Dimethyl acridine-based self-assembled monolayer as a hole transport layer for highly efficient inverted perovskite solar cells

Self-assembled monolayers (SAMs) have recently appeared as excellent hole transport materials in inverted perovskite solar cells (PSCs) since they can significantly minimize parasitic absorption, easily regulate energy level alignment, and passivate defects within perovskite. Herein, we design and synthesize a novel dimethyl acridine-based SAM, [2-(9, 10-dihydro-9, 9-dimethylacridine-10-yl)ethyl]phosphonic acid (abbreviated 2PADmA), and employ it as a hole-transporting layer (HTL) in inverted PSCs. Experimental results show that the 2PADmA SAM can modulate perovskite crystallization, facilitate the carrier transport, passivate perovskite defects, and reduce the nonradiative recombination. As a result, the 2PADmA-based device achieves an enhanced power conversion efficiency (PCE) of 24.01% along with an improved fill factor (FF) of 83.92% in comparison with the commonly reported 2PACz-based control device with a PCE of 22.32% and FF of 78.42%, while both devices present comparable open-circuit voltage (V_OC) and short-circuit current density (J_SC). In addition, 2PADmA-based devices exhibit outstanding ambient and thermal stabilities: the unencapsulated devices can retain respectively about 98% and 87% of their initial PCEs after storage in dark conditions for 1080 h and heating at 85°C for around 400 h, both of which are significantly superior to the control device.