Controlled synthesis of Bi-doped PbTe nanocubes with different Bi doping levels to tune the electrical transport properties. High density of grain boundaries and high density of dislocations within the grains provide full-length phonon scattering and lead to significantly reduced thermal conductivities. Secured a peak ZT of 1.35 at 675 K for the as-sintered Pb0.99Bi0.01Te pellet, which is one of the best n-type thermoelectric materials.