Fabrication of large area high density, ultra-low reflection silicon nanowire arrays for efficient solar cell applications

High density vertically aligned and high aspect ratio silicon nanowire (SiNW) arrays have been fabricated on a Si substrate using a template and a catalytic etching process. The template was formed from polystyrene (PS) nanospheres with diameter 30-50 nm and density 10(10)/cm(2), produced by nanophase separation of PS-containing block-copolymers. The length of the SiNWs was controlled by varying the etching time with an etching rate of 12.5 nm/s. The SiNWs have a biomimetic structure with a high aspect ratio (similar to 100), high density, and exhibit ultra-low reflectance. An ultra-low reflectance of approximately 0.1% was achieved for SiNWs longer than 750 nm. Well-aligned SiNW/poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) heterojunction solar cells were fabricated. The n-type silicon nanowire surfaces adhered to PEDOT:PSS to form a core-sheath heterojunction structure through a simple and efficient solution process. The large surface area of the SiNWs ensured efficient collection of photogenerated carriers. Compared to planar cells without the nanowire structure, the SiNW/PEDOT:PSS heterojunction solar cell exhibited an increase in short-circuit current density from 2.35 mA/cm(2) to 21.1 mA/cm(2) and improvement in power conversion efficiency from 0.4% to 5.7%.