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Genetic algorithm discovered unusual pattern was best at trapping light

A common problem in the design of thin film solar cells is how to develop optical materials and nanopatterns for those materials.  The ultimate goal is to trap and capture as much solar energy as possible.  The problem is far too challenging for naive searches based solely on human creativity.  Thus artificial intelligence is increasingly being employed to search for the optimal cell materials and nanopatterns.

Northwestern University Mechanical Engineering Professor Wei Chen and her graduate student Cheng Sun have published a new paper on how genetic algorithms -- an artificial intelligence technique based on evolutionary biology -- can be used to develop high performance nano-patterns.

Much like evolution and genetic processes serve in the real world serve to select creatures giving rise to fit species like humans or drug-resistant bacteria, genetic algorithms weed out bad candidates, while preserving and mixing elements of the fittest performers.

Starting with dozens of random designs, Prof. Chen's team "bred" the nanopatterns through 20 generations, employing genetic algorithm techniques like mutation and crossover.  

The result was a strike nanopattern that outperformed other designs.
Nanopatterned thin fillm
The "fittest" pattern [Image Source: Northwestern University]

The optimized 100-nanometer-thick organic dielectric "scattering layer" appears superb in simulations at trapping photons and transmitting them into the active layer.  In fact, the simulation results predict that the layer will surpass three-fold the Yablonovitch Limit; a thermodynamic limit developed in the 1980s that statistically describes how long a photon can be trapped in a semiconductor.

Current organic solar cells have traditional been, in a word, bad.  While relatively cheap to produce compared to their rare-metal thin film counterparts, their low efficiencies make them a disappointing dead end.  But the new design is intriguing as it may boost organic thin film cells into a regime in which they would actually be cost effective -- perhaps more so than rare-metal designs.

Comments Prof. Chen, "Due to the highly nonlinear and irregular behavior of the system, you must use an intelligent approach to find the optimal solution.  Our approach is based on the biologically evolutionary process of survival of the fittest."

Northwestern Univ. is currently working with Argonne National Laboratory to produce a prototype of the nanopatterned cell, for real world testing.

In the mean time, the work has been published in the peer-reviewed journal Scientific Reports, a Nature journal.

Sources: Northwestern University, Scientific Reports

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RE: evolution
By drycrust3 on 1/29/2013 3:52:52 PM , Rating: 2
You're not trying to prove evolution wrong

The simple fact that the theory of Evolution is a theory means there is a general acceptance there is a margin of error within the tenants it proposes. The question, scientifically speaking, isn't "Is it right or wrong" but "How much error does it have?", or more precisely, "Is its margin of error large or small?". As far as I can tell every one of the major tenants the theory of Evolution proposes has been proven to be incorrect, (e.g. the theory says there should be more diversity now than in the past, but the fossil record proves beyond any doubt by a factor of 50 times that there was more diversity in the past than we now see), which means the theory of Evolution has a large margin of error.
Even if the margin of error was astronomically huge, that still doesn't mean the theory of Evolution is actually wrong, although it does mean it should have very little scientific credibility. The fact it does have credibility when it shouldn't within the scientific community is just a legacy of the past.

RE: evolution
By Bubbacub on 1/29/2013 4:48:12 PM , Rating: 2
gravity is just a theory (an incorrect one at that) - doesnt mean that things don't fall down if you drop them.

general relativity has superseded newtons theory of universal gravitation. we are picking holes in relativity (it doesnt make sense at a sub atomic scale) and eventually it will be superseded by a theory which describes reality even closer.

at no point however will an apple stop falling to the ground if you let it go.

this is exactly analogous to evolution. the theory may not be totally right. it is however much MORE right than what some middle eastern blokes randomly thought was a good idea 4000 years ago.

we may/will come to find a more accurate theory of how life developed on earth - it isn't however going to include noah's ark - that would be akin to dropping an apple and have it hover in mid air miraculously.

"I modded down, down, down, and the flames went higher." -- Sven Olsen

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