Infrared Energy Harvesting in Millimeter-Scale GaAs Photovoltaics

The design and characterization of millimeter-scale GaAs photovoltaic (PV) cells are presented and demonstrate highly efficient energy harvesting in the near infrared (NIR). Device performance is improved dramatically by optimizing the device structure for the NIR spectral region and improving surface and sidewall passivation with the ammonium sulfide treatment and subsequent silicon nitride deposition. The power conversion efficiency of a 6.4-mm(2) cell under 660-nW/mm(2) NIR illumination at 850 nm is greater than 30%, which is higher than commercial crystalline silicon solar cells under similar illumination conditions. Critical performance limiting factors of submillimeter-scale GaAs PV cells are addressed and compared to theoretical calculations.