- New and improved solar panel materials have been analyzed
- Two key physics effects combine to create the improvements
- It could help panels break through the 33% energy conversion rate
There's a long-standing physics theory that suggests solar panels will only ever be able to convert a maximum of 33% of the sunlight that comes their way, but a team from the University of Groningen in the Netherlands has detailed a way to harvest extra energy from 'hot' electrons that could push through this limit.
Solar panels work by using the photons from sunshine to jump-start electrons. With the most energetic photons, the result is super-charged, so-called hot electrons, that have the potential to generate significantly more electricity — but the problem is they cool down too quickly and lose the energy as heat before it can be captured.
This new research builds on previous studies reporting a promising new tin-based solar panel material. The material has demonstrated it can keep the heat from hot electrons trapped for around 1,000 times longer — but there have been competing ideas about the mechanism making that possible.
Trying to clarify what was going on, though a series of computer simulations and experimental measurements, was the purpose of the new research: understanding the material's key properties will help scientists build on the potential of the material and potentially scale it up into something that's viable commercially.
Ultra-long cooling
The analysis carried out by the researchers determined that there were two different actions at work. First, an effect called a hot phonon bottleneck creates a heat trap: as the environment around the buzzing electrons warms up so quickly, the electrons end up reabsorbing the thermal energy again, keeping their heat for longer.
Second, what's known as the Burstein-Moss effect creates an atomic traffic jam. As hot electrons cool, they quickly fill up the lowest available energy states in the material, which means other hot electrons can't lose their heat as quickly — it's like an airplane filling up from the front, with passengers arriving later having to walk all the way to the back.
These two effects were already known about, but now we know they're the reason that these special solar panel materials work — and that in combination they provide the extended hot electron cooling that might help to nudge future solar panels above that crucial 33% ceiling, and create clean energy more efficiently.
"It is the simultaneous satisfaction of these electronic, phononic, and chemical criteria, operating under high-injection conditions, that enables the ultra-long cooling times necessary for practical devices," write the researchers in their published paper, which appears in the journal ACS Energy Letters.
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