Turning Heat Into Electricity

A new thin-film device turns an annoying optical effect into a means to convert infrared radiation directly into electricity (Nano Lett., DOI: 10.1021/nl203196z). Researchers hope it will lead to inexpensive, flexible films that could recoup wasted energy when wrapped around hot machines. The hotter an object is, the more infrared radiation it produces. The device relies on waves called plasmons, which are created when photons strike a metal surface. Plasmons decay quickly and transfer their energy to electrons in the metal. Normally, this decay process is a nuisance for optics researchers. But Nicholas Melosh of Stanford University decided to harvest the resulting high-energy electrons with a simple device consisting of two thin-film metal electrodes sandwiching an insulating layer. After a plasmon decays in the top electrode, the resulting excited electrons jump across the insulating layer to the other electrode, generating a current. Although the device’s efficiency is now only 1%, Melosh thinks that it would need to reach only 4 to 5% efficiency to be practical.