Dual-Junction GaAs Photovoltaics for Low Irradiance Wireless Power Transfer in Submillimeter-Scale Sensor Nodes

Dual-junction GaAs photovoltaic (PV) cells andmodules at submillimeter scale are demonstrated for efficient wireless power transfer for Internet of Things and bio-implantable applications under low-flux illumination. The dual-junction approach meets demanding requirements for these applications by increasing the output voltage per cell with reduced area losses from isolation and interconnects. A single PV cell (150 mu m x 150 mu m) based on the dual-junction design demonstrates power conversion efficiency above 22% with greater than 1.2 V output voltage under low-flux 850 nm near-infrared LED illumination at 6.62 mu W/mm2, which is sufficient for the batteryless operation of miniaturized CMOS IC chips. The output voltage of dual-junction PV modules with four series-connected cells demonstrates greater than 5 V for direct battery charging while maintaining a module power conversion efficiency of more than 23%.