Fabrication of MAPbI3 from non-toxic solvents for “greener” solution-processed perovskite solar cells

Feray Ünlü, Alejandra Florez, Keely Dodd-Clements, Carolin Rehermann, Matthias Grosch, Florian Mathies, Sanjay Sanjay, Eva Unger

Abstract:

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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Eva UNGER

Project Coordinator and WP1 Leader