The energy level matching of perovskites was regarded as the prerequisites for achieving high photovoltaic performance. Graphitic carbon nitride (g-C3N4) is a two-dimensional polymer semiconductor material, which has good semiconductor properties, suitable electronic band structure and excellent physical and chemical stability, and is widely used in energy and materials science fields such as photoelectric conversion. Graphene oxide (GO) is a two-dimensional π-conjugated carbon atom sheet formed by sp2 hybrid bonds. Due to its unique electronic properties, g-C3N4 is seamlessly splice with the two-dimensional domains of GO through continuous π-conjugated bonds, which not only effectively modify the electronic structure of g-C3N4, but also contribute to the unhindered separation and transfer of electrons and holes in the plane. Therefore, in this work, we can effectively passivate film trap defects and significantly reduce non-radiative recombination by constructing GO/g-C3N4 heterostructures as an ultra-thin interface modification layer between the perovskite layer and the electron transport layer (ETL). As a result, the addition of GO/g-C3N4 heterojunction modification layer exhibited a much-improved conversion efficiency, inhibited the recombination of carriers, and improved the mobility of carriers. The unpackaged device demonstrated excellent stability, maintaining an initial efficiency of more than 90% after over 1,000 hours of storage under ambient conditions.