Condensed Matter Physics Seminar: Lucy Whalley

The perovskite structure is a versatile host. Engineering chemical composition allows for a range of optoelectronic, vibrational and defect properties. Of particular note is the compositional engineering of halide perovskites, which has led to high-efficiency single junction (26.1%) and perovskite-silicon tandem (33.9%) photovoltaic cells [1]. 

The most stable and efficient halide perovskite-based devices employ mixed organic or inorganic cations on the A-site of the ABX₃ perovskite structure.  The A-site species indirectly determines various material properties via an influence on the symmetry and dynamic response of the crystal lattice. It is primarily used to improve thermal and chemical stability [2], whilst the impact of A-site mixing on defect activity is not fully understood [3]. In the first half of my talk I will share results from first-principles calculations to show that cation mixing in MA_1-xCs_xPbI₃ significantly adjusts the non-radiative carrier capture rate at the iodine interstitial defect site [4,5]. I will demonstrate that steric effects determine the defect behaviour, mediated by the phase and dynamical response of the lattice. This mechanism could enable defect properties to be tailored through steric engineering, without altering the metal–halide chemistry that is beneficial for photovoltaic performance.

In the second half of my talk I will move to an emerging class of materials, the chalcogenide perovskites. These materials are highly robust, non-toxic and show strong light absorption but device development is hindered by the high-temperatures typically required for synthesis. I will share our on-going work, based on first-principles lattice dynamics, exploring the thermodynamics of BaZrS3 phase formation [6]. In particular, I will discuss the presence of low-dimensional Ruddlesden-Popper materials Ba_n+1Zr_nS_3n+1 and how first-principles calculations can be used to support their experimental identification [7].

[1] M. A. Green, E. D. Dunlop, M. Yoshita et al., Prog. Photov., 2023, 32 (1), 3-13

[2] D. R. Ceratti, A. V. Cohen, R. Tenne et al., Mater. Horiz., 2021, 8, 1570-1586

[3] J.-W Lee, S. Tan, S. Seok et al., Science, 2022, 375 (6583)

[4] L. D. Whalley, P. van Gerwen, J. M. Frost et al., J. Am. Chem. Soc., 2021, 143 (24), 9123-9128

[5] L. D. Whalley, J. Phys. Chem. C, 2023, 127 (32), 15738–15746

[6] P. Kayastha, G. Longo, L. Whalley, 2024, arXiv:2401.06092

[7] P. Kayastha, D. Tiwari, A. Holland et al., Sol. RRL, 2023, 7 (9), 2201078