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Nano-sandwich material claimed to boost solar cell efficiency by 175 percent


December 7, 2012

The nanoscale metal mesh that makes up the top layer of the sandwich-like PlaCSH material

The nanoscale metal mesh that makes up the top layer of the sandwich-like PlaCSH material

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One of the main reasons that solar cells aren’t more efficient at converting sunlight into electricity is because much of that sunlight is reflected off the cell, or can’t be fully absorbed by it. A new sandwich-like material created by researchers at Princeton University, however, is claimed to dramatically address that problem – by minimizing reflection and increasing absorption, it reportedly boosts the efficiency of organic solar cells by 175 percent.

Developed by a team led by electrical engineer Prof. Stephen Chou, the material is known as a “plasmonic cavity with subwavelength hole array” or PlaCSH.

It consists of five very thin layers. On top is the “window layer” through which the sunlight first passes. It’s made from an extremely fine metal mesh, the diameter and spacing of its holes being measured in nanometers. Next is a layer of transparent plastic, followed by a layer of semiconductive material – although Chou used a plastic semiconductor, other materials could be used. This is followed by a layer of titanium oxide, with a layer of aluminum sitting at the bottom of the stack.

The five layers of the PlaCSH material

The combined thickness of all five layers is just 230 nanometers. This distance, along with the spacing and diameter of the holes in the mesh, is shorter than the wavelength of the sunlight itself. According to Chou, it is this property that allows only four percent of the light to be reflected, and up to 96 percent to be absorbed.

When it comes to converting direct sunlight into electricity, this translates into a 52 percent increase in efficiency over conventional organic solar cells. PlaCSH is also superior at capturing sunlight coming at steep angles, however. This ups its efficiency by an additional 81 percent, which when combined with other factors brings the total percentage of improvement to 175.

A comparison of sunlight reflected off a conventional organic solar cell and one using Pla...

A comparison of sunlight reflected off a conventional organic solar cell and one using PlaCSH

PlaCSH could reportedly be cost-effectively manufactured in large sheets. Besides providing greater efficiency, the material could also replace the costly indium-tin-oxide (ITO) electrodes in conventional organic solar cells, bringing their price down. As PlaCSH is more flexible than ITO, it should also make the cells less fragile.

Although Chou’s research regarding the use of PlaCSH in inorganic solar cells is not yet complete, he believes that the material should also allow them to achieve much greater efficiency. Additionally, because it could supposedly reduce the thickness of the silicon semiconductor in such cells by a thousand-fold, it should make them cheaper and more flexible.

A paper on the research was recently published in the journal Optics Express.

Source: Princeton University

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth

This sounds great, but the material will surely have to be protected under some sort of glazing, no? I sure wouldn't want to just stick that super thin gold mesh and titanium and all that out in the elements without protection. So you're back to losing a percentage to reflection.

Kim Holder
7th December, 2012 @ 04:41 pm PST

175% of what? Organic solar cells can be anywhere from under 4% to just around 10% conversion efficiency.

What is the actual relevant energy conversion efficiency including improvements?

My guess would be they are still not past good amorphous cells, nowadays approaching 20 % in the lab. (20% meaning 1000 Watts going in per square meter as sunlight, becoming 200 Watts coming out as electricity).

7th December, 2012 @ 06:09 pm PST

Naturally, this will all hinge on their ability to get manufacturing done cheaply and on a large scale.

Joel Detrow
7th December, 2012 @ 10:00 pm PST

the only reason 'organic' is good is because it's supposedly cheaper than processed silicon.

adding gold into the design defeats the purporse. organic solar cells ...keep on working on it. good luck. i feel like i'm watching a repeat of the process in the early 1910's where the first electric cars were still trying to catch up to the internal combustion engine and within a few years, they all just died off and the ice just became the only story in town.

the 'organic' solar cell is the early electric car. maybe in 80 years time there will be a ressurgence in this tech. when we have a silicon shortage of course. as if that could happen

8th December, 2012 @ 09:36 am PST

Its all about storage..... No matter how much you produce, you need to store it (energy). Without a breakthrough in storage everything else is academic.

S Michael
8th December, 2012 @ 09:26 pm PST

I hope Gizmag is capable of more by doing a better job at answering the obvious questions. Not to take anything away from the researchers in this work, but 175% improvement over what, and what coating is needed should have at least some precursory answers. Better grounding will improve Gizmag's perception tremendously. Many postings beg such obvious questions.

10th December, 2012 @ 03:13 am PST

Even at today's prices it would be less than $2 for the gold mesh used in a square meter. That's assuming the mesh surface is 95% holes and 5% gold . The cost of the gold certainly would not hurt the cost ratio since you'd only have to make about 60% of this new material to equal the output of normal organic cells.

10th December, 2012 @ 09:06 am PST

I think it was developed by Chou Lab at Princeton. They are saying it is ready to be worked into a production system. That is a process that will take time, not forgetting the major decision of who will get production rights and contracts.

Mary Alice Tanner
10th December, 2012 @ 12:27 pm PST

"Even at today's prices it would be less than $2 for the gold mesh used in a square meter. That's assuming the mesh surface is 95% holes and 5% gold "

Judging by visual aids, and the printed word, I would say that ratio would much closer to 50/50.

So add in a cost (by your numbers) of $40, not $2.

11th December, 2012 @ 04:28 pm PST
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