Self-assembled monolayers (SAMs) have recently emerged as excellent hole transport materials in inverted perovskite solar cells (PSCs) owing to their ability to minimize parasitic absorption, regulate energy level alignment, and passivate perovskite defects. Herein, we design and synthesize a novel dimethyl acridine-based SAM, [2-(9,10-dihydro-9,9-dimethylacridine-10-yl)ethyl]phosphonic acid (2PADmA), and employ it as a hole-transporting layer in inverted PSCs. Experimental results show that the 2PADmA SAM can modulate perovskite crystallization, facilitate carrier transport, passivate perovskite defects, and reduce nonradiative recombination. Consequently, the 2PADmA-based device achieves an enhanced power conversion efficiency (PCE) of 24.01% and an improved fill factor (FF) of 83.92% compared to the commonly reported [2-(9H-carbazol-9-yl)ethyl] phosphonic acid (2PACz)-based control device with a PCE of 22.32% and FF of 78.42%, while both devices exhibit comparable open-circuit voltage and short-circuit current density. In addition, 2PADmA-based devices exhibit outstanding dark storage and thermal stabilities, retaining approximately ~98% and 87% of their initial PCEs after 1080 h of dark storage and 400 h of heating at 85 °C, respectively, both considerably superior to the control device.