Navigation Links
Solar nanowire array may increase percentage of sun's frequencies available for energy conversion

ALBUQUERQUE, N.M. Researchers creating electricity through photovoltaics want to convert as many of the sun's wavelengths as possible to achieve maximum efficiency. Otherwise, they're eating only a small part of a shot duck: wasting time and money by using only a tiny bit of the sun's incoming energies.

For this reason, they see indium gallium nitride as a valuable future material for photovoltaic systems. Changing the concentration of indium allows researchers to tune the material's response so it collects solar energy from a variety of wavelengths. The more variations designed into the system, the more of the solar spectrum can be absorbed, leading to increased solar cell efficiencies. Silicon, today's photovoltaic industry standard, is limited in the wavelength range it can 'see' and absorb.

But there is a problem: Indium gallium nitride, part of a family of materials called III-nitrides, is typically grown on thin films of gallium nitride. Because gallium nitride atomic layers have different crystal lattice spacings from indium gallium nitride atomic layers, the mismatch leads to structural strain that limits both the layer thickness and percentage of indium that can be added. Thus, increasing the percentage of indium added broadens the solar spectrum that can be collected, but reduces the material's ability to tolerate the strain.

Cross-sectional images of the indium gallium nitride nanowire solar cell. (Image courtesy of Sandia National Laboratories) Click on thumbnail for a high-resolution image.

Sandia National Laboratories scientists Jonathan Wierer Jr. and George Wang reported in the journal Nanotechnology that if the indium mixture is grown on a phalanx of nanowires rather than on a flat surface, the small surface areas of the nanowires allow the indium shell layer to partially "relax" along each wire, easing strain. This relaxation allowed the team to create a nanowire solar cell with indium percentages of roughly 33 percent, higher than any other reported attempt at creating III-nitride solar cells.

This initial attempt also lowered the absorption base energy from 2.4eV to 2.1 eV, the lowest of any III-nitride solar cell to date, and made a wider range of wavelengths available for power conversion. Power conversion efficiencies were low only 0.3 percent compared to a standard commercial cell that hums along at about 15 percent but the demonstration took place on imperfect nanowire-array templates. Refinements should lead to higher efficiencies and even lower energies.

Several unique techniques were used to create the III-nitride nanowire array solar cell. A top-down fabrication process was used to create the nanowire array by masking a gallium nitride (GaN) layer with a colloidal silica mask, followed by dry and wet etching. The resulting array consisted of nanowires with vertical sidewalls and of uniform height.

Next, shell layers containing the higher indium percentage of indium gallium nitride (InGaN) were formed on the GaN nanowire template via metal organic chemical vapor deposition. Lastly, In0.02Ga0.98N was grown, in such a way that caused the nanowires to coalescence. This process produced a canopy layer at the top, facilitating simple planar processing and making the technology manufacturable.

The results, says Wierer, although modest, represent a promising path forward for III-nitride solar cell research. The nano-architecture not only enables higher indium proportion in the InGaN layers but also increased absorption via light scattering in the faceted InGaN canopy layer, as well as air voids that guide light within the nanowire array.

Contact: Neal Singer
DOE/Sandia National Laboratories

Related biology technology :

1. University of Florida physicists set new record for graphene solar cell efficiency
2. Taking solar technology up a notch
3. Tiny fractal trees for solar power
4. In solar cells, tweaking the tiniest of parts yields big jump in efficiency
5. Notre Dame researchers develop paint-on solar cells
6. Discovery of a dark state could mean a brighter future for solar energy
7. A light wave of innovation to advance solar energy
8. Pitt researchers coax gold into nanowires
9. Stanford engineers weld nanowires with light
10. Voltage increases up to 25 percent observed in closely packed nanowires at Sandia Labs
11. RayBiotech, Inc. and the University of Oslo Enter into Antibody Array Services Collaboration
Post Your Comments:
(Date:11/25/2015)... , November 25, 2015 ... Research Report is a professional and in-depth study ...      (Logo: ) , ... of the industry including definitions, classifications, applications and ... provided for the international markets including development trends, ...
(Date:11/24/2015)... ... ... The United States Golf Association (USGA) today announced Dr. Bruce Clarke, of ... since 1961, the USGA Green Section Award recognizes an individual’s distinguished service to the ... of Iselin, N.J., is an extension specialist of turfgrass pathology in the department of ...
(Date:11/24/2015)... 2015 /CNW/ - iCo Therapeutics ("iCo" or "the Company") ... for the quarter ended September 30, 2015. Amounts, ... and presented under International Financial Reporting Standards ("IFRS"). ... said Andrew Rae , President & CEO ... not only value enriching for this clinical program, ...
(Date:11/24/2015)... /PRNewswire/ - Aeterna Zentaris Inc. (NASDAQ:  AEZS) (TSX: AEZ) (the ... the Toronto Stock Exchange, confirms that as of the ... developments that would cause the recent movements in the ... --> About Aeterna Zentaris Inc. ... Aeterna Zentaris is a specialty biopharmaceutical company engaged in ...
Breaking Biology Technology:
(Date:11/12/2015)... CAMBRIDGE, Mass. , Nov. 12, 2015 /PRNewswire/ ... Broad Institute of MIT and Harvard for use ... chemical discovery information management tools. The partnership will ... share both biological and chemical research information internally ... tools will be used for managing the Institute,s ...
(Date:11/9/2015)... , Nov. 09, 2015 ... the addition of the "Global Law ... their offering. --> ) ... "Global Law Enforcement Biometrics Market 2015-2019" ... Research and Markets ( ) has ...
(Date:10/29/2015)... , Oct. 29, 2015  The J. Craig Venter ... titled, "DNA Synthesis and Biosecurity: Lessons Learned and Options ... of Health and Human Services guidance for synthetic biology ... --> --> ... has the potential to pose unique biosecurity threats. It ...
Breaking Biology News(10 mins):