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All-quantum-dot tandem solar cells are feasible

Natcore Technology Inc has fabricated two families of multilayer quantum dot films for solar photovoltaic (PV) cells.

By Kari Williamson

One of the 'families' was produced with silicon quantum dots and the other with germanium dots.

Each film is comprised of layers of silicon or germanium quantum dots embedded in a silica matrix. The silica matrix is produced using a Liquid Phase Deposition (LPD) silica growth technology that Natcore has exclusively licensed from Rice University.

Dr Dennis Flood, Natcore's Chief Technology Officer, says: "Our goal to show that multiple layers of quantum dots can be assembled using a low-cost, complete wet chemistry approach has been validated. The fact that we have demonstrated photocurrent generation in both Si and Ge quantum dot multilayer devices means that the entire solar cell could potentially be fabricated without the use of expensive silicon wafers for the bottom subcell of a two- or three-cell tandem device.

“We could do so by substituting a Ge quantum dot device for the silicon solar cell and achieve the same overall solar absorption as would have been achieved with the latter. This achievement could make it possible to use low-cost, roll-to-roll manufacturing techniques to achieve a truly low-cost solar module that would have twice the power output of the average solar module on the market today. "

The technology

Natcore's approach, unlike chemical vapor deposition (CVD) technology, decouples quantum dot formation from the silica layer growth and allows for independent selection of quantum dot type, size and spacing in the silica layer.

Natcore says the photo-generated current measurements are the first of their kind for this sort of structure and showed that both film types (Si quantum dots and Ge quantum dots) were photoactive in different spectral regions.

The larger Ge quantum dots were responsive to an infrared-rich light source and the Si quantum dots were responsive to a UV-rich light source, consistent with expectations.

Smaller quantum dots (the Si quantum dot diameters were between 1 nm and 2 nm) will respond more readily to shorter wavelengths of light, while larger quantum dots (the Ge quantum dot diameters were between 5 nm and 6 nm) will respond more readily to longer light wavelengths, precisely as observed, Natcore says.

The research into all-quantum-dots solar PV cells was carried out under a joint research agreement with Rice University.

Natcore says the technology could eliminate the need for a silicon wafer sub-cell, and could accelerate the company's drive towards a low-cost tandem solar PV cell.

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