Publications


Multi-band magnetotransport in exfoliated thin films of Cu x Bi2Se3.

Journal of physics. Condensed matter : an Institute of Physics journal 30 (2018) 155302-

JA Alexander-Webber, J Huang, J Beilsten-Edmands, P Čermák, Č Drašar, RJ Nicholas, AI Coldea

We report magnetotransport studies in thin (<100 nm) exfoliated films of Cu x Bi2Se3 and we detect an unusual electronic transition at low temperatures. Bulk crystals show weak superconductivity with [Formula: see text] K and a possible electronic phase transition around 200 K. Following exfoliation, superconductivity is supressed and a strongly temperature dependent multi-band conductivity is observed for T  <  30 K. This transition between competing conducting channels may be enhanced due to the presence of electronic ordering, and could be affected by the presence of an effective internal stress due to Cu intercalation. By fitting to the weak antilocalisation conductivity correction at low magnetic fields we confirm that the low temperature regime maintains a quantum phase coherence length [Formula: see text] nm indicating the presence of topologically protected surface states.


Multi-band magnetotransport in exfoliated thin films of Cu Bi 2 Se 3

Journal of Physics: Condensed Matter 30 (2018) 155302-155302

JA Alexander-Webber, J Huang, J Beilsten-Edmands, P Čermák, Č Drašar, RJ Nicholas, AI Coldea


Highly Crystalline Methylammonium Lead Tribromide Perovskite Films for Efficient Photovoltaic Devices

ACS ENERGY LETTERS 3 (2018) 1233-1240

NK Noel, B Wenger, SN Habisreutinger, JB Patel, T Crothers, Z Wang, RJ Nicholas, MB Johnston, LM Herz, HJ Snaith


Carbon Nanotubes in Perovskite Solar Cells

ADVANCED ENERGY MATERIALS 7 (2017) ARTN 1601839

SN Habisreutinger, RJ Nicholas, HJ Snaith


Impact of microstructure on the electron-hole interaction in lead halide perovskites

ENERGY & ENVIRONMENTAL SCIENCE 10 (2017) 1358-1366

AM Soufiani, Z Yang, T Young, A Miyata, A Surrente, A Pascoe, K Galkowski, M Abdi-Jalebi, R Brenes, J Urban, N Zhang, V Bulovic, O Portugall, Y-B Cheng, RJ Nicholas, A Ho-Baillie, MA Green, P Plochocka, SD Stranks


Ultrahigh magnetic field spectroscopy reveals the band structure of the three-dimensional topological insulator Bi2Se3

PHYSICAL REVIEW B 96 (2017) ARTN 121111

A Miyata, Z Yang, A Surrente, O Drachenko, DK Maude, O Portugall, LB Duffy, T Hesjedal, P Plochocka, RJ Nicholas


Investigating the Role of 4-Tert Butylpyridine in Perovskite Solar Cells

ADVANCED ENERGY MATERIALS 7 (2017) ARTN 1601079

SN Habisreutinger, NK Noel, HJ Snaith, RJ Nicholas


Two-Dimensional Excitonic Photoluminescence in Graphene on a Cu Surface.

ACS nano 11 (2017) 3207-3212

Y Park, Y Kim, CW Myung, RA Taylor, CCS Chan, BPL Reid, TJ Puchtler, RJ Nicholas, LT Singh, G Lee, C-C Hwang, C-Y Park, KS Kim

Despite having outstanding electrical properties, graphene is unsuitable for optical devices because of its zero band gap. Here, we report two-dimensional excitonic photoluminescence (PL) from graphene grown on a Cu(111) surface, which shows an unexpected and remarkably sharp strong emission near 3.16 eV (full width at half-maximum ≤3 meV) and multiple emissions around 3.18 eV. As temperature increases, these emissions blue shift, displaying the characteristic negative thermal coefficient of graphene. The observed PL originates from the significantly suppressed dispersion of excited electrons in graphene caused by hybridization of graphene π and Cu d orbitals of the first and second Cu layers at a shifted saddle point 0.525(M+K) of the Brillouin zone. This finding provides a pathway to engineering optoelectronic graphene devices, while maintaining the outstanding electrical properties of graphene.


Impact of the Halide Cage on the Electronic Properties of Fully Inorganic Cesium Lead Halide Perovskites

ACS ENERGY LETTERS 2 (2017) 1621-1627

Z Yang, A Surrente, K Galkowski, A Miyata, O Portugall, RJ Sutton, AA Haghighirad, HJ Snaith, DK Maude, P Plochocka, RJ Nicholas


Unraveling the Exciton Binding Energy and the Dielectric Constant in Single-Crystal Methylammonium Lead Triiodide Perovskite.

The journal of physical chemistry letters 8 (2017) 1851-1855

Z Yang, A Surrente, K Galkowski, N Bruyant, DK Maude, AA Haghighirad, HJ Snaith, P Plochocka, RJ Nicholas

We have accurately determined the exciton binding energy and reduced mass of single crystals of methylammonium lead triiodide using magneto-reflectivity at very high magnetic fields. The single crystal has excellent optical properties with a narrow line width of ∼3 meV for the excitonic transitions and a 2s transition that is clearly visible even at zero magnetic field. The exciton binding energy of 16 ± 2 meV in the low-temperature orthorhombic phase is almost identical to the value found in polycrystalline samples, crucially ruling out any possibility that the exciton binding energy depends on the grain size. In the room-temperature tetragonal phase, an upper limit for the exciton binding energy of 12 ± 4 meV is estimated from the evolution of 1s-2s splitting at high magnetic field.


Spatially resolved studies of the phases and morphology of methylammonium and formamidinium lead tri-halide perovskites.

Nanoscale 9 (2017) 3222-3230

K Galkowski, AA Mitioglu, A Surrente, Z Yang, DK Maude, P Kossacki, GE Eperon, JT-W Wang, HJ Snaith, P Plochocka, RJ Nicholas

The family of organic-inorganic tri-halide perovskites including MA (MethylAmmonium)PbI3, MAPbI3-xClx, FA (FormAmidinium)PbI3 and FAPbBr3 are having a tremendous impact on the field of photovoltaic cells due to the combination of their ease of deposition and high energy conversion efficiencies. Device performance, however, is known to be still significantly affected by the presence of inhomogeneities. Here we report on a study of temperature dependent micro-photoluminescence which shows a strong spatial inhomogeneity related to the presence of microcrystalline grains, which can be both bright and dark. In all of the tri-iodide based materials there is evidence that the tetragonal to orthorhombic phase transition observed around 160 K does not occur uniformly across the sample with domain formation related to the underlying microcrystallite grains, some of which remain in the high temperature, tetragonal, phase even at very low temperatures. At low temperature the tetragonal domains can be significantly influenced by local defects in the layers or the introduction of residual levels of chlorine in mixed halide layers or dopant atoms such as aluminium. We see that improvements in room temperature energy conversion efficiency appear to be directly related to reductions in the proportions of the layer which remain in the tetragonal phase at low temperature. In FAPbBr3 a more macroscopic domain structure is observed with large numbers of grains forming phase correlated regions.


Dopant-Free Planar n-i-p Perovskite Solar Cells with Steady-State Efficiencies Exceeding 18%

ACS ENERGY LETTERS 2 (2017) 622-628

SN Habisreutinger, B Wenger, HJ Snaith, RJ Nicholas


A low viscosity, low boiling point, clean solvent system for the rapid crystallisation of highly specular perovskite films

ENERGY & ENVIRONMENTAL SCIENCE 10 (2017) 145-152

NK Noel, SN Habisreutinger, B Wenger, MT Klug, MT Horantner, MB Johnston, RJ Nicholas, DT Moore, HJ Snaith


Independence of optical absorption on Auger ionization in single-walled carbon nanotubes revealed by ultrafast e-h photodoping

NEW JOURNAL OF PHYSICS 18 (2016) ARTN 023051

MD Anderson, MN Beattie, JA Alexander-Webber, RJ Nicholas, JM Fraser


Determination of the exciton binding energy and effective masses for methylammonium and formamidinium lead tri-halide perovskite semiconductors

ENERGY & ENVIRONMENTAL SCIENCE 9 (2016) 962-970

K Galkowski, A Mitioglu, A Miyata, P Plochocka, O Portugall, GE Eperon, JT-W Wang, T Stergiopoulos, SD Stranks, HJ Snaith, RJ Nicholas


Quantum dot-like excitonic behavior in individual single walled-carbon nanotubes.

Scientific reports 6 (2016) 37167-

X Wang, JA Alexander-Webber, W Jia, BPL Reid, SD Stranks, MJ Holmes, CCS Chan, C Deng, RJ Nicholas, RA Taylor

Semiconducting single-walled carbon nanotubes are one-dimensional materials with great prospects for applications such as optoelectronic and quantum information devices. Yet, their optical performance is hindered by low fluorescent yield. Highly mobile excitons interacting with quenching sites are attributed to be one of the main non-radiative decay mechanisms that shortens the exciton lifetime. In this paper we report on time-integrated photoluminescence measurements on individual polymer wrapped semiconducting carbon nanotubes. An ultra narrow linewidth we observed demonstrates intrinsic exciton dynamics. Furthermore, we identify a state filling effect in individual carbon nanotubes at cryogenic temperatures as previously observed in quantum dots. We propose that each of the CNTs is segmented into a chain of zero-dimensional states confined by a varying local potential along the CNT, determined by local environmental factors such as the amount of polymer wrapping. Spectral diffusion is also observed, which is consistent with the tunneling of excitons between these confined states.


Efficient perovskite solar cells by metal ion doping

ENERGY & ENVIRONMENTAL SCIENCE 9 (2016) 2892-2901

JT-W Wang, Z Wang, S Pathak, W Zhang, DW deQuilettes, F Wisnivesky-Rocca-Rivarola, J Huang, PK Nayak, JB Patel, HAM Yusof, Y Vaynzof, R Zhu, I Ramirez, J Zhang, C Ducati, C Grovenor, MB Johnston, DS Ginger, RJ Nicholas, HJ Snaith


The Impact of Phase Retention on the Structural and Optoelectronic Properties of Metal Halide Perovskites

Advanced Materials Wiley: 12 months (2016)

RJ Nicholas


Structured Organic-Inorganic Perovskite toward a Distributed Feedback Laser.

Advanced materials (Deerfield Beach, Fla.) 28 (2016) 923-929

M Saliba, SM Wood, JB Patel, PK Nayak, J Huang, JA Alexander-Webber, B Wenger, SD Stranks, MT Hörantner, JT-W Wang, RJ Nicholas, LM Herz, MB Johnston, SM Morris, HJ Snaith, MK Riede

A general strategy for the in-plane structuring of organic-inorganic perovskite films is presented. The method is used to fabricate an industrially relevant distributed feedback (DFB) cavity, which is a critical step toward all-electrially pumped injection laser diodes. This approach opens the prospects of perovskite materials for much improved optical control in LEDs, solar cells, and also toward applications as optical devices.


The Impact of Phase Retention on the Structural and Optoelectronic Properties of Metal Halide Perovskites.

Advanced materials (Deerfield Beach, Fla.) 28 (2016) 10757-10763

A Osherov, EM Hutter, K Galkowski, R Brenes, DK Maude, RJ Nicholas, P Plochocka, V Bulović, TJ Savenije, SD Stranks

The extent to which the soft structural properties of metal halide perovskites affect their optoelectronic properties is unclear. X-ray diffraction and micro-photoluminescence measurements are used to show that there is a coexistence of both tetragonal and orthorhombic phases through the low-temperature phase transition, and that cycling through this transition can lead to structural changes and enhanced optoelectronic properties.

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