Carbon-based, all-inorganic CsPbIBr2 perovskite solar cells (PSCs) have demonstrated to have superior stability and low cost, combine with a simple fabrication process. However, there are two vital factors that impede enhancement of the power conversion efficiency (PCE) of PSCs. One is the low energy level alignment matching between perovskite layer and carbon electrode, and the other one is defects of the perovskite film. Here, we introduce CsPbI2Br QDs as an interface between the CsPbIBr2 layer and carbon electrode to passivate the perovskite bulk film. The surface defects and charge carrier mobility of QDs are also modified using a bidentate chelating ligand, namely 4-mercaptobenzoic acid (4-MBA). By optimizing the energy level alignment at the interface, the hole extraction is promoted, and interfacial recombination is suppressed. Compared to the PSCs without the QDs layer, the QDs-passivated PSC achieved a PCE of 6.69%, leading to an increase of almost 31.43%. Furthermore, the PSCs with QDs passivation had better water resistance. This work provides a promising strategy to enhance both the stability and efficiency of carbon-based PSCs.