MRI Researchers Hope to Improve Solar Cell Efficiency Using Fly Eyes

An SEM image of a blowfly eye taken at 259x magnification shows the microscale features. Credit: Akhlesh Lakhtakia
An SEM image of a blowfly eye taken at 259x magnification shows the microscale features. Credit: Akhlesh Lakhtakia

The ability of the compound eyes of the tiny blowfly to capture light efficiently has inspired Penn State researchers to replicate those eyes in polymer to improve the light capturing efficiency of silicon solar cells.

Bioreplication attempts to duplicate exactly the features that nature has evolved over tens of millions of years. Until now, this kind of replication has had no real world applications, because it was not reproducible in quantity – one copy required the sacrifice of the original specimen. The breakthrough in this new technique is that it creates molds or stamps that are sturdy enough to be used to cheaply replicate large numbers of microscale features without the need for expensive microprocessing techniques.

The researchers, Akhlesh Lakhtakia, Drew Patrick Pulsifer, and Carlo Pantano of Penn State, and Raúl José Martín-Palma of the Universidad Autónomia de Madrid, Spain, used a technique developed at Penn State called conformalevaporated- film-by-rotation to coat an array of nine blowfly corneas with a 250 nm thick nickel film, after which a 60 micrometer thick structural layer of nickel was electroformed onto the thin layer to give the array the strength to be used as either a mold or a stamp. The polymer replicas that were then produced from the mold/stamp faithfully reproduced features of a few micrometers and larger.

A previous study by Lakhtakia and a team of Italian researchers had analyzed the utility of bioinspired compound lenses for solar cells http://iopscience.iop.org/1748-3190/5/2/026002, and found that properly designed compound lenses could significantly improve the light-harvesting performance of silicon solar cells when applied on their surface. The hemispherical compound eyes of many dipterans, or true flies, have adapted to see at a nearly 360 degree angle and in very low light conditions. These qualities could help solar cells to capture light without the necessity of adding expensive tracking systems to follow the sun. They could also capture ambient light, from a streetlamp or in a lighted room for example. The Penn State and Universidad Autónomia de Madrid researchers are continuing to develop their methods of bioreplication, which includes investigating how the microstructure of butterfly wings can produce color without the use of pigment.

The paper, “Mass Fabrication Technique For Polymeric Replicas Of Arrays Of Insect Corneas, http://stacks.iop.org/1748-3190/5/036001 was published July 22, 2010 in the journal Bioinspiration & Biomimetics. The authors are Drew Patrick Pulsifer, graduate student in engineering science and mechanics; Akhlesh Lakhtakia, Godfrey Binder Professor of Engineering Science and Mechanics; Carlo Pantano, distinguished professor of materials science and engineering and director of Penn State’s Materials Research Institute; and Raúl José Martín-Palma, professor of applied physics, Universidad Autónomia de Madrid.

For more details, please see the Penn State Live news release at http://live.psu.edu/story/47659.

This article was featured in Focus on Materials - Fall 2010.