silicon wire solar arrayScientists at the California Institute of Technology have developed a new type of solar cell that comprise of arrays of thin silicon wires embedded in polymer substrate. The unique optical interactions between these wires provide the cells with an enhanced light absorption capability and improved internal quantum efficiency over conventional solar cells. These new cells are much cheaper to produce on account of the very low amounts of silicon needed to build them. The superior structural flexibility possessed by the silicon wire array solar cells is expected to further reduce their production cost since they can be produced using a lower-cost process.

by Naimish Upadhyay, Green Economy Post

By employing long, thin silicon wires embedded in a polymer substrate, California Institute of Technology (Caltech) scientists have developed a new type of inexpensive solar cell that not only absorb more sunlight but is also more efficient at converting it into electrical power.

Scientists at Caltech’s Resnick Institute formed an array of very thin silicon wires, each measuring between 30 and 100 microns in length and only 1 micron in diameter. While each wire was known to act independently as a high-efficiency, high-quality solar cell, the researchers found that the efficiency of light absorption increased by bringing them together in an array.

When light falls on the silicon surface, only a portion of it gets absorbed and another portion scatters. By placing the wires next to each other, however, the collective scattering interactions between them result in an enhanced absorption – up to 96 percent of incident sunlight at a single wavelength and 85 percent of total collectible sunlight. These new solar cells thus surpass the conventional light-trapping limit for absorbing materials.

The scattering interaction effect occurs despite the sparseness of the wires in the array – they cover only between 2 and 10 percent of the cell’s surface area. When the researchers first began constructing on silicon wire-array solar cells, they assumed that sunlight would be wasted on the space between wires. But while quantifying the absorption, they realized that even relatively sparse wire arrays are able to produce effective optical concentration, thus enhancing the cell efficiency.

Caltech solar arrays also show improved performance in converting the absorbed sunlight into electrical power. According to reports, between 90 and 100 percent of the photons absorbed by the silicon wires are converted into electrons – in technical terms, near-perfect internal quantum efficiency.   It is this combination of high absorption and good conversion that makes the new solar cells high-quality.

Another breakthrough achieved in this research is that in terms of area or volume, just 2 percent of the array is silicon, and the rest (98 percent) is polymer. In other words, while these arrays have the thickness of a conventional crystalline solar cell, their volume is equivalent to that of a two-micron-thick film.

Since the silicon material is an expensive component of a conventional solar cell, a cell that requires just one-fiftieth of the amount of this semiconductor will be much cheaper to produce.

The composite nature of these solar cells also means that they are flexible. Given their flexibility, the thin films can be manufactured in a roll-to-roll process – an inherently lower-cost process than one that involves brittle wafers, like those used to make conventional solar cells.

The Caltech team is now working to increase the operating voltage and the overall size of their creation in order to scale them up to the size of conventional solar cells.

The scientific team is comprised of Harry Atwater, Director of Caltech’s Resnick Intitute, Nathan Lewis, professor of Chemistry at Caltech, and graduate student Michael Kelzenberg. In addition, the co-authors of this research are postdoctoral scholars Shannon Boettcher and Joshua Spurgeon; undergraduate student Jan Petykiewicz; and graduate students Daniel Turner-Evans, Morgan Putnam, Emily Warren, and Ryan Briggs.

This research has been published in the paper “Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications,” in the February 14, 2010 advance online edition of the journal Nature Materials.

Diagram Credit: Caltech/Michael Kelzenberg

© 2010, Naimish Upadhyay. All rights reserved. Do not republish.

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Author: Naimish Upadhyay (9 Articles)

Naimish Upadhyay recently graduated with an MS degree in Environmental Science & Policy from the University of South Florida, where he focused on sustainability policies of Florida businesses and local governments. While in graduate school, he was an active member of the Emerging Green Builder’s USF chapter ( as well as the Student Taskforce on Campus Sustainability at his university. Naimish previously taught college level Environmental Science and Environmental Biotechnology in India. Given his research and project experience, Naimish is eager to build a professional career in the areas of business sustainability, environmental management systems, sustainability assessment and reporting, and corporate social responsibility. Naimish looks forward to reader feedback and can be reached via email

  • Arun Kumar

    This is significant. If this can be scaled quickly in to manufacturing ht would add significant capacity to the insatiable demand for Solar PV technologies. Good write up.

  • David Lee

    Very good article – wld be interested in learning more on the R&D side. Plz contact me at

  • Linda slasberg

    This article was interesting.
    Speaking for myself, I am planning on buying a small house which right now does not have any heating at all. Basically its a “blank canvas” . I get to do what I want. However in saying that I am not a wealthy woman and will have a set sum of money in which to use. I would love to be able to install low energy heating system/solar or whatever but it looks as though the installation of such heating will be too expensive for me, certainly solar panels will be.
    If there is a less expensive way to go I would like to know of it.
    I live in Arizona so I get plenty of sun.
    Any thoughts and ideas I would be grateful.

    • Jordan

      Very good article, hope it comes out quickly.
      Hi Linda, well, I think if you have lots of sunshine and you want to heat your house, there are ways to make it work. If you can solve the problem of storage, for a few days, you are close. Can be done in a concrete floor, isolated. There are cheap solutions like blowing hot air from the loft to the ground floor, no tiles but partly transparant cover to make the loft a solar heat receiver, but write me

      • Bcydez

        Look over Natural Capitalism (Hawkins/Lovins/H Lovins) on building designs…in terms of your heating and cooling…keep your flooring available to wire up your solar and vent your house as well. minimizes the construction/contractor headaches with in wall and attic dynamics. Huge savings all the way around.

  • Jordan
  • Alan Langford

    Great article. With CalTech’s quality research efforts there’s hope for humanity. All of us are in- debted to everyone involved in this project.

    I can see naysayers saying these people are simply seeking ways to make a ton of money. If they (collectively) are, which I seriously doubt, good for them and I for 1 hope like hell that they are successful. In the final analysis thinking people represent the least expensive persons on this earth as well as the ONLY way humanity can continue to exist—–maybe rats and roaches but not mankind

    Again, great work.

    • Naimish

      Thank you for your words of appreciation Alan. I completely agree with your thoughts – in the end, it will be the solutions-driven innovative folks like these who will help the sustained co-existence of the human race and the environment.


  • Jay Cross

    I’ve seen a few press releases in the last few years about ideas similar to this – with vertically aligned Silicon fibers or Carbon Nanotubes being used to absorb photons. I’m curious as to the obstacles to commercial manufacture of useful panels made this way. I’d like an estimate in terms of years or decades to availability.

  • Bert


    Well, I’m starting to get very bored at announcements like that – every WEEK we get some “breakthrough” advancement in solar technology, yet the only cells available are still the same, old 1950s technology.

    It feels like the much awaited HIV vaccine, or cancer treatments… something everyone wants badly, there’s always someone to claim they found _THE_ ultimate thing, but when it comes to commercial availability “poof”… noone’s left.

    My 2cents..

  • Will

    Great numbers, sounds like the next SC generation! Well done California Institute of Technology, now for the next step. Now is a good time for production. When will these HESCs be manufactured? Who will manufacture them? Can they be mass manufactured yet?

    I would like to suit my home with this technology. When should I expect availability?

  • Paula

    Very Cool! What does the cost/kwh look like?

  • daniel maris

    Wow! These figures are incredible. Am I reading it right? Is it saying they can achieve 90% efficiency? That’s incredible – and able to do it more cheaply? Even more incredible.

    I hadn’t heard about this before – must be some issues over manufacture.

  • daniel maris

    I read up some more on the subject and found out (a) these figures are referring to quantum efficiency not energy efficiency – in terms of energy efficiency they are not as good as the best on the market but (b) it should end up being a much cheaper manufacturing process.

    Not quite the holy grail then.

  • William A. Branham

    21st Century Telecom, Inc. is a GE Ecomagination participant. The Company seeks to build a regional, national & global “wireless, Internet and mobile TV network with Comcast/NBCU.” It will serve as a renewal energy rural & community development initiative. The Company aims to broadcast “green content” on any device, anywhere, anytime by commercializing cutting edge innovative technology to increase sales, without sacrificing profitability, consistent with the availability of working capital.