Dresden 2020 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 19: Focus Session: When theory meets experiment: Hybrid halide perovskites for applications beyond solar II (joint session HL/CPP)
HL 19.2: Invited Talk
Monday, March 16, 2020, 15:30–16:00, POT 251
Solid state ionics of hybrid halide perovskites: equilibrium situation and light effects — •Alessandro Senocrate1,2, Gee Yeong Kim1, Tae Youl Yang1, Giuliano Gregori1, Michael Graetzel1,2, and Joachim Maier1 — 1Max Planck Institute for Solid State Research, Stuttgart, Germany — 2École polytechnique fédérale de Lausanne
In recent years, hybrid halide perovskites have been attracting great attention due to their exceptional photo-electrochemical properties. When used as light-harvesters in solar cells, device efficiencies exceeding 25% can be realized. We showed that a deeper understanding of (i) functionality, (ii) stability, as well as (iii) the possibility to improve the performance require a thorough insight into non-stoichiometry and ion transport.
In this contribution, we study the nature of the ionic conductivity in methylammonium lead iodide (MAPbI3), the archetypal halide perovskite, by means of a great number of electrochemical and nuclear magnetic techniques. To aid the experimental investigation, we include detailed defect chemical modelling describing the effects of varying iodine partial pressure (stoichiometry) and dopant content. By extending this study to the situation under illumination, we observe a striking enhancement of ionic conductivity by more than 2 orders of magnitude in MAPbI3, alongside the expected increase in electronic conductivity. We provide a mechanistic explanation of this astonishing phenomenon and discuss its relevance for the photo-stability of this class of materials.