Minimization of Optical Reflectance by Copper Assisted Etching of Crystalline Silicon Surface

Abstract

Reduction of the optical reflectance to an absolute minimum by the metalassisted chemical etching (MACE) is investigated for the p-type crystalline silicon (100) plane wafers. The amount of the Cu additive and the composition of the etching solution identified by the proportion HF/(HF þ H 2 O 2 ) are the main variable parameters controlling the one step MACE. Pyramid like structures are produced on the surfaces. An influence of the variables on the surface topography and the related optical reflectance spectra is studied by measuring the spectra in the interval of the wavelengths from 400 to 1400 nm. Presence of a minimum that limits a reduction of the optical reflectance by the maskless micro-texturing of a smooth surface of a silicon wafer is experimentally demonstrated. The crucial stage in the etching is identified by the relative depth of the etched dips that results in the lowest reflectance. Under strictly controlled conditions the minimum reflectance is obtained using etchant with 0.08 M Cu-added. The lower and higher amounts of added Cu lead to an increase in the reflectance. The etching is explained by the localized microscopic galvanic cell model including the formation of the Cu-nanoparticles during the MACE and the changes in the reflectance are related to an enlargement of the etched pyramids.

Photoluminescent or Blackened Silicon Surfaces Synthesized with Copper-assisted Chemical Etching: For Energy Applications

“…When Cu-ACE processing was carried out occurred under 100 W UV irradiation, the excited electrons could stabilize copper to catalytically enhance the etching, making the silicon surface rough. Due to the size and relative depth of the etched pits, 26 the surface of etched silicon appeared black in the absence of the PL phenomenon, regardless of the processing time, as shown in Fig. 3c and f.…”

“…Moreover, there are no significant limits to the feature size of the nanostructures obtained from MACE processes such as silicon nanowires and channels, because both of these items can range from several nanometers in diameter to a few micrometers. Furthermore, to create such nanostructures for large-scale and high-volume production, instead of using noble metals for MACE, 18,[21][22][23][24] copper-assisted chemical etching (Cu-ACE) 16,17,[25][26][27][28] has been developed for etching the silicon surface, having the characteristics of being simple, highly reproducible, and cost effective.…”

Optical Design of Inverted Pyramid Textured PERC Solar Cells

“…There are a variety of structures for surface texturization. − The upright pyramid texture has been widely used in monocrystalline passivated emitter and rear cell (PERC) solar cells, which is commonly obtained by etching (100)-oriented monocrystal silicon wafers in an aqueous alkali such as KOH, NaOH, or TMAH. , The inverted pyramid structure has superior optical properties compared to the upright pyramid structure, which has been suggested by several reports. , With the metal catalysis chemical etching (MCCE) technology or specific chlorine-containing mixtures, a random inverted pyramid structure on the micrometer scale can be fabricated in a low-cost and efficient way. − …”

Effect of Various Copper Salt Precursors on Metal-Assisted Chemical Etching of Silicon

“…1,2 In particular, copper-based MACE (Cu-MACE) has received renewed interest in recent years as a way of developing antireflective black silicon textures for use in costsensitive photovoltaic applications. [3][4][5][6][7][8][9][10][11][12][13][14] It competes here with other wet chemical etching methods commonly used to produce pyramidal structures, such as alkaline KOH 15 or isotropic hydrofluoric/nitric/acetic acid (HNA) etching. 16 Cu-MACE shares many similarities with the related MACE techniques that use other metals.…”

“…16 Cu-MACE shares many similarities with the related MACE techniques that use other metals. As is also common with silver MACE (Ag-MACE), the copper species can be introduced from salts either directly in the etching bath (1-step), [5][6][7][8][9][10][11][12]17 or beforehand through electroless deposition (2-step). 13,[18][19][20][21] The usual theory presented in the literature suggests that the copper acts only as a catalyst, and so another chemical species is required to oxidize silicon.…”