Halide perovskites exhibit outstanding opto-electronic properties e.g. long carrier lifetime and low defect densities. They have been attracting attention due to their solar power conversion efficiencies (surpassing sometimes 30%) outperform those of traditional materials such as silicon and therefore may well determine the future of photovoltaics.
It is well known that the dynamic structural instabilities in these materials are ubiquitous - in the Raman spectrum, they even show anharmonic thermal fluctuations resulting in diffuse inelastic scattering that increases towards 0 cm-1, which is usually the signature of a liquid [1]. This suggests that they could be associated with opto-electronic properties, but unfortunately previous attempts link dynamic structural instabilities to the opto-electronic properties have been incomplete [2, 3]. In our fundamental theoretical work, we introduce the concept of dynamic tilting based on a number of well-documented characteristic experimental signatures [4]. We show how dynamically unstable materials can be stabilized at T > 0, how this can give rise to new crystal symmetries in perovskites, and most importantly, how these dynamical instabilities can explain important properties of highly efficient photovoltaic materials.
References
[1] Gao, L., et al. "Metal cation’s lone-pairs increase octahedral tilting instabilities in halide perovskites." Materials Advances 2 (2021): 4610-4616.
[2] Steele, J.A., et al. "Role of electron–phonon coupling in the thermal evolution of bulk rashba-like spin-split lead halide perovskites exhibiting dual-band photoluminescence." ACS energy Lett. 4 (2019): 2205-2212.
[3] Marronnier, A., et al. "Structural instabilities related to highly anharmonic phonons in halide perovskites." J. Phys. Chem. Lett. 8 (2017): 2659-2665.
[4] Adams, D. J., and Churakov, S. V. "Classification of perovskite structural types with dynamical octahedral tilting." IUCrJ 10 (2023)
Full abstract:
The seminar will be chaired by S. Kamba, Department of Dielectrics.