< photonics.com - June 2014
More Efficient Solar Cells with a One-Step Process
HOUSTON, June 20, 2014 — A new one-step process for producing efficient antireflective materials could mean big things for solar cells.
A cross section shows inverted pyramids etched into silicon with a chemical mixture. Images courtesy of the Barron Group/Rice University.
Developed by a team at Rice University, the new process produces black silicon, which reflects almost no light. Its textured surface of nanoscale spikes and pores — which are smaller than the wavelength of visible light — is suited to solar cells because it allows efficient light collection from any angle at any time of day, the researchers said.
The new method for creating black silicon uses a chemical mix of copper nitrate, phosphorous acid, hydrogen fluoride and water applied to a silicon wafer. This creates copper nanoparticles, which attract electrons from the silicon wafer’s surface, oxidize it and allow hydrogen fluoride to burn pyramid-shaped nanopores into the silicon.
This top-down view shows pyramid-shaped pores etched into silicon.
With further study, the researchers also developed a black silicon layer that had pores as small as 590 nm. This layer allowed absorption of more than 99 percent of incident light (a typical layer of non-etched silicon reflects that much light).
The new process could replace an existing two-step method that involves metal deposition and electroless chemical etching. Traditional solar cells typically feature coatings that protect their active elements and allows some light to pass through, but the researchers said its antireflective surface is limited to a specific range of light, incident angle and wavelength.
The work was funded by Natcore Technology Inc., the Robert A. Welch Foundation and the Welsh Government Sêr Cymru Program. The research was published in the Journal of Materials Chemistry A
For more information, visit www.rice.edu