An American soldier on a mission may carry up to 9 kilograms (20 pounds) of batteries for communications and other electronics. Researchers at Florida International University (FIU) have proposed a device that can lighten this load: an ultrathin solar panel operating in two modes - it collects sunlight to generate electricity and itself emits light.
The name of the development is SOLED (half solar panel, half light-emitting diode, LED). It can be sewn into uniforms or equipment to obtain energy in remote areas without the noise, heat and bulk of a generator. In addition, the device opens up new possibilities for displays, sensors and other optoelectronic devices - that is, components that control light.
The work was published in the journal Nano Energy.
"When you can turn sunlight into energy and then use the same panel to produce light, you potentially reduce dependence on batteries, generators and supplies," FIU's press service quoted the head of the study, Daniela Radu, as saying. In her view, this increases energy resilience at the level of the individual soldier.
The device is based on perovskite, a semiconductor material that converts sunlight into electricity with an efficiency of up to 22%. This is comparable to commercial solar technologies. In the reverse mode, the panel emits light with an efficiency of almost 11% - a noticeable increase compared with earlier versions, the authors claim.
The glow is dim to the eye: the emission peak is at a wavelength of 818 nanometers, just beyond the visible light range, so it looks like a pink glow. But even this is useful: night-vision devices, biometric scanners and medical imaging operate at such wavelengths. The team is now trying to make the panels visually brighter.
Radu heads the Center for Advanced Excellence in Integrated Sustainable Energy Systems and Energy Storage (CIREES). FIU leads a multi-year project involving partners from Pennsylvania State University. The goal is to find energy solutions in support of the strategic course of the US Department of Defense, which considers the energy resilience of service members a national security priority.
The next step is to increase the size of the device. The panel is multilayer and thin, so scaling is difficult, but so far the team has managed without problems, says the first author of the study, Nitesh Kumar. A sample with an area of 1.1 square centimeters maintained an energy conversion efficiency above 20%, which confirms the technology's viability beyond tiny laboratory samples.
"Most solar cells made from such materials at the research stage are tested at an area of about 0.1 square centimeters, because that is what standard laboratory equipment is designed for," Kumar explains. "We increased the area to 1.1 and then to 2.1 square centimeters and still saw high performance. Our next goal is to continue scaling toward panels suitable for a product."