Transparent conductive material could lead to power-generating windows

Nov 03, 2010
Top: Scanning electron microscopy image and zoom of conjugated polymer (PPV) honeycomb. Bottom (left-to-right): Confocal fluorescence lifetime images of conjugated honeycomb, of polymer/fullerene honeycomb double layer and of polymer/fullerene honeycomb blend. Efficient charge transfer within the whole framework is observed in the case of polymer/fullerene honeycomb blend as a dramatic reduction in the fluorescence lifetime.

(PhysOrg.com) -- Scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Los Alamos National Laboratory have fabricated transparent thin films capable of absorbing light and generating electric charge over a relatively large area. The material, described in the journal Chemistry of Materials, could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity.

The material consists of a semiconducting polymer doped with carbon-rich fullerenes. Under carefully controlled conditions, the material self-assembles to form a reproducible pattern of micron-size hexagon-shaped cells over a relatively large area (up to several millimeters).

"Though such honeycomb-patterned thin films have previously been made using conventional polymers like , this is the first report of such a material that blends semiconductors and to absorb light and efficiently generate charge and ," said lead scientist Mircea Cotlet, a physical chemist at Brookhaven's Center for Functional .

Furthermore, the material remains largely transparent because the pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers. "The densely packed edges strongly absorb light and may also facilitate conducting electricity," Cotlet explained, "while the centers do not absorb much light and are relatively transparent."

"Combining these traits and achieving large-scale patterning could enable a wide range of practical applications, such as energy-generating solar windows, transparent , and new kinds of optical displays," said co-author Zhihua Xu, a materials scientist at the CFN.

"Imagine a house with windows made of this kind of material, which, combined with a solar roof, would cut its electricity costs significantly. This is pretty exciting," Cotlet said.

The scientists fabricated the honeycomb thin films by creating a flow of micrometer-size water droplets across a thin layer of the polymer/fullerene blend solution. These water droplets self-assembled into large arrays within the polymer solution. As the solvent completely evaporates, the polymer forms a hexagonal honeycomb pattern over a large area.

"This is a cost-effective method, with potential to be scaled up from the laboratory to industrial-scale production," Xu said.

The scientists verified the uniformity of the with various scanning probe and electron microscopy techniques, and tested the optical properties and charge generation at various parts of the honeycomb structure (edges, centers, and nodes where individual cells connect) using time-resolved confocal fluorescence microscopy.

The scientists also found that the degree of polymer packing was determined by the rate of solvent evaporation, which in turn determines the rate of charge transport through the material.

"The slower the solvent evaporates, the more tightly packed the polymer, and the better the charge transport," Cotlet said.

"Our work provides a deeper understanding of the optical properties of the honeycomb structure. The next step will be to use these honeycomb to fabricate transparent and flexible organic solar cells and other devices," he said.

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More information: Structural dynamics and charge transfer via complexation with fullerene in large area conjugated polymer honeycomb thin films: pubs.acs.org/doi/full/10.1021/cm102160m

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User comments : 4

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danman5000
not rated yet Nov 03, 2010
I guess I can see some possibilities for a transparent solar cell, but it sort of defeats the purpose doesn't it? A solar cell that's designed to let the majority of light pass through? That's inherently very inefficient. An ideal solar cell would be perfectly black, and should reside on the roof where it could get the maximum exposure to light.
Silverhill
4 / 5 (1) Nov 03, 2010
It may not be *designed* to let the majority of light through; it may simply be unable to absorb a majority of the light. What does not get absorbed can then be used for simple illumination -- or, maybe, passed through to a more-fully-absorbing solar cell?
CSharpner
not rated yet Nov 03, 2010
Seems like this might be a potential solution to the looming ITO shortage for toychscreens:

http://www.scienc...shortage
PinkElephant
4 / 5 (1) Nov 04, 2010
A solar cell that's designed to let the majority of light pass through?
It would make more sense to tune the solar cell, so that it passes visible light through while trapping and converting infrared light to electricity. This would work well on windows, since (particularly for the double-paned variety) they already just reflect infrared light back out like a mirror. Why waste something you could use?

But I think the main issue with organic solar cells is going to be UV exposure. Most organics decay under persistent UV. One way around this, would be to make windows from UV-blocking glass, and put the organic solar cell layer on the interior side of the window pane...