Ultrafast Photoexcited Carrier Dynamics in 2D/3D Lead-Tin Perovskites with Tuneable Dimensionality
Jake D. Hutchinson a, Edoardo Ruggeri b, Jack M. Woolley a c, Samuel D. Stranks b, Rebecca L. Milot a
a Department of Physics, University of Warwick, CV4 7AL, Coventry, United Kingdom
b Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge, UK
c Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kiongdom
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Jake D. Hutchinson, presentation 025
DOI: https://doi.org/10.29363/nanoge.hopv.2022.025
Publication date: 20th April 2022

Upon the addition of the organic molecule phenylethylammonium (PEA), mixed lead-tin perovskites have been demonstrated to form distinct domains dominated by either 2D Ruddlesden-Popper (RP) structures or 3D perovskite structures [1]. The formation of 3D domains is slowed by the presence of the precursor additive ammonium thiocyanate (AT), resulting in the increased prominence of 2D domains and allowing the proportions of 2D and 3D domains throughout the film to be tuned [1]. This has a marked effect on the overall emissive properties of the film with 2D domains emitting at higher energies with shorter photoluminescence (PL) lifetimes [1]. However, the effect of this dimensionality tuning on the excited charge carrier dynamics remains largely unstudied. By combining multiple ultrafast techniques, including transient absorption (TA) spectroscopy and optical pump – terahertz probe (OPTP) spectroscopy, we are able to form a more complete picture of carrier dynamics after excitation by a femtosecond laser pulse. OPTP is used to extract effective free carrier mobility, which is generally significantly reduced by confinement effects in 2D perovskites. Despite the notable increase in 2D-like behaviour, the dimensional tuning is shown to preserve the mobility of the material. This technique also allows the recombination dynamics of the films to be modelled while taking into account enhanced photon recycling effects and carrier redistribution. In addition to the mixed dimensionality films, we systematically studied analogous pure 2D and 3D perovskite films in order to clearly demonstrate the effect of these dimensional domains on the carrier dynamics. This is complimented by TA dynamics which highlight the effect that dimensional tuning has on the overall structure of the films, with a notable increase in prominence of the n=2 RP phase evident. This research opens avenues for the further development of perovskite thin films with the improved stability of 2D structures, without some of the drawbacks which are usually associated with RP perovskites.

JDH, JMW and RLM acknowledge the role of the Warwick Centre for Ultrafast Spectroscopy (WCUS) for the use of its facilities. JDH was supported by an EPSRC Departmental Graduate studentship. E. R. and S.D.S. acknowledge the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (HYPERION, grant agreement number 756962). E.R. was partially supported by an EPSRC Departmental Graduate Studentship. S.D.S. acknowledges funding from the Royal Society and Tata Group (UF150033).

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