIT.

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