New Carbon Nitride C3N3 Additive for Improving Cationic Defects of Perovskite Solar Cells

Due to the loss of organic amine cations and lead ions in the structure of the iodine–lead methylamine perovskite solar cell, there are a large number of defects within the film and the recombination loss caused by grain boundaries, which seriously hinder the further improvement of power conversion efficiency and stability. Herein, a novel carbon nitride C3N3 incorporated into the perovskite precursor solution is a multifunctional strategy, which not only increases the light absorption strength, grain size, and hydrophobicity of the perovskite film, but also effectively passivates the bulk and interfacial defects of perovskite and verified by the first‐principles density functional theory calculations. As a result, the efficiency and stability of perovskite solar cells are improved. The device with 0.075 mg mL−1 C3N3 additive delivers a champion power conversion efficiency of 19.91% with suppressed hysteresis, which is significantly higher than the 18.16% of the control device. In addition, the open‐circuit voltage of the modified device with the maximum addition as high as 1.137 V is 90.96% of the Shockley–Queisser limit (1.25 V). Moreover, the power conversion efficiency of the modified device without encapsulation can maintain nearly 90% of its initial value after being stored at 25 °C and 60% relative humidity for 500 h. This work provides a new idea for developing additives to improve the power conversion efficiency and stability of perovskite solar cells. C3N3 is utilized as an additive for the perovskite layer, which can not only interact with uncoordinated Pb2+ and MA+, decrease its surface and/or grain boundary defects, and suppress carrier recombination, but also improve the PCE and moisture stability of the PSC device. J‐V curves of control and CN‐7.5‐based devices, and inset schematic diagram of interaction sites between C3N3 and perovskite grain boundaries.