Reliable Atomic-Resolution Observations of the Nanoscopic Properties of Hybrid Perovskite Thin Films
Mathias Uller Rothmann a, Judy Kim b c d, Juliane Borchert a, Kilian Lohmann a, Colum O'Leary b, Alex Sheader b, Michael Johnston a, Henry Snaith a, Peter Nellist b, Laura Herz a
a Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
b Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH
c ePSIC, Diamond Light Source
d Rosalind Franklin Institute
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
Oral, Mathias Uller Rothmann, presentation 030
Publication date: 11th February 2019

Atomic resolution transmission electron microscope (TEM) studies have been invaluable in understanding the most fundamental properties of many crystalline semiconductor solar cell materials. The large electron energies involved in most TEM studies have, however, meant that studying the typically unstable photoactive hybrid perovskites reliably has been challenging.[1] Particularly the very close structural relationship between certain crystallographic orientations of the pristine perovskite structure and lead iodide has led to previous atomic resolution studies generating ambiguous result that do not correspond well to the crystallographic properties observed with other methods.[2] Using extremely low dose scanning TEM (STEM), we have been able to image hybrid perovskites, including MAPbI3 and FAPbI3, with atomic resolution in accordance to the generally agreed upon crystal structures. As a result, we have been able unequivocally to distinguish the different components of the perovskite structure within the crystal lattice. Furthermore, we have identified nanoscopic domains of PbI2 integrating seamlessly within the perovskite lattice, suggesting that the benign nature of the presence of some PbI2 can be due to the continuous nature of the crystal lattice. These findings pave the way for a significant shift in the level of detail with which the microscopic properties of hybrid photoactive perovskite can be studied, including the crystallographic nature of grain boundaries and the distribution of dopants.

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