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Posted: Sep 07, 2011
Natcore Scientists Prove Feasibility of All-Quantum-Dot Tandem Solar Cell
(Nanowerk News) A research team working under Natcore Technology Inc. co-founder Prof. Andrew Barron has fabricated two families of multilayer quantum dot films, one with silicon quantum dots and the other with germanium quantum dots, both of which have demonstrated the ability to produce a photo-generated current.
Natcore Technology scientists have fabricated two families of multilayer quantum dot films, both of which can produce a photo-generated current. This could have significant consequences for the tandem solar cells and thin-film cells that Natcore is developing. Natcore's process may allow production of tandem cells at a lower cost/watt than anything available today. By stacking three cells, each absorbing light from a different part of the spectrum, tandem cells increase efficiency to 30% or more, nearby doubling cell output.
Achieved under the Natcore joint research agreement with Rice University, this advance has significant consequences for the thin-film solar cells that Natcore is developing in its Research & Development Center at Kodak's Eastman Business Park in Rochester, NY. It could eliminate the need for a silicon wafer subcell, also accelerating Natcore's drive toward a low cost tandem solar cell.
Each film is comprised of layers of silicon or germanium quantum dots embedded in a silica matrix. The silica matrix is produced using the patented Liquid Phase Deposition (LPD) silica growth technology that Natcore has exclusively licensed from Rice University. Unlike preceding attempts to make such layers using chemical vapor deposition (CVD) technology, Natcore's approach decouples quantum dot formation from the silica layer growth and allows for completely independent selection of quantum dot type, size and spacing in the silica layer.
The photo-generated current measurements are the first of their kind for this sort of structure and showed unequivocally that both film types (i.e., with Si quantum dots or 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.
"This accomplishment by Professor Barron and his group is an outstanding achievement and confirms that making, and ultimately commercially producing, an all-quantum dot tandem solar cell using Natcore's LPD film growth technology is on target," said Dr. Dennis Flood, Natcore's Chief Technology Officer. "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. "