Passivation of the grain boundaries of CH₃NH₃PbI₃ using carbon quantum dots for highly efficient perovskite solar cells with excellent environmental stability

Organic-inorganic hybrid perovskites are prone to defect formation due to iodine and methylamine ion/defect migration, leading to the formation of lots of defects at the perovskite surface and grain boundaries. Passivation of the defects is an effective method to improve the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). To achieve stable passivation, the interaction between the perovskite and additive materials should be taken into consideration. In this work, we for the first time introduced carbon quantum dots (CQDs) as an additive for the stabilization of MAPbI₃via passivation of the grain boundaries of the perovskite. Because the carboxylic groups, hydroxyl groups and amino-groups on the edge of CQDs can bond with the uncoordinated Pb in MAPbI₃, strong and stable interactions between the perovskite and CQDs can be generated, inducing a lower trap-state density and better optoelectronic properties. The typical PCE of the PSCs based on CQD modified MAPbI₃ films increases from 17.59% to 18.81% and the PCE of the optimized champion PSCs reaches 19.38%. Furthermore, the hydrophobic CQD molecules can block the contact between water and MAPbI₃, and even if the CQD modified perovskite is kept under ambient atmosphere without controlling the humidity for 4 months, the MAPbI₃ film still retained its original black color.