Tin-lead Perovskites: Perfect Alloy or Nano-scale Tin-Lead Ratio Inhomogeneity
Larissa van de Ven a b, Daphne Antony a, Maria Antonietta Loi b, Bruno Ehrler a
a AMOLF Institute, Science Park 104, Amsterdam, 1098XG The Netherlands
b Zernike Institute for Advanced Materials, University of Groningen, Netherlands
Poster, Larissa van de Ven, 209
Publication date: 6th February 2024

In the progress towards all-perovskite tandem solar cells, significant effort is focused on half tin – half lead perovskites. Compared to their pure tin counterpart an even lower band gap can be obtained due to the “band-bowing effect”. [1] In addition, these perovskites have been found to suffer less severely from oxidation than pure tin perovskites, more so than can be explained by simply considering the lower tin concentration in the structure. [2] This stabilizing effect was suggested to be due to a perfect alloy nature of the tin-lead perovskite, where every tin cation has a lead cation in an adjacent octahedron that oxidizes much less readily. [2] At the same time, however, several groups observed inhomogeneity in the tin-lead ratio over the thin film and have connected it to the higher Lewis acidity of Sn2+, resulting in unsynchronized crystallization of the tin and lead precursors. [3, 4, 5] In this study, we investigate whether cluster formation occurs, and under which conditions it is relevant. We consider both the fully inorganic cesium-based tin-lead perovskite as well as a hybrid formamidinium-based tin-lead perovskite. To unravel the existence of inhomogeneity in the tin-lead ratio, we employ energy-dispersive X-ray spectroscopy, AFM-based techniques and solid-state NMR. In this way, we aim to understand what happens to the clusters under various external stimuli, upon degradation and how these clusters impact the thin film stability, the film quality and device performance.

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