Binary organic solar cells (OSCs) having a controllable phase-separated morphology of active layers and simple solution manufacturing are desirable for organic photovoltaic adaptation. However, low hole mobility and an unbalanced hole- and electron transport reduce the power conversion efficiency (PCE) of the OSCs. Here, a highly efficient binary OSC with a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) buffer layer as a hole transport layer (HTL) via using a water-soluble sulfonate to wrap the PEDOT:PSS core-shell structures in solutions is reported. The PEDOT:PSS buffer layers have good merits including i) a smooth, homogeneous, and hydrophilic surface for an intimate contact, ii) a high work function and raised surface potentials with much uniform distributions for an energy band alignment, and iii) a high optical transmittance in the broad spectral region from 400 to 1100 nm along with an improved electrical conductivity. Benefiting from a raised hole mobility and a better charge-mobility balance, the solution-processed binary OSCs yielded a high PCE of 18.62%. 18.62% is one of the highest values among these binary OSCs based on the PEDOT:PSS HTLs and PM6:L8-BO active layers. The PEDOT:PSS buffer layers are superior to the pristine PEDOT:PSS buffer layers in terms of raising the OSC efficiency.