Improving dielectric nanoresonator array coatings for solar cells.

Antireflection coatings based on dielectric nanosphere arrays are discussed in application to photovoltaic materials including silicon and gallium arsenide. We perform macro- and nanoscale characterization and finite-difference time-domain calculations demonstrating the enhanced optoelectronic properties. A significant absorptivity enhancement is achieved due to the collective resonant coupling of excited whispering gallery-like modes and thin-film interference effects. The resonant coupling is masked in macroscale measurements by the size variation of nanospheres, but it is clearly seen through imaging photocurrent at the nanoscale with near-field scanning photocurrent microscopy. The resonant coupling can be effectively tuned by the material, configuration, or size of nanospheres. Hybrid coatings combining nanospheres of different materials yield the highest efficiency gain, more than 30 %. We also evaluate an impact of manufacturing defects such as double layer formation. While the performance degrades, the antireflection coating still offers marked improvement in comparison with bare cells.