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%. Carbon-based perovskite solar cell (C-PSC) has attracted extensive attention for its low cost and super stability. However, C-PSCs always suffer from much lower power conversion efficiency (PCE) compared with PSCs with noble metal cathode. Herein, we report an effective method to improve the efficiency of C-PSC by adding graphitic carbon nitride (g-C3N4) into the perovskite. The addition of g-C3N4 significantly improves the crystal quality of the perovskite, which is characterized by its larger grain size, reduced defects and flatter surface coverage. The PCE of C-PSCs was improved from 10.5% to 12.8% because of the enhancement of the crystal quality. Furthermore, to enhance the correspondingly low open-circuit voltage (Voc) caused by a high charge recombination, an insulating layer was developed by spin-coating Al2O3 on the surface of the electron transport material (ETM). It can effectively hinder the recombination of the electrons in ETM layers with holes left in perovskite layers. As a result, an optimized device with a maximum PCE of 14.34% is obtained together with a distinct improvement in voltage from 0.92 V to 1.0 V. This work increases the possibility of the commercialization of high stable C-PSCs.