In Situ Hole-Transport Layer Formation and Concurrent Passivation for FA0.9Cs0.1PbI3 Perovskite Solar Cells

The buried interface between the hole transport layer (HTL) and the perovskite layer is critical to both the efficiency and stability of inverted perovskite solar cells (PSCs). The conventional sequential deposition approach, where the self-assembled monolayer (SAM)-based HTL is pre-deposited as a separate bottom layer prior to perovskite coating, faces inherent challenges, including insufficient interfacial wetting, high defect densities, and limited scalability. Herein, we introduce a dynamic self-assembly (DSA) approach to simultaneously fabricate the HTL and passivate the perovskite in a single step. By integrating a binary mixture of SAMs ([2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) and [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz)) and the monomer 2-(dimethylamino)ethyl methacrylate (DMAEMA) directly into the perovskite precursor, an in situ, uniform HTL forms during perovskite crystallization. The SAMs optimize energy alignment and interfacial contact, while the polymerized DMAEMA, localized at grain boundaries, passivates undercoordinated Pb2+ and suppresses iodide-related defects. This combined approach enhances film crystallinity, improves interfacial homogeneity, and drastically reduces non-radiative recombination. Consequently, the champion device achieves a power conversion efficiency (PCE) of 22.03% with a high open-circuit voltage (Voc) of 1.11 V, a short-circuit current density of 25.84 mA cm-2, and a fill factor of 77%. Moreover, the DSA-processed device remains operational throughout prolonged maximum power point (MPP) tracking under continuous illumination and elevated temperature. This work presents DSA as an effective strategy for simultaneous buried interface engineering and defect passivation in inverted PSCs.