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.
It is unexpected discoveries like these that offer the potential for cost effective solar power generation - and can render the currently leading technology obsolete overnight. A scary place to be investing but an exciting time for the future of affordable distributed power generation.
Lower cost with double the efficiency!! This seems to be first one of the breakthrough discoveries that is very much needed to take the solar power generation to the next milestone. Is there a plan to build a solar panel to demonstrate the efficiency that could be derived once it is produced commercially?
present is 36% efficiency. the new research here is for 44%. By about 8%. This the next major step towards higher efficiency. Low cost also. Coommercialisation will be fruitfull. So by 5 more years we reach about 60 to 70% efficiency.I forsee a great solar future in our earth planet.
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.