Black nonreflecting silicon surfaces for solar cells

Abstract

We present a wet chemical process for nanoscale texturing of Si surfaces, which results in an almost complete suppression of the reflectivity in a broad spectral range, leading to black Si surfaces. The process affects only the topmost 200–300nm of the material and is independent of the surface orientation and doping. Thus, it can be applied to various structural forms of bulk silicon (single, poly-, or multicrystalline) as well as to thin Si films (amorphous or microcrystalline). The optical properties of various black Si samples are presented and discussed in correlation with the surface morphology.

Nanostructured black silicon and the optical reflectance of graded-density surfaces

“…The resulting HF and H 2 O 2 dilutions in water are the same as previously used to black-etch Si. 3 Without added gold, we observe no R change. For black Si, we mix 5 nm colloidal gold particles in water ͑5 ϫ 10 13 / ml, Ted Pella͒ into an equal volume of the 1:5:2 solution in a beaker containing the silicon wafer and stir ultrasonically.…”

“…However, subwavelength surface texture on silicon is known to produce "black silicon" with a broadband antireflection at a far wider acceptance angle than single or multilayer antireflection films. [1][2][3][4][5] This nanometerscale texture also increases the Si surface area for other applications. [6][7][8] Black silicon texture has been produced by techniques including laser-chemical, 1 electrochemical, 2 and reactive-ion etching.…”

Sub-50-nm self-assembled nanotextures for enhanced broadband antireflection in silicon solar cells

“…The most straightforward approach places a single layer of intermediate optical index at the interface to create destructive interference in the reflected light, providing full antireflection at a single wavelength, l ¼ 4n i Á t, with material thickness (t) and refractive index n i ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffi n S Á n A p , where n S and n A are the refractive indices of the substrate and air, respectively. Increasing broadband coverage, for application in transparent window coatings [2][3][4][5] , military camouflage 6 or solar cells [7][8][9][10][11][12][13][14][15] , is possible using thin-film multilayer schemes 16 . An alternative to thin-film-coating strategies instead patterns the interface at subwavelength dimensions, creating an effective medium between the substrate and air, with n i changing gradually from n A to n S 10,11,17 .…”

“…Increasing broadband coverage, for application in transparent window coatings [2][3][4][5] , military camouflage 6 or solar cells [7][8][9][10][11][12][13][14][15] , is possible using thin-film multilayer schemes 16 . An alternative to thin-film-coating strategies instead patterns the interface at subwavelength dimensions, creating an effective medium between the substrate and air, with n i changing gradually from n A to n S 10,11,17 . Such structures, often called moth eyes because of their biomimicry, provide broadband antireflection over a wide range of incident light angles when subwavelength textures are taller than tB0.4 Á l and spaced closer than cBl/2n s 12,14,[18][19][20] .…”

Peculiarities of Photoluminescence in Porous Silicon Prepared by Metal-Assisted Chemical Etching

“…The increase First, we supposed that it is similar to "black" silicon having a needleshaped surface structure where needles are made of singlecrystal silicon and have a height above 10 microns and diameter less than 1 micron [21]. However, AFM investigation showed an absolutely other morphology (Figure 4) having macropores.…”