High-performance g-C3N4 added carbon-based perovskite solar cells insulated by Al2O3 layer

•g-C3N4 was introduced into perovskite.•Al2O3 insulating layers was inserted between the perovskite layer and the electron transport material (ETM).•The addition of g-C3 N4 significantly improves the crystal quality of the perovskite.•The Al2O3 insulating layer inhibits the charge recombination at the interface of ETM/perovskite.•The highest efficiency of the device we designed can reach 14.34%.