Enhancing the Efficiency and Stability of CsFA‐Based Perovskite Solar Cells: Defect Passivation Using Indoline‐Based D–π–A Configured Molecule as Additive

ABSTRACT The employment of rationally designed functional group‐bearing molecules as additives to passivate perovskite defects has emerged as a prevalent trend. Among the diverse array of passivation materials, donor‐π‐acceptor (D‐π‐A) structured molecules have attracted widespread attention due to their unique ability of simultaneously regulate the electron donor and acceptor units, thereby promoting coordination with undercoordinated ions of perovskite films. In this work, we introduce an indoline‐based D‐π‐A molecule (labeled as IHT) as an efficient passivator for perovskite solar cells (PSCs). The extraordinary electron‐donating capability of indoline moiety simultaneously endows the electron‐withdrawing cyanoacetic acid group with an elevated electron density, which is in favor of interaction with under‐coordinated Pb 2+ in the lattice, thus reducing the density of defective states within the perovskite films. Experimental outcomes underscore the efficacy of IHT as an additive in passivating CsFA‐based PSCs. The optimal devices demonstrate a remarkable champion photovoltaic conversion efficiency of 21.25%, with a notable improvement of 7.4% compared to the Cs‐FA‐PbI 3 devices. The stability assessments reveal that the unencapsulated IHT‐treated Cs‐FA‐PbI 3 devices retained 83% of the initial efficiency after 30 days in ambient air, whereas the untreated devices exhibited a decline to 54% under the same condition. This work indicates the profound significance of IHT in promoting the formation of dense perovskite film with passivation effect as well as enhancing the long‐term stability of PSCs.