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Start Over Author "Johnston, Michael" Journal nano letters
29 results on '"Johnston, Michael"'

5. Charge-Carrier Dynamics in 2D Hybrid Metal–Halide Perovskites

Author

Milot, Rebecca L., primary, Sutton, Rebecca J., additional, Eperon, Giles E., additional, Haghighirad, Amir Abbas, additional, Martinez Hardigree, Josue, additional, Miranda, Laura, additional, Snaith, Henry J., additional, Johnston, Michael B., additional, and Herz, Laura M., additional

Published
2016
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7. Enhanced Amplified Spontaneous Emission in Perovskites Using a Flexible Cholesteric Liquid Crystal Reflector

Author

Stranks, Samuel D., primary, Wood, Simon M., additional, Wojciechowski, Konrad, additional, Deschler, Felix, additional, Saliba, Michael, additional, Khandelwal, Hitesh, additional, Patel, Jay B., additional, Elston, Steve J., additional, Herz, Laura M., additional, Johnston, Michael B., additional, Schenning, Albertus P. H. J., additional, Debije, Michael G., additional, Riede, Moritz K., additional, Morris, Stephen M., additional, and Snaith, Henry J., additional

Published
2015
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9. Modulation Doping of GaAs/AlGaAs Core–Shell Nanowires With Effective Defect Passivation and High Electron Mobility

Author

Boland, Jessica L., primary, Conesa-Boj, Sonia, additional, Parkinson, Patrick, additional, Tütüncüoglu, Gözde, additional, Matteini, Federico, additional, Rüffer, Daniel, additional, Casadei, Alberto, additional, Amaduzzi, Francesca, additional, Jabeen, Fauzia, additional, Davies, Christopher L., additional, Joyce, Hannah. J., additional, Herz, Laura M., additional, Fontcuberta i Morral, Anna, additional, and Johnston, Michael B., additional

Published
2015
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10. Single Nanowire Photoconductive Terahertz Detectors

Author

Peng, Kun, primary, Parkinson, Patrick, additional, Fu, Lan, additional, Gao, Qiang, additional, Jiang, Nian, additional, Guo, Ya-Nan, additional, Wang, Fan, additional, Joyce, Hannah J., additional, Boland, Jessica L., additional, Tan, Hark Hoe, additional, Jagadish, Chennupati, additional, and Johnston, Michael B., additional

Published
2014
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27. Photon Reabsorption Masks Intrinsic Bimolecular Charge-Carrier Recombination in CH 3 NH 3 PbI 3 Perovskite.

Author

Crothers TW, Milot RL, Patel JB, Parrott ES, Schlipf J, Müller-Buschbaum P, Johnston MB, and Herz LM

Subjects
Diffusion, Electric Conductivity, Electron Transport, Nanotechnology, Photochemical Processes, Photons, Semiconductors, Terahertz Spectroscopy, Calcium Compounds chemistry, Iodides chemistry, Lead chemistry, Methylamines chemistry, Oxides chemistry, Titanium chemistry
Abstract

An understanding of charge-carrier recombination processes is essential for the development of hybrid metal halide perovskites for photovoltaic applications. We show that typical measurements of the radiative bimolecular recombination constant in CH 3 NH 3 PbI 3 are strongly affected by photon reabsorption that masks a much larger intrinsic bimolecular recombination rate constant. By investigating a set of films whose thickness varies between 50 and 533 nm, we find that the bimolecular charge recombination rate appears to slow by an order of magnitude as the film thickness increases. However, by using a dynamical model that accounts for photon reabsorption and charge-carrier diffusion we determine that a single intrinsic bimolecular recombination coefficient of value 6.8 × 10 -10 cm 3 s -1 is common to all samples irrespective of film thickness. Hence, we postulate that the wide range of literature values reported for such coefficients is partly to blame on differences in photon out-coupling between samples with crystal grains or mesoporous scaffolds of different sizes influencing light scattering, whereas thinner films or index-matched surrounding layers can reduce the possibility for photon reabsorption. We discuss the critical role of photon confinement on free charge-carrier retention in thin photovoltaic layers and highlight an approach to assess the success of such schemes from transient spectroscopic measurement.

Published
2017
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28. Ultrafast charge separation at a polymer-single-walled carbon nanotube molecular junction.

Author

Stranks SD, Weisspfennig C, Parkinson P, Johnston MB, Herz LM, and Nicholas RJ

Abstract

We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single molecular layer around a SWNT leads to an ultrafast (∼430 fs) charge transfer between the materials. The addition of excess P3HT leads to long-term charge separation in which free polarons remain separated at room temperature. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diameter tubes are individually embedded in the P3HT matrix.

Published
2011
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29. Carrier lifetime and mobility enhancement in nearly defect-free core-shell nanowires measured using time-resolved terahertz spectroscopy.

Author

Parkinson P, Joyce HJ, Gao Q, Tan HH, Zhang X, Zou J, Jagadish C, Herz LM, and Johnston MB

Subjects
Electric Conductivity, Materials Testing, Particle Size, Photochemistry, Surface Properties, Temperature, Time Factors, Arsenicals chemistry, Gallium chemistry, Nanotechnology methods, Nanowires chemistry, Terahertz Spectroscopy methods
Abstract

We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.

Published
2009
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