In-depth understanding the effect of electron-withdrawing/-donating groups on the interfacial carrier dynamics in naphthalimide-treated perovskite solar cells

Surface defect passivation of perovskite films through chemical interaction between specific functional groups and defects has been proven to be an effective technique for enhancing the performance and stability of perovskite solar cells (PSCs). However, an in-depth understanding of how these passivation materials affect the intrinsic nature of charge-carrier transfer kinetics in PSCs remains shielded so far. Herein, we have designed two naphthalimide-based perovskite surface passivators having electron-withdrawing (-CF₃, NSF) or electron-donating (-CH₃, NSC) substituents for use in PSCs. Transient absorption spectroscopy (TA) measurements confirmed how the electron-withdrawing and electron-donating groups can efficiently turn the hot carriers (HCs) cooling and injection, and interface recombination in the device. We found that NSC-passivated perovskite samples exhibit faster hot-carriers (HCs) injection from the perovskite layer into carrier transport layers before cooling to the crystal lattice compared with the NSF-based and control ones with the order: NSC > NSF > control. Fast HCs injection is advantageous to minimize the charge-carriers recombination and improve PSCs performance. The carrier lifetime in NSC-treated device measured by nanosecond TA exhibits nearly ∼2 times longer than that of NSF-based device, which demonstrates the decreased charge-carrier recombination in NSC-treated device. As expected, the power conversion efficiency (PCE) of the NSC-treated PSCs is improved to 23.04% compared with that of the device treated with NSF (21.81%). Our findings provide invaluable guide for developing highly efficient passivators to further boost PSCs photovoltaic performance.