The two-dimensional (2D) perovskites stabilized by alternating cations in the interlayer space (ACI) define a new type of structure with different physical properties than the more common Ruddlesden−Popper counterparts. However, there is a lack of understanding of material crystallization in films and its influence on the morphological/optoelectronic properties and the final photovoltaic devices. Herein, we undertake in situ studies of the solidification process for ACI 2D perovskite (GA)(MA) n Pb n I 3n+1 (⟨n⟩ = 3) from ink to solid-state semiconductor, using solvent mixture of DMSO:DMF (1:10 v/v) as the solvent and link this behavior to solar cell devices. The in situ grazing-incidence X-ray scattering (GIWAXS) analysis reveals a complex journey through disordered sol−gel precursors, intermediate phases, and ultimately to ACI perovskites. The intermediate phases, including a crystalline solvate compound and the 2D GA 2 PbI 4 perovskite, provide a scaffold for the growth of the ACI perovskites during thermal annealing. We identify 2D GA 2 PbI 4 to be the key intermediate phase, which is strongly influenced by the deposition technique and determines the formation of the 1D GAPbI 3 byproducts and the distribution of various n phases of ACI perovskites in the final films. We also confirm the presence of internal charge transfer between different n phases through transient absorption spectroscopy. The high quality ACI perovskite films deposited from solvent mixture of DMSO:DMF (1:10 v/v) deliver a record power conversion efficiency of 14.7% in planar solar cells and significantly enhanced long-term stability of devices in contrast to the 3D MAPbI 3 counterpart.

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Blade-coating has recently emerged as a scalable fabrication method for hybrid perovskite solar cells, but it currently underperforms spin-coating, yielding a power conversion efficiency (PCE) of ∼15% for CH 3 NH 3 PbI 3 (MAPbI 3 ). We investigate the solidification of MAPbI 3 films in situ during spin/blade-coating using optical and X-ray scattering methods. We find that the coating method and conditions profoundly influence the crystallization process, which proceeds through intermediate crystalline solvates. The polymorphism and composition of the solvates are mediated by the solvent removal rate dictated by the process temperature in blade-coating. Low to intermediate temperatures (25−80 °C) yield solvates with differing compositions and yield poor PCEs (∼5−8%) and a large spread (±2.5%). The intermediate solvates are not observed at elevated temperatures (>100 °C), pointing to direct crystallization of the perovskite from the sol−gel ink. These conditions yield large and compact spherulitic domains of perovskite and improve the PCE to ∼13−15% with a narrower spread (< ± 0.5%), while coating at 150 °C yields 17.5% solar cells by inducing in situ decomposition of a small amount of MAPbI 3 into PbI 2 . The insights into the crystallization pathway highlight the current challenges and future opportunities associated with scaling up hybrid perovskite solar cell manufacturing.

We report a Ruddlesden–Popper/3D heterostructure combined with molecule passivation within α-phase FAPbI3 films for high-performance and ambient-air-stable solar cells.

Perovskite solar cells based on two-dimensional/three-dimensional (2D/3D) hierarchical structure have attracted significant attention in recent years due to their promising photovoltaic performance and stability. However, obtaining a detailed understanding of interfacial mechanism at the 2D/3D heterojunction, for example, the ligand-chemistrydependent nature of the 2D/3D heterojunction and its influence on charge collection and the final photovoltaic outcome, is not yet fully developed. Here we demonstrate the underlying 3D phase templates growth of quantum wells (QWs) within a 2D capping layer, which is further influenced by the fluorination of spacers and compositional engineering in terms of thickness distribution and orientation. Better QW alignment and faster dynamics of charge transfer at the 2D/3D heterojunction result in higher charge mobility and lower charge recombination loss, largely explaining the significant improvements in charge collection and open-circuit voltage (V OC ) in complete solar cells. As a result, 2D/3D solar cells with a power-conversion efficiency of 21.15% were achieved, significantly higher than the 3D counterpart (19.02%). This work provides key missing information on how interfacial engineering influences the desirable electronic properties of the 2D/3D hierarchical films and device performance via ligand chemistry and compositional engineering in the QW layer.