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. "
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