Organic solar cells may be a better solution. These polymer solar
cells use organic materials to absorb light and convert it into
electricity but current designs have poor electrical properties. Instead
of attempting to increase efficiency by altering the thickness of the
solar cell's polymer layer, a tactic that has preciously garnered mixed
results, researchers at Northwestern University sought to design the
geometric pattern of the scattering layer to maximize the amount of time
light remained trapped within the cell - all by using a mathematical
search algorithm based on evolution.
The algorithm pinpointed a specific geometrical pattern that is optimal
for capturing and holding light in thin-cell organic solar cells,
resulting design exhibited a three-fold increase over the Yablonovitch
Limit, a thermodynamic limit developed in the 1980s that statistically
describes how long a photon can be trapped in a semiconductor.
The resulting pattern will be fabricated with partners at Argonne National Laboratory.
In their newly organic solar cell, light enters a 100-nanometer-thick
scattering layer, a geometrically-patterned dielectric layer designed
to maximize the amount of light transmitted into the cell. The light is
then transmitted to the active layer, where it is converted into
electricity.
"We wanted to determine the geometry for the scattering layer that
would give us optimal performance," said Cheng Sun, assistant professor
of mechanical engineering at Northwestern and co-author of the paper.
"But with so many possibilities, it's difficult to know where to start,
so we looked to laws of natural selection to guide us."
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