Path to Better OLEDs, Organic Solar Cells Found

Orienting the structure of organic glasses could enhance organic solar cells and OLEDs

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Path to Better OLEDs, Organic Solar Cells Found
During the deposition of an organic semiconductor glass, a temperature-gradient was maintained across the length of a strip of silicon. Because the silicon temperature controls the molecular orientation in the glass, the material makes a range of colors. High temperature [left] made the molecules lie down in the plane of the substrate; low temperatures [right] made the molecules stand up.
Photo: Diane Walters/University of Wisconsin-Madison

Researchers say they might have a way to  significantly enhance the performance of  organic light-emitting diodes (OLEDs) and some kinds of solar cells. They’ve discovered how to precisely order the molecules that make up the organic glasses that serve as the active semiconductor components in these devices.

Glasses are solids that lack the regular order of crystals. The most familiar kind of glass is based on silica, but other kinds of glass exist as well, such as organic glasses based on carbon.

Although one might expect the disorderly structure of glasses to orient their molecules in no particular direction, recent studies have found that molecules in organic glasses can be oriented in specific ways. This orientation can improve the efficiency and lifetime of the devices they are used in.

Organic glasses are typically produced in vacuum chambers from vapors that condense in thin films on a substrate. Now researchers find the substrate temperature is the key factor behind controlling molecular orientation within those glasses.

Scientists at the University of Wisconsin-Madison and the University of Chicago investigated the effect of substrate temperature on glasses of three organic semiconductors often used in electronics. They found they could easily and routinely impose order on these organic glasses by controlling substrate temperature, and that all three molecules could produce glasses with high levels of molecular orientation. The molecular orientation that results in the glasses is a remnant of the molecular orientation present in a liquid layer that can form on the substrate.

The researchers suggest these findings could optimize the performance of nearly any device based on organic glasses. They detailed their findings online 23 March in the journal Proceedings of the National Academy of Sciences.

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