Organic photovoltaic devices (OPVs) have attracted considerable attention because of their advantages of light-weight, low-cost, large-scale manufacturing process and mechanical flexibility. Unfortunately, in order to achieve efficient carrier extraction, the photoactive layer in OPVs must be rather thin (100 nm or less) due to its extremely low carrier mobilities for most of organic/polymer materials (on the order of 10 ^-4cm ²/(V·s)). Such thin photoactive layers lead to a significant loss of incident sunlight, thereby improving a final low light absorption efficiency and power conversion efficiency (PCE). To promote the light absorption and thus enhance PCE of OPVs, Au tetrahedron nanoparticles (NPs) are synthesized in this work and then they are wrapped with poly (sodium 4-styrenesulfonate) (PSS) to form core-shell structure tetrahedron NPs (Au@PSS tetrahedron NPs). They are further incorporated into the interface of hole extraction layer and light photoactive layer to improve PCE of OPVs by enhancing their surface plasmon resonance effect-induced light absorption. The influences of doping concentration and PSS shell thickness of theses Au tetrahedron NPs on device performances are explored. The results indicate that the best performing PCE occurs at 6% concentration of Au@PSS tetrahedron NPs, reaching 3.08%, while it is further improved to 3.65% with an optimized PSS shell thickness of 2.5 nm, showing an enhancement factor of 22.9% compared with that of the control counterpart. The performance improvement of OPVs mainly originates from the promoted light absorption of donor due to the location of the resonant absorption peak of Au@PSS tetrahedron NPs in the absorption region of donor. Simultaneously, the introduction of the PSS shell promotes the dissociation of excitons and charge transfer. All of these contribute to the increasing of short-circuit current, fill factor and PCE of OPVs.