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The Johnston Group is a research group within the sub-department of Condensed Matter Physics, which is part of the sub-faculty of Physics at the University of Oxford. Our current research may be divided into three themes (i) Semiconductor nanowires (ii) Terahertz photonic technologies and (iii) Vapour deposited Perovskite materials for photovoltaic applications.

For enquires about the group please contact:
Prof Michael B. Johnston (group leader), M.Johnston@physics.ox.ac.uk
Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.

Latest Publications


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Ultrafast photo-induced phonon hardening due to pauli blocking in $MAPbI_3$ single-crystal and polycrystalline perovskites
Xia et al. J. Phys-Mater., 4:044017 (Oct 2021)
[ pdf ][ DOI:10.1088/2515-7639/ac22b9 ]
We observed the shift of phonon modes in thin file and single crystals MAPbI3 that occurs when the materials are optically excited. We observe an ultrafast Pauli blocking effect with leads to phonon hardening / blue-shifting.

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Hot electron cooling in InSb probed by ultrafast time-resolved terahertz cyclotron resonance
Xia et al. Phys. Rev. B, 103:245205 (Jun 2021)
[ pdf ][ DOI:10.1103/PhysRevB.103.245205 ]
We develop and apply the technique of time resolved cyclotron resonance to observe electron cooling in the narrow bandgap semiconductor indium antimonide and find excellent agreement with first principles GW calculations.

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Limits to electrical mobility in lead-halide perovskite semiconductors
Xia et al. J. Phys. Chem. Lett., 12:3607-3617 (Apr 2021)
[ pdf ][ DOI:10.1021/acs.jpclett.1c00619 ]
We measure THz photoconductivity of single crystals and thin films of the prototypical metal halide perovskite MAPbI3. This direct comparison combined with DFT calculations allows us to study the influence of grain boundaries on charge-carrier scattering, and hence mobility.

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Three-dimensional cross-nanowire networks recover full terahertz state
Peng et al. Science, 368:510--513 (May 2020)
[ pdf ][ DOI:10.1126/science.abb0924 ]
We have developed a new nanowire-based THz sensor that recovers the full state of THz pulses.

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Trap states, electric fields, and phase segregation in mixed-halide perovskite photovoltaic devices
Knight et al. Adv. Energy Mater., 10:1903488 (Mar 2020)
[ pdf ][ DOI:10.1002/aenm.201903488 ]

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Light absorption and recycling in hybrid metal halide perovskite photovoltaic devices
Patel et al. Adv. Energy Mater., 10:1903653 (Mar 2020)
[ pdf ][ DOI:10.1002/aenm.201903653 ]
We use vapour co-deposition to control precisely the thickness of perovskite films, and study the effect of light management in thin film solar cells
Group members March 2017

News

New Postdoc Positions Available
[Dec 2020] We are currently recruiting new postdocs in THz spectroscopy and STM[more...]
New PhD / D.Phil Studentships
[Dec 2020] We are currently recruiting new PhD / D.Phil students [more...]