In the work, mechanisms behind various 3D nanocrystals enhanced performance of bulk heterojunction solar cells were studied comprehensively. Four types of gold nanoparticles (NPs) with distinctly different shapes and great uniformity were designed and synthesized, including cubes, rhombic dodecahedra (RD), edge- and corner-truncated octahedra (ECTO), and triangular plates, to systematically probe their influences on photovoltaics. RD and triangular plates show a higher growth rate, while slower growth favors cubes and ECTO formation by controlling the reduction agent and capping ion amount. NPs with increasing corners and proper size of cross-section induce stronger near-field coupling and far-field scattering in P3HT:PC61BM-based active layers. Both finite-difference time-domain simulation and UV-visible absorption spectra firmly support that RD exhibit the strongest localized surface plasmon resonance and optical scattering. With optimized conditions, a high power conversion efficiency exceeding 4% was reproducibly achieved.