Smashing Photons: Changing the Color of Light Supercharges Solar Energy, 3D Printing, and Night Vision

Color plays a huge role in most of our lives. It signals danger or caution, like the patterns on a poisonous frog or the color of a stoplight. It evokes joy and inspiration through nature, art, and fashion. It can even trigger the recollection of a favorite memory, through pictures of family and friends. ¶ In the technical world, the color of light is no less important. It affects the efficiency of solar cells, how far we can see inside our bodies, and the speed of 3D printing. ¶ But light can be useful only if you can actually get it where it needs to go; many materials will absorb or scatter the light long before it can reach its intended destination. ¶ We in the Congreve Lab at Stanford University became interested in changing the color of light for exactly this reason: It can help us get the right kind of light to the right place. ¶ Initially, we focused on developing color-changing technology for use in solar energy, where its usefulness is obvious. Photovoltaic cells harvest energy from only a limited range of energies—that is, colors. That range differs depending on the material used to produce the solar cell, but it's always limited. One approach to improving solar-cell efficiency has been to produce cells with multiple layers tuned to different energy levels. But there is another way to think about it: It could be simpler and more efficient to change the light to fit the cell.