Third Generation Solar Photovoltaic Cells

Paint-on semiconductors: quantum dots

Over half of the sun’s energy reaching the earth is invisible to us because it is delivered through infrared wave lengths. Current solar collectors only work under direct visible sunlight, “and if we don’t tap into [infrared light] in our solar cells then we throw away more than half of the potential sun’s energy that we could be using⁴ .”  The great advantage of this technology is that it captures infrared energy during the day - even when the sky is cloudy.  The basic building block of this technology is called the quantum dot. Quantum dots are nanoparticles consisting of extremely small (a billionth of a meter) collections of atoms of semiconducting material⁵ . It would take a chain of 4 million quantum dots to span the length of a penny.  These are the first solar cells that are able to harness the sun's infrared rays. The plastic material pictured here uses nanotechnology to improve the cell's efficiency.  "This breakthrough has led theorists to predict that plastic solar cells could one day become five times more efficient than current solar technology⁶ .” 

"Now nanotechnologists are breaking away from large, perfect, crystalline semiconductors. Instead they are building physically flexible solar fabrics. These photovoltaics are printed like newspapers, spinning seamlessly from roll to roll."⁷

Liquid silicon technology

This process involves the conversion of silicon form a solid into a liquid in order to increase the utility if the semi-conductor.  The technology takes tiny silicon particles (in powder form) called “nano-crystals” and chemically liquefies it into ink. At this point the substance can be used in a regular inkjet printer and solar cells can be printed on any surface. “This is a completely radical way to think about how a semiconductor material can be deployed⁸ .” This appears to be one of the most promising of the 'third generation' technologies. “This is a dramatic break though because it means that almost any surface can become a solar cell. We can paint silicon materials onto roofing and bring down the cost of having solar installations on you roof by a factor of 10. ⁹ ." 

Dye-sensitive solar paint

Dye-sensitive solar paint is a solar cell technology that is currently in the development stage. This photovoltaic paint “will be based on dye-sensitive solar cells” not silicon, making the technology relatively inexpensive. The difference between conventional solar panels and dye-sensitized solar paint is that “instead of absorbing sunlight using silicon…[it] uses dye molecules attached to the particles of the titanium dioxide pigment [found] in paint. Once light hits the dye, the electrons are ‘activated’ and they jump from the dye into a layer of electrolyte.¹⁰

The energy created from the activated electrons is then transferred to a collecting circuit before the electrons return to the dye, completing their cycle. There are some researchers are experimenting with fruit based dyes. After separating the dye from the heavy particles and sugar molecules, the dye is placed on a "conductive glass-coated with a film of titanium dioxide (the common material found in paint)."¹¹ This bonds the dye to the glass.

The installation process would be simple and can be applied directly to industrial steel. "The solar cells are built up in several layers. Firstly, a barrier of normal paint is laid directly on the steel, then the electrolyte and dye layers, and finally a clear protective film to guard against the elements."¹²

This technology could eventually be used with the steel sheets that are traditionally used to cover large buildings. The greatest advantage of this technology will be its low cost and its ability to be applied as a paste. Even though the solar paint is less efficient than the panels, its competitive advantage is reflected in its reduced cost.

Implication for energy policy

Third generation PV solar cells could become the most reliable source of clean energy if research efforts are adequately funded. "Eventually if research on third generation PV proves successful, it could lead to PV cells made, for example, from extremely of thin stacked plastic sheets, converting solar energy to electricity with very high efficiency at very low cost¹³ ." Some suggest that the technology might "double or triple the 15%-20% range currently targeted¹⁴ ."  technology may one day provide energy to the 2 billion people on this planet that live without electricity.

Footnotes

1. Boyle; pg.78, 82

2. Boyle, Jeffery. Renewable Energy:Oxford university Press, 2004; pg 68

3. Boyle; pgs 68

5. Bole; pg. 82

6. Sargent, Ted: Interview, http://www.youtube.com/watch?v=kLSARSw2JUQ

7. Sargent, Ted. The Dance of Molecules: How nanotechnology is changing our lives. Thunder Mountain Press. New York; 2006

8. Burke, Interview: http://www.youtube.com/watch?v=UPpvPAriAOY

9. Fred Krupp, President of Environmental Defense Fund: http://www.youtube.com/watch?v=UPpvPAriAOY

10. Marshall, Michael. Solar-power paint lets you generate as you decorate. New Scientist; Tech, March 2008: http://www.newscientist.com/article/dn13424

11. http://solar.calfinder.com/blog/news...d-solar-oh-my/

12. Marshall, http://www.newscientist.com/article/dn13424

13. Boyle; pg. 82

14. Green, M.A., Third generation photovoltaics: Ultra-high conversion efficiency at low cost. Progress in Photovoltaics: Research and Applications, 2001. 9(2): p. 123-135. doi:10.1002/pip.360

15. Sargent, Ted: Interview, http://www.youtube.com/watch?v=kLSARSw2JUQ

0.  ¹⁵

0.  Sargent, Ted. The Dance of Molecules: How nanotechnology is changing our lives. Thunder Mountain Press. New York; 2006

0.  Boyle; pg. 68