Tetrabutylammonium Additive Engineering to Sequentially Deposit Perovskite for Carbon‐Based Perovskite Solar Cells

With rapid development of perovskite solar cells (PSCs), high‐quality perovskite active layers can be obtained through various approaches. Defect passivation in the bulk or at the interface of the perovskite films has shown excellent effects on improving the power conversion efficiency (PCE) and long‐term stability of PSCs. Among various passivation strategies, quaternary ammonium salt passivators exhibit excellent application potential due to their dual functions of ionic defect compensation and crystallization kinetics modulation. Herein, two representative quaternary ammonium halides of tetrabutylammonium iodide (TBAI) and tetrabutylammonium bromide (TBAB) are applied in a sequential‐deposition process to passivate the defects of perovskite films. Their respective passivation effects are compared with an emphasis on the impact of different halogen atoms. It finds that TBAB outperforms TBAI in regulating crystallization kinetics, delaying nucleation, and reducing defect density, mainly because of the weaker interaction between TBA + and Br − than that of TBAI. During annealing, partially dissociated Br − ions can dynamically coordinate with the undercoordinated Pb 2+ , while TBAI remains more stable under similar conditions. The results indicated that TBAB‐modified carbon‐based perovskite solar cells (C‐PSCs) exhibited superior maximum PCE of 14.85%, compared to that of the TBAI‐based one with a 14.02% PCE. Additionally, long‐term stability of PSCs was also enhanced via the hydrophobic alkyl chains of the quaternary ammonium halides to form moisture‐resistant barriers. Remarkably, after 40 days of storage at 30%–40% relative humidity, the TBAI‐ and TBAB‐modified devices retained over 85% and 90% of their initial efficiency, respectively, demonstrating exceptional long‐term stability of the modified devices. These findings emphasize the key role of halide anion selection in the optimization of quaternary ammonium salt passivators, providing molecular design strategies for developing high‐efficiency, low‐cost C‐PSCs through multifunctional additive engineering.