Mobile quantum dots used to break barriers of solar cell efficiency

A highly efficient, transparent dye-sensitized solar cell (DSSC) using mobile quantum dots was developed.

Article  |  Spring 2014

The sun will hopefully be the energy source of the future, but currently, solar power provides less than 1% of global energy. The reason is not due to a conspiracy among fossil fuel companies, as some media outlets apparently believe, but because of multiple inherent problems with solar technology. In a nutshell, there is a tradeoff between efficiency and cost.

For example, the current world-record for efficiency (i.e., the ability to convert light into electricity) is 44.7%, held by a multi-junction solar cell used in concentrated photovoltaics. However, for various reasons, such systems are still expensive. Cheaper solar cells, such as the ones you can mount on the roof of your home, are more reasonably priced but have efficiencies around only 10 to 20%. Thus, the “holy grail” is a solar cell with high efficiency and low cost.

One possible avenue is a design referred to as a dye-sensitized solar cell (DSSC). In a DSSC, dye molecules attached to titanium dioxide absorb photons and release electrons, creating an electric current.

Recently, researchers from KAIST have added mobile quantum dots to the mix. Quantum dots (QDs) are nanoparticles that have a unique feature: they are able to generate more than one electron for every photon that is absorbed, a phenomenon known as “multiple exciton generation.” QD-DSSCs, therefore, have a higher efficiency than regular DSSCs (see figure).

DSSCs containing red quantum dots (R-QD) were the best at increasing both light absorption and external quantum efficiency (a measure of how many electrons are generated per photon absorbed).

In a recent e-mail, the authors told RealClearScience that the maximum efficiency of their system is 8.83%, which is obviously lower than most existing solar cell technologies. However, DSSCs are relatively cheap to produce, and with further research, the authors believe that they can crank up the efficiency well beyond 33.7% (the Shockley-Queisser limit, which is a theoretical limit on the efficiency of single junction solar cells).

Techies and investors should keep an eye on this emerging technology.