LONDON – The efficiency of solar cells could be doubled by the discovery of a quantum "shadow state" that allows two – rather than one – high-energy electrons to be produced by optoelectronic energy conversion. The latest research on the mechanisms of solar energy conversion was led by chemistry Professor Xiaoyang Zhu at The University of Texas at Austin and was published in Science magazine.
Zhu and his team have discovered that it's possible to double the number of electrons harvested from one photon of sunlight using pentacene, an organic plastic semiconductor material.
"Plastic semiconductor solar cell production has great advantages, one of which is low cost," said Zhu, in a statement. "Combined with the vast capabilities for molecular design and synthesis, our discovery opens the door to an exciting new approach for solar energy conversion, leading to much higher efficiencies."
The maximum theoretical efficiency of the silicon solar cell in use today is approximately 31 percent. This is because much of the photonic energy hitting the cell is not that at wavelengths that can be turned into usable electricity. That energy is instead lost as heat. Capturing the thermally excited hot electronic energy could potentially increase the efficiency of solar-to-electric power conversion to as high as 66 percent, according to the research team.
Zhu and his team previously demonstrated that those hot electrons could be captured using semiconductor nanocrystals. They published that research in Science in 2010, but Zhu says the actual implementation of a viable technology based on that research is very challenging. The primary one being that it requires focused sunlight rather than ambient light that typically hits a solar panel.
Zhu and his team have found an alternative. They discovered that in the semiconductor pentacene a photon produces a dark quantum "shadow state" from which two electrons can then be efficiently captured to generate more energy.
The absorption of a photon creates an excited electron-hole pair, called an exciton. The exciton is coupled quantum mechanically to a dark "shadow-state" called a multi-exciton. It so happens that the multi-exciton can be an efficient source of two electrons via transfer to an electron acceptor material such as fullerene, the ball-shaped 60-atom allotrope of carbon, which was used in the study. Exploiting this could raise pentacene solar cell efficiency to 44 percent without the need for a focused solar beam, according to the researchers.
The research team was led by Wai-lun Chan, a postdoctoral fellow in Zhu's group, with the help of postdoctoral fellows Manuel Ligges, Askat Jailaubekov, Loren Kaake and Luis Miaja-Avila.
In this case you'd probably want to aim for exactly the opposite... something that would not degrade. Having biodegradle replacements for things that are produced in huge quantities and often discarded... shopping bags, disposable plates, etc. is a great idea. An expensive device that should last as long as possible (20, 30 or more years) to make it economically feasible should simply be accepted as something that will take up a bit of room in a landfill if it can't be recycled.
Look carefully at real, manufacturable efficiencies. They are far less than what is obtained in the lab. Typical efficiencies for commercial solar cells are in the 8% to 17% range. This discovery will be great if the gain can be seen in mass produced solar cells.
I wonder what the cost per watt output will be for these? I did not see any roll-out plan and was hoping for hints about pre-production date, estimated final effective efficiency, etc.. It sounds like they are moving in the right direction but still have a lot of experimenting left to do. Good luck!
This is a very greatly written article, very nice precise and sufficient in terms of content.
It will be surely a very great gift to the mankind by the inventor if the commercial production of the material is possible. There also many other affecting factors a the material is being plastic.
For countries like Germany who pan to shout down their Nuclear power generation completely in the next decade , this news is encouraging. It tells us that Solar energy may become a economically viable and environmentally safe alternative to nuclear energy in the near future.
The work seems really interesting, but the confusion in the numbers makes me think that I have missed something. The headline clearly says "double". Why double? Does this leap require the use of focused light, for example? What performance improvement can we expect from solar panels as a result of this research? Thanks for any clarification.