Antireflection and light trapping of subwavelength surface structures formed by colloidal lithography on thin film solar cells

In this paper, we present a novel design of a surface nanostructure that suppresses the reflectivity and provides forward diffraction for light trapping. The structure under study comprises periodic nanoislands fabricated using self-assembly polystyrene spheres, which are applicable to large-area fabrication. We also show preliminary fabrication results of the proposed structure. The periodic nanoislands reduce the reflectivity through gradient effective refractive indices and enhance light trapping through diffraction in a periodic structure. We first systematically study the antireflection and light trapping effects using a rigorous coupled-wave analysis and then calculate the short-circuit current density of a 2-μm-thick crystalline silicon with periodic nanoislands and an aluminum back reflector. The optimum short-circuit current density with periodic nanoislands achieves 25mA/cm ² theoretically, which shows a 76.9% enhancement compared with that of bare silicon. Moreover, the structure also provides superior photocurrent densities at large angles of incidence, compared with conventional antireflection coatings.