Abstract Functional additives have recently been regarded as emerging candidates to improve the performance and stability of perovskite solar cells (PSCs). Herein, nicotinamide (N), 2‐chloronicotinamide (2Cl), and 6‐chloronicotinamide (6Cl) were employed as O‐ligands to facilitate the deposition of MAPbI3 (MA = methylammonium) and MA‐free FA0.88Cs0.12PbI2.64Br0.36 (FA = formamidinium) perovskite films by multifunctional anchoring. By density functional theory (DFT) calculations and ultraviolet photoelectron spectroscopy (UPS) measurements, it is identified that the highest occupied molecular orbital (HOMO) level for additive modified MAPbI3 perovskite could reduce the voltage deficit for hole extraction. Moreover, due to the most favorable charge distribution and significant improvements in charge mobility and defect passivation, the power conversion efficiency (PCE) of 2Cl‐MAPbI3 PSCs was significantly improved from 19.32% to 21.12%. More importantly, the two‐dimensional grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) analysis showed that PbI2 defects were effectively suppressed and femtosecond transient absorption (TA) spectroscopy demonstrated that the trap‐assisted recombination at grain boundaries was effectively inhibited in the 2Cl‐MA‐free film. As a result, the thermally stable 2Cl‐MA‐free PSCs achieved a remarkable PCE of 23.13% with an open‐circuit voltage (Voc) of 1.164 V and an ultrahigh fill factor (FF) of 85.7%. Our work offers a practical strategy for further commercializing stable and efficient PSCs.
