Wearable electronic devices, from heart rate monitors to temperature-changing materials, will require sustainable power sources that continue to function under the mechanical stress exerted on them by the moving body.
A team led by engineers at the Gwangju Institute of Science and Technology (GIST) in South Korea may have just the power source: an ultrathin, flexible solar cell that keeps working even when bent. The photovoltaic cell, which has an active layer made of gallium arsenide (GaAs), is just 1 μm thick. Standard photovoltaics (PVs) are typically hundreds of times thicker, and other thin PVs are 2–4 times thicker.
Thinner materials bend more easily. In general, however, reducing the thickness of the active layer in thin-film solar cells dramatically reduces the number of photons the material absorbs and thus the amount of electricity it produces. Methods have been developed to get around this problem (CEP, Aug. 2012, pp. 13–14). For example, instead of building the PV cells as vertical stacks, transfer-printing techniques can be used to print the electrode layers next to the active layer; each layer of the device, including the active layer, can be thicker without making the cell too thick to bend.
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