Aromatic ammonium salts have been regarded as the promising passivators in perovskite solar cell (PSC) fabrications. However, the complicated passivation procedure and inevitable formation of undesirable low‐dimensional (LD) perovskite layers limit further development. Furthermore, how the steric and electronic properties of different ammonium cations would influence the passivation is not well understood. Herein, two carefully engineered passivators based on the unique benzothiophene moiety involving the primary and secondary ammonium terminals, BTMA‐1 and BTMA‐2, respectively, are developed. It is shown that defects and, thus, nonradiative recombination reactions are effectively suppressed by simple posttreatments without the formation of LD perovskite. Interestingly, the champion efficiency of the BTMA‐2‐treated device increases to 23.10% from ≈20%, along with great stabilities and negligible hysteresis. An in‐depth understanding of the passivation effect influenced by steric and electronic properties is explored. The extra electron‐donating methyl on the ammonium nitrogen (BTMA‐2) increases the electron density on the N atom and the N–H+ ionic bond is, thus, boosted, which helps the positive terminal to anchor more tightly to the [PbI6]4− structure of the perovskite resulting in improved passivation effects. This novel and promising design strategy for ammonium passivators can promote PSCs to achieve further breakthroughs in both efficiency and stabilities.

The hole transport materials (HTMs) play important roles in transporting holes and regulating perovskite crystallization in inverted perovskite solar cells (PSCs). Concerning the solubility of small‐molecule‐type HTMs in perovskite precursor solution during fabrication, the strategies including tailoring and crosslinking have been developed. However, how these strategies will influence the solvent resistance of the resultant hole transport layers (HTLs) and the corresponding device performance have not been systematically evaluated. Herein, upon incorporating tailoring and crosslinking groups into diazafluorene backbones, AFL‐COOH and AFL‐ENE are designed. Compared to the control HTM (AFL‐3) with poor solvent resistance and AFL‐COOH, the best solvent resistance of crosslinked AFL‐ENE (AFL‐ENE‐CL) film leads to an HTL with the highest quality covered on electrode, which thus results in the lowest trap density, best surface contact, and hole extraction for devices involving the AFL‐ENE‐CL type HTL and the best power conversion efficiency of 20.8% (20.0% for AFL‐COOH, 18.1% for AFL‐3). Furthermore, high reproducibility and stabilities also realize for the AFL‐ENE‐CL‐based PSC.