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Interfacial nonradiative recombination loss is a huge barrier to advance the photovoltaic performance. Here, one effective interfacial defect and carrier dynamics management strategy by synergistic modulation of functional groups and spatial conformation of ammonium salt molecules is proposed. The surface treatment with 3‐ammonium propionic acid iodide (3‐APAI) does not form 2D perovskite passivation layer while the propylammonium ions and 5‐aminopentanoic acid hydroiodide post‐treatment lead to the formation of 2D perovskite passivation layers. Due to appropriate alkyl chain length, theoretical and experimental results manifest that COOH and NH3+ groups in 3‐APAI molecules can form coordination bonding with undercoordinated Pb2+ and ionic bonding and hydrogen bonding with octahedron PbI64−, respectively, which makes both groups be simultaneously firmly anchored on the surface of perovskite films. This will strengthen defect passivation effect and improve interfacial carrier transport and transfer. The synergistic effect of functional groups and spatial conformation confers 3‐APAI better defect passivation effect than 2D perovskite layers. The 3‐APAI‐modified device based on vacuum flash technology achieves an alluring peak efficiency of 24.72% (certified 23.68%), which is among highly efficient devices fabricated without antisolvents. Furthermore, the encapsulated 3‐APAI‐modified device degrades by less than 4% after 1400 h of continuous one sun illumination.

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Low-dimensional metal halide perovskites are attracting extensive attentions due to their enhanced quantum confinement and stability compared to three-dimensional perovskites. However, low dimensional connectivity in the inorganic frameworks leads to strongly bounded excitons with limited absorption properties, which impedes their application in photovoltaic devices. Here, we show that by incorporating a strong electron accepting methylviologen (MV) cation, charge transfer (CT) at the organic/inorganic interface can effectively tune the optical properties in one-dimensional (1D) lead-halide perovskites. Both 1D MVPb2I6 and MVPb2Br6 display expanded absorption and photoresponse activity compared to CT inactive cations. The photoinduced CT process in MVPb2I6 was further characterized by transient absorption spectroscopy, which shows an ultrafast CT process within 1 ps, generating charge separated states. Our work unveils the interesting photophysics of these unconventional 1D perovskites with functional organic chromophores.