Multifunctional Surface Modification Enables Efficient and Stable Carbon-Based Cspbi2br Perovskite Solar Cells

All-inorganic carbon-based CsPbI2Br perovskite solar cells (PSCs) have garnered considerable attention due to an appropriate trade-off between stability and power conversion efficiency (PCE). However, the CsPbI2Br perovskite films derived from solution process inevitably generate various defects at interfaces or grain boundaries, which can serve as non-radiative recombination centers for photogenerated carriers and are sensitive to water molecules to degrade, together with the energy level mismatch at the CsPbI2Br/carbon interface, thus reducing the PCE and stability of the devices. Herein, 1-benzyl-3-methylimidazolium hexafluorophosphate (1-B-3-MIMPF6), a multifunctional interface modifier with both defect passivation and hydrophobic functions, was utilized for modification of CsPbI2Br perovskite films. The results show that the PF6– ions of 1-B-3-MIMPF6 can passivate the positively charged halogen vacancies and the 1-B-3-MIM + ions can passivate the negatively charged cation vacancies, and the energy band alignment of the CsPbI2Br/carbon interface can be improved, thus promoting the photovoltaic performance of the devices (with an architecture of indium tin oxide/SnO2/CsPbI2Br/1-B-3-MIMPF6/carbon) with a champion PCE of 13.47%, an open circuit voltage of 1.20 V, a short circuit current density of 14.69 mA/cm2, and a fill factor of 76%. At the same time, the benzene rings and fluorine atoms can effectively block the intrusion of water molecules in the ambient air. The humidity stability of the optimized device has been greatly improved, with its PCE maintaining 78% of the initial after 24 hours at room temperature in a 30%–35% humidity environment, whereas that of the pristine device dropping to almost zero.