What with all the excitement over the “wonder” solar cell material perovskite, it’s easy to forget that just a few years ago graphene was all the rage for new clean tech. Well, graphene is still very much in the mix, and researchers are coalescing around the idea of combining it with perovskite in a new solar cell. Easier said than done!
Graphene + Perovskite In One Solar Cell
For those of you new to the topic, graphene is a two-dimensional material with unique and powerful electronic properties. It was discovered in 2004 after researchers peeled a piece of sticky tape from a chunk of graphite and began poking around in the structure of the ultra-thin film clinging to the tape.
Perovksite is also a mineral that lends itself to solar cell performance. Its origins go back a bit farther than graphene, having popped up in the Ural mountains in the 19th century. Nowadays, synthetic perovskite variants can be created with relative ease in the lab.
The challenge for solar cell design is that both materials are finicky. Graphene is notoriously difficult to work with, and perovskites have a durability issue that needs to be factored into the design.
If that sounds like a lot to handle in one device, it is. Nevertheless, researchers have been tinkering around with the graphene-perovskite combo. In the latest twist, a team based in Italy has designed a solar cell around those twin challenges, and achieved an impressive solar conversion efficiency of 26.3%.
Solving The Perovskite-Silicon Solar Cell Bottleneck
Actually, 26.3% is not quite a record for perovskite solar cells, the title for which stands at a hair over 29% in combination with silicon. However, when the tradeoff between conversion efficiency and cost comes into play, the advantage could go to solar cells that are amenable to high-volume, low cost manufacturing techniques.
The new research is a collaborative effort between the EU’s Graphene Flagship initiative at the University of Rome Tor Vergata, the Italian Institute of Technology, and an IIT spin-off, the graphene specialist BeDimensional and the Spanish clean tech company ENEA.
You can get all the details in the paper, “Mechanically Stacked, Two-Terminal Graphene-Based Perovskite/Silicon Tandem Solar Cell with Efficiency over 26%,” newly published in the latest issue of the journal Joule.
For those of you on the go, the team started with the premise that perovskite/silicon tandem solar cells could be the next big thing, due to a killer combo of relatively low manufacturing costs plus a decent chance at exceeding the solar conversion efficiency limits of silicon alone.
The bottleneck is — or was — on the manufacturing side, until the team figured out a workaround.
“The solution processing of perovskite solar cells directly onto the textured front surface of high-efficiency amorphous/crystalline silicon heterojunction cells is the main bottleneck,” the researchers explain. “Our simple two-terminal mechanical stacking of the sub-cells helps achieve highly performant PV devices.”
Basically, the new approach is to configure each part of the solar cell before hooking them all up together with an assist from graphene-based ink.
According to the researchers, the new technique can be applied to the existing crop of perovskite solar cells, using standard solution-based manufacturing methods.
Emmanuel Kymakis, Graphene Flagship Energy Generation Work Package Leader, provides the technical explainer (GRMs refers to graphene and other inks made with 2-D materials).
“This pioneering work demonstrates that the integration of GRMs inks with on-demand morphology and tuneable optoelectronic properties in a tandem structure, can lead to high-throughput industrial manufacturing,” he said. “Graphene and related materials improve the performance, stability and scalability of these devices.”
Onward & Upward For GRAPES
According to Kymakis, the new solar cell will be the foundation of the Graphene Flagship project GRAPES, which has its sights set on surpassing the 30% solar conversion mark while also bringing down the cost of manufacturing.
Maintaining high solar conversion efficiency while also increasing the size of the solar module is another key aim.
As an European Commission-funded project, GRAPES is carrying a lot of freight. The project is tasked with “improving Europe’s uptake of solar energy projects by improving the stability and efficiency of this technology when deployed on a large scale.”
GRAPES launched just last December and it looks like they’re moving along at a rapid clip. Next steps include finding locations for field-testing its perovskite based solar cells out in the open air, which is really where the rubber meets the road.
CleanTechnica is reaching out to see if it picked out a test site yet, so stay tuned for more on that.
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Photo (cropped): Perovskite PV cell via NREL (credit: Dennis Schroeder).