Fabrication of MAPbI3 from non-toxic solvents for “greener” solution-processed perovskite solar cells
Feray Ünlü a, Alejandra Florez b, Keely Dodd-Clements a, Carolin Rehermann a, Matthias Grosch c, Florian Mathies a, Sanjay Sanjay c, Eva Unger a
a Department of Solution-Processed Materials and Devices, HySPRINT Innovation Lab, Helmholtz-Zentrum Berlin für Materialen und Energie GmbH, Kekuléstraße 5, 12489 Berlin, Germany
b CIDEMAT, Universidad de Antioquia, Calle 67 52-20, Torre B, Piso de 4, Ruta N Complex, Medellín, Colombia
c Inorganic and Materials Chemistry, University of Cologne, Greinstr. 6, 50939 Cologne, Germany
Poster, Feray Ünlü, 226
Publication date: 6th February 2024

In this work, efforts were made to reduce the toxicity of MAPbI3 perovskite precursor ink by substituting toxic solvents with non-toxic alternatives. The introduction of the protic ionic liquid methylammonium propionate (MAP, [CH3NH3][C2H5COO]) played a pivotal role in dissolving the perovskite precursors, including lead acetate (Pb(OAc)2) and methylammonium iodide, in water and iso-propanol. For the first time, a stable water-containing perovskite precursor ink was presented, which is suitable for one-step thin film deposition. The solution chemistry of the water-based inks distinctly differs from that of DMF
and DMSO-based inks. This difference can be attributed to the stronger coordination strength of propionate, acetate, and water molecules in the new inks. In-situ photoluminescence (PL) measurements confirmed an intermediate-free liquid-to-solid transition. Additionally, in-situ mass spectrometry (MS) measurements indicated the evaporation of the organic molecules from the perovskite layer during annealing leading to a crystalline perovskite phase. After optimizing the solvent composition to H2O/IPA/MAP, we successfully conducted one-step slot-die coating for thin film deposition, resulting in high-crystallinity perovskite phases. By fine-tuning slot-die coating parameters such as coating speed,  substrate temperature, and nitrogen flow pressure, we achieved perovskite solar cells with power conversion efficiencies up to 10%. The green ink demonstrated reduced toxicity and environmental impact compared to the standard ink, with notable reductions in e.g. climate change impact, freshwater ecotoxicity, and water use. This environmentally friendly ink, combined with a longer shelf life, holds
promise for commercial applications, underscoring the importance of ongoing optimization in perovskite solar cell development.

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