Masoumeh Keshavarz, Molecular Imaging and Photonics, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium

Shedding light on the optoelectronic and structural properties of halide perovskites

January 21, 02:00 PM, Paris Time (GMT +1)

The extraordinary properties of metal halide perovskite materials have spurred intense research, as they have a realistic perspective to play an important role in future photovoltaic devices. In my talk, I will focus on the investigation of single crystals of different perovskite groups using temperature-dependent photoluminescence, magneto-transport under steady-state illumination [1] and thermal expansion between 4.2 K and room temperature [2]. The latter techniques are beyond conventionally employed characterization techniques for these materials. I will show that magnetotransport under steady-state illumination is a powerful tool to unravel the fundamental properties of charge carriers such as carrier density and mobility, and the underlying carrier scattering mechanisms at different temperatures. Perovskites are known to undergo structural phase transitions when cooling down from room temperature to 4.2 K starting from a high-temperature cubic phase via a tetragonal to a low temperature orthorhombic phase. Using a high-resolution capacitive dilatometer, the occurrence of structural phase transitions in a temperature range between 4.2 and 280 K for the single crystals can be illustrated. Depending on the material, abrupt changes in the linear thermal expansion ΔL(T)/L occur that are associated with structural phase transitions. The structure of the crystals in each phase is identified via single crystal XRD. These phase transitions can affect the optoelectronic properties of the materials, hence, be revealed in transport under steady-state illumination and in temperature dependent photoluminescence experiments. I will demonstrate how the latter technique provides access to the electron-phonon coupling and the dominant scattering mechanisms in these materials. These combined techniques can be applied and extended to other families of halide perovskite materials such as double perovskites, which are inherently more stable under ambient conditions compared to their “single” perovskite counterparts. However, their power conversion efficiencies in photovoltaic devices is still significantly lower compared to single perovskites. I will demonstrate that cation-substitution entails a tunability to double perovskites regarding the response to high-energy photon detection through X-ray detectors. Their response upon X-ray exposure drastically changes and their X-ray sensitivity outperforms other double perovskite-based devices reported [3].

The work that will be presented in my talk is a collective collaborative effort of : Masoumeh Keshavarz, Elke Debroye, Johan Hofkens : Molecular Imaging and Photonics, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium. Maarten Roeffaers, Julian Steele : Department of Molecular and Microbial Systems, KU Leuven, Belgium, Kasteelpark Arenberg, 23, Leuven, Belgium. Joris Van de Vondel : Quantum Solid-State Physics (QSP), Department of Physics and Astronomy, KU Leuven, Celestijnenlaan, 200D, Leuven 3000, Belgium. Steffen Wiedmann : High Field Magnet Laboratory, HFML-EMFL, Radboud University, The Netherlands. Robert Küchler : Max Planck Institute for Chemical Physics of Solids, Dresden, Nöthnitzer Straße, 40H, Dresden, Germany. Martin Ottesen, Martin Bremholm : Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark.

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