researchers have boosted
solar cell performance with quantum dots by embedding them in a forest of nanowires.
Photovoltaics (PVs) based on tiny colloidal quantum dots have several potential advantages over other approaches to making solar cells: They can be manufactured in a room-temperature process, saving energy and avoiding complications associated with high-temperature processing of silicon and other PV materials.
They can be made from abundant, inexpensive materials that do not require extensive purification, as silicon does. And they can be applied to a variety of inexpensive and even flexible substrate materials, such as lightweight plastics.
But there’s a tradeoff in designing such devices, because of two contradictory needs for an effective PV: A solar cell’s absorbing layer needs to be thin to allow charges to pass readily from the sites where solar energy is absorbed to the wires that carry current away — but it also needs to be thick enough to absorb light efficiently.
That’s where the addition of zinc oxide nanowires can play a useful role, says Joel Jean, a doctoral student in MIT’s Department of Electrical Engineering and Computer Science and the lead author of a paper to be published in the journal Advanced Materials.
These nanowires are conductive enough to extract charges easily, but long enough to provide the depth needed for light absorption, Jean says. Using a bottom-up growth process to grow these nanowires and infiltrating them with lead-sulfide quantum dots produces a 50 percent boost in the current generated by the solar cell, and a 35 percent increase in overall efficiency, Jean says.
The process produces a vertical array of these nanowires, which are transparent to visible light, interspersed with quantum dots.