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Researchers at the University of Michigan and the Chinese Academy of Science have developed a new kind of screen pixel that doubles as a solar cell and could boost the energy efficiency of cell phones and e-readers.

When you look at a traditional LCD, less than 8% of the backlight actually reaches your eyes. Color filters and polarizers absorb theReflective photovoltaic color filter devices are essentially colored solar panels that serve as energy-harvesting screen pixels. They could boost the efficiency of display screens and lead to decorative solar panels or energy-efficient billboards.Reflective photovoltaic color filter devices are essentially colored solar panels that serve as energy-harvesting screen pixels.Credit: Jay Guo. rest of the light. "This absorbed light is totally wasted," says Jay Guo, who led the researchers. "It becomes heat. You can feel it if you put your hand close to a monitor. Why not try to harvest some of this energy?"

The researchers developed a reflective photovoltaic color filter device that converts absorbed light to electricity. Reflective color filters produce visible color by absorbing certain wavelengths of light and reflecting, which is similar to the way that paint produces color. The researchers constructed filters for producing cyan, magenta, and yellow.

To make the new filters, the researchers added organic semiconductor solar cells to an ultra-thin color filter. It had conjugated polymer layers of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM) that were sandwiched by a gold nanograting layer and a continuous thick aluminum film. The nanogratings were typically 40 nm thick, and the PEDOT:PSS layer 30 nm thick.

The nanogratings acted as resonators, trapping and reflecting light of a particular color, depending on the space between the slits. The nanogratings also functioned as semitransparent anodes for organic photovoltaics. The PEDOT:PSS layer acted a the hole-transporting layer for the organic photovoltaic, and the P3HT and PCBM made a high-performance bulk-heterojunction (BHJ) photoactive layer that converted the absorbed light to a photocurrent.

The resulting filter converts about 2% of light that would otherwise be wasted to power. This could add up to a significant amount in small electronics, Guo says. Because it is only 200 nm thick 100 times thinner than traditional colorant-based filters it could be attractive for use in future ultrathin colored display devices. This technology also has the potential to be scaled up for use in energy-harvesting billboards or decorative solar panels.

The researchers are continuing to study these dual-function devices, and the University of Michigan is pursuing patent protection for the intellectual property.

Research Paper: Photonic Color Filters Integrated with Organic Solar Cells for Energy Harvesting, ACS Nano,2011, 5 (9), pp 70557060, DOI: 10.1021/nn201767e.

Written by Nancy Lamontagne, Contributing Editor - US, Solar Novus Today

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