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Silva, Carlos

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Author: Neutzner, Stefanie ×

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    Exciton-Polaron Spectral Structures in Two-Dimensional Hybrid Lead-Halide Perovskites
    (Georgia Institute of Technology, 2018-06-29) Neutzner, Stefanie ; Thouin, Félix ; Cortecchia, Daniele ; Petrozza, Annamaria ; Silva, Carlos ; Kandada, Ajay Ram Srimath
    Owing to both electronic and dielectric confinement effects, two-dimensional organic-inorganic hybrid perovskites sustain strongly bound excitons at room temperature. Here, we demonstrate that there are nonnegligible contributions to the excitonic correlations that are specific to the lattice structure and its polar fluctuations, both of which are controlled via the chemical nature of the organic countercation. We present a phenomenological yet quantitative framework to simulate excitonic absorption line shapes in single-layer organic-inorganic hybrid perovskites, based on the two-dimensionalWannier formalism.We include four distinct excitonic states separated by 35 ± 5 meV, and additional vibronic progressions. Intriguingly, the associated Huang-Rhys factors and the relevant phonon energies show substantial variation with temperature and the nature of the organic cation. This points to the hybrid nature of the line shape, with a form well described by a Wannier formalism, but with signatures of strong coupling to localized vibrations, and polaronic effects perceived through excitonic correlations. Our work highlights the complexity of excitonic properties in this class of nanostructured materials.
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    Stable Biexcitons In Two-Dimensional Metal-Halide Perovskites With Strong Dynamic Lattice Disorder
    (Georgia Institute of Technology, 2018-03-08) Thouin, Félix ; Neutzner, Stefanie ; Cortecchia, Daniele ; Dragomir, Vlad Alexandru ; Soci, Cesare ; Salim, Teddy ; Lam, Yeng Ming ; Leonelli, Richard ; Petrozza, Annamaria ; Kandada, Ajay Ram Srimath ; Silva, Carlos
    With strongly bound and stable excitons at room temperature, single-layer, two-dimensional organic-inorganic hybrid perovskites are viable semiconductors for light-emitting quantum optoelectronics applications. In such a technological context, it is imperative to comprehensively explore all the factors—chemical, electronic, and structural—that govern strong multiexciton correlations. Here, by means of two-dimensional coherent spectroscopy, we examine excitonic many-body effects in pure, single-layer (PEA)2PbI4 (PEA = phenylethylammonium). We determine the binding energy of biexcitons—correlated two-electron, two-hole quasiparticles—to be 44 ± 5meV at room temperature. The extraordinarily high values are similar to those reported in other strongly excitonic two-dimensional materials such as transition-metal dichalcogenides. Importantly, we show that this binding energy increases by ∼25% upon cooling to 5 K. Our work highlights the importance of multiexciton correlations in this class of technologically promising, solution-processablematerials, in spite of the strong effects of lattice fluctuations and dynamic disorder.