Exfoliated graphitic carbon nitride self-recognizing CH3NH3PbI3 grain boundaries by hydrogen bonding interaction for improved perovskite solar cells

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.