Tuning bands of PbSe for better thermoelectric efficiency

Improving the thermoelectric performance of PbSe over its previously reported maximum zT can be achieved by engineering its electronic band structure. We demonstrate here, using optical absorption spectra, first principles calculations, and temperature dependent transport measurements, that alloying PbSe with SrSe leads to a dramatic change of the band structure that increases the thermoelectric figure of merit, zT. The temperature where the two valence bands converge decreases with Sr addition. The zT value, when the carrier density is optimized, increases with Sr addition in Pb1-xSrSe and when x = 0.08 a maximum zT of 1.5 at 900 K is achieved. The net benefit in zT comes from the band structure tuning even though in other thermoelectric solid solutions it is the thermal conductivity reduction from disorder that leads to net zT improvement.