Preparation of Large Size Pyramidal Texture on N-Type Monocrystalline Silicon Using TMAH Solution for Heterojunction Solar Cells

Abstract

Pyramidal texture is one traditional method to realize antireflection for c-Si solar cells, due to its low cost and simplicity. As one high efficiency silicon solar cell, amorphous/crystalline silicon heterojunction (SHJ) solar cell has attracted much attention all over the world. The heterojunction interface with very low defects and interface states is critical to the SHJ solar cell performance. In order to obtain high quality interface passivation by depositing a very thin intrinsic amorphous silicon layer on the textured Si conformally, large size pyramidal texture with no metal ion contamination is required. In this work, we utilized tetra-methyl ammonium hydroxide (TMAH) instead of NaOH in the alkaline etching to prepare pyramidal texture on N-type monocrystalline silicon to avoid the possible Na+ contamination. By optimizing the etching conditions, uniform large size pyramidal texture with pyramid size of about 10 μm was fabricated successfully. Furthermore, excellent antireflection performance was demonstrated on such textured Si surface. The average reflectance was lower than 10% in the visible and near infrared spectrum range. Such pyramidally textured Si wafers will be very suitable for SHJ solar cells.

Pyramid textured Si{100} surface with low reflectivity in CMOS compatible solution

“…This results in the breaking of back bonds and subsequently Si(OH) 4 and H 2 are formed as products by removing the surface Si atom. These hydrogen bubbles are stuck on the Si surface and act as a pseudo‐mask during the etching process that results in the formation of micropyramids [21, 24].…”

“…To understand the importance of the results presented in this paper, Table 1 shows a comparison of the reflectance values obtained on the surfaces textured under various etching conditions in different concentrations of TMAH [4, 8, 14, 15, 21]. In this study, we have achieved the lowest R sw of 10% in the visible wavelength and minimum reflectance of 6.7% at 790 nm on the silicon surface etched at 85°C for 25 min, which is less than the values reported by other researchers on the silicon surface textured in TMAH solution under different etching conditions as can be noticed in Table 1.…”

“…In surface texturing, the Si surface is intentionally made rough to increase the optical path length by multiple internal reflections, which results in more photon generation and thus increase the efficiency [2]. Surface texturing is usually done by wet etching, dry etching, and lithography [3–23]. For generating anti‐reflective structures on Si surface, many techniques based on lithographies such as photolithography, electron‐beam lithography, and nanoimprint lithography have been used.…”

“…Moreover, other effects such as mechanical agitation on etched surface morphology have also been investigated [8]. In previous studies, 2% TMAH is reported as an optimal concentration for lower reflectance [3, 4, 8, 15, 21].…”

Surface Texturing of Silicon {100} in an Extremely Low Concentration TMAH for Minimized Reflectivity

“…[7][8][9] Numerous studies have been done to reduce the reflectance from Si surface by various methods such as additional anti-reflective coatings, [10][11][12] surface texturing using dry and wet etching processes. 13,14,[23][24][25][26][27][28][29][15][16][17][18][19][20][21][22] In the etching process, wet etching brings a good balance between efficiency and cost. 2,6,7 The structures created on the surface by utilizing wet etching cause multiple internal reflections of incident light that result in more photogeneration and increase of the short circuit current.…”