The projects listed below are available for self-funded MRes (1 year) or international/EU MRes+PhD (4 years) students for October 2017 start.  "Home" (UK national) applicants should choose from the list of funded projects. Due to funding restrictions, projects from the funded list are not available to international students. For more information about funding eligibility and scholarships, click here.

Please note that admissions for MRes and self-funded CDT applicants for October 2017 entry have now closed. Admissions for 2018 entry will open in November 2017.

Projects for Self-Funding Students - MRes or CDT

Dissolution and sorting of SWNTs for transparent electrodes and thin film transistors

Supervised by Prof Milo Shaffer (Chemistry, Imperial College) and Prof John de Mello (Chemistry, Imperial College)

Carbon-based electrodes promise both cheap, printable, flexible, transparent conductors and high performance thin film transistors, crucial for large area plastic electronics. A new process developed at Imperial/LCN/UCL allows dissolution of single-walled nanotubes, without any damaging sonication or oxidation; thus, in principle, very long SWNTs can be dispersed. The process produces charged nanocarbons, which are truly individualised in solution (as shown by neutron scattering), due to electrostatic repulsion. In addition, the charging process can be selective for metallic SWNTs, or semi-conducting SWNTs, and can be used to remove other unwanted impurities. The use of long, metallic nanotubes should provide the required significant improvements in transparent conducting network performance, since performance is dominated by junction resistance. The charge can be neutralised without damage, or exploited to control the deposition process, including creating hybrid composite films. The remaining semi-conducting SWNT fractions are of interest transistors and other Plastic Electronics applications; the LCN approach offers prospects of separating the semi-conducting species by band gap / type. Our SWNT separation/dispersion technology is already patented and licensed for commercialisation; the extension to further SWNT applications is very timely.

Existing separated SWNT materials are processed at minute scales and very high costs due to the intrinsically non-scalable approach to individualisation, whilst the damaging process reduces the length to less than a micron. Our approach is potentially truly scalable and directly feeds into deposition of excellent debundled films and other useful constructs of long SWNTs that are critical from a performance perspective. Semiconducting SWNT TFTs processed this way would be especially attractive, as they may be expected to best the mobility of all existing solvent deposited organics by 2-3 orders of magnitude.

Plan of Work:
Year 1: Exfoliation of SWNTs; extension up to and including “supergrowth”, 300 um SWNTs. Deposition protocols on plastic films, using physical and chemical means. Microstructural characterisation by SEM and (conductive) AFM. Transparency/conductivity determination. 
Year 2: Determination of key network controlling parameters / influence of SWNT characteristics (length dependence, degree of purification/metallicity). Development of nanocarbon / polymer / inorganic hybrid systems. Determination of performance enhancements.
Year 3: Demonstration device fabrication incorporating hybrid systems as electrodes. Development of selective separation of semi-conducting SWNT species, and deposition of films for transistor applications. 
Year 4: Exploitation of transparent conductive and semi-conducting films for improved proof-of-concept device structures for transistors, LEDs, and PV.

For more information, contact Prof Milo Shaffer: m.shaffer@imperial.ac.uk

A robotic system for the automated fabrication of plastic electronic devices

Supervised by Prof John de Mello (Chemistry, Imperial College) and Dr James Bannock (Chemistry, Imperial College)

Standard practice in plastic electronics research is to fabricate devices by hand – a slow, error-prone process with poor reproducibility. This project involves the development of an automated robotic system for fabricating organic devices, which will provide greater control, versatility, reproducibility and throughput than manual fabrication. The system will enable the fabrication of organic solar cells (OSCs), light-emitting diodes (OLEDs) and thin-film transistors (OTFTs) via spin-coating, and will comprise five main parts: (i) a solution carousel for preparing solutions of tuneable composition; (ii) a pipette gantry for collecting solutions from the carousel and dispensing them on a substrate; (iii) a spin-coater for casting uniform films; (iv) a gradient hot-stage for simultaneously annealing multiple substrates at different temperatures; and (v) an articulated arm for moving substrates between the spin-coater, hot-bench and evaporation mask. The system will be configured such that an evaporation mask will be loaded with blank substrates at the start of the fabrication run; and at the end of the run it will contain the same substrates in the same positions, now coated and ready for deposition of the top electrode. (This last step, which cannot easily be automated without significant additional expenditure, will take place in an evaporator housed inside a glove box).

The system will permit the fabrication of both single and multilayer devices; have the ability to deposit layers of tuneable composition from solvent mixtures; offer full control over the deposition and annealing conditions; be of a size that can (if necessary) be accommodated within a glove-box for the handling of air-sensitive materials; and will readily handle materials at the 10s of mg scale – an important consideration for new materials that are invariably in limited supply.

For more information, contact Prof John de Mello: j.demello@imperial.ac.uk

Ultrafast spectroscopy of organic and hybrid heterojunctions for solar energy conversion

Supervised by Prof James Durrant (Chemistry, Imperial College) and Dr Artem Bakulin (Chemistry, Imperial College)

Photoinduced charge separation is the primary step in almost all solar energy conversion devices. This charge separation spatially separates photogenerated electrons and holes; efficient device operation requires this charge separation to occur with minimal energy loss. This project will be focused on charge separation at organic and hybrid donor / acceptor heterojunctions. The successful applicant will address these charge separation dynamics using a set of optical and electronic techniques including ultrafast and polarisation-sensitive transient absorption to observe motion of carriers as well optoelectronic measurements such as multi-pulse photocurrent techniques sensitive to the bound and trapped states potential in such devices. The applicant will also have the opportunity to develop an ultrafast optical microscope using a high-repetition laser and white light supercontinuum fibre source. This will provide opportunities for spatially-resolved characterisation of crystalline organic and perovskite materials to address the effects of grain boundaries and heterointerfaces. These techniques will be applied to a range of state of the art organic and hybrid materials and devices available in the applicants’ groups, and through their external partners, including in particular the Gwangju Institute of Science and Technology, Korea, such as polymer sensitized perovskite devices.

For organic donor / acceptor junctions, substantial progress has been made both in fundamental understanding of development of efficient organic solar cells is the determination of materials structure / device function relationships. This project will focus in particular upon how materials and film structure impacts upon the charge separation and recombination dynamics in organic solar cells, and thereby determines device efficiency. The project will employ a range of transient optical and optoelectronic technics to elucidate the function of new organic semiconductors developed in the McCulloch group, building upon our previous studies in this area, and thus enabling systematic optimisation of materials and device design.

For more information, contact Prof James Durrant: j.durrant@imperial.ac.uk

Novel chiral molecular photodetectors for biomedicine and quantum telecommunication

Supervised by Prof Alasdair Campbell (Physics, Imperial College) and Dr Matthew Fuchter (Chemistry, Imperial College)

Photon spin can be used to transmit information in optical quantum computing, long-range optical quantum telecommunication, as well as in the detection of biomolecules such as chain-folded proteins, and in medical tomographic imaging. To really develop these technologies requires the ability to detect right-handed and left-handed circularly polarized (CP) photons across a range of wavelengths. At Imperial a novel type of CP optoelectronic photodetector was created using a chiral molecular semiconductor (Nature Photonics, 7, 634 (2013)). The helically shaped molecular semiconductor comes in both left- and right-handed chiral forms, giving it the ability to preferentially absorb and transmit either left- or right-handed CP photons. Using this semiconductor we were able to create micron-scale CP light detecting phototransistors on Si. This PhD project is to build upon this discovery and: (i) to extend the detection range from the UV to the NIR, targeting both biomolecule and telecom relevant wavelengths; (ii) to increase sensitivity and efficiency to detect lower photon counts; (iii) and to increase response time into the ns range. This will be done using new chiral materials, multilayer device structures and blend systems, as well as different types of thin-film photodiode and phototransistor architectures. The project will involve collaborating with colleagues in the Department of Chemistry and in industry regarding state-of-the-art materials; also with academic collaborators regarding structural measurements and analysis and spin transport studies of chiral molecular films. 

For more information, contact Prof Alasdair Campbell: alasdair.campbell@imperial.ac.uk

Circularly Polarized Organic Light Emitting Devices

Supervised by Prof Alasdair Campbell (Physics, Imperial College) and Dr Matthew Fuchter (Chemistry, Imperial College)

Right-handed and left-handed circularly polarized (CP) light is made up of photons in the two different spin states. Directly emitting CP light sources therefore have potential application in optical spintronics, optical quantum computing, and optical quantum telecommunication (quantum cryptography). Additionally, most displays in current mobile phones, tablets and TVs have a circularly polarizing filter to improve contrast; such circularly polarizing filters can also be used to generate 3D images. Such filters discard 50% of the generated light, halving battery lifetime in portable products and doubling the display carbon-footprint. A directly emitting CP light source would solve this issue, and could additionally be used as a highly efficient LCD backlight. At Imperial we have invented a novel type of CP emitting polymer organic light emitting diode (OLED) (Advanced Materials, 25, 2624 (2013)) as such a CP light source. This involved inducing CP emission from a light emitting polymer by blending it with an intrinsically chiral, helically-shaped organic semiconducting molecule known as a helicene. Collaborating with Cambridge Display Technology Ltd, we have extended this technology in the display area. We have also started to develop novel metal complex helicenes for CP phosphorescent OLEDs (PhOLEDs). This PhD project is to build upon on his work and develop further novel CP organic light emitting devices. Potential target devices include: inverted bilayer CP-OLEDs and PhOLEDs; CP-OLEDs with spin-filter injection layers; large-area gravure printed CP-OLEDs for flexible displays; CP organic light emitting transistors (CP-OLETs) for quantum optics. The project will involve collaborating with CDT regarding state-of-the-art materials, with the photonics theory group regarding device modelling, and with other colleagues at UCL and St Andrews involved in spintronics and fast spectroscopy techniques.

For more information, contact Prof Alasdair Campbell: alasdair.campbell@imperial.ac.uk

Nanoscale Circularly Polarised Light Detecting Organic Field Effect Transistors

Supervised by Dr Matthew Fuchter (Chemistry, Imperial College) and Prof Alasdair Campbell (Physics, Imperial College)

Circularly polarized (CP) light is central to many photonic technologies, including CP-ellipsometry based tomography, optical communication of spin information, and quantum-based optical computing and information processing. To develop these technologies to their full potential would require the miniaturization and integration of suitable CP photo-detecting devices. Very recently, we have been the first to discover that unique helical semiconducting molecules called helicenes can be used to prepare a CP light emitting OLEDs and CP light detecting organic field effect transistors (CP-photoFETs). The photo-response to CP light of such CP-photoFETs is directly related to the handedness, or molecular chirality, of the helicene molecule.

The overall aim of this project is to take this preliminary research much further, developing new helicene derivatives with optimized hole injection and transport properties for p-type transistors, as well as study the physical behaviour of these materials on different surfaces, optimising their dynamic molecular aggregation, packing and nanocrystallinity to maximize the charge carrier mobility and CP response. The precise focus of a given studentship (synthesis, materials characterization, device fabrication) will depend on a given student’s interests and skill set.

For more information, contact Dr Matthew Fuchter: m.fuchter@imperial.ac.uk

Platinum Metallahelicenes in Circularly Polarised Phosphorescent Organic Light Emitting Diodes (CP-PHOLEDs)

Supervised by Dr Matthew Fuchter (Chemistry, Imperial College) and Prof Alasdair Campbell (Physics, Imperial College)

Circularly polarised (CP) light emitting devices have enormous potential, particularly in lighting applications. CP organic light emitting dioides (CP-OLEDs) could be used as an alternative LCD backlight, potentially doubling efficiency by halving the light lost at the first polariser layer, or as the emitting elements in AMOLED displays, again potentially doubling efficiency by halving the light lost at the contrast enhancing CP surface filter. Very recently, we have been the first to discover that unique helical semiconducting molecules called helicenes can be used to prepare a CP light emitting OLEDs and CP light detecting organic field effect transistors (CP-photoFETs).

Our previous work employed the simple blending of an enantiopure helicene dopant and a conjugated polymer to induce CP-emission from the polymer. A procedurally analogous, but conceptually different approach would be to use a polymeric host, with an emissive helicene dopant. This studentship will explore the potential of such an approach, using the highly phosphorescent metallahelicenes as the chiral emissive dopant, building on our recently published preliminary results (3). The precise focus of a given studentship (synthesis, materials characterization, device fabrication) will depend on a given student’s interests and skill set.

For more information, contact Dr Matthew Fuchter: m.fuchter@imperial.ac.uk

Deposition of organic and inorganic layers on polymer substrates by roll-to-roll coating in vacuum

Supervised by Dr Hazel Assender (Materials, Oxford University)

NB: This project is not available for MRes. For a CDT project, the MRes year will be based at Imperial College, then the student will transfer to Oxford for a DPhil. 

The project will make use of our unique roll-to-roll polymer web coater to deposit, under vacuum, acrylate or other organic layers on polymer substrates, followed by evaporation or magnetron sputtering deposition of thin film inorganic layers such as metals or oxides. The resulting materials will then be characterized using a suite of methods. Applications of layers will be tailored towards gas barrier films (often for electronics applications), thin film electronics, phase change materials or organic PV for wearable and flexible technologies.

For more information, contact Dr Hazel Assender: hazel.assender@materials.ox.ac.uk

An Auxetic Heart Patch Based on Well-Defined Conductive Oligomers

Supervised by Prof Molly Stevens (Materials, Imperial College) and Prof Martin Heeney (Chemistry, Imperial College)

Cardiovascular diseases are the number one cause of death worldwide. There are but a few therapeutic options available following myocardial infarct as cardiac tissues possess relatively low reparative and regenerative capabilities. This situation imposes an enormous global socioeconomic burden and biomaterial-based strategies could prove to be the much needed, innovative solution. The main challenges regarding materials design relate to achieving polymer-based electroactive biomaterials that are also biocompatible, bear relevant mechanical properties that are compatible with the strenuous and dynamic mechanical environment of cardiac tissues and capable of controlling and supporting healthy responses from cardiac cells following infarct.

The aim of this project is to we will design and develop the first electroactive auxetic patch that withstands the stringent mechanical forces within the native physiological environment using elegant chemical approaches that yield conductive oligomer components. The unique auxetic nature means that the patch will expand in both axes and match the motion of the heart. In-house designed chemistries that result in homogenous electroactive (e.g. thiophene-based) oligomers that can be selectively end-functionalised and crosslinked to form electroresponsive scaffold systems will be used. This project is extremely multidisciplinary and will draw from the wide breadth of expertise present within the Stevens Group, which includes materials science, polymer chemistry, scaffold construction, cellular assays and tissue engineering and synthetic chemistry in the Heeney Group.

Plan of work:
Year 1 (MRes): The student will create prototypes of an auxetic patch using laser ablation and trial a number of polymer-based materials, such as polyaniline and other similar synthetically sourced electroactive materials. These will be characterised and studied to identify the ideal dimensions and the desired anisotropic ratio of stiffness, Young’s modulus and porosity. The electrical dopant and surface biofunctionalisation will be investigated to increase the translation potential of this first prototype. Additionally the student will be trained in chemical protocols to produce defined oligomeric components serving as chain ends that enable scaffold biofunctionalisation, designed within this CDT. 
Years 2-3 (PhD): Several parameters defined during the MRes component of this Plastics Electronics CDT will be used as a platform to build a more complex auxetic patch. The architecture will utilise an array of well-defined, easily functionalised, conjugated oligomers, based on our in-house developed chemical protocols capable of readily producing various constructs with controlled lengths, which can be easily incorporated within larger constructs to impart tunable electroactivity. The student will also continue mechanical and physical characterisation of the patches, as well as in vitro cellular assays using cardiomyocytes. The biocompatibility of the patch will be evaluated using biological protocols and and assays available within the Stevens labs, which will be optimised via controlled functionalisation using bioactive moieties, while the impact of the electrical properties on cellular behaviour of the auxetic patch will also be studied in vitro.
Year 4 (PhD): In vitro investigations will be concluded to assess the patch’s candidacy as a biomaterial. The student will optimise the material design for the purpose of its implementation in animal models (supported by other projects and via strong collaborations at Imperial).

For more information, contact Prof Molly Stevens: m.stevens@imperial.ac.uk

 

Stabilising Perovskite Photovoltaics using Atomic Layer Deposition

Supervised by Dr Martyn McLachlan (Materials, Imperial College) and Dr Russell Binions (Engineering & Materials Science, QMUL)

The objective of this project is to address a rapidly developing area of solar energy harvesting based on a materials system capable of affording compatibility with large-area, low-cost deposition techniques. This material system, so-called organic-inorganic perovskite, was recently discovered to be an outstanding absorbing layer in this application, producing exceptional efficiencies. The further development of this perovskite technology is, however, hindered by the poor stability and inherent device hysteresis. From recent developments in the McLachlan research group it has become apparent that the device interlayers can play a significant role in overcoming these shortfalls. Thus this project aims to directly address issues of stability and efficiency improvements in perovskite solar cells.

This project will involve the use of atomic layer deposition (ALD) to deposit specific device interlayers that will achieve the objectives through careful selection of materials and with unparalleled control of surface and near interfacial properties. Growth of materials by ALD proceeds through repetition of exposure of a substrate to alternating, gaseous precursors which undergo self-limiting reactions with surface chemical groups, followed by purging, resulting in very repeatable, layer-by-layer growth. The deposition process is low temperature (generally 80-250 °C) and the self-limiting nature of the reactions ensures extremely uniform coating with sub-nanometre thickness control for all surface geometries, from planar to 3D.

Plan of work:
1. Using model systems, the stability of perovskite layers on ideal surfaces e.g. single crystal substrates will be explored. As received substrates can be cleaned and prepared to allow the perovskite deposition to be on a pristine surface, the surfaces yielding the best stability will be prepared using ALD and the new soft epitaxy method. Here it is necessary to understand not only orientation but also how orientation affects contact potential, wetting behaviour, Fermi level, roughness and the nature of surface absorbates. TiO2 is often implemented as an ETL, despite having lower conductivity than ZnO. The issue of surface polarity in ZnO may be one of the origins of instability that aim to overcome. During the soft epitaxy we have recently discovered that simple doping of ZnO can increase the stability to rival that of TiO2 and therefore this opens up a huge area of investigation and potential.
2. Taking advantage of the ALD system design we will dose the ETL and/or the perovskite layer with water to give precise control of the water content and establish the quantity of water that is beneficial for perovskite solar cells, as some actually report water being necessary in small quantified concentrations but also acknowledging that too much can cause degradation. Our reactive metal-alkyl precursors used in ALD are extremely efficient water scavengers thus any water present in the perovskite can be completely eliminated when exposed to the reactive precursors, indeed this is the basic principle of ALD thus we can completely eliminate water from the system.
3. Finally, and in parallel with the activities above, we shall explore the use of ALD to deposit charge selective interlayers below the perovskite layer, and directly above the perovskite (novel). The extremely low-temperature conditions of which our ALD system is capable will allow such deposition without thermally induced degradation occurring and may, based on the outcomes of 1-2 above, provide further benefits to the devices if the exact impact of water addition/removal can be established.

In all cases the performance and lifetimes of the as-prepared devices will be assessed with that data from each series of experiments being used to prepare a library of conditions-stabilities that can be used as a reference tool for accelerating the development of these materials.

For more information, please contact Dr Martyn McLachlan: martyn.mclachlan@imperial.ac.uk

Developing Conductive Inks based on Si Nanowires for Printed Electronics and Sensors

Supervised by Dr Firat Güder (Bioengineering, Imperial College) and Prof Ji-Seon Kim (Physics, Imperial College)

Currently, there are no low-cost inks to print conductive patterns with metallic conductivities on flexible substrates, especially on cellulose paper and textiles. Inks containing large amounts of silver powders are commonly used for the fabrication of conductive electrodes and wires for applications related to diagnostics and electronics. Why do we need conductive inks based on Si nanowires? Ag-based inks are probably the most commonly used metallic inks for printing high conductivity patterns on flexible substrates. Ag-based conventional conductive inks, however, have three shortcomings: i) Insulating polymer binders in Ag inks reduce the conductivity of the electrodes deposited ii) When printed on porous substrates such as paper or textiles, the inks fill the pores, reducing the surface area (a disadvantage for applications concerning sensing) and preventing the flow of liquids.[1] iii) The use of large amounts of silver powders to achieve percolation and the use of propriety solvents render the price of Ag-based inks prohibitive (250 gr Ag ink can cost in excess of 300 GBP) thus making the inks less accessible; a major limitation for research labs and companies developing technologies for the developing world.

This project will focus on developing conductive inks based on Si nanowires (NWs) via solution processing at room temperature and standard pressure. The conductive inks synthesized in this project will be used for the fabrication of disposable diagnostic devices (e.g., electrochemical DNA biosensors) and electronic circuits, such as printed RFID antennas, flexible circuit boards for wearable textile electronics and other flexible electronic devices including printed OLEDs and OPVs. The nanostructures and inks produced will be electrically and structurally characterized and their chemical activity (as a catalyst) will be investigated for electroless plating. 

In this project, the synthesis of conductive inks based on Si nanowires (NWs) will be investigated as a replacement for expensive Ag inks. The use of Si NWs has the following three main advantages: i) high aspect-ratio Si NWs reach the percolation threshold, to create conductive networks, at much lower concentrations compared to Ag powders, reducing the amount of material required. ii) Unlike Ag-based inks, Si NWs in the Si NW ink formulations can be used as catalysts for the electroless deposition of metals. They can also be used as conductive seed layers for conventional electroplating of metals. This new class of Si NW-based conductive inks can be considered as “wild card” inks. They can be used alone or as catalyst/seed layers for the growth of metals. iii) Si is an abundant material hence it is inexpensive. Furthermore, Si NW inks will be essential in a broad range of applications including biosensing, printed RFID tags, flexible circuit boards for wearable textile electronics, printed batteries, LEDs, even solar cells.

For more information, contact Dr Firat Güder: guder@imperial.ac.uk

Kirigami engineered polymer (nano)composites for self-powered sensors and smart materials

Supervised by Dr Emiliano Bilotti (Engineering & Materials Science, QMUL) and Dr Ettore Barbieri (Engineering & Materials Science, QMUL)

Electric and electronic elements and devices (such as electrodes, sensors, storage devices, heating/cooling elements) that are able to sustain large strains are indispensable components of recently emerging fields like wearable electronics, flexible displays, stretchable circuits, and conformal skin sensors [1-3]. However, it is fundamentally very difficult to retain functional properties, like electrical conductivity, when a material is subjected to high strain. Various approaches have been employed to achieve flexible and stretchable devices, such as thin film bendable devices [4], buckling-based stretchable devices [5], pre-strained substrates [6] and elastomeric polymer nanocomposites containing aligned high aspect ratio nanoparticles [7] or conductive materials in liquid state [8]. Recently, an approach based on kirigami - the Japanese art of paper cutting and folding - was adopted to engineer macroscale structures capable of high strains and unusual mechanical properties, including metamaterials [9]. Shyu et al. [10] demonstrated that a network of notches in brittle (conductive) nanocomposite films substantially increases the ultimate strain at break and, more interestingly, provides a constant electrical conductance up to 300% strain.

This project will explore the opportunities offered by the ancient art of paper cutting and folding (kirigami) to tackle two major technological challenges: 1. Retain functional properties of conductive polymers and polymer (nano-)composites under high strains; 2. Develop potentially scalable and continuous production methods to create 3D structures and devices from patterned multilayer (nanocomposites) polymer films.

The high strain offered by kirigami-engineering will be extended to a series of other functional properties possessed by conductive polymers composites (CPC) like: energy harvesting, pyroresistivity for self-regulating heaters and self-powered (degradation, damage and gas/liquid) sensing. Kirigami offers another interesting opportunity; during the deformation process caused by a planar force exceeding a certain threshold, kirigami-patterned sheets exhibit out-of-plane deflection. Ultimately the structure densifies perpendicular to the pulling direction. We believe this could be used to manufacture, for the first time, intricate 3D structures and devices in a potentially scalable and continuous manner. An example of application is in organic thermoelectrics (TE) generators (TEG). We envisage the design and preparation of kirigami-engineered multilayer polymer films, with n-type and p-type organic/inorganic patterns, which would form a 3D structure similar to the one of traditional TEG (with n-type and p-type ‘legs’ connected in series) once a certain tensile deformation is applied.

In order to achieve the above aims it is necessary to develop a novel continuum simulation method able to contemplate the common traits of kirigami-engineered thin and foldable nanocomposites films: cuts, creases as well as sharp inclusions (e.g. nanoparticles). Unfortunately, traditional simulation methods, based on shell theories at the continuum scale (> 1 µm) and available as commercial software (like finite-element methods (FEM)), cannot reproduce these singularities. This project will use an advanced mesh-free (a finite element without elements) FEM to remove the limitations of conventional finite-element software and simulate cracks and sharp inclusions. The novelty of this project relies in applying, for creases and sharp inclusions, the same approach used for the cracks. We believe it is possible to introduce discontinuities in the derivatives of the displacements, hence being able to simulate all the stages of folding. Moreover, it would be possible to simulate simultaneously the propagation of cracks and creasing, and the relative change in the position of sharp inclusions.

For more information, contact Dr Emiliano Bilotti: e.bilotti@qmul.ac.uk

Light‐harvesting materials for organic photovoltaics: cyclic versus linear pi-conjugated molecules

Supervised by Prof Laura Herz (Physics, Oxford University) and Prof Harry Anderson (Chemistry, Oxford University)

NB: This project is not available for MRes. For a CDT project, the MRes year will be based at Imperial College, then the student will transfer to Oxford for a DPhil. 

Efficient light harvesting lies at the core of our efforts to utilize sun light for environmentally sustainable power generation. However, most of the pi-conjugated molecules currently employed in organic photovoltaics (OPV) are based on linear oligomer or polymer structures that feature strongly allowed dipole transitions to their energetically lowest states. As a result, strong absorption, but also strong charge recombination occurs, with the former necessary for light absorption, but the latter detrimental to charge extraction in an organic solar cell.

In this project, we will explore the potential of cyclic pi-­conjugated molecules to induce a paradigm shift in organic materials for photovoltaics. Unlike in linear pi-­conjugated molecules, the lowest transition in cyclic systems is dipole-­forbidden by symmetry. Hence a situation similar to the indirect semiconductor silicon may be created, featuring strong absorption into higher lying allowed states, but reduced radiative recombination from the ground state into which the system subsequently relaxes. As such, cyclic molecules can therefore be seen as the “silicon of OPV”.

The use of cyclic light­‐harvesting systems here has interesting parallels to ring-­like natural systems found e.g. in purple bacteria. Natural evolution very early on solved the problem of how to capture light and use it to initiate the primary electron transfer reactions of photosynthesis in a surprisingly efficient manner. Such systems feature ring assemblies of chromophores with a dipole­‐forbidden lowest state, and high excitation delocalization, that still allows for efficient energy transfer and harvesting. For natural scientists striving to create new molecular light­‐harvesting materials for applications such as photovoltaics, the designs nature has invented for us are fantastic templates to learn from. Yet, despite its successes in natural light­‐harvesting systems, the suitability of synthetic cyclic pi-­conjugated molecules for OPV is still entirely untested.

This project will explore the question of whether ring-­like systems are better suited than linear molecules as light harvesters in man-­made applications. By creating interfaces with electron­‐accepting molecules we will create light­‐harvesting layers that rival their natural counterparts in photon conversion efficiency. We will study energy transfer within and between large pi-­conjugated porphyrin nanorings that directly mimic natural light‐harvesting chlorophyl ring assemblies and that we have recently shown to support highly delocalized electronic states. For example, we will investigate two­‐dimensional assemblies porphyrin nanorings that are found to form with amazing regularity on certain surfaces. These resemble the biological assemblies found on membranes of purple light­‐harvesting bacteria for which inter‐ring energy transfer has been found to be highly efficient. We will establish whether despite their dipole­forbidden lowest transition, such high excitation and charge delocalization still allows for efficient charge-and energy‐transfer between rings. We will investigate whether ring­‐like pi-­conjugated molecules will allow better design of materials for organic photovoltaics by comparing their performance to corresponding linear oligomers. Charge transfer at interfaces between porphyrin nanoring layers and small-­molecular layers with suitable energy level offsets will be explored with a view towards creating full charge-­separating structures to be embedded in solar cell devices. A comparison between linear and cyclic molecules will elucidate whether dipole­‐forbidden ground states of cyclic molecules allow for more effective charge harvesting as a result of suppressed competing charge recombination.

For more information, contact Prof Laura Herz: Laura.Herz@physics.ox.ac.uk

Novel Chiroptical Light Emitting Devices based on Polymer/Helicene Blends

Supervised by Prof Alasdair Campbell (Physics, Imperial College) and Dr Matt Fuchter (Chemistry, Imperial College)

Right-handed and left-handed circularly polarized (CP) light is made up of photons in the two different spin states. Directly emitting CP light sources therefore have potential application in optical spintronics, optical quantum computing, and optical quantum telecommunication (quantum cryptography). Additionally, most displays in current mobile phones, tablets and TVs have a circularly polarizing filter to improve contrast; such circularly polarizing filters can also be used to generate 3D images. Such filters discard 50% of the generated light, halving battery lifetime in portable products and doubling the display carbon-footprint. A directly emitting CP light source would solve this issue, and could additionally be used as a highly efficient LCD backlight. CP light sources also have application in the life sciences in the detection of biomolecules such as chain-folded proteins, and in medical tomographic imaging.

At Imperial we have invented a novel type of CP emitting polymer organic light emitting diode (OLED) as such a CP light source. This involved inducing CP emission from the achiral light emitting polymer (LEP) F8BT by blending it with an intrinsically chiral organic semiconducting molecule known as a helicene. Collaborating with Cambridge Display Technology Ltd (CDT), we have extended this technology in the display area. We also have a new collaborative project starting with the University of Sheffield and CDT to investigate the fundamental materials science beind this induced chiroptical effect.

This project aims to investigate this induced chiroptical effect in polymer/helicene blends in other LEPs and hole transport layer (HTL) polymers, and to investigate ways to optimize processing and novel device architectures to maximize CP light emisson.

For more information, contact Prof Alasdair Campbell: alasdair.campbell@imperial.ac.uk

Low band gap polymers for solar cells from sustainable feedstocks

Supervised by Prof Martin Heeney (Chemistry, Imperial College) and Dr Martyn McLachlan (Materials, Imperial College)

Conjugated polymers have attracted significant interest due to their fascinating combination of electrical conductivity and solution processability. They have been investigated extensively as the photoactive layer in organic solar cells, where the ability to print the active layer facilitates the production of large area, ultra-flexible devices. Solar cell efficiencies above 10% have now been demonstrated but many of the photoactive polymers currently used are based upon fossil fuel derived feedstocks which are ultimately non-sustainable. This project will develop conjugated polymers to be utilized in organic solar cells from biorenewable furan sources.

This project will focus initially on the development of novel, fused aromatic building blocks incorporating furan. This synthesis of these building blocks will involve a range of modern cross-coupling chemistries with a particular focus on direct arylation methodologies to minimize waste and maximise atom efficiency. Co-polymers will be prepared and their properties investigated in solar cell devices.

For more information, contact Prof Martin Heeney: m.heeney@imperial.ac.uk

Efficient and stable organic NIR photodetectors

Supervised by Prof Ji-Seon Kim (Physics, Imperial College) and Prof Martin Heeney (Chemistry, Imperial College)

Organic sensor devices such as organic photodetectors (OPDs) are important optoelectronic applications using organic semiconductors as a light detecting active medium. OPDs have attracted significant interest in the last two decades due to the possibility for using them for a variety of industrial and scientific applications such as environmental monitoring, communications, remote control, surveillance, and chemical/biological sensing, with low-cost, light-weight, high efficiency and high environmental friendliness. For OPD applications, it is critical for organic semiconductors to have efficient light harvesting (with high photocurrent and low dark current) and high spectral selectivity (from UV to NIR/IR) properties.  Although the rich variety of organic compounds with their absorption spanning from the UV to NIR offers unique possibilities for these required properties, organic semiconductors with a large photoresponse at NIR spectral ranges (>700 nm) with efficient light harvesting and air stability are still very difficult to find. 

This project aims to develop key fundamental understanding of organic sensor materials towards high-performance and high-stability NIR photodetector applications. Particular attention will be paid to: (1) investigating optoelectronic properties of new organic photodetector materials (low-band gap conjugated polymer donors and non-fullerene acceptors); (2) controlling and characterising the thin film nanostructures formed in donor-acceptor blends and bilayers; (3) fabricating highly efficient and stable organic NIR photodetectors by utilising various charge transport/extraction organic and hybrid materials as an interlayer in a device. Profs Kim and Heeney have recently been awarded the Samsung Global Research Outreach (GRO) programme grant to develop organic NIR photodetectors; materials developed under the Samsung GRO program will be used to accelerate the outputs of this project. This project is linked to the project "Synthesis of novel near-IR organic semiconductors for NIR photodetectors" (details below).

For more information, contact Prof Ji-Seon Kim: ji-seon.kim@imperial.ac.uk

Synthesis of novel near-IR organic semiconductors for NIR photodetectors

Supervised by Prof Martin Heeney (Chemistry, Imperial College) and Prof Ji-Seon Kim (Physics, Imperial College)

Organic sensor devices such as organic photodetectors (OPDs) are important optoelectronic applications using organic semiconductors as a light detecting active medium. OPDs have attracted significant interest in the last two decades due to the possibility for using them for a variety of industrial and scientific applications such as environmental monitoring, communications, remote control, surveillance, and chemical/biological sensing, with low-cost, light-weight, high efficiency and high environmental friendliness. For OPD applications, it is critical for organic semiconductors to have efficient light harvesting (with high photocurrent and low dark current) and high spectral selectivity (from UV to NIR/IR) properties.  Although the rich variety of organic compounds with their absorption spanning from the UV to NIR offers unique possibilities for these required properties, organic semiconductors with a large photoresponse at NIR spectral ranges (>700 nm) with efficient light harvesting and air stability are still very difficult to find.

In this project, we will synthesis novel near-IR absorbing organic semiconductors for utilisation in OPD devices. The project will involve a variety of heterocyclic and cross-coupling chemistry, as well as a strong element of materials characterisation. The candidate will work as part of a multi-disciplinary team focussed on these devices. This project is linked to the project "Efficient and stable organic NIR photodetectors" (details above).

For more information, contact Prof Martin Heeney: m.heeney@imperial.ac.uk

Characterisation and design of organic heterostructures for photocatalysis

Supervised by Prof Jenny Nelson (Physics) and Dr Andreas Kafizas (Chemistry)

Development of efficient solar energy conversion technologies for energy generation and storage is critical to future low carbon energy supplies.    While solar-to-electric (photovoltaic) energy conversion is widely used, the storage of solar energy in the form of fuels is much less advanced.  Photocatalytic fuel generation involves using a light-absorbing material to generate charges that can drive chemical reactions to generate a fuel, such as water photolysis into hydrogen and oxygen.  Molecular semiconductors are extremely interesting for this application due to their tuneable, sharp and strong light absorption, low impact fabrication, and opportunity to control surface area. 

A key issue is the efficiency of the absorbed photon to charge transfer process. Even in the best functioning organic photocatalytic systems, the quenching of the photogenerated exciton is relatively weak. This stage can be improved through control of the dielectric environment,  control of the microstructure of the catalyst, and by use of a heterojunction structure to drive the dissociation of excitons into separated charges.  

This project will explore the relationship between chemical structure, physical environment and photocatalytic activity of polymer based photocatalysts.  Transient optical spectroscopy will be used as a tool to probe the efficiency of photoinduced charge transfer in different conditions. The project will investigate the advantages of using (a)  nanostructured materials and (b) heterojunction structures, either based on organic-organic or hybrid organic – metal oxide heterojunctions, in improving photocatalytic activity. In particular we will investigate the trade off between light harvesting and generation of chemical potential when using heterojunction structures . 

For more information, contact Prof Jenny Nelson (jenny.nelson@imperial.ac.uk) or Dr Andreas Kafizas (a.kafizas@imperial.ac.uk)