Proceedings of MATSUS Spring 2024 Conference (MATSUS24)
DOI: https://doi.org/10.29363/nanoge.matsus.2024.041
Publication date: 18th December 2023
Two-dimensional (2D) metal halide perovskite semiconductors have promising prospects for enhancing the stability of perovskite-based photovoltaic devices. In addition, these low-dimensional materials with electronic confinement offer further opportunities in light emission and quantum technologies. However, their technological applications still require a comprehensive understanding of the nature of charge carriers and their transport mechanisms.
In this work, we employ ultrafast optical and terahertz spectroscopy to investigate the exciton formation dynamics, the charge-carrier mobilities, and the charge-phonon couplings of 2D Ruddlesden-Popper perovskites (PEA)2PbI4 and (BA)2PbI4 (where PEA is phenylethylammonium and BA is butylammonium). We reveal band transport with high in-plane mobilities that give rise to efficient long-range conductivity. We show how the organic cation moderates the coupling of charge carriers to optical phonon modes, impacting the charge-carrier mobilities. Furthermore, we demonstrate a new experiment for simultaneously recording the terahertz and optical transmission transients, thus allowing us to monitor the exciton formation dynamics over the picosecond timescale. The observed dynamics reveal a long-living population of free charge-carriers that greatly surpasses the theoretical predictions of the Saha equation even at temperatures as low as 4K.
Our findings provide new insights into the temperature-dependent interplay of exciton and free charge carriers in 2D Ruddlesden-Popper perovskites. Furthermore, the sustained free charge-carrier population and high mobilities revealed by this work demonstrate the potential of these semiconductors for applications that require efficient charge transport, such as solar cells, transistors, and electrically driven light sources.
The authors gratefully acknowledge support from the Engineering and Physical Sciences Research Council (EPSRC), Prosperity Partnership (EP/S004947/1).
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