Co‐Assembly with Donor‐Acceptor Self‐Assembled Monolayers to Enhance Interfacial Hole Extraction, Wettability, and Crystallization in Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) are commonly employed as hole-selective layers in inverted perovskite solar cells. However, the widely used Me-4PACz (Me4) often faces issues such as solution aggregation, poor precursor wettability, insufficient interfacial contact, and suboptimal crystallinity at the perovskite buried interface, leading to non-radiative losses. This study proposes two newly designed donor-acceptor (D-A) SAMs, LYS-H and its fluorinated derivative LYS-F, and employs a co-assembly strategy with Me4 to overcome these limitations. The D-A structure enhances interfacial dipole moments to facilitate hole extraction, while distinct functional groups enable effective passivation at the perovskite buried interface. Additionally, the multi-directional phenyl rings of the triphenylamine (TPA) group in LYS-H and LYS-F can interact with the carbazole units of Me4 via π-π stacking. This interaction helps suppress Me4 aggregation and enhances the uniformity of SAM. This approach simultaneously improves precursor wettability and promotes enhanced perovskite crystallinity. Compared to LYS-H, fluorination of LYS-F deepens its highest occupied molecular orbital (HOMO) and increases its effective work function, enabling better alignment with the perovskite valence band. The Me4+LYS-F-based device demonstrates superior interfacial energy level alignment and reduced interface defects, ultimately achieving a power conversion efficiency of 25.02% and a high fill factor of 83.64%. Furthermore, both unencapsulated Me4+LYS-H and Me4+LYS-F devices demonstrate substantially improved operational stability compared to the pristine Me4 device, when measured in air (RH ≈ 30%) under dark conditions at 25 °C.