Side and top views of the (a) armchair and (b) zigzag PSi photodetector irradiated by the polarized light, and θ is the polarization angle. The blue and gray atoms are corresponding to the Si and P atoms. Display omitted •A graphene-like honeycombed PSi monolayer has been found by our group with its thermodynamical, dynamical and mechanical stability having been listed.•When the linearly polarized light illuminates on the armchair or zigzag photodetector, due to the C1 symmetry of PSi monolayer the PSi photodetector can directly produce high photocurrents.•The produced photocurrents show the relations cos(2θ) and sin(2θ) on the polarization angle θ for the armchair and zigzag photodetector, respectively.•The vacancy- and substitution-doping in the PSi photodetector can enhance the generated photocurrents. Using particle swarm optimization methodology for crystal structure prediction and first-principles density functional theory, a graphene-like honeycombed PSi monolayer has been found by our group with its thermodynamical, dynamical and mechanical stability having been listed. To extend the application of the PSi monolayer, the armchair and zigzag photodetector devices based on the photogalvanic effect have been built. When the linearly polarized light illuminates on the armchair or zigzag photodetector, due to the C1 symmetry of PSi monolayer the PSi photodetector can directly produce high photocurrents. In addition, the produced photocurrents show the relations cos(2θ) and sin(2θ) on the polarization angle θ for the armchair and zigzag photodetector, respectively. Moreover, the value of photon energy can effectively influence the distribution of generated photocurrents, namely the relations on the angle θ. Especially, the vacancy- and substitution-doping in the PSi photodetector can enhance the generated photocurrents. These results demonstrated great potential applications of the PSi monolayer on the low energy-consumption optoelectronics devices.