Metal-halide perovskites - new fascinating playground for exciton physics
Prof. Michał Baranowski
Wroclaw University of Science and Technology
Institute of Physics
Organic and inorganic metal-halide perovskites have emerged in recent decades as revolutionary semiconductor materials for energy harvesting, light emission and scintillator applications. The unique synergy of soft lattice and optoelectronic properties is often invoked to explain superior characteristics of perovskite materials in applications. At the same time, such unique synergy creates a fascinating playground for exciton physics which challenges our understanding of this elementary excitation. For instance, the soft and ionic lattice form a complex background for electronic excitation where polaronic effects cannot be neglected. While this feature of perovskites has been already used to explain some of the puzzling aspects of carrier transport in these materials, the impact of polaronic effects on the optical response, especially excitonic properties, is much less explored.
In this seminar, I will demonstrate that excitonic properties in metal-halide perovskites are profoundly shaped by carrier-lattice interactions, significantly affecting their optical response. Using magneto-optical spectroscopy, I will reveal the non-hydrogenic nature of excitons in 3D metal-halide perovskites, arising from strong Fröhlich coupling. These findings are well-explained by the polaronic-exciton model, wherein electron-hole interactions deviate from a simple Coulomb potential [1]. Additionally, I will present experimental evidence that carrier-phonon interactions lead to an enhanced effective carrier mass.
The discussion will then shift to 2D derivatives of perovskites, where the intrinsic softness of these materials offers a platform for tuning effective mass. I will illustrate how structural distortions induced by organic spacers govern the effective mass, enabling its tailoring over a broad range [2,3]. Lastly, I will examine the evolution of exciton fine structure between 2D and 3D limits [4] and explore how the interplay between excitons fine structure and phonons results in the complex absorption and emission spectra observed in 2D perovskites [5–7].
[1] ACS Energy Letters 9, 2696-2702
[2] ACS Energy Letters 5 (11), 3609-3616
[3] The Journal of Physical Chemistry Letters 12 (6), 1638-1643
[4] Journal of the American Chemical Society 146 (7), 4687-4694
[5] The Journal of Physical Chemistry Letters 13 (20), 4463-4469
[6] Nanomaterials 13 (6), 1119
[7] Advanced Optical Materials 12 (8), 2300877
Hosted by Prof. Janko