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

Abstract

ABSTRACT 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‐ μ m‐thick crystalline silicon with periodic nanoislands and an aluminum back reflector. The optimum short‐circuit current density with periodic nanoislands achieves 25 mA/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. Copyright © 2011 John Wiley & Sons, Ltd.