An effective way to simultaneous realization of excellent optical and electrical performance in large‐scale Si nano/microstructures

Abstract

Despite the optical advantage of near-zero reflection, the silicon nanowire arrays (SiNWs)-based solar cells cannot yet achieve satisfactory high efficiency because of the serious surface recombination arising from the greatly enlarged surface area. The trade-off between reflection and recombination fundamentally prevents the conventional SiNWs structure from having both minimal optical and electrical losses. Here, we report the simultaneous realization of the best optical anti-reflection (the solar averaged reflectance of 1.38%) and electrical passivation (the surface recombination velocity of 44.72 cm/s) by effectively combining the Si nano/microstructures (N/M-Strus) with atomic-layer-deposition (ALD)-Al 2 O 3 passivation. The composite structures are prepared on the pyramid-textured Si wafers with large-scale 125 × 125 mm 2 by the two-step metal-assisted chemical etching method and the thermal ALD-Al 2 O 3 treatment. Although the excellent optical anti-reflection is observed because of the complementary contribution of Si N/M-Strus at short wavelength and ALD-Al 2 O 3 at long wavelength, the low recombination has also been realized because the field effect passivation is enhanced for the longer and thinner SiNWs through the more effective suppression of the minority carrier movement and the reduction of the pure-pyramid-textured surface recombination. We have further numerically modeled the Al 2 O 3 -passivated Si N/M-Strus-based solar cell and obtain the high conversion efficiency of 21.04%. The present work opens a new way to realize high-efficiency SiNWs-based solar cells.

One-step-MACE nano/microstructures for high-efficient large-size multicrystalline Si solar cells

“…Fig. 4 (b) shows that τ eff of the one-step-MACE-smoothened N/M-Strus for both the as-etched and SiN x :H-passivated cases, slightly decrease with increasing β, which is consistent with the previous results [19][20][21]. Obviously, all the four series for the as- where Kerr Auger recombination model [37] is considered.…”

“…For the as-etched case, the reflectance of the 500s series is slightly lower than that of reference in the whole range of 300-1100 nm, while for the SiN x :H-coated case the reflectance difference between the two series has been enlarged in the wavelength ranges of 300-600 nm and 900-1100 nm (highlighted by dashed circles). The enhanced antireflection is attributed to the complementary antireflection effect of the density-graded N/MStrus at short wavelength and the SiN x :H thin films at long wavelength [20]. Fig.…”

“…Since the optical characteristics of the Si N/M-Strus can directly affect the number of the photons entering into the solar cells [11,20], a good optical performance is the prerequisite to gaining the high η of solar cells. In this section, we lay emphasis on the antireflection characteristics of the one-step-MACE-smoothened N/M-Strus in various conditions including the as-etched, PSGremoved, SiN x :H-coated and cell cases.…”

“…However, the optical advantage of Si nanostructures has not been facile to be fully converted into the η-gain of solar cells [4][5][6][7][8][9][10][11][12][13][14][15], which is mainly ascribed to the poor electrical properties, i.e., high recombination on the surface and in the bulk of Si nanostructures. Over the past several years, substantial progresses in improvement of the electric performance have been made by carrying out various process methods such as the surface passivation [16][17][18][19][20], properly increasing sheet resistance [21,22] and optimization of morphology of mc-Si nanostructures [11,13,14,19]. Using the optimized textured structure, Zhong et al, [23] and Xiao et al, [24] have reported ηs of 15.99% and 17.46% for mc-Si nanostructures based solar cells with the standard solar wafer size of 156 Â 156 mm 2 through reactive ion etching (RIE), respectively.…”

“…As an morphology-easily-controlled method to prepare Si nanostructures, the widely studied metal-assisted chemical etching (MACE) has demonstrated promising advantages for mass productions due to its simplicity, room-temperature process, low cost, and compatibility with current production lines [5,17,19,20]. Generally, MACE is divided into one-step (direct etching) and twostep (depositing and etching) MACE, and the difference between these two methods lies mainly in the less process step and the absence of H 2 O 2 (oxidant) for the one-step MACE.…”