Solar panels have been synonymous with meter-wide and tall silicon panels that occupy entire roofs. While the extra protective layer that generates free energy is a great feature, using too much space is a big problem for solar panels' progress into the future. Advanced solar panels will need to be smaller and more efficient to power more than just a wristwatch or a calculator with a small strip.
Fortunately, the future is bright because researchers are looking for ways to make solar panels head in such a progressive direction. Silicon is an efficient key solar panel component, but it has many shortcomings, such as being bulky, relatively heavy, and inflexible.
The new transition metal dichalcogenides or TMDs are the logical descendants of silicon solar panels because they are thinner and can deliver potentially high efficiency — at least in theory until the technology can catch up to it. Read more about it in Stanford's Academic Journal.
Chief among the benefits of these transition metal dichalcogenides – or TMDs – is that they absorb ultrahigh levels of the sunlight that strikes their surface compared to other solar materials.
“Imagine an autonomous drone that powers itself with a solar array atop its wing that is 15 times thinner than a piece of paper,” said Koosha Nassiri Nazif, a doctoral scholar in electrical engineering at Stanford and co-lead author of a study published in the Dec. 9 edition of Nature Communications. “That is the promise of TMDs.”
The search for new materials is necessary because the reigning king of solar materials, silicon, is much too heavy, bulky and rigid for applications where flexibility, lightweight and high power are preeminent, such as wearable devices and sensors or aerospace and electric vehicles.
“Silicon makes up 95 percent of the solar market today, but it’s far from perfect. We need new materials that are light, bendable and, frankly, more eco-friendly,” said Krishna Saraswat, a professor of electrical engineering and senior author of the paper.
A competitive alternative
While TMDs hold great promise, research experiments to date have struggled to turn more than 2 percent of the sunlight they absorb into electricity. For silicon solar panels, that number is closing in on 30 percent. To be used widely, TMDs will have to close that gap.
The new Stanford prototype achieves 5.1 percent power conversion efficiency, but the authors project they could practically reach 27 percent efficiency upon optical and electrical optimizations. That figure would be on par with the best solar panels on the market today, silicon included.
Moreover, the prototype realized a 100-times greater power-to-weight ratio of any TMDs yet developed. That ratio is important for mobile applications, like drones, electric vehicles and the ability to charge expeditionary equipment on the move. When looking at the specific power – a measure of electrical power output per unit weight of the solar cell – the prototype produced 4.4 watts per gram, a figure competitive with other current-day thin-film solar cells, including other experimental prototypes.
“We think we can increase this crucial ratio another ten times through optimization,” Saraswat said, adding that they estimate the practical limit of their TMD cells to be a remarkable 46 watts per gram.
Their biggest benefit, however, is their remarkable thinness, which not only minimizes the material usage and cost but also makes TMD solar cells lightweight and flexible and capable of being molded to irregular shapes – a car roof, an airplane wing or the human body. (Continue reading here to learn more about the future of solar panel tech)
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