DOI: https://doi.org/10.29363/nanoge.emlem.2023.039
Publication date: 18th August 2023
Perovskite semiconductors are appealing for optoelectronic and photonic applications. The knowledge currently available about the energy structure of photoexcited electrons, holes and exciton complexes, their interaction, binding energy, and relaxation dynamics are far from being complete. Conventional time-integrated reflectivity or photoluminescence techniques alone often do not allow one to make unambiguous conclusions about the energy structure due to inhomogeneous broadening of optical transitions and complex dynamics of photoexcited carriers. Here, nonlinear optical techniques based on photon echoes or two-dimensional Fourier spectroscopy provide unique access to the energy structure of perovskite semiconductors.
We investigate the coherent dynamics of excitons in halide perovskites materials of different composition and dimensionality. Most importantly, the exciton itself serves as a probe for the interaction with the crystal lattice, local potential fluctuations, other excitons and charge carriers in our studies. First, the results on single bulk crystals are presented. Here, the magnitude of fluctuations of the energy bandgap is evaluated. We observe exceptionally long exciton coherence time up to 80 ps at low temperature of 1.5K in mixed mixed-halide perovskite crystals due to the localization of excitons at the scale of tens to hundreds of nanometers [1]. Next, the role of exciton-exciton interactions in bulk crystals is discussed. In particular, polarization resolved transient signals provide rich information about the biexciton binding energy and spin dependent interactions in dense exciton ensembles [2]. Finally, we study coherent optical response from lead-halide nanocrystals where quantum beats in the photon echo signal are observed due to excitons fine structure and strong interaction with optical phonons.
Financial support by the Deutsche Forschungsgemeinschaft via the SPP2196 Priority Program (Project AK 40/13-1) is acknowledged.
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