Energy Focus: New process enables ultrathin, ultraflexible GaAs photovoltaics
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ocus New process enables ultrathin, ultraflexible GaAs photovoltaics
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y modifying a commonly used technique for printing solar cells on flexible materials, a team of South Korean scientists have created photovoltaics so flexible that they can bend around a pencil. As reported in a recent issue of Applied Physics Letters (doi:10.1063/1.4954039), the photovoltaics are based on ultrathin solar cells that are as effi cient as similarly formed thicker cells, but can withstand extreme bending. These properties are ideal for powering wearable electronics like fitness trackers, as well as other devices that require mechanically fl exible power sources. The researchers created their ultrathin solar microcells out of gallium arsenide (GaAs). They stamped the cells directly onto a flexible substrate covered in gold using a modified version of a process called transfer-printing. Transferprinting usually involves stamping solar cells onto an adhesive layer that lies on top of a substrate electrode. In this case, however, the team bypassed the adhesive layer altogether. The researchers used heat and pressure to adhere the solar microcells directly to the gold-covered substrate. This process also melted a preexisting layer of photoresist over the microcells. The photoresist acted as a temporary adhesive and protected the microcells from damage when the stamp was peeled away. The photoresist was then removed, leaving behind a photovoltaic just 1 μm thick and extremely flexible.
and turning off the applied field resembles the “read” mode. “In principle, our artificial magnetic charge ice could benefit the investigations and applications in any twodimensional materials systems that change properties in a magnetic field,” Wang says. “The paper demonstrates a method of directly writing patterns into specific
moments of an artificial ice array of nanomagnets,” says Peter E. Schiffer, professor of physics and Vice Chancellor for Research at the University of Illinois at Urbana-Champaign. “Through the clever use of array geometry and external magnetic field, this microscopic control opens the door to new flexibility in the study of artificial spin ice.” YuHao Liu
The key to their success is the adhesive process, according to Jongho Lee, a professor at Gwangju Institute of Science and Technology and the leader of this research group. “Others usually use an interlayer adhesive between the solar cells and substrate. The interlayer adhesive, even with a conductive adhesive, increases the electrical and thermal resistance, reducing electrical performance.” The interlayer adhesive, even with a conductive adhesive, increases the electrical and thermal resis- An optical image of the solar microcells wrapped tance, reducing electrical perfor- around the edge of a glass slide 1 mm thick. mance.” By eliminating the inter- Credit: Photo by Juho Kim. Reproduced with permission from Appl. Phys. Lett. 208, 253101 (2016); layer, the researchers eliminated doi: 10.1063/1.4954039. © 2016 AIP Publishing. this loss and reduced the thickness of the photovoltaic. Most phot
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