The thermoelectric properties of a highperformance electron-conducting polymer, (P(NDIOD-T2), extrinsically doped with dihydro-1H-benzoimidazol-2-yl (NDBI) derivatives, are reported. The highest thermoelectric power factor that has been reported for a solution-processed n-type polymer is achieved; and it is concluded that engineering polymerdopant miscibility is essential for the development of organic thermoelectrics.