Resonant coupling of nano-resonator coatings measured by near-field scanning photocurrent microscopy

Dielectric arrays of nano-resonators as antireflection coatings is a potential candidate for improving efficiency of photovoltaic cells. Currently, the evaluation and optimization of the coatings relies on calculations and macro-/mesoscale experiments that are not fully consistent. We demonstrate how collective optical resonances within a monolayer of nano-resonators improve efficiency of solar cells using near-field scanning photocurrent microscopy. At wavelengths corresponding to the excitation of whispering gallery mode, we detect strong photocurrent enhancement over each nano-resonator. Combining nanoscale photocurrent imaging and macroscale experiments and calculations, we show that the collective optical couplings including whispering gallery modes and thin-film interference improve the photocurrent of solar cells by more than 20 %. We also examine the properties of multiple layers of nano-resonators by the near-field scanning photocurrent microscopy to evaluate the role of possible manufacturing imperfections.