High thermoelectric properties with low thermal conductivity due to the porous structure induced by the dendritic branching in n-type PbS

PbS-based thermoelectric materials have attracted extensive attention in recent years for the advantages of earth abundancy and low cost, which is considered to be a substitute for traditional PbTe material. However, their high thermal conductivity restricts its development. Hence, in order to improve their thermoelectric performance from reducing the thermal conductivity, a kind of dendritic PbS with controlled crystal grain and morphology are obtained by solution synthesis. By adjusting the amount of surfactant (CTAB), the specific formation process of dendrites is regulated. After sintering, the dendritic PbS nanoparticles are easy to form porous structure due to the overlapping and staggered arrangement of dendritic branches. For comparison, we also prepare a kind of regular octahedral PbS and a dense packing arrangement is formed because of the integrity of the octahedral structure. DFT-based Boltzmann transport equation is used to prove the crucial role of porous structure in scattering phonon. Finally, a maximum zT = 1.0 at 773 K in n-type PbS is obtained, which still keep a high-speed growth and is expected to get higher zT value in a higher temperature region. Our work may shed light to other thermoelectric materials from the formation of porous structure to reduce the thermal conductivity.