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Carbon Nanotube Antennas Could Make PV Cells More Efficient

An international team of researchers led by Michael Strano at MIT has used carbon nanotubes to concentrate solar energy 100 times more than a regular photovoltaic cell. Such nanotubes could form antennas that capture and focus light energy, potentially allowing much smaller and more powerful solar arrays. A paper on their work was published online 12 Sep in the journal Nature Materials.

Instead of having your whole roof be a photovoltaic cell, you could have little spots that were tiny photovoltaic cells, with antennas that would drive photons into them.

—Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering

Their new antennas might also be useful for any other application that requires light to be concentrated, such as night-vision goggles or telescopes. The work was funded by a National Science Foundation Career Award, a Sloan Fellowship, the MIT-Dupont Alliance and the Korea Research Foundation.

The antenna—which boosts the number of photons that can be captured—consists of a fiber about 10 micrometers long and four micrometers thick, containing about 30 million carbon nanotubes. Strano’s team built, for the first time, a fiber made of two layers of nanotubes with different electrical properties—specifically, different bandgaps. Strano’s team is the first to construct nanotube fibers in which they can control the properties of different layers, an achievement made possible by recent advances in separating nanotubes with different properties.

In any material, electrons can exist at different energy levels. When a photon strikes the surface, it excites an electron to a higher energy level, which is specific to the material. The interaction between the energized electron and the hole it leaves behind is called an exciton, and the difference in energy levels between the hole and the electron is known as the bandgap.

The inner layer of the antenna contains nanotubes with a small bandgap, and nanotubes in the outer layer have a higher bandgap. That’s important because excitons like to flow from high to low energy. In this case, that means the excitons in the outer layer flow to the inner layer, where they can exist in a lower (but still excited) energy state.

Therefore, when light energy strikes the material, all of the excitons flow to the center of the fiber, where they are concentrated. Strano and his team have not yet built a photovoltaic device using the antenna, but they plan to. In such a device, the antenna would concentrate photons before the photovoltaic cell converts them to an electrical current. This could be done by constructing the antenna around a core of semiconducting material.

The interface between the semiconductor and the nanotubes would separate the electron from the hole, with electrons being collected at one electrode touching the inner semiconductor, and holes collected at an electrode touching the nanotubes. This system would then generate electric current. The efficiency of such a solar cell would depend on the materials used for the electrode, according to the researchers.

Strano’s team is now working on ways to minimize the energy lost as excitons flow through the fiber, and on ways to generate more than one exciton per photon. The nanotube bundles described in the Nature Materials paper lose about 13% of the energy they absorb, but the team is working on new antennas that would lose only 1%.


  • Jae-Hee Han, Geraldine L. C. Paulus, Ryuichiro Maruyama, Daniel A. Heller, Woo-Jae Kim, Paul W. Barone, Chang Young Lee, Jong Hyun Choi, Moon-Ho Ham, Changsik Song, C. Fantini & Michael S. Strano (2010) Exciton antennas and concentrators from core–shell and corrugated carbon nanotube filaments of homogeneous composition. Nature Materials. doi: 10.1038/nmat2832



Price? Ease of manufacture?

Putting this antenna on a solar cell sounds easy enough to see in public demonstration this week.


Does this mean you will be able to build concentrating solar that does not need to track the sun accurately ?

That would be an advance.
You would be able to use 36% efficient triple layer solar cells with a non tracking concentrator (or a roughly tracking concentrator).

But like all things, the devil is in the details.
So lets see what comes of it.


Exactly the question I was thinking of mahonj: Does this mean that we don't have to use a tracking array now? Would a tracking array make it even more efficient? What about mirrors to bring in even more light? Could this be like a multiplier where it would use all of the extra light provided by the mirrors 100 times more efficiently?

It will be interesting to see the price and ease of manufacturing and how it works in the real world.


Might be interesting to make cable out of these tubes with the PV semi-conductor at the core. The cable, strung as a dipole antenna would then deliver current to a storage unit or power control system.

Or you might build tall poles dense with nanotubes layers - each directing excitons toward the core PV material. A light pole.


This is a good idea, if they can make it work. They have not built one yet, so it is still theoretical. Not having to track the sun is a big plus. If they could keep the cost down, it could be more reliable and cost effective...we will see.


With some much efficiency, this could turn out to be some sort of sun energy amplifier. If it can be mass produced at an affordable price, most home owners could produce all the clean energy required for the residence and electrified family vehicles.

A very interesting development.

Wish that it will become reality.


An angle on this that works both ways (maybe)
Today 14-9-010

Since 2006, the team has used the Australian Astronomical Observatory at Coonabarabran to painstakingly measure the positions of more than 200,000 distant galaxies, to reveal how they were clustered together four to eight billion years ago.

The robot-driven instrument can position optical fibres to observe light from almost 400 galaxies at a time for the project, called WiggleZ, which is expected to be completed by the end of the year.

Q: Might there be application for optical information gathering via these carbon nano tubes's?

Q: Will see smart nanos that can track the sun?


One thing is certain. Current low efficiency sun energy converters (avg 15%) will progressively be replaced with much higher efficiency, lower cost converters. In the not too distant future, 50+ % efficiency converters (mounted on doors, windows roofs etc) will be more than enough to power a residence + 3 BEVs. Coupled with effective energy storage devices, it would solve future energy needs. The world will never be short of clean energy as long as the sun is shinning.



The things you're talking about are theoretical at this point. While it would be great if quantum dots could deliver panels with 50% efficient conversion (off of a theoretical 60% peak at the cell level), there have been no break throughs that allow us to even make a fact-based estimate as to when rudimentary quantum dot panels arrive, let alone optimized panels. At least none that I've heard of.


The biggest advance is likely to be multiple excitons per photon. Like the similar scheme using quantum dots to confine high-energy electrons so they liberate additional electrons instead of dissipating all energy above the band gap as heat, this can boost the efficiency and output.

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