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
a École Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin-Film Electronics Laboratory (PV-Lab), Rue de la Maladière 71b, Neuchâtel 2002, Switzerland
b CSEM, PV-Center, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland
c Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam-Golm, Germany
d Young Investigator Group Perovskite Tandem Solar Cells, Helmholtz-Zentrum Berlin, Berlin, Germany
e PGMICRO, Instituto de Física, UFRGS, Av. Bento Gonçalves 9500, Porto Alegre-RS, Brazil
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, Terry Chien-Jen Yang, presentation 151
Publication date: 11th February 2019

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.

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