SKM 2021 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 1: Focus Session: When theory meets experiment: Hybrid halide perovskites for applications beyond solar
HL 1.4: Invited Talk
Monday, September 27, 2021, 11:45–12:15, H4
Solid state ionics of hybrid halide perovskites: equilibrium situation and light effects — •Alessandro Senocrate1,2, Gee Yeong Kim1, Tae-Youl Yang1, Giuliano Gregori1, Michael Grätzel1,2, and Joachim Maier1 — 1Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany — 2École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
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. Such analyses are then extended to other halide perovskite compositions. While discussing these results, a mechanistic explanation of this astonishing phenomenon arises, which has relevance for photo-stability and photo-demixing processes.