p‐Type Carbon Dots for Effective Surface Optimization for Near‐Record‐Efficiency CsPbI2Br Solar Cells

Abstract Interface modification to minimize charge recombination and trapping for efficient charge transport is crucial for the performance of perovskite solar cells (PSCs). Herein, functionalized p‐type blue carbon dots (B‐CDs) are ventured as an interface passivation layer to enhance the efficiency and long‐term stability of all‐inorganic CsPbI2Br PSCs. It is found that first the blue carbon dots with abundant NH, CN, CO, and CO functional groups effectively passivate defects by reacting with I− and Pb2+ ions in the perovskite through hydrogen and coordinative bonds. Second, the p‐type B‐CDs modifiers form a P–N junction with the n‐type perovskite to provide efficient pathways for hole transfer and electron blocking. Third, the B‐CDs increase the hydrophobicity of the perovskite film to improve the stability of CsPbI2Br PSCs. With the above advantages, the CsPbI2Br PSC with B‐CDs modification shows an efficiency as high as 16.76%, one of the highest for its type. In addition, the modification renders significant improvement of air and light stability, with 95.33% of the initial PCE retained after storage in the ambient environment for 1000 h. This work demonstrates the great potential of B‐CDs application in perovskite‐based optoelectronic devices.