Several developments in polymers and polymer blends are underway across the globe to make solar cells lighter, more flexible, more efficient. Current commercially produced solar panels use silicon cells to efficiently convert sunlight to energy. But silicon panels are too heavy to be used in energy-producing coatings for buildings and cars, or for flexible and portable power supplies for use in remote areas. Polymer cells are better suited to these potential uses.
A University of Cincinnati research partnership is reporting advances on how to make solar cells stronger, lighter, more flexible and less expensive when compared with the current silicon or germanium technology on the market. Yan Jin, a UC doctoral student in the materials science and engineering program, Department of Biomedical, Chemical, and Environmental Engineering reported results. A blend of conjugated polymers resulted in structural and electronic changes that increased efficiency three-fold, by incorporating pristine graphene into the active layer of the carbon-based materials. The technique resulted in better charge transport, short-circuit current and a more than 200% improvement in the efficiency of the devices. “We investigated the morphological changes underlying this effect by using small-angle neutron scattering (SANS) studies of the deuterated-P3HT/F8BT with and without graphene,” says Jin. The partnership with the Oak Ridge National Laboratory, U.S. Department of Energy, is exploring how to improve the performance of carbon-based synthetic polymers, with the ultimate goal of making them commercially competitive.
A new antireflective coating inspired by the compound lenses in moth eyes could help boost the efficiency of solar cells and sharpen the view of image sensors. Using a simple method to stamp patterned lenses over large areas, researchers in Singapore have come up with a process that could make manufacturing such coatings easier, as per cens.acs.org. Antireflective coatings help solar cells collect as much of the sun’s light as possible, boosting the power output. But typically, these thin-film coatings work best at preventing the reflection of a specific wavelength of light, hitting perpendicular to the surface. They don’t catch light of different wavelengths, coming in at other angles. Layering films of different materials of varying thicknesses yields more absorptive coatings, but that approach is expensive and difficult to do over large areas. Nature provides an alternative design strategy for an affordable, broadband antireflective coating. Nocturnal moths navigate under the dim light of the moon and stars thanks to eyes made of arrays of microsized lenses called ommatidia, which are further patterned with dome-shaped nanostructures. This hierarchical design reduces reflection and also prevents water from beading up on the creatures’ eyes. But re-creating such a design in the lab, by using moth eyes as tiny stamps or by plasma etching, has proved laborious. To solve this problem, Raut and Mohammad S. M. Saifullah of the Agency for Science, Technology & Research, Singapore, turned to nano imprint lithography, a method for stamping high-resolution, nanoscale patterns over large areas. To create a reusable stamp, the two first made two sets of nickel molds, one patterned with 200-nm-diameter domes and one with micro lenses 2 to 25 μm in diameter. The researchers then used these molds to pattern films of polycarbonate. First they stamped the nano domes and protected that pattern by spinning a thin coating of a sacrificial polymer on top. Afterwards, they stamped the larger micro lenses. Finally, they washed away the sacrificial polymer, leaving a polycarbonate micro lens array. The researchers then tested the moth-inspired arrays, comparing them with micro lens arrays without the nano domes, to see how much light they reflected. From 400 to 1,000 nm in wavelength, the moth-inspired arrays reflected just 4.8% of light, compared with 8.7% reflected by the simple micro lenses. When they varied the incident angle of the light, the nano dome-decorated arrays continued to perform about twice as well. The nano domes also repelled water, which could help keep solar cells clean. The antireflective coatings perform impressively, says Jiang, who is also making bioinspired antireflective coatings. The group now needs to demonstrate that these methods can scale up to make coatings square meters in size.