Next-Generation and Nano-Architectured Photovoltaics: A Field of Great Promises and Risks

Converting the widely available solar energy into electricity provides a necessary solution to the energy crisis we currently face. As we move towards a higher standard of living in the 21st century with an ever growing population, it will be difficult to live on a dwindling supply of fossil fuels. Although photovoltaic (PV) technology, more colloquially solar cells, has been widely used and established, the major obstacle that still hinders its development and large-scale application is the high cost of commercially available inorganic semiconductor-based solar cells. Recently developed photovoltaics (OPVs), however, offer an alternative route to solar cell technology by converting sunlight directly into current, creating electric power.[1] Though these devices show much promise, the most complicated issue is in electron transport through the layers of the devices. Despite this mechanistic challenge, the efficiency can be improved through systematic nano-engineering and the development of nano-architecture that is optimally matched to the properties of these photovoltaic materials.

Enter Titanium Nanorods!

A new approach towards higher efficiencies of solar cells incorporates the use of nanotechnology. For instance, at the National Taiwan University, efficient photo-induced charge transfer has been shown to occur at titanium nanorod/polymer interfaces, which enhances the separation of charges, resulting in current.[2] Approximately 35 nm in length and 4 nm in diameter, the TiO2 nanorods act as highways for charge transfer and extend the interfacial area for photogenerated charge transfer, due to their large surface-to-bulk ratio. Additionally, the introduction of TiO2 nanorods further reduces disorder in the morphology of the devices, which increasing efficiency in the photovoltaic devices. In terms of applications, nanorods will be more suitable for polymer solar cells with respect to the widely used CdSe nanorods. However, despite these promising results, there are still problems of carrier mobility, stability and the length and diameter of the TiO2 nanorods and their alignment within the polymer, which will affect the energy output.

Figure 1. TEM image of TiO2 nanorods with a size of 4–5 nm in diameter and 20–40 nm in length.

Figure 1. TEM image of TiO2 nanorods with a size of 4–5 nm in diameter and 20–40 nm in length.


Oooo….Quantum Dots!

Besides nanorods, quantum dots (QDs) are also another area of interest. QDs, or tiny semiconductor particles generally no larger than 10 nanometers, can be made to fluoresce in different colors depending on their size. What makes them special is that they last much longer than conventional dyes used to tag molecules, which usually stop emitting light within seconds. Also, only a single container, or “pot,” is needed to prepare these QDs within a few hours. In the area of energy applications, QDs can produce electrons when they absorb light, making possible extremely efficient solar-energy devices via multiple exciton generation (MEG). Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), collaborating with Innovalight, Inc., have shown that an important effect called Multiple Exciton Generation (MEG) occurs efficiently in silicon nanocrystals, or quantum dots. Essentially, MEG results in the formation of more than one electron per absorbed photon, and so far has only been reported to occur only in quantum dots of semiconductor materials. For comparative purposes, when today’s photovoltaic solar cells absorb a photon of sunlight, about 50% of the incident energy is lost as heat, but MEG is capable of converting this energy lost as heat into additional electricity.[3]

a 1 μm x 1 μm surface imaging of InAs quantum dots on GaAs/InP, (inset) a single InAs quantum dot.

AFM micrographs of: a 1 μm x 1 μm surface imaging of InAs quantum dots on GaAs/InP, (inset) a single InAs quantum dot.

Ambiguous Risks

It is clear that the field requires materials advances, fundamental advances in physical understanding, as well as technological improvements. The central challenges include improved physical understanding, materials, transport and surfaces, and more importantly, the health and environmental risks of this type of nano-engineering.

Whether it be quantum dots, nanorods, or carbon nanotubes, they are all microscopically sized and exhibit unique properties potentially useful in electronics, optics and various other materials. They are manufactured and synthesized in many different ways, and produce different results when trying to assess their safety. “To confound the situation further,” University of Oregon’s Jim Hutchinson writes, “the methods of production are still immature for most materials, often resulting in batch-to-batch variability in composition and purity.” [4] Impurities, are hard to detect, difficult to extract and may obscure the real effects of nanomaterials. He believes the way to go is to employ green chemistry before the field of nanomaterials and nanoparticles becomes fully launched.

Nanomaterials are complex, as are their interactions with biological organisms and the environment. However, based on known studies, the concentration and distribution of surface oxides exert a profound influence on the aquatic stability and sorption properties of multiwalled carbon nanotubes (MWCNTs).[5]

More aggressive oxidizing conditions lead to larger changes in the surface oxygen content without altering the physical characteristics of individual MWCNTs (e.g., length and structural integrity).

Oxides on carbon nanotubes

Oxides on carbon nanotubes

By identifying the interplay between the MWCNTs surface chemistry and other properties, we can more adequately prevent the dispersion of toxic chemicals in water and biological media like in people. It is important to understand the mechanistic aspects of CNT aggregation and deposition and to conduct transport studies to measure the mobility of oxidized MWCNTs through porous media with and without the presence of contaminants.

Influence of oxygen functional group distribution on the aquatic stability of oxidized MWCNTs. The solution chemistry of three vials, each containing an equal concentration of oxidized MWCNT particulates (overall oxygen concentration shown on the cap of each vial) at pH7, has been modified by the addition of 0.07MNaCl, vortexed and allowed to settle under the influence of perikinetic flocculation for 120 min.

Influence of oxygen functional group distribution on the aquatic stability of oxidized MWCNTs. The solution chemistry of three vials, each containing an equal concentration of oxidized MWCNT particulates (overall oxygen concentration shown on the cap of each vial) at pH7, has been modified by the addition of 0.07MNaCl, vortexed and allowed to settle under the influence of perikinetic flocculation for 120 min.

The Future of Nanomaterials

The rise of solar energy, in one form or another

The rise of solar energy, in one form or another

Though there are various benefits of nanomaterials, the quality of our environment, the future vitality of the American economy, and the health of workers and consumers are all at risk to some extent. Hence, it is especially ciritical to examine the risks and remedy them for the continuing progress of nanotechnology. Before nanotechnology can gain mainstream acceptance in solar cells, for example, there needs to be a more comprehensive research strategy, involving input from academia, industry, consumer and environmental groups.



[1] “Another Silicon Valley?” The Economist. http://www.economist.com/specialreports/displaystory.cfm?story_id=11565636. 30 January 2009.

[2] Lin, Yu-Ting Lin, et al. Nanotechnology 17 (2006) 5781.

[3] M.C. Hanna, et al. “Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation”. NREL. 2007.

[4] “Potential Nanotech Hazards Are Hard to Determine, Researchers Urge Proactive Approach.” http://www.sciencedaily.com/releases/2008/03/080331130252.htm. 27 January 2009.

[5] Fairbrother, Howard, et al. Surface Oxides on Carbon Nanotubes (CNTs): Effects on CNT Stability and Sorption Properties in Aquatic Environments. Nanoscience and Nanotechnology. 2008.

“Doing More With Less” using the Bucky Ball

It is incredible how Buckminster Fuller, “the little, penniless, unknown individual was able to do effectively on behalf of all humanity”.[1] Like Feynman, he had a vision. But the two men differed in that Fuller devoted his life to provide “more and more life support for everybody, with less and less resources” by being practical, utilitarian, and economical. His lifelong experiment to create affordable and environmentally sustainable shelter resulted in the famous Dymaxion House, a consequence of his extensive analyses on geodesic domes and structures. However, it was not mass produced due to high materials cost and its “one size fits all” approach.[2] Similarly, his Dymaxion car, though having potential in terms of mileage per gallon of gasoline, was not implemented due to an unfortunate car accident, which killed the driver of his Dymaxion car. Though his inventions did not result in huge success in his lifetime, his manipulation of geometric structures sparked interest in the generations to come. From chemistry to biology, his ideas continue to be resounding and extremely practical.

Figure 1. Fuller in front of his geodesic dome.

The Bucky Ball: A Building Block

Little did Fuller know that his legacy would transverse the decades into the field of chemistry. In 1985, a small group of chemists, Kroto, Smalley, and Curl earned a Nobel Prize in Chemistry for discovering fullerenes, a class of closed cage structures, largely inspired by Fuller’s geodesic dome. Though C60 is the most common form of the fullerenes, other derivatives such as C70 and C80 have been extensively used as well.[3]

Figure 2. Buckminsterfullerene C60

The discovery in 1985 opened doors to modern research in buckypaper, a thin film of nanotubes which consist of fullerenes weaved together. Scientists have made great strides in improving the strength and bonding of buckypaper, resulting in material ten times lighter than steel and 500 times stronger when pressed together. Combined with its good conductivity, buckpaper can potentially replace steel making and improve building material, cars, planes, military armor, and stealth technology![4] Further, if exposed to an current, buckypaper could be used to illuminate computer and television screens. This is beneficial, as it could be more energy-efficient, lighter, and could allow for a more uniform level of brightness than current cathode ray tubes (CRTs) and liquid crystal display (LCD) technology. Though the question of waste and its potential impacts on the environment remain unknown, the fact that buckypaper requires so little to make such large improvements is a testament to Fuller’s vision of doing more with less.

Video: http://www.youtube.com/watch?v=hkijxr4z_mY

Figure 3. Magnified buckypaper structure.

Bucky…Hair?

Bucky’s vision does not stop with the buckypaper though. Researchers at the Rensselaer Polytechnic Institute have also played around with copper nanotubes…by coating them on the inner walls of cooking pots! This novel technique can increase the efficiency of energy transfer from the pot to the water it holds by an order of magnitude.[5] Why? Well, under the appropriate magnification, the surface of the cooking vessel looks hairy, whose structure is ideal for transfer of energy. Like the hirsute microvilli lining our intestines, the hair like structures of the nanotubes increase the surface area, improving energy transfer greatly. This means that not only does the water get hot faster, but we would start actually cooking with it sooner, saving time AND money. The only factor withholding them from mass production is the safety concern involving nanotubes and their unknown reactivity with foods and other biological materials.

Company representatives also believe that the same material have potential in improving efficiency of solar thermal power plants by applying “hairy” solar cells, or with “popcorn ball” dye-sensitized solar cells to increase light absorption.[6]

Figure 4. Magnified hairs on carbon nanotubes.

Molecular Bucky Structures?

Aside from the materials world, DNA nanotubes and synthetic nanostructures have much potential application into extremely microscopic electronic and biomedical innovations. A research group has revealed the 3D character of DNA nanotubules, rings and spirals, each a few hundred thousandths the diameter of a human hair! Their research is one step towards resolving the construction of molecular-level forms in three dimensions by using gold nanoparticles. “When placed on single-stranded DNA, these flexible molecular tile arrays bend away from the nanoparticles, curling into closed loops or forming spring-like spirals or nested rings, roughly 30 to 180 nanometers in diameter”.[7] For the very first time, DNA nanotubules can be specifically directed to curl into closed rings with high yield! It is utterly amazing how scientists can make strides on the molecular level as well!

Figure 5. Representation of carbon nanotubes transforming into DNA helical structures.

Video: http://www.youtube.com/watch?v=qJUaIIYN7y4&feature=related

“Smart” Bucky Materials

How can fullerenes be “smart”, you may ask? Italian and Swiss researchers have shown that carbon nanotubes show promise in the search to find ways to “bypass” faulty brain wiring. Neurons and carbon nanotubes surprisingly are both electrically conductive and form tight contacts with each other. Unlike the metal electrodes that are currently used in research and clinical applications, the nanotubes can create shortcuts between the distal and proximal compartments of the neuron, resulting in enhanced neuronal excitability. This result is extremely relevant for the emerging field of neuro-engineering and neuroprosthetics, because the nanotubes could be used as a new building block of novel “electrical bypass” systems for treating traumatic injury of the central nervous system. This new innovation offer an alternative to metal parts used for deep brain stimulation for patients with Parkinson’s disease or severe depression. Not only that, these whole new class of “smart” materials may be used in a wide range of potential neuroprosthetic applications! Before that happens though, a deeper understanding of neuromechanisms and their reactivity with carbon nanomaterials in the body is warranted.

Bucky’s Legacy

When Fuller commented that “it is highly feasible to care of all of humanity higher at a higher standard of living without having anyone profit at the expense of others so that everyone can enjoy the whole earth”, he was not joking.[8] Whether it be the “smart” brain material or the hairy teapots, they are all a testament to Bucky’s practical vision. Though in the experimental stage, these innovative materials, all originating with the buckminsterfullerne, continue to gather momentum. The chances of it losing popularity and importance will not die out anytime soon.


[2] “Dymaxion House.” http://en.wikipedia.org/wiki/Dymaxion_house. 23 January 2009.

[4] “FSU buckypaper research honored for nanotech innovation.” http://www.fsu.edu/news/2008/07/21/buckypaper.honored/. 20 November 2008.

[5] “On the Boil: New Nano Technique Significantly Boosts Boiling Efficiency.” http://news.rpi.edu/update.do?artcenterkey=2464. 19 January 2009.

[6] Richard, Michael. “Copper Nanorods Increase Boiling Water Bubbles 3,000%!” http://www.treehugger.com/files/2008/07/nanotechnology-copper-nanorods-water-boiling-faster-bubbles.php. 13 January 2009.

[8] Buckminster Fuller. http://tw.youtube.com/watch?v=v7OBTiyMoSE. 19 January 2009.

Feynman’s Legacy on Modern Nanotechnology

In his talk “Infinitesimal Machinery”, Richard Feynman discussed his rudimentary, yet plausible, vision of nanotechnology for the future. He discusses how to make nanomachines, how they could be used in computers and tools, and how to supply a driving force to move these nanomachines using electrostatic actuation and flagella like structures. Since Feynman believed that refined and grand objects could be made from crude and simple parts, he foresaw the creation of miniature manufacturing and computing systems. If these nanomachines were developed, which could theoretically build even smaller manufacturing systems, Feynman asserted that these nanoassemblers had the potential to build with atom-by-atom control. His ideas seemed farfetched at the time, yes. But it opened a door to a world of unlimited possibilities and one unanswered central question–how far can people go to arrange and rearrange atoms to create technological and biological objects exhibiting different properties? This area stimulated continues to be a subject of popular interest, heated debate, and misinterpretation.

Development of Feynman’s Vision

Feynman’s ideas spread like wildfire. In fact, shortly after giving his challenge to make a “motor measuring 1/64 of an inch on a side” (Feynman 5), someone by the name of McClellan actually successfully fulfilled the challenge. Not only did this show how much the scientific community respect him, but it suggested the feasibility of Feynman’s ideas, which employed mostly the bottom-up approach. This approach involves using the smallest components to create tiny objects. In the past, the top-down approach, involving the miniaturization of components used in the construction of working devices, was used extensively. However, because increasingly smaller pieces of solid equipment and parts became necessary for application, the method of bottom-up fabrication became increasingly more relevant, as we see products synthesized in the latter half of the twentieth century gradually using more nanotechnology.

Successful Realizations of Feynman’s Principles

microbrite2

As humans, we all need to use our teeth to chew and tear food, so we will often find food particles and films in and between our teeth, which may be detrimental to tooth enamel due to the acidic pH. I found the Nanoceuticals™ Microbrite Tooth Powder to be potentially beneficial, since “it consists of molecular cages, 1-5 nanometers in diameter, made from a silica-mineral hydride complex” (Microbrite). Besides teeth protection, the product also releases dietary supplements! Basically, this product is a two-in-one formula!

Similarly, the silver nanoparticle Fresh Box super airtight food storage containers preserves food longer so you throw away less. Due to the “naturally anti-fungal, anti-bacterial and anti-microbial properties of the finely dispersed nanosilver particles” within the containers, foods spoil less, which means that we can save money and conserve our resources.

62_-_car-wash1

G-WASH™ Heavy Duty Hydrophpobic Car Wash, a highly concentrated cleaner/degreaser which uses the power of nanotechnology, to clean cars brings very relevant applications to everyday usage. Formulated with “hydrophobic solution that causes water to bead up and roll off” and blend of natural plant based products, the car wash is not only waterless but ecofriendly, a plus for today’s increasingly greener world.


Additionally, I found the nanocomposite material on the General Motors® Automotive Exterior to be very applicable in that the exterior application adds more sturdiness to the vehicle. It is indeed very impressive to use nanofillers, with a “thickness of one-billionth of a metre or about 1/100,000 the width of a human hair” to provide stronger material. This is just one example of the potential of nanocomposite material.

Even more impressive is NutraLease, which uses “nano-capsules to enhance the biodelivery of nutrients” in Canola Active cooking oil, and has been shown to lead to up to a 14% reduction in LDL cholesterol levels. Now, that’s really something to reduce your risk of cardiovascular disease and increase absorption within the intestines.

Feynman’s Vision Obscured

cocochanel2

Feynman prompted us to imagine that if nanoscale robots could be created, then these nanomachines had the potential to assemble nanomachinery with atomic precision. From Feynman’s vision, nanotechnology held enormous potential, but, if misused, could open a Pandora’s box. Though his vision has produced positive results, his message has tempted specialists to reconstruct their nanoscale research under the title “nanotechnology”. Thus, we see products such as Chanel, created the Coco Mademoiselle Fresh Mist for women. Essentially, body mist can simply be sprayed on for moisturization and scent-enhancing purposes. However, I completely didn’t see why adding the prefix “nano” into their product description really made it a product of nanoscience.

hairiron2

Similarly, the fact that “nano-silver spray” covers the body of Nano Silver Hair Irons to make them look “more luxurious” does not seem to benefit any entity except perhaps appease the eyes.


washingsamsung2

Samsung Washing Machine jumps on the bandwagon as well, using “Silver nano wash that sterilizes your clothes”. This turns out to be just a chemical solution which has nothing to do with nanoscience at all.  These are all examples of marketing schemes, which employ the word or part of the word “nanotechnology” to simply promote their product in the public eye. These products were obviously conceived with an obscured vision of Feynman’s principles.

Feynman’s Legacy

Instead of focusing on the laboratory accomplishments of his day, Feynman conceived visions of miniature manufacturing systems, which motivated assemblers and molecular manufacturing. No wonder so many of my professors idolize Richard Feynman–he was an incredibly intelligent man with admirable visions for the world. It seems as if Richard Feynman extended his influence to not only physics and mathematics but also the field of nanotechnology, which has experienced only rapid development and expansion. If we use an analogy, Feynman basically wrote down a brief introduction and a few bullet points for nanotechnology and allowed future scientists to fill in the rest. Who knew that Feynman’s vision of miniaturizing objects would have such countless modern applications?