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

Abstract

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%.

Broadband light absorption of silicon nanowires embedded in Ag nano-hole arrays

“…Compared with Fig. 3(a), the lowest five guide modes contribute to the light absorption and the absorptivity of SiNWs AgNHAs exceeds 70% from 500 nm to 1100 nm as denoted by 2 .…”

“…After embedding SiNWs into Ag nano-hole arrays, the waveguide modes of SiNWs AgNHAs are extended into the original leaky regions in SiNWs and totally restricted inside SiNWs AgNHAs. The light waves of the waveguide modes can be thereby fully absorbed as they propagate along Z direction, which results in high absorptivity as denoted by 2 . It should be noted that, in absorptivity calculation, we include material absorption loss, while in band diagram and field profile calculations, we exclude material absorption loss.…”

“…On the contrary, the reflectivity of SiNWs presents extremely low from 400 nm to 500 nm corresponding to its excellent antireflection property. [2][3][4] Therefore, in order to enhance light absorption at wavelength from 400 nm to 500 nm, SiNWs should be attached to the air side, meaning that the thickness t should be shortening down.…”

“…It can be seen that, the absorptivity of SiNWs exceeds 80% at wavelength from 400 nm to 600 nm and approaches its maximum value of 100% at 480 nm, while it decreases gradually to zero along with Fabry-Perot oscillations as wavelength further increases from 600 nm to 1100 nm. On the contrary, the absorptivity of SiNWs AgNHAs decreased significantly from 400 nm to 500 nm and reaches its minimum value of 42% at 450 nm as denoted by 1 , while it exceeds 70% average absorptivity from 500 nm to 1100 nm as denoted by 2 . It can be concluded that, after embedded into the Ag nano-hole arrays, the absorptivity of SiNWs decreases from 400 nm to 500 nm denoted by 1 but increases significantly from 500 nm 1100 nm denoted by 2 .…”

“…[1][2][3] The light absorption by SiNWs has been demonstrated empirically for its efficient antireflection and enhanced absorption. 4,5 The optimal designs of major structural parameters, such as filling ratio, periodicity, diameter, and length to enhance light absorption in SiNWs solar cells have been reported.…”