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By: Prof. Dr. Yana Vaynzof, Technical University of Dresden, Germany

Abstract: The last decade has witnessed remarkable progress in the field of lead halide perovskite materials and devices. An examination of the existing body of literature reveals a particularly wide spread in the photovoltaic (PV) performance and stability of devices. Focusing on two model systems, namely methylammonium lead triiodide (MAPbI3) and triple cation perovskite, we investigate how minor, likely unintentional, variations in the fabrication procedure of the perovskite layer may affect its properties and consequently those of the complete PV devices. In the case of MAPbI3, we demonstrate that fractional deviations in precursor stoichiometry result in significant changes to the surface composition and energetics, crystallinity, emission efficiency and the energetic disorder of the perovskite layers. These variations result in a spread of PV performance and significant disparities in device stability,[1] related to differences in the density of ionic defects in the perovskite active layers.[2,3]

In the case of triple cation perovskites, we find that it is the antisolvent quenching step that determines the reproducibility of the fabricated devices. Specifically, the duration for which the perovskite is exposed to the antisolvent has a dramatic impact on the final device performance, a variable which had, until now, gone unnoticed in the field. We show that this is related to the fact that certain antisolvents may at least partly dissolve the precursors of the perovskite layer, thus altering its final composition. Additionally, the miscibility of antisolvents with the perovskite solution solvents influences their efficacy in triggering crystallization. We demonstrate that depending on these two properties, it is possible to fabricate efficient perovskite solar cells from any antisolvent.[4] Finally, we show that by modifying the method of antisolvent deposition, it is possible to far better preserve the intended stoichiometry of the perovskite layers, thus increasing the photovoltaic device performance.[5]

References: [1] P. Fassl et al, Energy Environ. Sci. 2018,11, 3380. [2] P. Fassl et al, J. Mater. Chem. C 2019, 7 (18), 5285. [3] S. Reichert et al, Nat. Commun. 2020, 11, 6098. [4] A. D. Taylor et al, Nat. Commun. 2021, 12, 1878. [5] O. Telschow et al, submitted.

Introductory talk: "From materials to highly efficient and stable devices" by Masoud Karimipour, Postdoctoral Researcher at Nanostructured Materials for Photovoltaic Energy Group at ICN2