The effects of triphenylphosphine (PPh3)-based n-doping and hexagonal boron nitride (h-BN) insertion on a tungsten diselenide (WSe2) photodetector are systematically studied, and a very high performance WSe2/h-BN heterostucture-based photodetector is demonstrated with a record photoresponsivity (1.27 x 10(6) A W-1) and temporal photoresponse (rise time: 2.8 ms, decay time: 20.8 ms) under 520 nm wavelength and 5 pW power laser illumination.