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20 February 2020

Quantum dots make an early appearance at 16.6% efficiency

There is not a day that goes by without one researcher or other claiming a breakthrough in solar, but the one this week comes from engineers at the University of Queensland where Professor Lianzhou Wang and his team say they have broken records in the yields for quantum dots.

Conversion was previously at around 13.4% of energy alighting on them, but Wang has now increased that to 16.6% and the US National Energy Research Laboratory has recognized it as a record. What can we take out of this and over what time frames?

In an earlier life we witnessed the emergence from research paper to live products, as quantum dots were introduced into the TV space as a way of illuminating television sets instead of LEDs and LCD shutters. It took about 7 years from R&D to product.

This solar is the same effect in reverse – passing a charge over the dots made them issue lights of a particular color. In reverse that means that different sized dots absorb light of differing colors, and when that color is shone on them, they give off electricity.

The beauty in the TV world was its simplicity – dots of larger or smaller sizes interacted with different frequencies of light, and if multiple colors were lit, one behind each other, the lights combined to create the required screen color in a pixel. In reverse this will mean that light of frequencies that do not trigger electricity production will travel through the dots, and still be able to stimulate say a silicon layer offering a hybrid PV effect. This is somewhat similar to the thin film layers that Oxford PV is building out using a perovskite layer and a silicon layer.

But actually what the researchers say they have done is bring closer the idea of spraying on a solar “skin” on things like a phone or a window or a car bonnet and using that to generate power. This is because quantum dots can be literally printed onto flexible sheets of material, which can then be attached to any surface. We would have thought some kind of hybrid would be more important, but as soon as we tried to look into that we got out of our depth knee deep in scientific articles, which mostly never reach this magic 16.6% anyway, so perhaps we’re wrong here.

The team expects to be able to go on in the same vein and find further improvements, but says that at 16.6% efficiency, there are already applications for these dots, crossing the line from where “quantum dot solar cell technology can be an exciting prospect to one which is commercially viable.”

It is incredibly light weight, can bend and the cells produced are not brittle and still work in weak light, including indoors. Once the team hits 20% efficiency, they say they will begin to simply “print” solar cells.

Asa we said it took about 7 years for quantum dots to make an appearance in TV sets after the research was revealed, and so Wang’s belief that this could happen within three to five years for rooftop solar, is not out of the ball park. They two key elements will be price and how long the panel will last, but it should certainly be cheap depending upon what the dots are made from which could even be carbon.