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101. Nanowires: a New Horizon for Polarization-resolved Terahertz Time-domain Spectroscopy

Author

Peng, Kun, primary, Jevtics, Dimitars, additional, Zhang, Fanlu, additional, Sterzl, Sabrina, additional, Damry, Djamshid A., additional, Rothmann, Mathias U., additional, Guilhabert, Benoit, additional, Strain, Michael J., additional, Tan, Hoe, additional, Herz, Laura M., additional, Fu, Lan, additional, Dawson, Martin D., additional, Hurtado, Antonio, additional, Jagadish, Chennupati, additional, and Johnston, Michael B., additional

Published
2021
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105. Atomic-scale microstructure of metal halide perovskite

Author

Rothmann, Mathias Uller, primary, Kim, Judy S., additional, Borchert, Juliane, additional, Lohmann, Kilian B., additional, O’Leary, Colum M., additional, Sheader, Alex A., additional, Clark, Laura, additional, Snaith, Henry J., additional, Johnston, Michael B., additional, Nellist, Peter D., additional, and Herz, Laura M., additional

Published
2020
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109. A piperidinium salt stabilizes efficient metal-halide perovskite solar cells

Author

Lin, Yen-Hung, primary, Sakai, Nobuya, additional, Da, Peimei, additional, Wu, Jiaying, additional, Sansom, Harry C., additional, Ramadan, Alexandra J., additional, Mahesh, Suhas, additional, Liu, Junliang, additional, Oliver, Robert D. J., additional, Lim, Jongchul, additional, Aspitarte, Lee, additional, Sharma, Kshama, additional, Madhu, P. K., additional, Morales‐Vilches, Anna B., additional, Nayak, Pabitra K., additional, Bai, Sai, additional, Gao, Feng, additional, Grovenor, Chris R. M., additional, Johnston, Michael B., additional, Labram, John G., additional, Durrant, James R., additional, Ball, James M., additional, Wenger, Bernard, additional, Stannowski, Bernd, additional, and Snaith, Henry J., additional

Published
2020
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110. Three-dimensional cross-nanowire networks recover full terahertz state

Author

Peng, Kun, primary, Jevtics, Dimitars, additional, Zhang, Fanlu, additional, Sterzl, Sabrina, additional, Damry, Djamshid A., additional, Rothmann, Mathias U., additional, Guilhabert, Benoit, additional, Strain, Michael J., additional, Tan, Hark H., additional, Herz, Laura M., additional, Fu, Lan, additional, Dawson, Martin D., additional, Hurtado, Antonio, additional, Jagadish, Chennupati, additional, and Johnston, Michael B., additional

Published
2020
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114. An experimental comparison of viewpoint-specific and viewpoint-independent models of object representation

Author

Johnston, Michael B. and Hayes, Anthony

Subjects
Visual perception -- Psychological aspects, Recognition (Psychology) -- Research, Mental representation -- Psychological aspects, Cognition -- Psychological aspects, Psychology and mental health
Abstract

Four experiments were used to investigate the influence of viewpoint on the cognitive representation and subsequent recognition of objects. Rotating objects during recognition tasks resulted in a significant decrease in performance. These findings suggest that object representations are specific to learned viewpoints.

Published
2000

115. Thermally Stable Passivation toward High Efficiency Inverted Perovskite Solar Cells

Author

Oliver, Robert D.J., Lin, Yen Hung, Horn, Alexander J., Xia, Chelsea Q., Warby, Jonathan H., Johnston, Michael B., Ramadan, Alexandra J., Snaith, Henry J., Oliver, Robert D.J., Lin, Yen Hung, Horn, Alexander J., Xia, Chelsea Q., Warby, Jonathan H., Johnston, Michael B., Ramadan, Alexandra J., and Snaith, Henry J.

Abstract

Although metal halide perovskite photovoltaics have shown an unprecedented rise in power conversion efficiency (PCE), they remain far from their theoretical PCE limit. Among the highest efficiencies to date are delivered when polycrystalline films are enhanced via "molecular passivation", but this can introduce new instabilities, in particular under severe accelerated aging conditions (e.g., at 85 °C in the dark or under full spectrum simulated sunlight). Here, we utilize a benzylammonium bromide passivation treatment to improve device performance, achieving the champion stabilized power output (SPO) of 19.5 % in a p-i-n device architecture. We correlate the improved device performance with a significant increase in charge carrier diffusion lengths, mobilities, and lifetimes. Furthermore, treated devices maintain an increased performance during 120 h combined stressing under simulated full spectrum sunlight at 85 °C, indicating that enhancement from this passivation treatment is sustained under harsh accelerated aging conditions. This is a crucial step toward real-world operation-relevant passivation treatments. © 2020 American Chemical Society. All rights reserved.

Published
2020

116. Elucidating the Role of a Tetrafluoroborate-Based Ionic Liquid at the n-Type Oxide/Perovskite Interface

Author

Noel, Nakita K., Habisreutinger, Severin N., Wenger, Bernard, Lin, Yen Hung, Zhang, Fengyu, Patel, Jay B., Kahn, Antoine, Johnston, Michael B., Snaith, Henry J., Noel, Nakita K., Habisreutinger, Severin N., Wenger, Bernard, Lin, Yen Hung, Zhang, Fengyu, Patel, Jay B., Kahn, Antoine, Johnston, Michael B., and Snaith, Henry J.

Abstract

Halide perovskites are currently one of the most heavily researched emerging photovoltaic materials. Despite achieving remarkable power conversion efficiencies, perovskite solar cells have not yet achieved their full potential, with the interfaces between the perovskite and the charge-selective layers being where most recombination losses occur. In this study, a fluorinated ionic liquid (IL) is employed to modify the perovskite/SnO2 interface. Using Kelvin probe and photoelectron spectroscopy measurements, it is shown that depositing the perovskite onto an IL-treated substrate results in the crystallization of a perovskite film which has a more n-type character, evidenced by a decrease of the work function and a shift of the Fermi level toward the conduction band. Photoluminescence spectroscopy and time-resolved microwave conductivity are used to investigate the optoelectronic properties of the perovskite grown on neat and IL-modified surfaces and it is found that the modified substrate yields a perovskite film which exhibits an order of magnitude lower trap density than the control. When incorporated into solar cells, this interface modification results in a reduction in the current–voltage hysteresis and an improvement in device performance, with the best performing devices achieving steady-state PCEs exceeding 20%. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Published
2020

117. A piperidinium salt stabilizes efficient metal-halide perovskite solar cells

Author

Lin, Yen-Hung, Sakai, Nobuya, Da, Peimei, Wu, Jiaying, Sansom, Harry C., Ramadan, Alexandra J., Mahesh, Suhas, Liu, Junliang, Oliver, Robert D. J., Lim, Jongchul, Aspitarte, Lee, Sharma, Kshama, Madhu, P. K., Morales-Vilches, Anna B., Nayak, Pabitra K., Bai, Sai, Gao, Feng, Grovenor, Chris R. M., Johnston, Michael B., Labram, John G., Durrant, James R., Ball, James M., Wenger, Bernard, Stannowski, Bernd, Snaith, Henry J., Lin, Yen-Hung, Sakai, Nobuya, Da, Peimei, Wu, Jiaying, Sansom, Harry C., Ramadan, Alexandra J., Mahesh, Suhas, Liu, Junliang, Oliver, Robert D. J., Lim, Jongchul, Aspitarte, Lee, Sharma, Kshama, Madhu, P. K., Morales-Vilches, Anna B., Nayak, Pabitra K., Bai, Sai, Gao, Feng, Grovenor, Chris R. M., Johnston, Michael B., Labram, John G., Durrant, James R., Ball, James M., Wenger, Bernard, Stannowski, Bernd, and Snaith, Henry J.

Abstract

Longevity has been a long-standing concern for hybrid perovskite photovoltaics. We demonstrate high-resilience positive-intrinsic-negative perovskite solar cells by incorporating a piperidinium-based ionic compound into the formamidinium-cesium lead-trihalide perovskite absorber. With the bandgap tuned to be well suited for perovskite-on-silicon tandem cells, this piperidinium additive enhances the open-circuit voltage and cell efficiency. This additive also retards compositional segregation into impurity phases and pinhole formation in the perovskite absorber layer during aggressive aging. Under full-spectrum simulated sunlight in ambient atmosphere, our unencapsulated and encapsulated cells retain 80 and 95% of their peak and post-burn-in efficiencies for 1010 and 1200 hours at 60 degrees and 85 degrees C, respectively. Our analysis reveals detailed degradation routes that contribute to the failure of aged cells., Funding Agencies|U. K. Engineering and Physical Sciences Research Council (EPSRC)Engineering & Physical Sciences Research Council (EPSRC) [EP/S004947/1, EP/P006329/1]; EPSRCEngineering & Physical Sciences Research Council (EPSRC) [EP/M018237/1]; Rhodes Scholarship (India); Penrose Scholarship; Rhodes Scholarship (Worcester)

Published
2020
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118. Interplay of Structure, Charge‐Carrier Localization and Dynamics in Copper‐Silver‐Bismuth‐Halide Semiconductors.

Author

Buizza, Leonardo R. V., Sansom, Harry C., Wright, Adam D., Ulatowski, Aleksander M., Johnston, Michael B., Snaith, Henry J., and Herz, Laura M.

Subjects
SEMICONDUCTORS, BINDING energy, VALENCE bands, SOLID solutions, PHOTOCONDUCTIVITY
Abstract

Silver‐bismuth based semiconductors represent a promising new class of materials for optoelectronic applications because of their high stability, all‐inorganic composition, and advantageous optoelectronic properties. In this study, charge‐carrier dynamics and transport properties are investigated across five compositions along the AgBiI4–CuI solid solution line (stoichiometry Cu4x(AgBi)1−xI4). The presence of a close‐packed iodide sublattice is found to provide a good backbone for general semiconducting properties across all of these materials, whose optoelectronic properties are found to improve markedly with increasing copper content, which enhances photoluminescence intensity and charge‐carrier transport. Photoluminescence and photoexcitation‐energy‐dependent terahertz photoconductivity measurements reveal that this enhanced charge‐carrier transport derives from reduced cation disorder and improved electronic connectivity owing to the presence of Cu+. Further, increased Cu+ content enhances the band curvature around the valence band maximum, resulting in lower charge‐carrier effective masses, reduced exciton binding energies, and higher mobilities. Finally, ultrafast charge‐carrier localization is observed upon pulsed photoexcitation across all compositions investigated, lowering the charge‐carrier mobility and leading to Langevin‐like bimolecular recombination. This process is concluded to be intrinsically linked to the presence of silver and bismuth, and strategies to tailor or mitigate the effect are proposed and discussed. [ABSTRACT FROM AUTHOR]

Published
2022
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120. Growth modes and quantum confinement in ultrathin vapour-deposited MAPbI₃ films

Author

Parrott, Elizabeth S., Patel, Jay B., Haghighirad, Amir-Abbas, Snaith, Henry J., Johnston, Michael B., and Herz, Laura M.

Subjects
Physics, ddc:530
Abstract

Vapour deposition of metal halide perovskite by co-evaporation of precursors has the potential to achieve large-area high-efficiency solar cells on an industrial scale, yet little is known about the growth of metal halide perovskites by this method at the current time. Here, we report the fabrication of MAPbI3 films with average thicknesses from 2–320 nm by co-evaporation. We analyze the film properties using X-ray diffraction, optical absorption and photoluminescence (PL) to provide insights into the nucleation and growth of MAPbI3 films on quartz substrates. We find that the perovskite initially forms crystallite islands of around 8 nm in height, which may be the cause of the persistent small grain sizes reported for evaporated metal halide perovskites that hinder device efficiency and stability. As more material is added, islands coalesce until full coverage of the substrate is reached at around 10 nm average thickness. We also find that quantum confinement induces substantial shifts to the PL wavelength when the average thickness is below 40 nm, offering dual-source vapour deposition as an alternative method of fabricating nanoscale structures for LEDs and other devices.

Published
2019

124. Metal composition influences optoelectronic quality in mixed-metal lead–tin triiodide perovskite solar absorbers

Author

Klug, Matthew T., primary, Milot, Rebecca L., additional, Patel, Jay B., additional, Green, Thomas, additional, Sansom, Harry C., additional, Farrar, Michael D., additional, Ramadan, Alexandra J., additional, Martani, Samuele, additional, Wang, Zhiping, additional, Wenger, Bernard, additional, Ball, James M., additional, Langshaw, Liam, additional, Petrozza, Annamaria, additional, Johnston, Michael B., additional, Herz, Laura M., additional, and Snaith, Henry J., additional

Published
2020
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136. Elucidating the long-range charge carrier mobility in metal halide perovskite thin films

Author

Lim, Jongchul, Hörantner, Maximilian T., Sakai, Nobuya, Ball, James M., Mahesh, Suhas, Noel, Nakita K., Lin, Yen Hung, Patel, Jay B., McMeekin, David P., Johnston, Michael B., Wenger, Bernard, Snaith, Henry J., Lim, Jongchul, Hörantner, Maximilian T., Sakai, Nobuya, Ball, James M., Mahesh, Suhas, Noel, Nakita K., Lin, Yen Hung, Patel, Jay B., McMeekin, David P., Johnston, Michael B., Wenger, Bernard, and Snaith, Henry J.

Abstract

Many optoelectronic properties have been reported for lead halide perovskite polycrystalline films. However, ambiguities in the evaluation of these properties remain, especially for long-range lateral charge transport, where ionic conduction can complicate interpretation of data. Here we demonstrate a new technique to measure the long-range charge carrier mobility in such materials. We combine quasi-steady-state photo-conductivity measurements (electrical probe) with photo-induced transmission and reflection measurements (optical probe) to simultaneously evaluate the conductivity and charge carrier density. With this knowledge we determine the lateral mobility to be ~2 cm 2 V -1 s -1 for CH 3 NH 3 PbI 3 (MAPbI 3 ) polycrystalline perovskite films prepared from the acetonitrile/methylamine solvent system. Furthermore, we present significant differences in long-range charge carrier mobilities, from 2.2 to 0.2 cm 2 V -1 s -1 , between films of contemporary perovskite compositions prepared via different fabrication processes, including solution and vapour phase deposition techniques. Arguably, our work provides the first accurate evaluation of the long-range lateral charge carrier mobility in lead halide perovskite films, with charge carrier density in the range typically achieved under photovoltaic operation.

Published
2019

137. An Ultrafast Switchable Terahertz Polarization Modulator Based on III-V Semiconductor Nanowires

Author

Boland, Jessica L., Baig, Sarwat A., Damry, Djamshid A., Tan, H. Hoe, Jagadish, Chennupati, Joyce, Hannah J., Johnston, Michael B., Joyce, Hannah [0000-0002-9737-680X], and Apollo - University of Cambridge Repository

Subjects
parylene, nanowire, GaAs, polarizer, Terahertz (THz), Physics::Optics, modulator
Abstract

Progress in the terahertz (THz) region of the electromagnetic spectrum is undergoing major advances, with advanced THz sources and detectors being developed at a rapid pace. Yet, ultrafast THz communication is still to be realized, owing to the lack of practical and effective THz modulators. Here, we present a novel ultrafast active THz polarization modulator based on GaAs semiconductor nanowires arranged in a wire-grid configuration. We utilize an optical pump–terahertz probe spectroscopy system and vary the polarization of the optical pump beam to demonstrate ultrafast THz modulation with a switching time of less than 5 ps and a modulation depth of −8 dB. We achieve an extinction of over 13% and a dynamic range of −9 dB, comparable to microsecond-switchable graphene- and metamaterial-based THz modulators, and surpassing the performance of optically switchable carbon nanotube THz polarizers. We show a broad bandwidth for THz modulation between 0.1 and 4 THz. Thus, this work presents the first THz modulator which combines not only a large modulation depth but also a broad bandwidth and picosecond time resolution for THz intensity and phase modulation, making it an ideal candidate for ultrafast THz communication.

Published
2017
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140. Elucidating the long-range charge carrier mobility in metal halide perovskite thin films

Author

Lim, Jongchul, primary, Hörantner, Maximilian T., additional, Sakai, Nobuya, additional, Ball, James M., additional, Mahesh, Suhas, additional, Noel, Nakita K., additional, Lin, Yen-Hung, additional, Patel, Jay B., additional, McMeekin, David P., additional, Johnston, Michael B., additional, Wenger, Bernard, additional, and Snaith, Henry J., additional

Published
2019
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141. CsPbBr3 Nanocrystal Films: Deviations from Bulk Vibrational and Optoelectronic Properties.

Author

Motti, Silvia G., Krieg, Franziska, Ramadan, Alexandra J., Patel, Jay B., Snaith, Henry J., Kovalenko, Maksym V., Johnston, Michael B., and Herz, Laura M.

Subjects
THIN films, NANOCRYSTAL synthesis, CHARGE carriers, PHOTOCONDUCTIVITY, NANOCRYSTALS, BULK solids
Abstract

Metal‐halide perovskites (MHP) are highly promising semiconductors for light‐emitting and photovoltaic applications. The colloidal synthesis of nanocrystals (NCs) is an effective approach for obtaining nearly defect‐free MHP that can be processed into inks for low‐cost, high‐performance device fabrication. However, disentangling the effects of surface ligands, morphology, and boundaries on charge‐carrier transport in thin films fabricated with these high‐quality NCs is inherently difficult. To overcome this fundamental challenge, terahertz (THz) spectroscopy is employed to optically probe the photoconductivity of CsPbBr3 NC films. The vibrational and optoelectronic properties of the NCs are compared with those of the corresponding bulk polycrystalline perovskite and significant deviations are found. Charge‐carrier mobilities and recombination rates are demonstrated to vary significantly with the NC size. Such dependences derive from the localized nature of charge carriers within NCs, with local mobilities dominating over interparticle transport. It is further shown that the colloidally synthesized NCs have distinct vibrational properties with respect to the bulk perovskite, exhibiting blue‐shifted optical phonon modes with enhanced THz absorption strength that also manifest as strong modulations in the THz photoconductivity spectra. Such fundamental insights into NC versus bulk properties will guide the optimization of nanocrystalline perovskite thin films for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Published
2020
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