Metal assisted chemical etching (MacEtch) is a recently developed anisotropic wet etching method that is capable of producing high aspect ratio semiconductor nanostructures from patterned metal film. In this review article, we highlight the characteristics of MacEtch of silicon (Si) including controllability of the produced sidewall roughness, the inherent high aspect ratio, the weak crystal orientation dependence, impurity doping and solution concentration dependent porosity, as well as the applicability of MacEtch to non-Si based semiconductor materials including III–V compound semiconductors. Also reviewed are applications of MacEtch produced high aspect ratio Si nanostructures in photovoltaics, where the p–n junction can be in the planar Si tray, core–shell, or axial geometry, with nanowire, micropillar, or hole arrays serving as light trapping or carrier collection structures. The prospect of using MacEtch to improve the cost and efficiency of photovoltaic cells is discussed.

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Metal assisted chemical etching for high aspect ratio nanostructures: A review of characteristics and applications in photovoltaics

We characterize the optical and carrier-collection physics of multi-scale textured p-type black Si solar cells with conversion efficiency of 17.1%. The multi-scale texture is achieved by combining density-graded nanoporous layer made by metal-assisted etching with micron-scale pyramid texture. We found that (1) reducing the thickness of nanostructured Si layer improves the short-wavelength spectral response and (2) multi-scale texture permits thinning of the nanostructured layer while maintaining low surface reflection. We have reduced the nanostructured layer thickness by 60% while retaining a solar-spectrum-averaged black Si reflectance of less than 2%. Spectral response at 450 nm has improved from 57% to 71%.

Multi-scale surface texture to improve blue response of nanoporous black silicon solar cells

A novel method to produce black silicon for solar cells

Laser surface treatment of multicrystalline silicon for enhancing optical properties

In this paper low cost and earth abundant Al nanoparticles are simulated and compared with noble metal nanoparticles Ag and Au for plasmonic light trapping in Si wafer solar cells. It has been found tailored Al nanoparticles enable broadband light trapping leading to a 28.7% photon absorption enhancement in Si wafers, which is much larger than that induced by Ag or Au. Once combined with the SiNx anti-reflection coating, Al nanoparticles can produce a 42.5% enhancement, which is 4.3% higher than the standard SiNx due to the increased absorption in both the blue and near-infrared regions.

https://researchbank.swinburne.edu.au/file/67e28fce-c165-498f-81d1-102b902796e2/1/PDF (Published version).pdf

Low cost and high performance Al nanoparticles for broadband light trapping in Si wafer solar cells

Two kinds of surface texturization of mc-Si obtained by wet chemical etching are investigated in view of implementation in the solar cell processing The first one was the acid texturization of saw damage on the surface of multicrystalline silicon (mc-Si) The second one was macro-porous texturization prepared by double-step chemical etching after KOH saw damage layer was previously removed Both methods of texturization are realized by chemical etching in HF-HNO3-H2O with different additives Macro-porous texturization allows to obtain effective reflectivity (Reff) in the range 9–20% from bare mc-Si This Reff value depends on the time of second step etching that causes porous structure modification The internal quantum efficiency (IQE) of cells with this kind of texturization has possibility to reach better conversion efficiency than the standard mc-Si solar cells However, low shunt resistance depends on morphology of porous layer and it is the main factor which can reduce open circuit voltage and conversion efficiency of cells The effective reflectivity is about 17% for acid texturized mc-Si wafer The investigation of surface morphology by scanning electron microscopy (SEM) revealed that the dislocations are appearing during chemical etching and they can reduce open circuit voltage The density of the dislocations can be reduced by controlling depth of etching and optimisation of acid solution

Texturization of multicrystalline silicon by wet chemical etching for silicon solar cells

OBJECTIVE
The aim: To determine whether VPA pharmacotherapy, mainly in the group of patients using subtherapeutic doses of VPA, could contribute to the occurrence of cognitive impairment.


PATIENTS AND METHODS
Materials and methods: The study involved 14 patients: six women and eight men, aged 24 - 77 years (mean SD ± - 52.36±13.71) diagnosed with epilepsy in accordance with the ILAE criteria (International League Against Epilepsy), in whom the main clinical complaint, in addition to poor control of epileptic seizures, were impaired concentration, attention and memory impairment.


RESULTS
Results: Mild cognitive impairment - MCI was diagnosed in 4 patients (28.57%) (3 with elevated ammonia levels, 1 without), in 1 patient (7.14%) there was a mild level of dementia. In only one MCI case, elevated serum concentrations of valproic acid were also recorded. It is very important to highlight that cognitive impairment has never been diagnosed before (prior to VPA therapy) in this group. Of these 5 patients, in four cases, after discontinuation of the drug, an improvement in the clinical condition was achieved. In a patient with mild level dementia, the termination of therapy did not give a similar effect. This proves the possibility of other mechanisms responsible for generating these sometimes irreversible disorders.


CONCLUSION
Conclusions: Regardless of the dose and concentration of ammonia in blood serum of patients diagnosed with epilepsy, VPA therapy may cause various, significant dysfunctions that significantly impair quality of life.

J. Dutkiewicz

Papers

Texturization of multicrystalline silicon by wet chemical etching for silicon solar cells

Hyperammonaemia and cognitive impairment in epilepsy patients treated with valproic acid - preliminary study.

Porous surface silicon layers in silicon solar cells