Integrated optical nanostructures for wide-angle antireflection and light trapping in III/V solar cells

Abstract

The use of subwavelength-scale dielectric nanostructures for both reduced surface and interface reflectance and long-wavelength light trapping in III/V thin-film solar cells is demonstrated and characterized. Antireflection coatings incorporating submicron pyramidal “nanoislands” are fabricated on GaAs thin-film solar cells using a low-cost nanosphere lithography (NSL) process, and shown to improve external quantum efficiency (E.Q.E.) compared to that achieved using a thin-film planar Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> antireflection coating, with the largest improvements occurring for large angles of incidence. Such structures are also shown to enable, simultaneously, reduced surface reflectance and long-wavelength light trapping, as demonstrated in GaAs/InGaAs quantum well solar cells. Finally, the simultaneous use of subwavelength “moth-eye” structures fabricated in polymer packaging material using NSL and solar cell antireflection structures incorporating dielectric “nanoislands” is demonstrated and analyzed, enabling increases in short-circuit current density of ~1.1× to 1.67×, depending on angle of incidence, compared to structures using conventional two-layer thin-film antireflection coatings and unpatterned polymer packaging.