Artificial light-harvesting method achieves 100% energy transfer efficiency

Sep 01, 2011 by Lisa Zyga feature
By arranging porphyrin dye molecules on a clay surface using the “Size-Matching Effect,” researchers have demonstrated an energy transfer efficiency of approximately 100%, which is an important requirement for designing efficient artificial light-harvesting systems. Image credit: Ishida, et al. ©2011 American Chemical Society

(PhysOrg.com) -- In an attempt to mimic the photosynthetic systems found in plants and some bacteria, scientists have taken a step toward developing an artificial light-harvesting system (LHS) that meets one of the crucial requirements for such systems: an approximately 100% energy transfer efficiency. Although high energy transfer efficiency is just one component of the development of a useful artificial LHS, the achievement could lead to clean solar-fuel technology that turns sunlight into chemical fuel.

The researchers, led by Shinsuke Takagi from the Tokyo Metropolitan University and PRESTO of the Japan Science and Technology Agency, have published their study on their work toward an artificial LHS in a recent issue of the .

“In order to realize an artificial light-harvesting system, almost 100% efficiency is necessary,” Takagi told PhysOrg.com. “Since light-harvesting systems consist of many steps of , the total energy transfer efficiency becomes low if the energy transfer efficiency of each step is 90%. For example, if there are five energy transfer steps, the total energy transfer is 0.9 x 0.9 x 0.9 x 0.9 x 0.9 = 0.59. In this way, an efficient energy transfer reaction plays an important role in realizing efficient sunlight collection for an artificial light-harvesting system.”

As the researchers explain in their study, a natural LHS (like those in purple or plant leaves) is composed of regularly arranged molecules that efficiently collect sunlight and carry the excitation energy to the system’s reaction center. An artificial LHS (or “artificial leaf”) attempts to do the same thing by using functional dye molecules.

Building on the results of previous research, the scientists chose to use two types of porphyrin dye molecules for this purpose, which they arranged on a clay surface. The molecules’ tendency to aggregate or segregate on the clay surface made it challenging for the researchers to arrange the molecules in a regular pattern like their natural counterparts.

“A molecular arrangement with an appropriate intermolecular distance is important to achieve nearly 100% energy transfer efficiency,” Takagi said. “If the intermolecular distance is too near, other reactions such as electron transfer and/or photochemical reactions would occur. If the intermolecular distance is too far, deactivation of excited dye surpasses the energy transfer reaction.”

In order to achieve the appropriate intermolecular distance, the scientists developed a novel preparation technique based on matching the distances between the charged sites in the porphyrin molecules and the distances between negatively charged (anionic) sites on the clay surface. This effect, which the researchers call the “Size-Matching Rule,” helped to suppress the major factors that contributed to the porphyrin molecules’ tendency to aggregate or segregate, and fixed the molecules in an appropriate uniform intermolecular distance. As Takagi explained, this strategy is significantly different than other attempts at achieving molecular patterns.

“The methodology is unique,” he said. “In the case of usual self-assembly systems, the arrangement is realized by guest-guest interactions. In our system, host-guest interactions play a crucial role for realizing the special arrangement of dyes. Thus, by changing the host material, it is possible to control the molecular arrangement of dyes on the clay surface.”

As the researchers demonstrated, the regular arrangement of the molecules leads to an excited energy of up to 100%. The results indicate that porphyrin dye and clay host materials look like promising candidates for an artificial LHS.

“At the present, our system includes only two dyes,” Takagi said. “As the next step, the combination of several dyes to adsorb all sunlight is necessary. One of the characteristic points of our system is that it is easy to use several dyes at once. Thus, our system is a promising candidate for a real light-harvesting system that can use all . We believe that even photochemical reaction parts can be combined on the same clay surface. If this system is realized and is combined with a photochemical reaction center, this system can be called an ‘inorganic leaf.’”

Explore further: New startup will develop non-stick surfaces for broad range of industrial applications

More information: Yohei Ishida, et al. “Efficient Excited Energy Transfer Reaction in Clay/Porphyrin Complex toward an Artificial Light-Harvesting System.” Journal of the American Chemical Society. DOI:10/1021/ja204425u

4.8 /5 (45 votes)

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NotAsleep
3 / 5 (2) Sep 01, 2011
Am I correct in assuming they're trying to design a perfect blackbody? The article doesn't specify how they're measuring energy transfer efficiency and I can't access the original article ($$$)

I'm sure they're designing this with the actual energy transfer portion in mind... but the article isn't that exciting without noting it
TAz00
4 / 5 (4) Sep 01, 2011
Also, i'd be happy with 90% of free energy
axemaster
not rated yet Sep 01, 2011
The article doesn't say much, but I'd expect they are using lattice vibration to transfer the energy.
NotAsleep
5 / 5 (13) Sep 01, 2011
They drew a picture and labeled it "100% energy transfer". I tried that on a test before... it's apparently not enough proof to get the question correct
GSwift7
4.2 / 5 (5) Sep 01, 2011
Cool stuff, but the following is a poor choice of words:

If this system is realized and is combined with a photochemical reaction center, this system can be called an inorganic leaf.


I seriously hope that phrase doesn't stick. Porphyrin is an organic dye. Maybe 'synthetic leaf'? 'Semi-organic leaf'? Without the organic dye it's just a sun-shade.
El_Nose
5 / 5 (1) Sep 01, 2011
not a blackbody at all --- this merely states that whatever energy is captured can be transferred - distinctly different from capturing all energy.
NotAsleep
not rated yet Sep 01, 2011
not a blackbody at all --- this merely states that whatever energy is captured can be transferred - distinctly different from capturing all energy.


But their end goal is to capture all light...
DoubleD
2.5 / 5 (8) Sep 01, 2011
they cant capture 100% of the light... the thing would be invisible if it didnt reflect anything. i believe that the goal is to keep 100% of the energy harvested, not harvest 100% of the energy.
Javinator
5 / 5 (12) Sep 01, 2011
they cant capture 100% of the light... the thing would be invisible if it didnt reflect anything.


If it didn't reflect anything it would be black. It would be invisible if light were bent around it.
kaypee
not rated yet Sep 01, 2011
1. If the energy just turns into heat -- via non-coherent lattice vibrations, then I'm doing nearly as well with a cup of coffee.
2. I presume there's some kind of anti-reflection coating on the coated substrate?
SteveL
5 / 5 (1) Sep 01, 2011
What I thought was strange: "In an attempt to mimic the photosynthetic systems found in plants and some bacteria, scientists have taken a step toward developing an artificial light-harvesting system (LHS) that meets one of the crucial requirements for such systems: an approximately 100% energy transfer efficiency."

If they are trying to "mimic" photosynthetic systems, they have set the bar rather low as there are large swaths of the spectrum that are not used photosynthetically. Mainly the greens.

I don't see any use for this other than solar-thermal, which in my opinion at least shows more promise than PV systems.
Eikka
5 / 5 (5) Sep 01, 2011

I don't see any use for this other than solar-thermal, which in my opinion at least shows more promise than PV systems.


But least in the fact that you then have to turn the heat into electricity or chemical reactions.

What they're doing here is a part of the photosynthesis machinery that transfers energy from the point where the photon hits the leaf to the nearest point where the photosynthesis actually happens.

They could use it to directly synthesize fuels for example, because the energy is in the form of excitation states of the dyes, which can then drive chemical reactions. It's a less of a brute force method than driving the reactions via electrolysis or just plain heat and hoping that the pieces fall into place.

It's like they made a rain catcher for energy, except it doesn't come with holes.
GSwift7
3.7 / 5 (3) Sep 01, 2011
I agree with Eikka. That's a very usefull analogy to describe what they are attmepting. What they are doing could eventually store the energy in a portable and very useful chemical form. It's kida like charging a rechargeable battery. You could produce methane, ethane, starches and sugars, alcohol, etc. depending on the exact setup. It could be very useful for a number of reasons. Dense liquid fuel is prefered for transportation needs right now, since batteries aren't quite up to par yet.

The one doubt I would have right now, is that it looks like it might be a lot simpler to use something like algea and end up with better results in a shorter time. I heard yesterday that the Pentagon is backing research into algea fuel production and they expect it to really gain momentum as the economy of scale comes into play. Gotta love the Pentagon sometimes. Say thanks for cell phones and the internet, for example. If not for them it would have taken forever to get funding for early adoption.
Kedas
1 / 5 (1) Sep 02, 2011
they cant capture 100% of the light... the thing would be invisible if it didnt reflect anything.


If it didn't reflect anything it would be black. It would be invisible if light were bent around it.

Not reflecting can mean passing through (glass) or absorbing (black)
So you are both right and wrong.

SteveL
5 / 5 (5) Sep 02, 2011
@kevintrs: Evolution is not god, nor is science. That's just your perception from your frame of reference. Evolution just is. It's a fact and it explains what has happened, what is happening and what will continue to happen. Using your frame of reference: if you can't comprehend his distinction we can't "save" you.
Javinator
5 / 5 (1) Sep 02, 2011
Not reflecting can mean passing through (glass) or absorbing (black)
So you are both right and wrong.


Fair enough. The person I was responding to was referring to capturing (ie. abosrbing) light so I'd assume he was talking about the second option.
MorituriMax
not rated yet Sep 02, 2011
Also, i'd be happy with 90% of free energy

I think with operation, maintenance and upkeep costs it would be better to have as close to 100% as possible.
wwqq
5 / 5 (1) Sep 03, 2011
Also, i'd be happy with 90% of free energy


You'd be lucky to get a percent or two of the incident energy by mimicking ridiculously inefficient photosynthesis.
KomMaelstrom
5 / 5 (1) Sep 03, 2011
itt: trolls.
GSwift7
3.7 / 5 (3) Sep 06, 2011
Also, i'd be happy with 90% of free energy

I think with operation, maintenance and upkeep costs it would be better to have as close to 100% as possible


This article isn't saing that they are nearly capturing 100% of the sun's energy. They are capturing around 5-10% and transfering nearly 100% of that to the chemical process that follows. The collection efficiency is not same as the transfer efficiency. Those are two seperate terms. They are talking about getting near to the theoretical limit on efficiency in one part of the process. Collection is one part of the process, transfer is another. They are not talking about collection efficiency here. Read carefully and learn.
aroc91
not rated yet Sep 06, 2011
Believing in evolution is a devotion to a religion which one has to dogmatically defend since it's asserting facts without true knowledge.


Again, kevin. TOO OBVIOUS
vidyunmaya
1 / 5 (2) Sep 07, 2011
Sub:Catch-up flow concepts-Nature Provides-Cosmology Vedas Leads.
A four-flow mode is photographed and from-Earth-Sun -Life Support links .Light-Flow strikes van-Allen belts as well. This is enlightened Spirit -for evolution to catch-up beyond Darwin concepts -to creation. This a reality.
Search Cosmology vedas interlinks-Books-Vidyardhi nanduri

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