A U.S. soldier can carry up to 20 pounds of batteries to run radios and other electronics on a mission. Engineers at Florida International University (FIU) have built a thin device that could cut that load by turning sunlight into power and then doubling as a light source.The device, called SOLED, is half solar panel and half light-emitting diode (LED). Backed by a $10 million Department of War grant, it is razor-thin and could be stitched onto a uniform or gear, giving troops in remote locations a quiet way to make power without the noise, heat or bulk of a generator.Perovskite, run both waysSOLED is built from perovskite, a versatile semiconductor. As a solar cell, it converts sunlight to electricity at up to 22% efficiency, which the team says is competitive with commercial solar technology. Run in reverse, it emits light at nearly 11% efficiency, a significant jump over earlier versions of the technology, the researchers said.That light is not bright to the naked eye. It peaks at 818 nanometers, just past the edge of visible light, and appears as a faint pink glow. Even so, night-vision sensors, biometric scanners and medical imaging equipment read wavelengths like this one. The team is now working to make the panels visibly brighter.Less reliance on resupplyDaniela Radu, the lead researcher and chair of FIU’s mechanical and materials engineering department, said a panel that makes power and then light could reduce dependence on batteries, generators and resupply. “This is how we can increase energy resilience at the level of individual soldiers,” she said.FIU says the technology could also enable new displays, sensors and other optoelectronic devices, offering flexibility when supply routes are threatened.Scaling upLab tests of perovskite solar cells typically use samples around 0.1 square centimeters (about 0.016 square inches), because that is what standard equipment is built for, said Neetesh Kumar, an FIU assistant research professor and the study’s lead author. The team pushed SOLED to 1.1 square centimeters (about 0.17 square inches), where it kept power-conversion efficiency above 20%, and then to 2.1 square centimeters (about 0.33 square inches), still with strong performance.Scaling is difficult because the panel is thin and multilayered, but the team has not run into problems so far, Kumar said. The next goal is panel sizes that could go into a product.Part of a larger programThe work grows out of the Department of War grant that funds the Center of Excellence for Integrated Resilient Energy and Energy Storage, or CIREES, which Radu leads. FIU runs the multiyear project, with collaborators from Pennsylvania State University, aimed at making warfighter energy resilience a national security priority.FIU did not give a timeline for a wearable version. For now, the results show power-conversion efficiency holding above 20% beyond the smallest lab samples.The work was published in the journal Nano Energy.