Cu nanoparticle-processed n-type Bi2Te2.7Se0.3 alloys for low-temperature thermoelectric power generation

•Cu-doped Bi2Te2.7Se0.3 was first synthesized by using Cu nanoparticle precursor.•The power factor is enhanced by the substitutional Cu doping in quintuple layers.•Substantial reduction of electronic thermal conductivity originates from Cu doping.•Average zT value at 300–500 K for 2% Cu–Bi2Te2.7Se0.3 increased to 0.79.•The power generation efficiency can be enhanced by 25% from the pristine sample.