A ultrahydrophobic polylectrolyte (PVPy-F) based on poly(4-vinylpyridine) is applied to polymer solar cell (PSC) as a cathode buffer layer. The Kelvin probe microscopy measurement support the formation of favorable interface dipole between the active layer and the cathode. PSC with the PVPy-F as a cathode buffer layer demonstrate the power conversion efficiency (PCE) of 3.46% (open circuit voltage (V-oc) = 0.62V, short circuit current (J(sc)) = 10.8mA/cm(2), fill factor (FF) = 51.7%), which is better than the device without interlayer (PCE = 2.88%, V-oc = 0.61V, J(sc) = 9.15mA/cm(2), FF = 51.6%). This is due to that the reduction of a Schottky barrier at the cathode interface. Most increase in the PCE of the devices with interlayer is resulted from enhancement of the J(sc).