Enhanced Solar Cells for Unmanned Aircraft Systems

Sola-powered Unmanned Aircraft Systems (UASs) have the potential to revolutionize Intelligence Surveillance and Reconnaissance (ISR) for the US Department of Defense (DoD) and also directly impact large commercial markets including 5G telecommunications and remote geospatial sensing. Solar cells are a critical technology for these aircraft, which must be cost effective, lightweight, and high performance. Current solar-powered UASs leverage one of two cell technologies: Gallium Arsenide (GaAs) or silicon. For many DoD and commercial applications, the performance of silicon cells is too low to meet mission needs but the cost of upgrading to GaAs cells is prohibitively expensive. A new type of solar cell is needed that can outperform standard silicon cells but without the high cost of GaAs. A recent study published by our research partner at the University of Tulsa demonstrated the ability to enhance the performance of medium-grade silicon cells by 10% to 54% after applying a thin film layer of nano particles made of semiconductor oxides (ZnO). The team found that the nano-particle layer was able to capture energy in the UV spectrum and down-convert the light into visible wavelengths that could be captured by silicon. Based on these positive results, the team conducted a phase-1 project with AFWERX to test whether the performance gains achieved using medium-grade silicon cells could also be achieved with high-grade silicon cells used on solar UASs. The results from the phase-1 effort showed that an application of 3 layers of semiconductor oxides were able to boost the solar conversion efficiency of high-performance silicon cells by 9.91%. This was a significant result considering that the benchmark efficiency level for silicon solar cells had only increased by 5% from 2015 to 2021 despite significant global investment. These “enhanced” silicon solar cells have the potential to significantly impact commercial markets that rely on low-cost high performance solar arrays. These results also provide a path to improve the efficiency of solar-powered UASs and enable persistent ISR. Based on the success of the phase-1 effort, the team is proposing a phase-2 project to build a flight-ready solar array using the enhanced silicon cells developed in phase-1 and test the performance of these cells in off-nominal conditions that commonly arise in UAS flight profiles. The team will design and build a wing-mounted solar array and integrate it onto the Skydweller UAS and perform pre-flight ground tests and power-generation demonstrations. The Skydweller UAS is currently the focus of an ongoing Joint Technology Capability Demonstration (JCTD) program. By aligning the phase-2 project with the Skydweller JCTD program, we have a clear and direct transition path to fielded operations with strong COCOM support, multi-service stakeholders, and phase-3 funding sources.