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Tin-based perovskites are promising alternative absorber materials for leadfree perovskite solar cells but need strategies to avoid fast tin (Sn) oxidation. Generally, this reaction can be slowed down by the addition of tin fluoride (SnF2) to the perovskite precursor solution, which also improves the perovskite layer morphology. Here, this work analyzes the spatial distribution of the additive within formamidinium tin triiodide (FASnI(3)) films deposited on top of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layers. Employing time-of-flight secondary ion mass spectrometry and a combination of hard and soft X-ray photoelectron spectroscopy, it is found that Sn F2 preferably accumulates at the PEDOT:PSS/perovskite interface, accompanied by the formation of an ultrathin SnS interlayer with an effective thickness of approximate to 1.2 nm. This project received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 850937 (PERCISTAND). H.-G.B. and D.D. are very grateful to the Research Foundation Flanders (FWO) for funding the HAXPES-lab instrument within the HERCULES program for Large Research Infrastructure of the Flemish government. P.S. thanks the French Agence Nationale de la Recherche for funding under the contract number ANR-17-MPGA-0012. This work was supported by the Federal Ministry for Economic Affairs and Energy (BMWi) Germany under the contract number 03EE1038A (CAPITANO) and financed by the Ministry of Science, Research and the Arts of Baden-Wurttemberg as part of the sustainability financing of the projects of the Excellence Initiative II (KSOP).

Perovskite solar cells (PSCs) have recently gained power conversion efficiencies (PCEs) of up to 25.5% on a lab scale, which are nearly exclusively processed from precursor solutions involving harmful and polluting solvents like dimethylformamide (DMF). However, solution processing of green and environmentally safe solvents such as dimethyl sulfoxide (DMSO) via scalable printing is challenging mainly because of two reasons: first is the pronounced precursor solution dewetting on the subjacent layer and second its complex quenching process. In this work, we report on one-step blade coating of inverted (p-i-n) double-cation PSCs using solely DMSO at low processing temperatures. To avoid dewetting of the DMSO-based solution on the hydrophobic hole transport layer (HTL) and to realize adequate quenching, a blade-coated wetting agent of silicon oxide nanoparticles at the HTL/perovskite interface and gas stream-assisted drying are applied, respectively. Trends in absorber grain size, morphology, crystallinity, and elemental composition of samples from both toxic and green solvent concepts are compared, revealing analogous findings. Consequently, PSCs blade-coated from DMSO achieve PCEs of up to 16.7% on a 0.24 cm2active area comparable to the ones from a DMF:DMSO mixture (16.9%), thus demonstrating that using toxic DMF is unnecessary. This represents an important step for bringing PSCs solution-processed from environmentally friendly precursor solvents closer to industrial implementation.