Stanford University researchers have developed new photovoltaic materials to be used in mobile applications, from self-powered wearable devices and sensors to lightweight aircraft and electric vehicles, with the researchers achieving record efficiencies in a promising group of photovoltaic materials.
The scientists brought what is known as Transition Metal Dichalgonides’ to the fore.
A major benefit of the TMD is that is that they absorb ultrahigh levels of the sunlight that strikes their surface compared to other solar materials.
Transition metal dichalcogenide solar cells on a flexible polyimide substrate. Credit: Koosha Nassiri Nazif
Koosha Nassiri Nazif, doctoral scholar in electrical engineering at Stanford and co-lead author of a study published in the December 9 edition of Nature Communications analyzed it when he said:
“Imagine an autonomous drone that powers itself with a solar array atop its wing that is 15 times thinner than a piece of paper. That is the promise of TMDs.”
Cross-section schematic of the device. Credit: Koosha Nassiri Nazif
The forage for new materials is predicated on the fact the silicon, undoubtly the king of solar materials is too heavy, bulky, and rigid for applications that requires flexibility, lightweight and high power. Examples are wearable devices and sensors or aerospace and electric vehicles.
A professor of electrical engineering and senior author of the paper, Krishna Saraswat, explained this further when he said: “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”.
TMDs brings to the equation a competitive alternative, with past and present research experiments struggling to convert more than the 2 percent they absorb into electricity. But the number is closing to 3o percent with silicon solar panels and to be used widely, TMD will step in to close that gap further.
There is already a 5.1 percent power conversion efficiency with the Standford model, with the authors of the project affirming that they could reach a 27 percent efficiency with optical and electrical optimizations, a figure that would be on par with the best solar panels in the world.
The prototype achieved a 100-times greater power-to-weight ratio of any TMDs yet developed, a ratio important for mobile applications, like drones, electric vehicles, and the ability to charge expeditionary equipment on the move. Taking cognizance of the measure of electrical power output per unit weight of the solar cell, the prototype dolled out 4.4 watts per gram, a significant figure aligning 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, noting that the team estimated the practical limit of their TMD cells to be a remarkable 46 watts per gram.
One of TMDs downsides is however laced in the engineering intricacies of mass production. The TMD layer gets damaged when the ultrathin layer of TMD is transferred to a flexible, supporting material.
Alwin Daus, a co-lead author on the study with Nassiri Nazif, while devising the transfer process that affixes the thin TMD solar arrays to the flexible substrate, noted that the technical challenge was considerable. Daus added that there is one step involved transferring the layer of atomically thin graphene onto a flexible substrate just a few microns thick.
This knotty process of doing this will have TMD fully embedded in the flexible substrate leading to greater durability. The team then proceeded to test the flexibility and robustness of their devices by bending them around a metal cylinder less than a third of an inch thick.
“Powerful, flexible and durable, TMDs are a promising new direction in solar technology,” Nassiri Nazif concluded.
Reference: “High-specific-power flexible transition metal dichalcogenide solar cells” by Koosha Nassiri Nazif, Alwin Daus, Jiho Hong, Nayeun Lee, Sam Vaziri, Aravindh Kumar, Frederick Nitta, Michelle E. Chen, Siavash Kananian, Raisul Islam, Kwan-Ho Kim, Jin-Hong Park, Ada S. Y. Poon, Mark L. Brongersma, Eric Pop and Krishna C. Saraswat, 9 December 2021, Nature Communications.