New roadmap identifies critical priorities for commercialization of tandem solar cells

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Researchers led by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) recently studied tandem PV technologies, specifically tandems from a range of established and emerging PV technologies. They reviewed their technical status and prospects to be able to assess what needs to happen to enable mass production.

The study is unique in the range of tandem technologies assessed, including two-terminal (2T), three-terminal (3T) devices, and two types of four-terminal (4T) tandem devices, stacked 4T and spectral splitting 4T, although the latter is not discussed in-depth. It includes perovskite as sub-cell materials but also delves into thin-film tandems made with cadmium telluride (CdTe), organic PV (OPV), and copper indium gallium diselenide (CIGS).

For each category of tandem solar cell, the team looks at the technology at the cell level, scaling level, cell-to-module, manufacturing, reliability, costs, environmental impact topics, and commercialization risks, with a focus on challenges and opportunities.

“These include technical challenges as well as business-centered challenges,” NREL scientist and corresponding author Kirstin Alberi told pv magazine.

When asked if the research revealed which technology is most viable in terms of commercialization looking at general 2T, 3T, or 4T cell types, Alberi replied that there are benefits and drawbacks to all architectures, as summarized in a key section of the paper that says that 4T configurations have the potential to leverage the ability to manufacture top and bottom junctions separately, giving it design and process flexibility advantages, which could help in the development of early products.

“But given the amount of effort going into 2T architectures, they may also reach the market on a similar timeline. Demonstrations of each architecture at module scale will be critical to assess the viability of each configuration,” said Alberi. “At the cell level, 2T is easier, but that may not be true at the module scale.”

While the answer to which type of tandem is going to be first is still to be revealed, the researchers provide a list of twelve physical and economic needs to be addressed if the technology is to reach 2% of market share by 2030, as is estimated by the International Technology Roadmap for Photovoltaic (ITRPV).

“Many of the short-term needs are actively being addressed by research institutions and industry. Several of them will be challenging, but given the pace of work, we are optimistic that the next 6 years will yield significant advances toward tandem commercialization,” explained Albieri. “Although it is early days, the reaction to the paper has been positive so far. We know from our interactions with others in the tandems development community that they are thinking about many of these topics. From some of our discussions, the topic of planning for scaling and manufacturing at an earlier stage in their development has also resonated with many people.”

The hope is that researchers and manufacturers will continue to team up, collaborate, and work in parallel to speed up the progress toward mass production.

The review was presented in “A roadmap for tandem photovoltaics,” published in Joule, with contributions by scientists from NREL, the University of Colorado, and the Rochester Institute of Technology.

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