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 (~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%.

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In this work, microcrystalline silicon nanostalagmite [μc-SiNS] arrays have been successfully fabricated on glass by catalytic etching process through a template. The template, polystyrene [PS] nanospheres, with diameter and density of 30 to approximately 50 nm and 1010/cm2, respectively, was obtained by a modified nanophase separation of PS-containing block copolymer. The length of μc-SiNS could be controlled by the duration of etching time. The μc-SiNS exhibits ultra-low reflection approximately 0.3% and absorption around 99% over 300 to 800 nm in wavelength. Reflection is also suppressed for a wide range of angles of incidence in wide range of wavelength. This indicates the extensive light-trapping effect by the μc-SiNS and could possibly harvest a large amount of solar energy at infrared regime.

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In this work, we demonstrate the absorption of the light with wavelength close to the absorption edge of materials could be largely enhanced by the incorporation of irregular metal nanodots. These nanodots were accomplished by low-cost method with negligible amount of usage. The metal nanodots works as nano-antenna and nano-cavities for light coupling and guiding. At 800 nm, the organic material exhibit approximately 30 % light absorption, which is almost zero without Au nanodots. For the In-organic material, the light absorption increase from ~ 10 % to ~ 50 % at 800 nm with the incorporation of Au nanodots. This enhancement indicate with minimum usage of metal, the light absorption could be largely enhanced, and is useful for high efficiency solar cells.Index Terms -irregular metal nanodots, nano-cavities, absorption enhancement, near band-edge .