Enhanced thermoelectric performance in topological crystalline insulator n-type Pb0.6Sn0.4Te by simultaneous tuning of the band gap and chemical potential

Abstract

Tailoring the electronic structure of topological crystalline insulators (TCIs) is necessary to enhance their thermoelectric (TE) performance. p-Type chemical doping in a TCI such as Pb_0.6Sn_0.4Te exhibited a significantly high TE figure of merit (zT), but the n-type Pb_0.6Sn_0.4Te is still elusive and is urgently needed for thermoelectric applications. Herein, we report enhanced thermoelectric performance in n-type iodine (I) doped Pb_0.6Sn_0.4Te. Aliovalent I⁻ doping in the Te²⁻ sublattice of Pb_0.6Sn_0.4Te widens the band gap via breaking of local crystal mirror symmetry, which decreases the bipolar conduction and pushes the Seebeck maxima towards high temperatures. Iodine doping in Pb_0.6Sn_0.4Te significantly increases the n-type carrier concentration and shifts the chemical potential (Fermi level) inside the conduction band of Pb_0.6Sn_0.4Te, thus improving the electrical transport properties. We report a maximum zT of 1.05 in the n-type Pb_0.60Sn_0.40Te_0.995I_0.005 sample at 620 K, which is 483% higher than pristine Pb_0.6Sn_0.4Te.