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Charge Carrier Dynamics in 2D Hybrid Metal Halide Perovskites

DOI: 10.1021/acs.nanolett.6b03114 DOI Help

Authors: Rebecca L. Milot (Department of Physics, University of Oxford) , Rebecca J. Sutton (University of Oxford) , Giles E. Eperon (Department of Physics, University of Oxford) , Amir Abbas Haghighirad (University of Oxford) , Josue Martinez Hardigree (University of Oxford) , Laura Miranda (Oxford Photovoltaics Ltd) , Henry J. Snaith (Department of Physics, University of Oxford) , Michael B Johnston (Department of Physics, University of Oxford) , Laura M. Herz (Department of Physics, University of Oxford)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Nano Letters

State: Published (Approved)
Published: September 2016
Diamond Proposal Number(s): 12690

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%).

Journal Keywords: Charge-carrier mobility, recombination, THz spectroscopy, GIWAXS, photovoltaics

Subject Areas: Physics, Energy, Materials


Instruments: I07-Surface & interface diffraction