First saw this written about in the Independent today, though it failed to provide a link to the original research — which I eventually tracked down to the Physics Dept at Lehigh University in Pennsylvania, and a paper authored by professor Chinedu Ekuma and doctoral student Shihari Kastuar that was just published in Science Advances yesterday. Unfortunately, the scientific paper really requires a PhD in Physics to properly understand the import of their research, but a much more useful review is provided by techxplore:
New quantum material promises up to 190% quantum efficiency in solar cells
When I initially saw this headline, my first thought was “how can anything be more than 100% efficient”? The key here is the ‘quantum’ qualifier, or more specifically, the External Quantum Efficiency (EQE) related to the number of free electrons produced per photon of incoming light in a solar cell. And in conventional silicon-based solar cells, the theoretical maximum EQE is well below 100%, which is a good part of the reason solar cells are not all that efficient in converting sunlight into electricity to begin with (with a maximum theoretical efficiency of about 32-33% according to the Shockley-Queisser Limit).
However, in the 2-D quantum materials the researchers were experimenting on [atoms of zerovalent copper between layers of a two-dimensional material made of germanium selenide (GeSe) and tin sulfide (SnS)], a single photon is able to generate an average of 1.9 electrons through the ‘magic’ of multiple exciton generation (MEG) which involves quantum effects within "van der Waals gaps":
In the Lehigh-developed material, the intermediate band states enable the capture of photon energy that is lost by traditional solar cells, including through reflection and the production of heat.
The researchers developed the novel material by taking advantage of "van der Waals gaps," atomically small gaps between layered two-dimensional materials. These gaps can confine molecules or ions, and materials scientists commonly use them to insert, or "intercalate," other elements to tune material properties.
Additionally, this new type of material offers considerable economic and environmental benefits over existing silicon-based solar cells. From the original paper by the authors:
First, GeSe exhibits low toxicity and offers a cost advantage as it is less expensive compared to materials like Ge and Sb2Se3. Moreover, GeSe is more than six times more earth abundant than Sb, making it a highly accessible resource (10–14). Second, the intrinsic intermolecular bonding of van der Waals interactions within the interlayer planes of 2D-based group IV monochalcogenides make them an attractive material for photovoltaic, offering a solution to the dangling bond issues that affect conventional solar absorbers. These features make them an emerging material for photovoltaic applications over conventional commercial solar cell–based materials such as Cu(In,Ga)Se2 and CdTe, which require toxic or rare earth elements (15, 16).
All-in-all, this looks like a very promising bit of research that could radically transform the whole solar photovoltaic industry in the years to come.
