Nanopore-type black silicon anti-reflection layers fabricated by a one-step silver-assisted chemical etching

Yen-Tien Lu and Andrew R.Barron

Department of Chemistry
Rice University
6100 Main St. MS60
Houston, TX 77005

            Recently, an economical approach for black Si manufacturing called metal-assisted chemical etching has been developed to cut down the cost of anti-reflection layer fabrication of Si-based solar cells. In the typical two-step metal-assisted chemical etching method, a noble metal, such as Ag and Au, is deposited on a Si surface as nanoparticles to induce formation of SiO2 by attracting electrons from the underneath Si surface. Next, the as-formed SiO2 is etched by HF and pits are produced under the nanoparticles. As these reactions occur in a continuous process the pits become deeper and ultimately connect with each other forming black Si consisting of a Si nanowire or nanopore structure. The proposed one-step Ag-assisted chemical etching method here is an even easier technique which synthesizes black Si in minutes. During this process, the Ag nanoparticle deposition and the Si chemical etching occurred simultaneously. The wafers were etched in a solution consisting of HF, H2O2, H2O, and AgNO3 at room temperature.

The effects on the surface morphology and the corresponding surface reflectivity of the component concentrations and etching time have been systematically investigated. With [Ag+] of 500 μM, no nanopores appear on the Si wafer surface causing the relative reflectivity of the wafer surface to not be effectively improved. As the [Ag+] decrease to 50 μM, long nanopores are formed and possess the lowest relative reflectivity, 0.17%, with the HF:H2O2:H2O ratio of 1:5:2. However, as the [Ag+] further decreases to 5 μM, a low relative reflectivity, 2.60%, and a much shorter nanopore length, < 250 nm, is obtained by 10 minute etching time and a HF:H2O2:H2O ratio of 5:1:20. These results indicate that this method is a facile (one-step), economical (low [Ag+]), and energy efficient (room temperature) method for fabricating anti-reflection layers for Si-based solar cell applications.

DIELECTRIC COATED SI OR GE QDS FOR IMPROVEMENT OF SOLAR CELLS

Brittany L. Oliva-Chatelain, Andrew R. Barron

Department of Chemistry
Rice University
6100 Main St. MS60
Houston, TX 77005

Abstract:
Hydrophilic silicon and germanium quantum dots (QDs) were synthesized with a “bottom-up” approach using micelles to control particle size. The quantum dots were then coated with silica using two different liquid phase deposition methods. The first liquid phase deposition method uses dodecyltrimethylammonium bromide (DTAB) as a surfactant to yield uniform spheres. The second method was a modified Stöber method with L-lysine to control particle size. The preferred coating method was found to be the modified Stöber method because it did not produce toxic byproducts, and it yielded better QD···QD distances (10 nm). The silica coated quantum dots were then arrayed using a vertical evaporation deposition method on quartz slides. The silica coated QDs were characterized by UV-visible spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and energy disperisve X-ray spectroscopy (EDS).

Superparamagnetic Metal Oxide Nanoparticles as Tracers in Wells

Lauren Morrow and Andrew R. Barron

Department of Chemistry
Rice University
6100 Main St. MS60
Houston, TX 77005

Superparamagnetic ternary metal oxide nanoparticles consisting of combinations of Fe, Mn and Zn, as well as Fe, Gd, and Al, were synthesized via thermal decomposition of metal acetylacetonates.  The Fe-Mn-Zn oxide nanoparticles were also synthesized via a metal-oleate complex in an attempt to scale up to industrial quantities.  Each distinct composition gives a unique magnetic susceptibility signal, which can be distinguished against a background of magnetic material, particularly that found in oil wells.  Thus, these particles can be used as a means of tracing fracture jobs to ensure the fractures were done well, as well as being able determine if a well is leaking into the local water supply.  The various nanoparticles were characterized via transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), small angle X-ray scatter (SAXS), and X-ray diffraction (XRD).   A methodology for concentrating and removing the nanoparticles from water was developed using a filtration system and a low magnetic field.