Although photodetection based on two-dimensional (2D) van der Waals (vdWs) P–N heterojunction has attracted extensive attention recently, their low responsivity (R) due to the lack of carrier gain mechanism in reverse bias or zero bias operation hinders their applications in advanced photodetection area. Here, a black phosphorus/rhodamine 6G/molybdenum disulfide (BP/R6G/MoS₂) photodiode with high responsivity at reverse bias or zero bias has been achieved by using interfacial charge transfer of R6G molecules assembled between heterojunction layers. The formed vdWs interface achieves high performance photoresponse by efficiently separating the additional photogenerated electrons and holes generated by R6G molecules. The devices sensitized by the dye molecule R6G exhibit enhanced photodetection performance without sacrificing the photoresponse speed. Among them, the R increased by 14.8–20.4 times, and the specific detectivity (D*) increased by 24.9–34.4 times. The strategy based on interlayer assembly of dye molecules proposed here may pave a new way for realizing high-performance photodetection based on 2D vdWs heterojunctions with high responsivity and fast response speed.