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Tin is one of the most promising alternatives to lead to make lead-free halide perovskites for optoelectronics. However, the stability of tin-based perovskites is hindered by the oxidation of Sn(II) to Sn(IV). Recent works established that dimethyl sulfoxide, which is one of the best-performing solvents for processing perovskite, is the primary source of tin oxidation. The quest for a stable solvent could be a game-changer in the stability of tin-based perovskites. Starting from a database of over 2000 solvents, we identified a series of 12 new solvents suitable for the processing of formamidinium tin iodide perovskite (FASnI3) by investigating (1) the solubility of the precursor chemicals FAI and SnI2, (2) the thermal stability of the precursor solution, and (3) the possibility of forming perovskite. Finally, we demonstrate a new solvent system to produce solar cells outperforming those based on DMSO. Our work provides guidelines for further identification of new solvents or solvent mixtures for preparing stable tin-based perovskites.

Tin halide perovskites attract incremental attention to deliver lead free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn II oxidation to Sn IV , limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n butylammonium acetate BAAc is used to tune the tin coordination with specific O Sn chelating bonds and N amp; 63743;H X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn IV and related chemical defects are found for the BAAc containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10 . This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin based perovskite crystallization for stable and efficient lead free perovskite photovoltaics

Low toxicity and an ideal energy bandgap make two-dimensional (2D) Ruddlesden–Popper tin-based halide perovskites a promising photovoltaic material. However, the disordered crystal orientation and the oxidation of Sn2+ to Sn4+ still need to be addressed. Here, we demonstrate that the annealing of FASnI3 assisted by phenyl ethylammonium chloride enables the formation of more ordered 2D tin-based perovskite crystals oriented vertically. We use in situ synchrotron-based grazing incident X-ray diffraction to correlate the higher crystal orientation to the better device performance. We measured a maximum power conversion efficiency of more than 9%. Furthermore, we demonstrate that the phenyl ethylammonium chloride acts as a barrier layer at the surface of the crystals protecting the tin from the oxidation. Hence, this work paves the way for more efficient and stable lead-free perovskite solar cells.