Rationally optimized carrier effective mass and carrier density leads to high average ZT value in n-type PbSe

Abstract

Among the intricately coupled thermoelectric parameters, carrier effective mass (m*) and carrier density (n) are two key parameters to determine the electrical transport properties. To enhance the broad-temperature thermoelectric performance in n-type PbSe, this work elaborately optimizes its power factor with the intrinsically proportional relationship between carrier effective mass and carrier density, n ∼ (m*)^3/2. Herein, the carrier effective mass in n-type PbSe is first optimized with Sn alloying and undergoes a decrease from ∼0.34m_e in PbSe to ∼0.25m_e in Pb_0.77Sn_0.23Se because of band sharpening. This reduced carrier effective mass contributes to an obvious enhancement of carrier mobility, thereby boosting the maximum power factor from ∼16.8 μW cm⁻¹ K⁻² in PbSe to ∼20.5 μW cm⁻¹ K⁻² in Pb_0.85Sn_0.15Se. Moreover, to match the reduced carrier effective mass in n-type Pb_0.85Sn_0.15Se, its carrier density is well tuned with Ag counter doping, which further facilitates a high average power factor in the whole working temperature range. The average power factor in Pb_0.85Sn_0.15Se systems increases from ∼15.6 μW cm⁻¹ K⁻² with a carrier density of ∼6.21 × 10¹⁹ cm⁻³ to ∼17.6 μW cm⁻¹ K⁻² with a carrier density of ∼2.12 × 10¹⁹ cm⁻³ at 300–873 K. Finally, an average ZT (ZT_ave) of ∼0.95 is achieved in the n-type Pb_0.85Sn_0.15Se sample at 300–873 K, and the sample outperforms most other n-type PbSe-based thermoelectric materials.