8 research outputs found

    2D metal halide perovskites: a new fascinating playground for exciton fine structure investigations

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    Two-dimensional (2D) metal halide perovskites are natural quantum wells which consist of low bandgap metal-halide slabs, surrounded by organic spacers barriers. The quantum and dielectric confinements provided by the organic part lead to the extreme exciton binding energy which results in a huge enhancement of exciton fine structure in this material system. This makes 2D perovskites a fascinating playground for fundamental excitonic physics studies. In this review, we summarize the current understanding and quantification of the exciton fine structure in 2D perovskites. We discuss what is the role of exciton fine structure in the optical response of 2D perovskites and how it challenges our understanding of this fundamental excitation. Finally, we highlight some controversy related to particularly large bright-dark exciton states splitting and high efficiency of light emission from these materials. This can result from the unique synergy of excitonic and mechanical properties of 2D perovskites crystals

    Quantification of Exciton Fine Structure Splitting in a Two-Dimensional Perovskite Compound

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    International audienceApplications of two-dimensional (2D) perovskites have significantly outpaced the understanding of many fundamental aspects of their photophysics. The optical response of 2D lead halide perovskites is dominated by strongly bound excitonic states. However, a comprehensive experimental verification of the exciton fine structure splitting and associated transition symmetries remains elusive. Here we employ low temperature magneto-optical spectroscopy to reveal the exciton fine structure of (PEA)2PbI4 (here PEA is phenylethylammonium) single crystals. We observe two orthogonally polarized bright in-plane free exciton (FX) states, both accompanied by a manifold of phonon-dressed states that preserve the polarization of the corresponding FX state. Introducing a magnetic field perpendicular to the 2D plane, we resolve the lowest energy dark exciton state, which although theoretically predicted, has systematically escaped experimental observation (in Faraday configuration) until now. These results corroborate standard multiband, effective-mass theories for the exciton fine structure in 2D perovskites and provide valuable quantification of the fine structure splitting in (PEA)2PbI4

    Polaronic Mass Enhancement and Polaronic Excitons in Metal Halide Perovskites

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    International audienceIn metal halide perovskites, the complex dielectric screening together with low energy of phonon modes leads to non-negligible Fröhlich coupling. While this feature of perovskites has already been used to explain some of the puzzling aspects of carrier transport in these materials, the possible impact of polaronic effects on the optical response, especially excitonic properties, is much less explored. Here, with the use of magneto-optical spectroscopy, we revealed the non-hydrogenic character of the excitons in metal halide perovskites, resulting from the pronounced Fröhlich coupling. Our results can be well described by the polaronic-exciton picture where electron and hole interactions are no longer described by a Coulomb potential. Furthermore, we show experimental evidence that the carrier-phonon interaction leads to the enhancement of the carrier’s effective mass. Notably, our measurements reveal a pronounced temperature dependence of the carrier’s effective mass, which we attribute to a band structure renormalization induced by the population of low-energy phonon modes. This interpretation finds support in our first-principles calculations

    Quantification of Exciton Fine Structure Splitting in a Two-Dimensional Perovskite Compound

    No full text
    Applications of two-dimensional (2D) perovskites have significantly outpacedthe understanding of many fundamental aspects of their photophysics. The optical response of2D lead halide perovskites is dominated by strongly bound excitonic states. However, acomprehensive experimental verification of the excitonfine structure splitting and associatedtransition symmetries remains elusive. Here we employ low temperature magneto-opticalspectroscopy to reveal the excitonfine structure of (PEA)2PbI4(here PEA is phenyl-ethylammonium) single crystals. We observe two orthogonally polarized bright in-plane freeexciton (FX) states, both accompanied by a manifold of phonon-dressed states that preservethe polarization of the corresponding FX state. Introducing a magneticfield perpendicular tothe 2D plane, we resolve the lowest energy dark exciton state, which although theoreticallypredicted, has systematically escaped experimental observation (in Faraday configuration)until now. These results corroborate standard multiband, effective-mass theories for theexcitonfine structure in 2D perovskites and provide valuable quantification of the finestructure splitting in (PEA)2PbI
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