Enhancement of thermoelectric performance of n-Type PbSe by Cr doping with optimized carrier concentration

Ti, V, Cr, Nb, and Mo are found to be effective at increasing the Seebeck coefficient and power factor of n-type PbSe at temperatures below 600 K. It is found that the higher Seebeck coefficients and power factors are due to higher Hall mobility ≈1000 cm² V^-1s^-1 at lower carrier concentration. A larger average ZT value (relevant for applications) can be obtained by an optimization of carrier concentration to ≈10¹⁸-10¹⁹ cm^-3. Even though the highest room temperature power factor ≈3.3 × 10^-3 W m^-1 K^-2 is found in 1 at% Mo-doped PbSe, the highest ZT is achieved in Cr-doped PbSe. Combined with the lower thermal conductivity, ZT is improved to ≈0.4 at room temperature and peak ZTs of ≈1.0 are observed at ≈573 K for Pb_0.9925Cr_0.0075Se and ≈673 K for Pb_0.995Cr_0.005Se. The calculated device efficiency of Pb_0.995Cr_0.005Se is as high as ≈12.5% with cold side 300 K and hot side 873 K, higher than those of all the n-type PbSe materials reported in the literature. Transition metals (Ti, V, Cr, Nb, and Mo) are used as donors in PbSe to increase the average ZT of n-type PbSe. A larger average ZT value can be obtained by an optimization of carrier concentration to ≈10¹⁸-10¹⁹ cm^-3. The calculated device efficiency of Pb_0.995Cr_0.005Se is as high as ≈12.5% with cold side 300 K and hot side 873 K.