Enhanced thermoelectric performance of n-type MgZnO enabled via synergy of chemical bonding and grain boundaries modulation

•Synthesized the MgZnO nanoparticles by changing the copper and zinc content using a hydrothermal method.•Growth of MgZnO nanoparticles and confirmed the pure and secondary phase formation by XRD, Raman.•The grain size of the MgZnO composite decreases by variation of atomic mole concentration of Mg and Zn.•The thermoelectric performance increase via string chemical bonding and energy filtering effect at the grain boundaries.