OSC Special Presentation: Optical Probes of Metal Halide Perovskites for Photovoltaic Applications by Prof Laura Herz

    Tuesday, June 1, 2021 - 8:30am

    Join Zoom Meeting


    Organic-inorganic metal halide perovskites have emerged as attractive materials for solar cells with power-conversion efficiencies now exceeding 25%. Optical probes have been at the forefront of research unravelling the fundamental processes enabling these materials to be such efficient light-harvesters and charge collectors. They have also been critical tools to address remaining challenges and opportunities relating to material microstructure, ionic migration and toxicity.

    In this presentation, we discuss our recent work exploring these promising materials with a host of spectroscopic and combinatorial optical techniques. We demonstrate that the intrinsic mobility of charge carriers is governed by their interactions with optical vibrations of the lead halide lattice (Fröhlich interactions)[1]. We reveal that bimolecular (band-to-band) recombination, which dominates the charge-carrier losses near the fundamental Shockley-Queisser efficiency limit of solar cells, is an inverse-absorption process following the principle of detailed balance.[2]  In addition, highly effective photon reabsorption is shown to be operational in lead halide perovskites, further boosting attainable power conversion efficiencies beyond the Shockley-Queisser limit.[3] Our analysis of intrinsic photophysical parameters opens the promise of targeted material design for solar energy harvesting, based on readily accessible parameters, such as band structure, phonon frequencies and the dielectric function.

    We further examine how the optoelectronic properties of hybrid perovskites are governed by their nanostructure. We show that lead halide perovskites can exhibit intrinsic quantum confinement, apparent through surprising oscillatory features in the absorption spectrum.[4]Such materials may thus offer the sought-after target of bottom-up nanostructuring. In addition, we discuss our recent discovery[5]of the atomic-scale microstructure in lead halide perovskites, demonstrating coherent interfaces with precursor remnants, sharp interfaces between perovskite grains, and a surprisingly resilient nature of the lattice with respect to partial loss of the organic cation. Finally, we outline some of the remaining challenges in the field, relating to ionic migration and toxicity of lead,[6]and present an outlook towards future materials discovery.

    [1] A.D. Wright, C. Verdi, R.L. Milot, G. E. Eperon, M. A. Pérez-Osorio, H. J. Snaith, F. Giustino, M. B. Johnston, L. M. Herz, Nature Communications 7, 11755 (2016)

    [2] C. L. Davies, M. R. Filip, J. B. Patel, T. W. Crothers, C. Verdi, A. D. Wright, R. L. Milot, F.  Giustino, M. B. Johnston, L. M. Herz, Nature Communications 9, 293 (2018)

    [3] S. G. Motti, T. Crothers, R. Yang, Y. Cao, R. Li, M. B. Johnston, J. Wang, and L. M. Herz, Nano Letters 19, 3953 (2019).

    [4] A. D. Wright, G. Volonakis, J. Borchert, C. L. Davies, F. Giustino, M. B. Johnston, and L. M. Herz, Nature Materials 19, 1201 (2020).

    [5] M. U. Rothmann, J. S. Kim, J. Borchert, K. B. Lohmann, C. M. O’Leary, A. A. Sheader, L. Clark, H. J. Snaith, M. B. Johnston, P. D. Nellist, and L. M. Herz, Science 370, eabb5940 (2020).

    [6] A. J. Knight, J. Borchert, R. D. J. Oliver, J. B. Patel, P. G. Radaelli, H. J. Snaith, M. B. Johnston, and L. M. Herz, 
    ACS Energy Letters 6, 799 (2021).

    Speaker Bio(s): 

    Laura Herz is a Professor of Physics at the University of Oxford where she directs the Semiconductors Group at the Clarendon Laboratory, and is the Associate Head of the Mathematical, Physical and Life Sciences Division for Research. She received her PhD in Physics from the University of Cambridge in 2002 and was a Research Fellow at St John's College Cambridge from 2001 – 2003, after which she moved to a faculty position at Oxford Physics. She held an Advanced Research Fellowship by the Engineering and Physical Sciences Research Council from 2006-2012. Professor Herz has published over 170 peer-reviewed research articles (>33500 citations, h-index 68 – Google Scholar 2021) and has been listed by Clarivate Analytics/Web of Science as a Highly Cited Researcher since 2018. Recently, she was awarded the Nevill Mott Medal and Prize by the Institute of Physics and the Friedrich-Wilhelm-Bessel Award of the Alexander von Humboldt Foundation for her research, and a student-led teaching award, by the Oxford Student Union, in the category "Outstanding Graduate Supervisor". She is an Associate Editor of Applied Physics Reviews, Chemical Physics Reviews (AIP) and a member of the editorial advisory boards for ACS Energy Letters and The Journal of Physical Chemistry Letters. Prof Herz is a Fellow of the Royal Society of Chemistry, the Institute of Physics, and University College Oxford. She currently holds an Honorary Professorship at the Australian National University, and a Hans-Fischer Senior Fellowship at the Institute of Advanced Study at the Technical University Munich (TUM).