Untangling free carrier and exciton dynamics in layered hybrid perovskites using ultrafast optical and terahertz spectroscopy

Balogun, F. H., Gallop, N. P., Sirbu, D., Hutchinson, J. D., Hill, N., Woolley, J. M., Walker, D., York, S., Docampo, P. and Milot, R. L. (2024) Untangling free carrier and exciton dynamics in layered hybrid perovskites using ultrafast optical and terahertz spectroscopy. Materials Research Express, 11(2), 025503. (doi: 10.1088/2053-1591/ad14c2)

Abstract

Layered hybrid perovskites (LPKs) are promising as alternatives or additives to 3D metal halide perovskites for optoelectronic applications including photovoltaic cells, LEDs and lasers due to their increased stability. However, high exciton binding energies in these materials mean that excitons are the majority species under the operating conditions of many devices. Although the efficiency of devices that incorporate LPKs has been increasing, much is still unknown about the interplay of excitons and free charge-carriers in these materials, which is vital information for understanding how optoelectronic properties dictate device efficiency. In this work, we employ optical pump/THz probe spectroscopy (OPTP) and visible transient absorption spectroscopy (TAS) to analyse the optoelectronic properties and charge-carrier dynamics of phenylethylammonium lead iodide (PEA)2PbI4. By combining these techniques, we are able to disentangle the contributions from excitons and free charge-carriers. We observe fast cooling of free charge-carriers and exciton formation on a timescale of ∼400 fs followed by slower bimolecular recombination of residual free charge-carriers with a rate constant k 2 ∼ 109 cm3s−1. Excitons recombine via two monomolecular processes with lifetimes t 1 ∼ 11 ps and t2 ∼ 83 ps. Furthermore, we detect signatures of exciton–phonon coupling in the transient absorption kinetic traces. These findings provide new insight into the interplay between free charge-carriers and excitons as well as a possible mechanism to further understand the charge-carrier dynamics in LPKs.

• Item Type: Articles
• Additional Information: RLM and NPG acknowledge funding from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/V001302/1. The majority of the equipment used in this work was housed within the Research Technology Platforms at Warwick. David Walker acknowledges funding from EPSRC grant EP/ V007688/1, and PD acknowledges funding from EPSRC grants EP/S031103/1, EP/T010568/1.
• Keywords: transient absorption spectroscopy, 2D perovskites, terahertz spectroscopy, excitons, Ruddlesden-Popper, layered hybrid perovskites
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Docampo, Dr Pablo
• Authors: Balogun, F. H., Gallop, N. P., Sirbu, D., Hutchinson, J. D., Hill, N., Woolley, J. M., Walker, D., York, S., Docampo, P., and Milot, R. L.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Materials Research Express
• Publisher: IOP Publishing
• ISSN: 2053-1591
• ISSN (Online): 2053-1591
• Copyright Holders: Copyright: © 2024 The Author(s)
• First Published: First published in Materials Research Express 11(2): 025503
• Publisher Policy: Reproduced under a Creative Commons licence

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
310679		Hybrid Perovskite Heterojunctions (AoE ENG Materials & Manufacturing)	Pablo Docampo	Engineering and Physical Sciences Research Council (EPSRC)	EP/T010568/1	Chemistry