Material selection and fabrication parameters for antireflective nanostructures integrated with multijunction photovoltaics

Multijunction photovoltaic devices with four or more junctions require low reflection over a wavelength range that is nearly 50% wider than what is required for a triple-junction design. Antireflective nanostructures can drastically reduce reflection across this range; however careful design is necessary for integration with multijunction devices. In this work, we address the design trade-offs imposed by material availability by modeling absorption and reflection loss for various configurations. We find that the best performance is obtained using a hybrid design that combines antireflective nanostructures with a thin-film optical coating. Our models show that this configuration can increase transmitted power into the solar cell by 2.1% compared to the best standalone nanostructure configuration and 1.3% compared to an optimal thin-film antireflection coating. We also detail a fabrication process for integrating this hybrid design onto an active photovoltaic device.