Solar Panels From CPT Break Efficiency Barrier

In 1961, William Shockley and Hans-Joachim Queisser[1] calculated that the maximum theoretical efficiency of a silicon-based solar panel is 30%. In other words, less than a third of the sunlight that strikes a solar panel can be turned into electricity.

Today, only high end solar panels intended for use in spacecraft get near that maximum efficiency limit. Those panels are far too expensive for normal commercial use[2]. The average panels used on rooftops and in solar farms are much less expensive, but have an efficiency of around 22%.

The problem is that silicon only responds to certain wavelengths, particularly those in the red and yellow portion of the electromagnetic spectrum. Longer light waves in the infrared part of the spectrum are too weak to create an electrical current. Shorter light waves in the blue and green part of the spectrum don’t create any electrical current when they strike the silicon in a solar cell — at most, they bounce off. At worst, they generate heat, which degrades the efficiency of panels.

A Bright Idea Becomes A New Business

In 2014, Akshay Rao and a team of researchers at the University of Cambridge had a bright idea. What if there was a way to convert those blue and green light waves into red light waves? That would boost the efficiency of a solar panel to around 35% — roughly 50% more than the conventional solar panels in use today. Can you image what that would mean to the world of renewable energy?

The University of Cambridge took that idea and used it as the basis of a new technology company known as Cambridge Photon Technology[3]. Here’s how it works, according to a study published in the journal Nature[4].

“Rao developed a photon multiplier film made up of a layer of an organic polymer called pentacene studded with lead selenide quantum dots — small, light emitting clumps of inorganic material. The polymer absorbs blue and green photons and converts them into pairs of excitons. These excitons flow to the quantum dots, which absorb them and emit lower energy red or infrared photons.

“When the film is placed on top of a silicon solar cell, the light from the quantum dots shines onto the silicon. Meanwhile, the red and infrared wavelengths directly from the sun pass through the polymer film and hit the silicon as they normally would. The result is that more usable photons strike the silicon, increasing production of electrical current.”

“You’re preserving the total energy that comes in and out, but you’re making the silicon receive a higher photon flux in the portion of the spectrum that it’s good at converting into electricity,” Wilson says. For more on how this works, see the video below.

Progress Takes Time

Did you notice that the research that started this all began in 2014? Here we are 8 years later, and Rao says he hopes to have a working prototype that is 31% efficient by the end of 2022. The target for the panel that is 35% efficient is 2025 at the earliest. Notice how this news is similar to the stories we report on all the time about breakthroughs in battery technology. Coming up with new ideas is easy. Turning them into commercially viable products is hard.

The key to the CPT approach is that its photon splitting layer can be applied to any solar panel during the manufacturing process without any significant changes in the production phase. That’s a critical consideration if the new technology is to have any hope of being commercially successful. “Our whole approach has been…to make a simple, non-toxic material with no electrical connections that add very little complication to existing design,” Wilson says.

Once CPT proves its technology is viable, the potential pay-off could be great, Wilson says. “It’s really clear that there’s a fairly urgent need and this technology, if it works as promised, will go a long way to meeting that need.” We — and the world[5] — can hardly wait.

A tip of the CleanTechnica hat to Dan Allard, who has nothing better to do than to watch videos like this. Thanks, Dan. 


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  1. ^ William Shockley and Hans-Joachim Queisser (
  2. ^ too expensive for normal commercial use (
  3. ^ Cambridge Photon Technology (
  4. ^ Nature (
  5. ^ and the world (
  6. ^ CleanTechnica Member, Supporter, Technician, or Ambassador (
  7. ^ Patreon (
  8. ^ Contact us here (

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