Artifact-Free Depth Profiles Acquired by ToF-SIMS and Their Utility in Revealing Perovskite Solar Cells' Natures
Cheng-Hung Hou a, Jing-Jong Shyue a, Shu-Han Hung a, Li-Ji Jhang a
a Academia Sinica
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Cheng-Hung Hou, 024
Publication date: 11th February 2019

Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) is a powerful analytical tool that provides one-dimensional (depth profile), two-dimensional (image mapping) and three-dimensional (3D tomography) composition information and recently it was used to probe perovskite solar cells (PSCs) for getting insights into this emerging technology. However, very few have been aware that when probing the perovskite films usingToF-SIMS, the applied ion beams must be carefully chosen otherwise misleading artifacts will appear. In this study, we firstly verified that when using the commonly applied O2+ sputter beam, the organic component (MA+ or FA+) was removed at a much higher rate than the inorganic components (Pb2+, I- and Br-). The unequal sputter rates of the film components, which are also known as preferential sputtering, could result in a false component gradient in the depth profile. Here, we demonstrated that by substituting Ar+ or the bulky ion (C60+ or Ar4000+) sputter beam for O2+ sputter beam, preferential sputtering can be significantly suppressed, yielding a depth profile without anomalous concentration gradient. Using Ar+ sputter beam, we verified that the ideal morphology for PSCs was achieved when all the components were uniformly distributed throughout the perovskite film. Such morphology can be realized effortlessly via solvent-engineering procedure. We also provided unambiguous evidence showing that halogenation of Ag electrode is the main deteriorating mechanism of inverted PSCs. This study highlights the importance of proper ToF-SIMS data acquiring condition and, more importantly, it demonstrates ToF-SIMS as a powerful analytical tool which provides crucial evidences that lay foundations for further scientific explorations.

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