"We have used our patterning methods to modify the geometry of interfaces in plastic solar cells for light-trapping purposes," Olle Inganäs of Linköping University told nanotechweb.org. "We can enhance quantum efficiencies significantly by introducing these geometrical disturbances. We also use this patterning to enhance light outcoupling from luminescent polymer films."
The scientists made nanowires from the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate). PEDOT-PSS, as the material is known for short, is often used as a metal substitute in polymer electronics devices.
In the first stage of the process, the researchers made stamps by casting an elastomer onto diffraction gratings with lines at a spacing of either 1200 or 3600 lines/mm. Then they placed the stamp onto the wafer surface and added a drop of the polymer in aqueous solution. The polymer solution migrated into the stamp's capillaries and, after time for the polymer to dry out, removal of the stamp exposed polymer nanowires with a repeat period of 833 or 278 nm. Inganäs and colleagues are confident that using a smaller template and a different elastomer to fabricate the stamp could produce nanowires of less than 100 nm wide.
The nanowires made with the 3600 lines/mm stamp were roughly 25 nm high, while the nanowires resulting from the 1200 lines/mm grating were 70 nm high. To create shallower nanowires, the researchers placed a weight on top of the stamp and also diluted the polymer solution. This decreased the height of the nanowires from the 1200 lines/mm stamp to around 6 nm.
The team also made nanowires from the semiconducting, fusible polymer POMeOPT by soft-embossing. They spin-coated the polymer onto a substrate, placed an elastomer stamp on top of it and heated the film until the polymer was able to flow. After cooling and removal off the stamp, the result was a nanowire structure. By repeating the process with the stamp rotated through 90° the scientists made nanodots measuring 10 nm high and 278 nm square.
The researchers reported their work in Nano Letters.