Analysis of the degradation products of hybrid perovskite by correlative electron microscopy
Salim Mejaouri a b, Stéfania Cacovich a c, Iwan Zimermman a, Armelle Yaiche a b, Dominique Loisnard d, Stéphane Collin a e, Jean Rousset a b
a IPVF, Institut Photovoltaïque d’Ile-de-France, 18 Boulevard Thomas Gobert, 91120 Palaiseau, France
b EDF R&D, 7 boulevard Gaspard Monge, 91120 Palaiseau, France
c CNRS, École Polytechnique, IPVF, UMR 9006, 18, Boulevard Thomas Gobert, 91120 Palaiseau, France
d EDF Lab Les Renardières, Avenue des Renardières, 77250 Écuelles, France
e C2N, Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Saclay, 10 Boulevard Thomas Gobert, 91120 Palaiseau, France
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Salim Mejaouri, presentation 152
Publication date: 20th April 2022

Improving the stability of lead halide perovskite (LHP) solar cells is a major challenge towards their industrialization. Nowadays, most studies are focused on the impact of the environment on the device performances, like temperature sensitivity or photo-instability. However, an in-depth knowledge of internal degradation mechanisms is still lacking.

In this context, it has been shown that moisture induces changes in global Perovskite Solar Cell (PSC) performances. It comes with alterations of the absorber nature like phase transition or segregation. Understanding how the material evolves in a wet environment is mandatory to optimize device performances and stability. It requires advanced characterization techniques with nanoscale spatial resolution.

In the present work, we investigate the chemical and structural evolution of triple cation mixed halide perovskite thin-film (Cs0.05MA0.45FA0.5Pb(I0.83Br0.17)3)  after ageing under controlled humidity. The analysis is performed at different scales, through Photolomuniscence (PL), X-ray  Diffraction Spectroscopy (XRD), Cathodoluminescence (CL), Selected Area Diffraction (SAED), and Energy Dispersive X-ray Spectroscopy (EDS) in a SEM and a STEM. Special care was taken during specimen preparation and characterization to perform SEM-based (CL and EDS) and TEM-based (STEM-EDS and SAED) measurements in the same regions.

We correlate optical and chemical variations to morphological changes at a microscopic level from the analysis of the perovskite layer’s degradation products. We evidence the formation of lead-iodide (PbI2), inorganic mixed halide (CsPb(BrxI1-x)3) and lead-rich (CsPb2(BryI1-y)5) perovskite phases. They demonstrate a high degree of crystallinity that induces unique geometrical shapes. By correlating high-resolution characterizations techniques, we identify the precise nature of these specific species. This work provides insights in the degradation mechanisms of hybrid perovskite materials.

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