Photoinduced Halide Segregation and Diffusion in Mixed-halide Perovskite Solar Cells

Terry Chien-Jen Yang^a, Pietro Caprioglio^c^,^d, Fan Fu^a, Peter Fiala^a, Martin Stolterfoht^c, Florent Sahli^a, Ricardo Razera^a^,^e, Matthias Bräuninger^a, Steve Albrecht^d, Dieter Neher^c, Quentin Jeangros^a, Christophe Ballif^a^,^b

^aÉcole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin-Film Electronics Laboratory (PV-Lab), CH, Rue de la Maladière, 71, Neuchâtel, Switzerland

^bCSEM, PV-Center, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland

^cUniversity of Potsdam, Institute of Physics and Astronomy, Karl-Liebknecht-Str 24-25, Potsdam, 14476, Germany

^dHelmholtz-Zentrum Berlin für Materialien und Energie GmbH, Young Investigator Group Perovskite Tandem Solar Cells, Berlin, Germany

^ePGMICRO, Instituto de Física, UFRGS, Av. Bento Gonçalves 9500, Porto Alegre-RS, Brazil

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)

Roma, Italy, 2020 May 12th - 14th

Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo

Oral, Terry Chien-Jen Yang, presentation 151
DOI: https://doi.org/10.29363/nanoge.hopv.2020.151
Publication date: 6th February 2020

Photoinduced halide segregation, a phenomenon first shown by Hoke et al. [1] (2014) via photoluminescence (PL) peak shifting over time, poses a serious problem for high-bandgap mixed-halide perovskites which are used in high-efficiency multijunction solar cells (e.g. perovskite-silicon, perovskite-Cu(In,Ga)Se₂ and perovskite-perovskite tandems) [2]. The main issue is that a proportional increase in bandgap with increasing bromide-to-iodide ratio does not yield the same increase in open-circuit voltage, thus limiting their performance. In this work, we investigate the diffusion controlled mechanisms behind photoinduced halide segregation in long-term stable cesium-formamidinium perovskites, fabricated via a 2-step hybrid deposition technique [3], as well as fully evaporated all-inorganic Cs-based perovskites. Temperature-dependent PL show distinct peak shifts attributed to the parting of iodide and bromide into separate domains, while the diffusion process slows down and eventually stops with a decrease in temperature. Therefore, solid-state diffusion models [4] can be used to fit the temperature-dependent PL of these mixed iodide-bromide compositions providing quantitative insights into the diffusion controlled mechanisms. In addition to peak shifting, for some samples, absolute PL measurements revealed increasing PL quantum yields in excess of 22% over time under constant illumination, after the phases segregate. The influence of this photoinduced halide segregation and diffusion on perovskite solar cell properties will be discussed at the conference.

References:

[1] Hoke, E. T.; Slotcavage, D. J.; Dohner, E. R.; Bowring, A. R.; Karunadasa, H. I.; McGehee, M. D. Reversible Photo-Induced Trap Formation in Mixed-Halide Hybrid Perovskites for Photovoltaics. Chem. Sci. 2015, 6 (1), 613–617

[2] Yang, T. C. J.; Fiala, P.; Jeangros, Q.; Ballif, C. High-Bandgap Perovskite Materials for Multijunction Solar Cells. Joule 2018, 2 (8), 1421–1436

[3] Sahli, F.; Werner, J.; Kamino, B. A.; Brauninger, M.; Yang, T. C.-J.; Fiala, P.; Nogay, G.; Fu, F.; Monnard, R.; Walter, A.; et al. Hybrid Sequential Deposition Process for Fully Textured Perovskite/Silicon Tandem Solar Cells. 2018 IEEE 7th World Conf. Photovolt. Energy Convers. (A Jt. Conf. 45th IEEE PVSC, 28th PVSEC 34th EU PVSEC) 2018, 3571–3574

[4] Khawam, A.; Flanagan, D. R. Solid-State Kinetic Models: Basics and Mathematical Fundamentals. J. Phys. Chem. B 2006, 110 (35), 17315–17328

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