Caltech gurus whip up highly efficient, low cost flexible solar cell
By Darren Murph 
posted February 28th 2010 1:11AM
posted February 28th 2010 1:11AM
Solar cells are cute and all, but let's be real -- these things are far too inefficient for mainstream use. Scientists at the California Institute of Technology are working hard to remedy that very issue, and they've recently concocted a "new type of flexible solar cell that enhances the absorption of sunlight and efficiently converts its photons into electrons." The solution relies on arrays of long, thin silicon wires embedded onto a polymer substrate, which uses just a fraction of the expensive semiconductor materials required by conventional solar cells. According to professor Harry Atwater, these cells have "surpassed the conventional light-trapping limit for absorbing materials" for the first time, and we're told that the arrays can convert between 90 and 100 percent of the photons they absorb into electrons, and yes, that does mean that they have a near-perfect internal quantum efficiency. Hit the source link for all the technobabble, and cross your fingers for this stuff to get the honored approval of the Governator.
@andromeda05
85% (as per the source link), so we're talking 77-85% energy conversion here, which is fantastic.
@grobbo
Actually (see my earlier posts) it's 77-85% EQE, not energy conversion :(
Even if this technology was the second coming of jesus as they say, wouldn't it be stifled into obscurity by the powers that be?
A tear came down my eye when i read this.
@Atkins All ground breaking innovations are based on very simple ideas, but conceiving that idea is not simple.
What's the cost per watt ?
That's the only question that matters in terms of commercialization.
Boo -- sloppy science reporting :(
IQE < EQE and EQE != actual energy conversion efficiency.
Since sunlight is composed of a broad range of frequencies and this is a single bandgap device (just Si), you lose all above-bandgap energy to heat --> max efficiency of Si cell ~ 31%. Tandems, thermophotovoltaics, etc, are the ways you can break this limit and get into the 40% range or higher.
In fact, this isn't even a solar cell -- it's just intrinsic Si as far as I can tell -- no junction. It just shows how materials can be reduced to reproduce existing device efficiencies.
This is not to diminish their work at all, which is pretty sweet...
@pk000h
??
IQE is larger than EQE.
@grobbo
Sorry, you are right that the number for IQE will be larger than EQE. I meant to say that IQE is a measure of less photon absorption than EQE.
90% quantum efficiency is not as much as you would think, cause it is basically the efficiency if you light the solar cell with only the spectrum of light that it can use which is mainly ultra violet and small bandwidth. only a very small amount of the real sunlight is within that usable range so you would have to multiply the very small percentage of that light within sunlight times the 90% quantum efficiency to get somewhere near the usable efficiency. in fact even that would be a way to high estimate cause sunlight heats the black solar cells and heat reduces the efficiency also clouds often lead indirect lighting of the solar cell which also greatly reduces the efficiency.
by stating 90% quantum efficiency they sure generate some buzz out here but the truth is that number alone doesn't mean anything for the real world efficiency. i would be amazed if the real world efficiency of these cells is near 20% but i don't think that is the case.
Um. They're more efficient than a combustion engine.
@BigD145 Actually... NO!
@TRRosen Well, they are more efficient at converting solar energy to electricity than an internal combustion engine... :)
90-100%
Can you say "Holy Grail"?!?!
(not that I fully believe in overly optimistic claims such as that, but even if it's a fraction of that efficiency, it's still HUGE news)
@Atkins
Tee hee... Why I bother...
I think most people are missing the point. This isn't the magic cure to energy production. Something showing these kind of efficiencies, cheap to produce, and flexible - well that just means we have more options for solar enhancement of power systems. A flexible and inexpensive solar cell system could be applied all over things like electric vehicles, for example, to assist in recharging. As many mentioned, put them on the roofs of houses, and you have some basic power that might be able to assist in heating/cooling of a residence. Smaller variants for mobile electronics. It's the packaging and cost effectiveness that is the great news, particularly if they can accomplish similar (or better) performance to current solar energy options.
Let me remind you that converting 90-100% of photons does not equate any efficiency close to those numbers. All it means, is that it can theoretically get 90-100% close to the maximum theoretical efficiency of a SI based solar cell, which is 43.87%.
It's the cost which is great news here, there is no breakthrough in efficiency right here.
This isn't real is it? At 90-100% efficiency at direct sunlight batteries would charge at nearly the same rate as if you plugged them into an outlet. It's way too good to be true, it can't be real.
i think if you look at energy produced per unit area the bloom box would be a better option. I know many people from the green bandwagon are going to hate me for saying this but if you think about it solar is neither practicable nor affordable in terms of cost, land usage or large scale adoption. If bloom box aint a long term solution i would say it is atleast a short to medium term one.