Proceedings of MATSUS Fall 2024 Conference (MATSUSFall24)
DOI: https://doi.org/10.29363/nanoge.matsusfall.2024.142
Publication date: 28th August 2024
To make better electronic and light-based devices using advanced materials, we need to understand how their structure affects their properties. Hybrid organic/inorganic perovskites are promising new materials, which are both soft and ionic, i.e. atoms can wiggle around their equilibrium positions and they are highly charged1. Transitions of electrons to different bands will distort the crystal lattice, and it will do so along specific vibrational coordinates. While there is consensus that electron-phonon interactions in these materials are crucial in determining their optoelectronic properties, i.e. EPC limits the maximum charge-carrier mobility2, it has been extremely challenging to obtain direct- and mode specific information on these interactions.
The big question is: which vibrational modes are coupled how strong to which electrons? And how do we measure this?
Here, we will dive into the world of (multidimensional) THz spectroscopy to answer the above questions. I will highlight our recently developed 2D-electron-phonon-coupling spectroscopy (2D-EPC), which can extract direct information on mode-specific electron-phonon interactions. We benchmarked this technique on prototypical methylammonium lead iodide, and show there is distinct behavior of the coupling of electrons between two different vibrational modes. Temperature dependent experiments allow us to follow the EPC over the tetragonal-to-orthorhombic phase transition, and polarization dependence allows us to study mode-specific and direction-dependent dispersion of this coupling3.
We also varied the A-site cation in three prototypical ‘black-phase’ perovskites: methylammonium (MA) lead iodide, formamidinium (FA) lead iodide and Cesium lead iodide, and demonstrate differences in the coupling between vibrational modes of the inorganic lattice and electrons with different energies.
V.K.S. and F.P. acknowledge funding by the Deutsche Forschungsgemeinschaft (DFG) through the Collaborative Research Center TRR 288 (project number 422213477, project B09). H.K. and S.Q. thank the DFG for financial support through the Collaborative Research Center TRR 288 (project number 422213477, project B07). J.J.G. gratefully acknowledges support through an Alexander von Humboldt fellowship. This work was also supported by the National Research Foundation (NRF) of Korea (grant number 2021R1A6A1A10042944).
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