X-PEEM Investigation of Chemical and Eectronic Surface Properties of Solution Processed Perovskite-Based Thin-Film Solar Cell Structures

Evelyn Handick^a, Claudia Hartmann^a, Regan G. Wilks^a^,^c, Marcus Bär^a^,^c^,^g, Golnaz Sadoughi^b, Henry Snaith^b, Simone Raoux^c^,^e^,^f, Hagen W. Klemm^d, Gina Peschel^d, Ewa Madej^d, Alexander B. Fuhrich^d, Thomas Schmidt^d

^aDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom

^bDepartment of Chemical Physics – Spectro-Microscopy Group, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, 14195 Berlin, Germany

^cHumboldt-Universität, Institut für Physik, Brook-Taylor-Straße, 6, Berlin, Germany

^dInstitut für Physik und Chemie, Brandenburgische Technische Universität Cottbus-Senftenberg, D-03046 Cottbus, Germany

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV16)

Swansea, United Kingdom, 2016 June 29th - July 1st

Organizers: James Durrant, Henry Snaith and David Worsley

Oral, Claudia Hartmann, presentation 049
Publication date: 28th March 2016

Solid-state hybrid solar cells using a newly developed class of solution-processable organolead trihalide compounds – specifically the perovskite material system (AMX₃, with A = e.g., CH₃NH₃⁺ or CH(NH₂)₂⁺; M = e.g., Pb or Sn; and X = I, Cl, or Br) – as absorbers have already achieved conversion efficiencies exceeding 20 %.[1] Respective devices can be produced by using low cost absorber fabrication methods, i.e. deposition from solution at low process temperatures 2. Using photoemission electron microscopy (PEEM) to investigate the interface of the 300 nm CH₃NH₃PbI_(3-x)Cl_x perovskite thin film on planar compact TiO₂ (c-TiO₂) on FTO/glass substrates provides us with insight into coverage, morphology, and local elemental composition of the sample. Based on the collected PEEM data (and complementary scanning electron microscopy images) we find an incomplete coverage, with holes reaching to the c-TiO₂ substrate, as revealed by spatially resolved Ti L_2,3-edge x-ray absorption PEEM measurements. In fact, three different topologies can be distinguished in our PEEM images, reflecting different degrees of coverage as well as chemical composition. Depending on the degree of coverage, energy filtered PEEM data indicates enhanced iodine oxidation and/or the formation of metallic Pb in the proximity of the c-TiO₂ substrate.In our contribution, a detailed spatially resolved picture of the chemical structure of the CH₃NH₃PbI_(3-x)Cl_x perovskite/c-TiO₂ will be presented. These findings might lead to potential pathways to improve coverage and chemical homogeneity of the solution processed perovskite absorber layer.

[1] http://www.dyesol.com/media/wysiwyg/Documents/2015-asx-announcements/2015-12-08-DYE0397_-_EPFL_achieves_21_efficiency.pdf

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