EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The use of light-trapping (LT) techniques to boost photon capture thus increasing the photocurrent is a very effective way to improve the solar cell’s efficiency. Among the different LT strategies available, metal-assisted chemical etching (MACE) is one of the most simple and cost-effective. MACE has already proved its ability to strongly reduce the reflectivity of the silicon surface and enhance solar cell efficiency [1]. In this abstract are presented the results obtained using a maskless MACE method, based on the hydrofluoric acid (HF) and hydrogen peroxide (H202) as etching agents and silver nitride (AgNO3) as source of silver ions, which catalyse the reaction promoting the formation of steep and anisotropic nanostructures. The method was previously characterized in terms of dependence on temperature, etchants molar ratio (ρ=[HF]/[HF]+[ H202]), and etching time (t_etch) [2].
In the present study, mono-c Si p-type wafers with resistivities of 1-3 Ω.cm and n-type wafers with 3-7 Ω.cm, both (100) oriented, were used. Spectral reflectance measurements of the etched surfaces were performed, and the nanostructures morphology was characterized by scan electron microscope observations.
For both silicon types a strong reduction of the reflectance over the range of interest for silicon solar cells (350-1050 nm) was observed, leading to effective reflectivity (Reff) values (normalized to the AM1.5 spectrum) under 5%. As expected, the etching rate for the n-type silicon is significantly higher than for p-type, and it was shown that for n-type monocrystalline wafers an Reff~3% can be obtained for t_etch<1 min. The textured surfaces are now being passivated with atomic layer deposited alumina with promising first results.
[1] J. Oh et al ‘An 18.2%-efficient black-silicon solar cell achieved through control of carrier recombination in nanostructures’ Nat. Nanotechnol. (2012).
[2] I. Costa et al. ‘Improving light capture on crystalline silicon wafers’, Materials Letters 272 (2020) 127825.