ORCID Profile
0000-0001-9025-0465
Current Organisation
University of Oxford
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Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4OB02507E
Abstract: We report the synthesis of four new cationic push–pull membrane probes based on a thiophene core and evaluate their photobiological properties.
Publisher: Wiley
Date: 22-02-2013
Abstract: A scalable method to coat monochiral (7,5) semiconducting single-walled carbon nanotubes with a monolayer coating of a range of technologically useful polymers such as poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) is presented. Optical spectroscopy and atomic force microscopy measurements show that the semiconducting tube purity (>99%) obtained from the selective wrapping of nanotubes by polymers such as poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) can be transferred to these other nanotube-polymer combinations by polymer exchange.
Publisher: Wiley
Date: 02-12-2015
Abstract: 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.
Publisher: American Chemical Society (ACS)
Date: 05-12-2014
DOI: 10.1021/NN505860A
Abstract: Organic and hybrid organic-inorganic systems are promising candidates for low cost photovoltaics. Recently, perovskite-based systems have been attracting a large amount of research attention, where the highest performing devices employ a small molecule (2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene) (Spiro-OMeTAD) hole transporter. Here, we demonstrate the production of single-walled carbon nanotube (SWNT)/single molecule nanostructures using a simple solution processing technique for effective and strong binding of Spiro-OMeTAD to in idual polymer-wrapped SWNTs. These small molecules bind very strongly, which causes both large mechanical strain of the nanotubes and also improves the separation of in idual SWNTs, thus improving the nanotube photoluminescence quantum efficiency by 1 order of magnitude compared to simple polymer-nanotube nanohybrids. Using absorption and photoluminescence measurements, we show that there is a dramatic variation in the electronic properties of the polymer-NT nanocomposites due to the band alignment formed with Spiro-OMeTAD. These self-assembled nanocomposites offer the potential for integration into high performance optoelectronic such as photovoltaic cells and light emission devices.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6EE02373H
Abstract: We present a new solvent system which has the potential to overcome the manufacturing barriers associated with the currently used toxic high boiling point solvents.
Publisher: Wiley
Date: 24-02-2011
Publisher: American Chemical Society (ACS)
Date: 20-06-2012
DOI: 10.1021/NN301133V
Abstract: We describe studies of new nanostructured materials consisting of carbon nanotubes wrapped in sequential coatings of two different semiconducting polymers, namely, poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT). Using absorption spectroscopy and steady-state and ultrafast photoluminescence measurements, we demonstrate the role of the different layer structures in controlling energy levels and charge transfer in both solution and film s les. By varying the simple solution processing steps, we can control the ordering and proportions of the wrapping polymers in the solid state. The resulting novel coaxial structures open up a variety of new applications for nanotube blends and are particularly promising for implementation into organic photovoltaic devices. The carbon nanotube template can also be used to optimize both the electronic properties and morphology of polymer composites in a much more controlled fashion than achieved previously, offering a route to producing a new generation of polymer nanostructures.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6EE01969B
Abstract: Realizing the theoretical limiting power conversion efficiency (PCE) in perovskite solar cells requires a better understanding and control over the fundamental loss processes occurring in the bulk of the perovskite layer and at the internal semiconductor interfaces in devices.
Publisher: Wiley
Date: 27-05-2013
Abstract: We describe two methods in which we manipulate the binding of multiple conjugated polymers to single-walled carbon nanotubes (SWNTs) to produce new and novel nanostructures. One method fi rst utilizes the selective binding of poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) to a narrow distribution of semiconducting SWNTs and then uses a polymer exchange to transfer this purity to other nanotube-polymer combinations, using technologically useful polymers such as poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluoreneco -benzothiadiazole) (F8BT) as fi rst ex les. The other method involves controlling the competitive binding of P3HT and F8BT to SWNTs to produce coaxial nanostructures consisting of both polymers simultaneously bound in ordered layers. We show that these two simple solution-processing techniques can be carried out sequentially to afford new dual-polymer nanostructures comprised of a semiconducting SWNT of a single chirality. This allows the favorable properties of both polymers and purified semiconducting SWNTs to be implemented into potentially highly efficient organic photovoltaic devices.
Publisher: Springer Science and Business Media LLC
Date: 16-11-2016
DOI: 10.1038/SREP37167
Abstract: 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 in idual polymer wrapped semiconducting carbon nanotubes. An ultra narrow linewidth we observed demonstrates intrinsic exciton dynamics. Furthermore, we identify a state filling effect in in idual 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.
Publisher: American Chemical Society (ACS)
Date: 28-04-2023
DOI: 10.1021/JACS.3C01531
Publisher: IOP Publishing
Date: 07-1993
Publisher: American Chemical Society (ACS)
Date: 17-09-2009
DOI: 10.1021/JP907195T
Publisher: Springer Science and Business Media LLC
Date: 27-11-2012
DOI: 10.1038/NCOMMS2235
Publisher: Springer Science and Business Media LLC
Date: 15-06-2015
DOI: 10.1038/NPHYS3357
Publisher: American Physical Society (APS)
Date: 24-08-2010
Publisher: American Chemical Society (ACS)
Date: 29-08-2014
DOI: 10.1021/NL502016Q
Abstract: Semiconducting carbon nanotubes (CNTs) provide an exceptional platform for studying one-dimensional excitons (bound electron-hole pairs), but the role of defects and quenching centers in controlling emission remains controversial. Here we show that, by wrapping the CNT in a polymer sheath and cooling to 4.2 K, ultranarrow photoluminescence (PL) emission line widths below 80 μeV can be seen from in idual solution processed CNTs. Hyperspectral imaging of the tubes identifies local emission sites and shows that some previously dark quenching segments can be brightened by the application of high magnetic fields, and their effect on exciton transport and dynamics can be studied. Using focused high intensity laser irradiation, we introduce a single defect into an in idual nanotube which reduces its quantum efficiency by the creation of a shallow bound exciton state with enhanced electron-hole exchange interaction. The emission intensity of the nanotube is then reactivated by the application of the high magnetic field.
Publisher: American Chemical Society (ACS)
Date: 22-09-2014
DOI: 10.1021/NL501982B
Abstract: Organic-inorganic perovskite solar cells have recently emerged at the forefront of photovoltaics research. Power conversion efficiencies have experienced an unprecedented increase to reported values exceeding 19% within just four years. With the focus mainly on efficiency, the aspect of stability has so far not been thoroughly addressed. In this paper, we identify thermal stability as a fundamental weak point of perovskite solar cells, and demonstrate an elegant approach to mitigating thermal degradation by replacing the organic hole transport material with polymer-functionalized single-walled carbon nanotubes (SWNTs) embedded in an insulating polymer matrix. With this composite structure, we achieve JV scanned power-conversion efficiencies of up to 15.3% with an average efficiency of 10 ± 2%. Moreover, we observe strong retardation in thermal degradation as compared to cells employing state-of-the-art organic hole-transporting materials. In addition, the resistance to water ingress is remarkably enhanced. These are critical developments for achieving long-term stability of high-efficiency perovskite solar cells.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5EE03435C
Abstract: The reduced effective mass ( μ ) and excitonic Rydberg ( R *) are measured by magneto-optics for new perovskite semiconductors.
Publisher: Wiley
Date: 19-10-2016
Abstract: 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.
Publisher: IEEE
Date: 09-2012
Publisher: Springer Science and Business Media LLC
Date: 2011
DOI: 10.1557/OPL.2011.230
Abstract: We report the observation of an ultrafast (~ 430 fs) charge transfer process at the interface between a single-walled carbon nanotube (SWNT) wrapped by a semi-conducting polymer, poly(3-hexylthiophene) (P3HT), creating free polarons on both materials. The addition of excess P3HT as a surrounding network allows these free polarons to be long-lived at room temperature. Our results suggest that SWNT-P3HT blends incorporating only 1% fractions of SWNTs can achieve a charge separation efficiency comparable to a conventional 60:40 P3HT-fullerene blend, provided small-diameter tubes are embedded in an excess P3HT matrix.
Publisher: American Chemical Society (ACS)
Date: 24-11-2010
DOI: 10.1021/NL1036484
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 in idually embedded in the P3HT matrix.
Publisher: American Chemical Society (ACS)
Date: 20-11-2014
DOI: 10.1021/JZ5021795
Abstract: Here, we report the use of polymer-wrapped carbon nanotubes as a means to enhance charge extraction through undoped spiro-OMeTAD. With this approach a good solar cell performance is achieved without the implementation of conventional doping methods. We demonstrate that a stratified two-layer architecture of sequentially deposited layers of carbon nanotubes and spiro-OMeTAD, outperforms a conventional blend of the hole-conductor and the carbon nanotubes. We also provide insights into the mechanism of the rapid hole extraction observed in the two-layer approach.
Publisher: AIP Publishing
Date: 28-05-2014
DOI: 10.1063/1.4879895
Abstract: We demonstrate ultrafast modulation of terahertz radiation by unaligned optically pumped single-walled carbon nanotubes. Photoexcitation by an ultrafast optical pump pulse induces transient terahertz absorption in nanowires aligned parallel to the optical pump. By controlling the polarisation of the optical pump, we show that terahertz polarisation and modulation can be tuned, allowing sub-picosecond modulation of terahertz radiation. Such speeds suggest potential for semiconductor nanowire devices in terahertz communication technologies.
Publisher: American Chemical Society (ACS)
Date: 28-02-2011
DOI: 10.1021/NN103588H
Abstract: We report on the noncovalent binding of conjugated porphyrin oligomers to small diameter single-walled carbon nanotubes (SWNTs) and highlight two remarkable observations. First, the binding of the oligomers to SWNTs is so strong that it induces mechanical strain on the nanotubes in solution. The magnitudes of the strains are comparable to those found in solid-state studies. Comparable strains are not observed in any other SWNT-supramolecular complexes. Second, large decreases in polymer band gap with increasing length of the oligomer lead to the formation of a type-II heterojunction between long chain oligomers and small-diameter nanotubes. This is demonstrated by the observation of enhanced red-shifts for the nanotube interband transitions. These complexes offer considerable promise for photovoltaic devices.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Robin Nicholas.