Aug 7, 2020

New paper in Nature Materials

The technology that we are developing for direct plasmonic solar cells is brand new – so new that there has hardly been anything published on the research behind it. A new paper published in Nature Materials, co-authored by our founder and CTO Jacinto Sá, describes some of the new findings that make our ultra-high transparency cells possible.

We use something called plasmonic nanoparticles, which are metallic nanoparticles from the gold group in the periodic table. The Nature Materials article focuses on gold nanoparticles, while our cells use silver, but the mechanism is the same. These nanoparticles are extremely good light absorbers – so good, in fact, that only a tiny amount of light needs to be intercepted to absorb a significant amount of energy. In other light absorbing materials, a lot of the light that falls on the material is wasted. The reason why it is generally hard to make transparent solar cells is not that all the light is needed, but that most of the light is wasted.

Peafowl founder and CTO Jacinto Sá

The light absorbing properties of plasmonic materials have been long known, but the challenge has been to turn that absorbed light into electricity. When the nanoparticles absorb light both positive and negative electrical charges are created. These are referred to as “hot” charges. The negative charges are electrons, and the positive charges are “holes”, a charge particle describing the missing electron in the valence band. As you might expect, the normal thing that happens if you create a positive charge and a negative charge in the same place at the same time is that they immediately reunite and cancel each other out.

In 2013 however, our founder Jacinto Sá and his colleagues published an article about formation and collection of hot electrons in semiconductors before their reunion with holes. This prolongs the lifetime of the electrons so that they can be used in solar cells to produce electricity, and the discovery was the first step towards the founding of Peafowl Solar Power. In the new Nature Materials article the researchers have instead been focusing on the positive charges, the hot holes. They have now been able to collect more than 80% of the positive charges, which is remarkable – this is three times more than they had themselves expected. The process is incredibly fast: less than 200 fs, or 0.00 0000000002 seconds.

The ability to efficiently collect not only the electrons but also the positive charges means that direct plasmonic solar cells can be improved both by boosting performance and by better voltage regulation, while maintaining the colorless high-transparency look. A beautiful future awaits!

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