Under the joint research agreement between Natcore Technology and Rice University, researchers, led by Professor Andrew Barron, announced that they had constructed two sets of multilayer quantum dot films: one with silicon (Si) quantum dots and the other with germanium (Ge) quantum dots. The team notes that both dot films have shown the ability to create a photo-generated current and that the thin-film solar cell advancement could eradicate the need for a silicon wafer subcell.

"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 CTO.  "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 researchers advised that each film is made up of layers of silicon or germanium quantum dots embedded in a silica matrix with the silica matrix constructed using Natcore’s LPD silica growth technology. The research team maintains that this development differs from previous attempts to make layers using chemical vapor deposition (CVD) since it decouples quantum dot formation from the silica layer growth and lets an independent selection of quantum dot type, size and spacing in the silica layer.

According to the researchers, the photo-generated current measurements showed that both the Si quantum and the Ge quantum dots were photoactive in different spectral regions. The larger Ge quantum dots reacted to an infrared-rich light source and the Si quantum dots responded to a UV-rich light source. The researchers additionally found that Si quantum dots that were between 1nm and 2nm would react more quickly to shorter wavelengths of light, while larger Ge quantum dots, with diameters between 5nm and 6nm, responded better to longer light wavelengths.