Solar Heat To Electric Power Generation
Heat produced by infrared photons emitted by the sun is currently not harvested and represents lost energy. Additionally, heat from car braking and the engine is not being efficiently utilized. Thermoelectric materials provide a way to directly convert heat to electrical power, but currently this conversion process is inefficient. Researchers in the CfSE are looking at new thermoelectric materials as well as doing fundamental studies on the thermoelectric properties of these materials.
Nanowire Thermoelectric Materials
The figure-of-merit for state-of-the-art thermoelectric materials, ZT, has been stuck at 1.0 - 1.2 since the discovery of Bi2Te3 fifty years ago. According to theory, nanowires may exhibit ZT values considerably larger than 1.0. However, few experimental measurements of ZT for nanowires have been reported, due to the difficulty of the measurements. One experimental problem is that nanowires must be extremely long in addition to having nanoscopic width to be made into a device and have good thermoelectric properties, respectively.
A schematic of a nanowire thermoelectric device utilizing wasted solar heat.
Stoichiometric and single-phase lead telluride (PbTe) nanowire arrays have been prepared using a new method, photoresist-bottomed lithographically patterned nanowire electrodeposition (PB-LPNE). PB-LPNE provides for control over wire width and thickness, photolithographic patterning, and the suspension of nanowires across 25-micrometer air gaps separating photoresist supports. The resulting nanowire-substrate system provides new opportunities for the investigation of optical, electrical, and thermoelectric properties.
Electron microscopy images of air-suspended PbTe nanowires. The air gap between the PbTe nanowires and the glass surface is 2 micrometers. PR stands for photoresist.