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Instruments / Technical Area	Publication Details	Published	Actions
I07-Surface & interface diffraction	Resolving the ultrafast charge carrier dynamics of 2D and 3D domains within a mixed 2D/3D lead-tin perovskite Jake D. Hutchinson , Edoardo Ruggeri , Jack M. Woolley , Geraud Delport , Samuel D. Stranks , Rebecca L. Milot Advanced Functional Materials 32 DOI: 10.1002/adfm.202305736 Diamond Proposal Number(s): [17223] Open Access Show Abstract ▼ Abstract: Mixed 2D/3D perovskite materials are of particular interest to the photovoltaics and light- emitting diode (LED) communities due to their impressive opto-electronic properties alongside improved moisture stability compared to conventional 3D perovskite absorbers. Here, a mixed lead-tin perovskite containing distinct, self-assembled domains of either 3D structures or highly phase-pure Ruddlesden–Popper 2D structures is studied. The complex energy landscape of the material is revealed with ultrafast optical transient absorption measurements. It is shown that charge transfer between these microscale domains only occurs on nanosecond timescales, consistent with the large size of the domains. Using optical pump-terahertz probe spectroscopy, the effective charge-carrier mobility is shown to be an intermediary between analogous pure 2D and 3D perovskites. Furthermore, detailed analysis of the free carrier recombination dynamics is presented. By combining results from a range of excitation wavelengths within a full dynamic model of the photoexcited carrier population, it is shown that the 2D domains in the film exhibit remarkably similar carrier dynamics to the 3D domains, suggesting that long-range charge-transport should not be impeded by the heterogeneous structure of the material.	Aug 2023
I07-Surface & interface diffraction	Charge-carrier dynamics in 2D hybrid metal–halide perovskites Rebecca L. Milot , Rebecca J. Sutton , Giles E. Eperon , Amir Abbas Haghighirad , Josue Martinez Hardigree , Laura Miranda , Henry J. Snaith , Michael B Johnston , Laura M. Herz Nano Letters DOI: 10.1021/acs.nanolett.6b03114 Diamond Proposal Number(s): [12690] Open Access Show Abstract ▼ Abstract: Hybrid metal halide perovskites are promising new materials for use in solar cells, however, their chemical stability in the presence of moisture remains a significant drawback. Quasi two-dimensional perovskites that incorporate hydrophobic organic interlayers offer improved resistance to degradation by moisture, currently still at the cost of overall cell efficiency. To elucidate the factors affecting the optoelectronic properties of these materials, we have investigated the charge transport properties and crystallographic orientation of mixed methylammonium (MA)/phenylethylammonium (PEA) lead iodide thin films as a function of MA:PEA and thus the thickness of the ‘encapsulated’ MA lead halide layers. We find that monomolecular charge-carrier recombination rates first decrease with increasing PEA fraction, most likely as a result of trap passivation, but then increase significantly as excitonic effects begin to dominate for thin confined layers. Bimolecular and Auger recombination rate constants are found to be sensitive to changes in electronic confinement, which alters the density of states for electronic transitions. We demonstrate that effective charge-carrier mobilities remain remarkably high (near 10 cm2/Vs) for intermediate PEA content and are enhanced for preferential orientation of the conducting lead-iodide layers along the probing electric field. The tradeoff between trap reduction, electronic confinement and layer orientation leads to calculated charge-carrier diffusion lengths reaching a maximum of 2.5 µm for intermediate PEA content (50%).	Sep 2016

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