High thermoelectric performance due to nano-inclusions and randomly distributed interface potentials in N-type (PbTe_0.93-:XSe_0.07Cl_x)_0.93(PbS)_0.07 composites

In a composite of two dissimilar or homologous semiconductors with different energy band gaps or metal/semiconductor composites, we expect a band bending effect at the interfaces. The band bending effect induced by the different Fermi levels of two compounds can selectively scatter carriers due to energy-dependent scattering time, resulting in enhancement of the Seebeck coefficient. In addition, nano-inclusions in a matrix will effectively scatter phonons. Here, we demonstrate the effects of electron and phonon scattering by nano-inclusions in n-type (PbTe_0.93-xSe_0.07Cl_x)_0.93(PbS)_0.07 (x = 0.0005, 0.01, 0.1 and 0.2) composites. In the matrix, the nano-inclusions increased the Seebeck coefficient while reducing lattice thermal conductivity in (PbTe_0.93-xSe_0.07Cl_x)_0.93(PbS)_0.07. The chlorine doping increases the Fermi level to the bottom of the conduction band giving rise to increased electron concentration. The simultaneous emergence of the high Seebeck coefficient and low thermal conductivity resulted in the exceptional ZT value of 1.52 at 700 K for low chlorine doping (x = 0.0005), which is a very high value in n-type thermoelectric materials. The randomly distributed interface potential, induced by Fermi level tuning, with nano-inclusions is a new criterion for investigating thermoelectric properties.