Subwavelength nanostructures integrated with polymer-packaged iii-v solar cells for omnidirectional, broad-spectrum improvement of photovoltaic performance

Reduction in surface and interface reflectance via the integration of subwavelength nanostructures in flexible polymer packaging material combined with incorporation of dielectric nanoislands into a conventional two-layer antireflection coating has been demonstrated, analyzed and optimized. Transmittance measurements of moth-eye textured polymer packaging sheets with different tapered pillar heights fabricated by reactive-ion etching and nanosphere lithography provide insights into the choice of the optimum nanostructure dimensions. Detailed computational modeling and simulations elucidate the physical nature of the antireflection performance of dielectric nanoisland structures integrated with a commercial two-layer antireflection coating, and provide guidance for design of the nanoisland structure for optimum antireflection performance. Measurements show that the integration of appropriately designed nanostructures in both polymer packaging material and conventional antireflection layers enables substantial increases in external quantum efficiency (E.Q.E.) and short-circuit current density (J(sc)) over a broad range of incident angles, compared to structures with conventional bilayer antireflection coatings and unpatterned polymer packaging sheets. A 1.1x increase in J(sc), derived directly from E.Q.E. measurements, at normal incidence, increasing to 1.67x improvement at 80 degrees angle of incidence, suggests that such an approach is promising for a variety of photovoltaic applications, particularly those where solar tracking is not feasible or practical. Copyright (C) 2014 John Wiley & Sons, Ltd.