A thermoelectric figure of merit ZT has been mainly improved by reducing thermal conductivity, resulting record high performance in several important thermoelectric (TE) systems. Their thermal conductivity rapidly approaches to the amorphous limit. In contrast, power factor (PF) does not have the theoretical upper bound, and it directly determines the output power of TE modules. However, enhancing PF is highly challenging, especially for Bi2Te3-based compounds that are representative TE materials near ambient temperature. Here we report ultrahigh power factor and carrier mobility in new n-type Bi2Te3-based materials, which are stabilized under excess Cu and Te conditions. The enhanced power factor is attributed to markedly high carrier mobility and electrical conductivity, which increase with the higher extent of Cu.