The investigation of chemical and optoelectronic properties of halide perovskite layers and associated interfaces is crucial to harness the full potential of perovskite solar cells. Depth-profiling photoemission spectroscopy is a primary tool to study the chemical properties of halide perovskite layers at different scales from the surface to the bulk. The technique employs ionic argon beam thinning that provides accurate layer thicknesses. However, there is an urgent need to corroborate the reliability of data on chemical properties of halide perovskite thin films to better assess their stability. The present study addresses the question of the Ar+ sputtering thinning on the surface chemical composition and the optoelectronic properties of the triple-cation mixed-halide perovskite by combining X-ray photoemission spectroscopy (XPS) and photoluminescence (PL) spectroscopy. First, XPS profiling is performed by Ar+ beam sputtering on a half-cell: glass/FTO/c-TiO2/perovskite. The resulting profiles show a very homogeneous and reproducible element distribution until near the buried interface; therefore, the layer is considered as quasihomogeneous all over its thickness, and the sputtering process is stable. Second, we evaluated a set of thinned perovskite layers representative of selected steps along the profile by means of PL imaging optical measurements in both steady-state and transient regimes to assess possible perturbation of the optical properties from the surface to bulk. Obtained PL spectra inside the resulting craters show no peak shift nor phase segregation. Accordingly, the transient PL measurements do not reveal any changes of the surface recombination rate in the sputtered areas. This demonstrates that there is no cumulative effect of sputtering nor drastic chemical and optoelectronic modifications, validating the determination of the in-depth composition of the perovskite layer. Combining XPS profiling with PL characterization can be a precise tool to be applied for an extensive study of the multiple layers and mixed organic/inorganic interfaces of photovoltaic devices.

Slot‐die coating is a promising technique paving the way for large‐area perovskite deposition and commercially relevant solar device fabrication with sharp control over the thickness and material composition. However, before transferring perovskite solar cells technology to commercial applications, it is required to develop ink formulations, guaranteeing high homogeneity over a wide surface and leading to large, defect‐free, and well‐crystallized perovskite grains to maximize the device performances. A one‐step slot‐die deposition route, combining ink tailoring and vacuum aspiration solvent extraction, affording the deposition of a high‐bandgap multication perovskite, is reported. One important key is the introduction of methylammonium chloride in the ink formulation, which substantially enhances the film quality over a large area. Although the efficacy of antisolvent dripping is demonstrated on a small area, it is not compatible with larger areas. This work compares the latter with a vacuum quench protocol, allowing efficient extraction of the solvents. Considering both ink formulation engineering and vacuum solvent extraction, a stabilized power conversion efficiency of up to 17.5% is reached. This constitutes, to the best of our knowledge, the highest reported value for a high‐bandgap absorber deposited by slot‐die coating. Moreover, stability over 180 h under maximum power point conditions is herein demonstrated.

The formation of a two-dimensional (2D) three-dimensional (3D) perovskite heterostructure has lately proved to be a promising way to improve the interface between the perovskite and electron/hole transport layers in perovskite solar cells, which is crucial for better device efficiency and stability. Herein, a spacer cation, 4-fluorophenethylammonium iodide, in isopropyl alcohol was used to form a thin 2D perovskite layer on top of a 3D triple-cation perovskite by a spin-coating deposition process. Therefore, a significant improvement in the device open-circuit voltage is obtained, leading to an enhanced power conversion efficiency. The formation mechanism of the 2D perovskite layer was studied by analyzing the structural, chemical, and optoelectronic properties of the layer, while varying several synthesis parameters. We reveal the presence of bromide inside the 2D phase and conclude with the existence of a concomitant formation mechanism, besides the most commonly described one involving the lead iodide (PbI2) excess contained in the 3D bulk. Therefore, we demonstrate how the stoichiometry of the 2D perovskite is affected by the chemical composition of the 3D layer underneath. This work provides new insights into the synthesis mechanisms of 2D/3D perovskite heterostructures, which could help to optimize their fabrication processes and develop new efficient and functional 2D/3D structures.