MIT researchers have produced a new form of photovoltaic cell based mostly on sheets of versatile graphene coated with a layer of nanowires. The strategy could result in low-cost, clear and versatile solar cells that could be deployed on home windows, roofs or different surfaces.
The new strategy is detailed in a report revealed within the journal Nano Letters, co-authored by MIT postdocs Hyesung Park and Sehoon Chang, affiliate professor of supplies science and engineering Silvija Gradečak, and eight different MIT researchers.
While most of as we speak’s solar cells are product of silicon, these stay costly as a result of the silicon is usually extremely purified after which made into crystals which might be sliced skinny. Many researchers are exploring options, akin to nanostructured or hybrid solar cells; indium tin oxide (ITO) is used as a clear electrode in these new solar cells.
“Currently, ITO is the material of choice for transparent electrodes,” Gradečak says, akin to within the contact screens now used on smartphones. But the indium utilized in that compound is dear, whereas graphene is produced from ubiquitous carbon.
The new materials, Gradečak says, could also be an alternative choice to ITO. In addition to its decrease value, it supplies different benefits, together with flexibility, low weight, mechanical power and chemical robustness.
Building semiconducting nanostructures instantly on a pristine graphene floor with out impairing its electrical and structural properties has been difficult as a result of graphene’s steady and inert construction, Gradečak explains. So her group used a collection of polymer coatings to change its properties, permitting them to bond a layer of zinc oxide nanowires to it, after which an overlay of a cloth that responds to light waves — both lead-sulfide quantum dots or a sort of polymer referred to as P3HT.
Despite these modifications, Gradečak says, graphene’s innate properties stay intact, offering important benefits within the ensuing hybrid materials.
“We’ve demonstrated that devices based on graphene have a comparable efficiency to ITO,” she says — within the case of the quantum-dot overlay, an total energy conversion effectivity of 4.2 p.c — lower than the effectivity of basic goal silicon cells, however aggressive for specialised purposes. “We’re the first to demonstrate graphene-nanowire solar cells without sacrificing device performance.”
In addition, in contrast to the high-temperature progress of different semiconductors, a solution-based course of to deposit zinc oxide nanowires on graphene electrodes might be carried out solely at temperatures beneath 175 levels Celsius, says Chang, a postdoc in MIT’s Department of Materials Science and Engineering (DMSE) and a lead creator of the paper. Silicon solar cells are sometimes processed at considerably larger temperatures.
The manufacturing course of is very scalable, provides Park, the opposite lead creator and a postdoc in DMSE and in MIT’s Department of Electrical Engineering and Computer Science. The graphene is synthesized by means of a course of referred to as chemical vapor deposition after which coated with the polymer layers. “The size is not a limiting factor, and graphene can be transferred onto various target substrates such as glass or plastic,” Park says.
Gradečak cautions that whereas the scalability for solar cells hasn’t been demonstrated but — she and her colleagues have solely made proof-of-concept gadgets a half-inch in measurement — she doesn’t foresee any obstacles to creating bigger sizes. “I believe within a couple of years we could see [commercial] devices” based mostly on this expertise, she says.
László Forró, a professor on the Ecole Polytechnique Fédérale de Lausanne, in Switzerland, who was not related to this analysis, says that the thought of utilizing graphene as a clear electrode was “in the air already,” however had not really been realized.
“In my opinion this work is a real breakthrough,” Forró says. “Excellent work in every respect.”
He cautions that “the road is still long to get into real applications, there are many problems to be solved,” however provides that “the quality of the research team around this project … guarantees the success.”
The work additionally concerned MIT professors Moungi Bawendi, Mildred Dresselhaus, Vladimir Bulovic and Jing Kong; graduate college students Joel Jean and Jayce Cheng; postdoc Paulo Araujo; and affiliate Mingsheng Wang. It was supported by the Eni-MIT Alliance Solar Frontiers Program, and used amenities offered by the MIT Center for Materials Science Engineering, which is supported by the National Science Foundation.