The development of copper chalcogenide nanomaterials has shown a potential for advanced energy application, because copper chalcogenide are p-type semiconductors with high hole concentration. In this study, copper sulfide (CuS) was synthesized and alloyed with Se via a water-based method without the use of organic solvent. We demonstrated that Se alloying to CuS nano-particles (NPs) could improve oxidation stability of dispersion in aqueous solution. Through this, the NPs were integrated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) into a simple mixing strategy, and used as a hole transporting materials with PEDOT:PSS for organic photodiodes (OPDs). OPD device with NPs showed suppressed dark current and remarkably enhanced detectivity in all wavelength regions due to formation of electron barrier compared to pristine PEDOT:PSS device. Moreover, when exposed to signal pulses, the photocurrent is improved, and the noise current is suppressed for the OPD with NPs. Therefore, incorporating stable copper chalcogenide NPs can improve performance, leading to cost-effective optoelectronic devices.