Condition for perfect resonant antireflection in solar cells

Antireflection coatings are necessary components in solar cells. It has recently been experimentally demonstrated that a periodic array of resonant subwavelength objects placed at an air-dielectric interface can significantly reduce reflection. We introduce the theoretical condition for complete reflection cancellation in this resonant antireflection scheme. First, the periodicity of the array needs to be smaller than the free-space wavelength of the incident light for normal incidence; second, the resonances in the subwavelength objects need to radiate into air and the dielectric in a balanced fashion. We use both intuitive arguments and the temporal coupled-mode theory, validated by full-field electromagnetic simulations.