Lower silicon solar cell and upper perovskite solar cell with transparent contacts (Niels van Loon).

TNO, TU Eindhoven, imec and TU Delft, partners in Solliance, joined forces to further push the conversion efficiency of tandem solar cells to beyond the boundaries of today’s business photovoltaic (PV) modules.

For the primary time, four-terminal perovskite/silicon tandem devices with an authorized top cell passed the barrier of 30%. Such high efficiency enables more power per square meter and fewer cost per kWh. The result’s presented through the eighth World Conference on Photovoltaic Energy Conversion (WCPEC-8) in Milan, and it has been achieved by combining the emerging perovskite solar cell with conventional silicon solar cell technologies. The perovskite cell, which features transparent contacts and is a component of the tandem stack, has been independently certified.

Moreover, achieving high-power density will create more opportunities to integrate these solar cells into construction and constructing elements, in order that more existing surface area may be covered with PV modules. Breaking the 30% barrier is subsequently an enormous step in accelerating the energy transition and improving energy security by reducing the dependency on fossil fuels.

The perfect of each worlds

Tandem devices can reach higher efficiencies than single junction solar cells due to a greater utilization of the solar spectrum. The currently emerging tandems mix business silicon technology for the underside device with perovskite technology, featuring highly efficient conversion of ultraviolet and visual light and excellent transparency to close infrared light.

In four-terminal (4T) tandem devices the highest and bottom cells operate independently of one another, which makes it possible to use different bottom cells in this sort of devices. Industrial PERC technology in addition to premium technologies like heterojunction or TOPCon or thin-film technology akin to CIGS may be implemented in a 4T tandem device with hardly any modifications to the solar cells. Moreover, the four-terminal architecture makes it clear-cut to implement bifacial tandems to further boost the energy yield.

Researchers from the Netherlands and Belgium have successfully improved the efficiency of the semi-transparent perovskite cells as much as 19.7% with an area of three×3 mm2 as certified by ESTI (Italy). “Any such solar cell incorporates a highly transparent back contact that permits over 93% of the near infrared light to succeed in the underside device. This performance was achieved by optimizing all layers of the semi-transparent perovskite solar cells using advanced optical and electrical simulations as a guide for the experimental work within the lab,” says Dr. Mehrdad Najafi of TNO.

“The silicon device is a 20×20-mm2 wide, heterojunction solar cell featuring optimized surface passivation, transparent conductive oxides and Cu-plated front contacts for state-of-the-art carrier extraction” says Yifeng Zhao, Ph.D. student at TU Delft, whose results have been recently published in Progress in Photovoltaics: Research and Applications. The silicon device optically stacked under the perovskite contributes with 10.4% efficiency points to the full solar energy conversion.

Combined, 30.1% is the conversion efficiency of this non-area-matched 4T tandem devices operating independently. This world’s best efficiency is measured in accordance with generally accepted procedures.

Way forward for 4 terminal tandem PV modules

This isn’t all: Combining this highly transparent perovskite cell with other silicon-based technologies, akin to back contact (metal wrap through and interdigitated back contact cells) and TOPCon solar cells, has also delivered conversion efficiencies approaching 30%. This demonstrates the potential of highly transparent perovskite solar cells and their flexibility to be combined with already commercialized technologies.

These world best efficiencies obtained on a mess of incumbent technologies is an additional milestone towards industrial deployment. “Now we all know the ingredients and are capable of control the layers which can be needed to succeed in over 30% efficiency. Once combined with the scalability expertise and knowledge gathered prior to now years to bring material and processes to large area, we will focus with our industrial partners to bring this technology with efficiencies beyond 30% into mass production” says Prof. Gianluca Coletti, Program Manager Tandem PV technology and application at TNO.

Publication Referenced within the Article:

Yifeng Zhao et al, Effects of ( i )a‐Si:H deposition temperature on high‐efficiency silicon heterojunction solar cells, Progress in Photovoltaics: Research and Applications (2022). DOI: 10.1002/pip.3620

This text was written by Eindhoven University of Technology.


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