Exciton formation dynamics and band-like free charge-carrier transport in 2D metal halide perovskite semiconductors

Journal article

Metal halide perovskite (MHP) semiconductors have driven a revolution in optoelectronic technologies over the last decade, in particular for high-efficiency photovoltaic applications. Low-dimensional MHPs presenting electronic confinement have promising additional prospects in light emission and quantum technologies. However, the optimisation of such applications requires a comprehensive understanding of the nature of charge carriers and their transport mechanisms. This study employs a combination of ultrafast optical and terahertz spectroscopy to investigate phonon energies, charge-carrier mobilities, and exciton formation in 2D (PEA)₂PbI₄ and (BA)₂PbI₄ (where PEA is phenylethylammonium and BA is butylammonium). Temperature-dependent measurements of free charge-carrier mobilities reveal band transport in these strongly confined semiconductors, with surprisingly high in-plane mobilities. Enhanced charge-phonon coupling is shown to reduce charge-carrier mobilities in (BA)₂PbI₄ with respect to (PEA)₂PbI₄. Exciton and free charge-carrier dynamics are disentangled by simultaneous monitoring of transient absorption and THz photoconductivity. A sustained free charge-carrier population is observed, surpassing the Saha equation predictions even at low temperature. These findings provide new insights into the temperature-dependent interplay of exciton and free-carrier populations in 2D MHPs. Furthermore, such sustained free charge-carrier population and high mobilities demonstrate the potential of these semiconductors for applications such as solar cells, transistors, and electrically driven light sources.

Authors: Motti, SG; Kober-Czerny, M; Righetto, M; Holzhey, P; Smith, J

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Wiley
• Journal: Advanced Functional Materials
• Volume: 33
• Issue: 32
• Article number: 2300363
• Publication date: 2023-05-01
• DOI: 10.1002/adfm.202300363
• EISSN: 1616-3028
• ISSN: 1616-301X
• Language: English
• Keywords: 2D perovskites; excitons; perovskite semiconductors; photoconductivity; FFR