In CH3NH3PbI3 based perovskite solar cells (PSCs), the subtle pinholes and grain boundaries are hardly avoided in the formation of perovskite film. The defected film often leads to a reduced efficiency due to a larger amount of electron trap sites which induce carrier recombination leading to electron loss. In this work, ultrafine exfoliated graphitic carbon nitride (E-g-C3N4) nanoparticles are successfully synthesized by H2SO4 intercalation and NH3 stripping. The E-g-C3N4 has a lot of N-H or O-H groups, which could coil into nanoparticles spontaneous from nanosheets by hydrogen bonds. As an application in PSCs, the E-g-C3N4, as doping materials between MAPbI(3) and the hole transport materials (HTMs), could magically self-recognize CH3NH3PbI3 grain boundaries and locate on them. Electron-hole recombination is greatly reduced even after incorporating trace of E-g-C3N4 by decreasing the deep electron trap centers at grain boundaries. As a result, the power conversion efficiency (PCE) of 15.8% is achieved for the MAPbI(3) based PSCs, which is 35% higher than the reference cell. Thus, it is a universal and efficient method to weaken the influence of unavoidable defects existing in pinholes and grain boundaries, and develop the low-cost preparation for large-area PSCs in general conditions.