While potentially much more efficient, than conventional photovoltaic systems, quantum dot solar cells are still at a pre-commercialization stage. In a new paper, to be published in the journal Advanced Materials, researchers propose to improve quantum dot solar cell design with nanowires.
To put it simply, quantum dot is a portion of matter that has electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. Quantum dot solar cell could potentially have an efficiency of 65% (for conventional solar cells efficiency cannot exceed 31% if one uses a single material for a solar cell). They can also potentially offer increased mechanical flexibility, lower cost and a simpler manufacturing method.
There are, however, several unsolved problems. For example, you don’t want the solar cell’s absorbing layer to be too thin or it wouldn’t efficiently absorb light, but if it is too thick, the electric charges wouldn’t be able to pass from the absorption site to the wires that carry electrical current away.
Authors of the paper in Advanced Materials propose to use vertical arrays of ZnO nanowires to decouple light absorption from carrier collection in PbS quantum dot solar cells. This upgrade allows to increase energy conversion efficiencies of the quantum dot solar cells by 35% and achieve overall system efficiency of 4.9% (commercial silicon-based photovoltaic cells have an efficiency of about 17%). With further research it might be possible to develop a quantum dot solar cell with an efficiency of 10% or even higher.
Recently we have published an article about another technique, developed by University of Toronto Engineering Professor Ted Sargent and his research group. In a paper “Jointly-tuned plasmonic-excitonic photovoltaics using nanoshells,” published in the journal Nano Letters, researchers describe a technology that increases quantum dot solar cell light absorption and provides a more than one-third enhancement in photocurrent in the near-infrared portion of the sun’s spectrum.