Untangling Free Carrier and Exciton dynamics in Layered Hybrid Perovskites using Time-Resolved Terahertz Spectroscopy
Folusho Helen Balogun a, Dumitru Sirbu b, Nathaniel P. Gallop a, Jake D. Hutchinson a, Nathan Hill b, Jack M. Woolley a, Michael Staniforth a, Pablo Docampo c, Rebecca L. Milot a
a Department of Physics, University of Warwick, Coventry CV4 7AL.
b Department of Chemistry, University of Newcastle, Newcastle upon Tyne, NE1 7RU
c Department of Physics, University of Glasgow, Glasgow, G12 8QQ.
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, Folusho Helen Balogun, presentation 084
DOI: https://doi.org/10.29363/nanoge.hopv.2022.084
Publication date: 20th April 2022

The interplay between free charge-carriers and excitons has long been explored in two-dimensional (2D) metal halide perovskites using ultrafast spectroscopy techniques, especially transient absorption spectroscopy (TAS) (1). Nevertheless, there is still not a cohesive understanding of what the underlying mechanisms are of carrier generation and relaxation, and a range of phenomena that have been investigated including exciton-phonon coupling, the presence of polarons formation, and even the existence of biexcitons (2,3). Due to quantum confinement and the high exciton binding energy (Eb) in 2D perovskites, the dominant species present under ambient conditions is excitons rather than free charge-carriers. This results in different optoelectronic properties compared to three-dimensional (3D) metal halide perovskites such as a shorter charge-carrier lifetime and decreased effective charge-carrier mobilities (4). Optical pump/ terahertz probe (OPTP) is a time-resolved spectroscopic technique that preferentially measures mobile species such as free charge-carriers but is not sensitive to excitons with high Eb, making it an advantageous technique in elucidating the underlying mechanism(s) taking place between the free charge-carriers and excitons. In this work, we employ OPTP to analyse the dynamics of free charge carriers in (PEA)2PbI4, and observe fast carrier cooling and exciton formation followed by slower bimolecular and monomolecular recombination processes.   With those results, we can disentangle the dynamics between excitons and free charge-carriers to analyse transient absorption spectroscopy measurements, exploring exciton-phonon coupling, charge-carrier cooling, and exciton formation.

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