Solvent Vapour Annealing of Methylammonium Lead Halide Perovskite: What's the catch?
Onkar S. Game a, Joel A. Smith a, Tarek I. Alanazi a, Michael Wong-Stringer a, Vikas Kumar b, Cornelia Rodenburg b, Nick J. Terril c, David G. Lidzey a
a Department of Physics and Astronomy, University of Sheffield, UK, Hounsfield Road, United Kingdom
b Department of Materials Science and Engineering, The University of Sheffield
c Diamond Light Source, Didcot OX11 0DE, UK.
Proceedings of Online International Conference on Hybrid and Organic Photovoltaics (OnlineHOPV20)
Online, Spain, 2020 May 26th - 29th
Organizers: Tracey Clarke, James Durrant, Annamaria Petrozza and Trystan Watson
Poster, Joel A. Smith, 133
Publication date: 22nd May 2020

Solvent vapour annealing (SVA) is a common post-processing technique used to increase the average grain size of lead halide perovskite films and thus enhance device performance.[1] The prevailing wisdom is that large grain perovskite films lead to enhanced stability, however, we observed the reverse in MAPI with dimethylformamide vapour treatment compared to non-SVA controls.[2] Using a range of microstructural characterisation techniques, we reveal that SVA is not a chemically benign grain-growth process, but leads to substantial stoichiometric changes in the perovskite films. Intrinsic material degradation is investigated under external loading with in-situ X-ray scattering, and combined with lifetime testing on full devices. We show that the operational stability of SVA devices greatly depends on the initial stoichiometry of the MAPI with PbI2-excess compositions being least stable. However, the incorporation of excess organic-halides in the precursor solution helps to mitigate the deleterious effects of SVA on device stability. This work critically re-evaluates current thinking around grain structure and stoichiometry in achieving long-term stability for perovskite solar cells.

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