My research programs are centered on understanding the physical properties of functional electronic materials and applying this fundamental understanding to develop improved materials and devices for application in electronics, displays, lighting, energy generation & harvesting and different sensor technologies. I am also interested in innovative manufacturing technologies for large-area nano-electronics where device –and ultimately system– performance is determined by key device dimensions rather than strictly by the physical properties of the active material(s) used. Ultimate aim is the development of advanced device concepts and their application in future generations of ubiquitous large-area opto-electronics.
The Advanced Materials & Devices (AMD) group
Examples of Ongoing Projects
Transparent interlayer materials for application in photovoltaics
Research focuses on developing novel solution processable transparent semiconductors for application in photovoltaics. Material under investigation include high mobility electron and hole transporting systems based on organic, inorganic and hybrid compounds. Chemical doping is also explored as a versatile tool for tuning the conductivity of these interlayers without reducing their extreme optical transparency. Further details can be found in Adv. Ene. Mat. (2014), DOI: 10.1002/aenm.201401529.
LOW-DIMENSIONAL SEMICONDUCTORS FOR NEXT GENERATION LARGE-AREA ELECTRONICS
Research focuses on the development of low-dimensional (nm-thick) semiconducting layers from solution phase at low temperatures (<200 C) and their incorporation in heterojunction and multilayer superlattices. Electronic devices based on such simple to fabricate “artificial” semiconductors exhibit superior charge transport characteristics as compared to devices based on conventional single semiconductors. Further details can be found in Advanced Science (2015), DOI: 10.1002/advs.201500058. Use of these low-dimensional structures for the development of quantum effect electronics is also being explored, see - Adv. Fun. Mater. (2015), DOI: 10.1002/adfm.201403862.
This work focuses on the use of molecular, ultra-thin, self-assembling monolayer (SAM) nanodielectrics for the production of low-power graphene transistors, sensors and integrated optoelectronics. In addition to their ultra-thin nature, SAM nanodielectrics can be processed from solution at temperatures compatible with low-cost substrate materials such plastic. By combining different SAM nanodielectrics with solution-transferred CVD graphene, we have recently been able to demonstrate the first low-power flexible graphene transistors manufactured on plastic substrates (figure below). Further details can be found in Nanotechnology 23 344017 (2012).
Graphene electrodes for large-area electronics
This work focuses on the use of interlayer lithography (ILL) for patterning highly conductive solution processed reduced graphene oxide source and drain electrodes (S/D) down to few microns gaps. The patterned electrodes are then used to fabricate high performance thin-film transistors and integrated circuits based on organic semiconductors. The method is simple, scalable and offers a viable route towards organic electronics fabricated entirely by solution processing. The figure below shows patterned graphene S/D electrodes using the ILL method.
Solution-processable high-k oxide dielectrics
In this work we use spray pyrolysis to sequentially deposit layers of high-k oxide dielectrics (e.g. ZrO2) and high mobility n-channel oxide semiconductors, such as ZnO and Li doped ZnO, onto conductive indium tin oxide layers acting as the gate electrodes. Using these structures we have been able to fabricate thin-film transistors with operating voltage below l6l Volt and maximum electron mobility over 85 cm2/Vs.
Ambipolar organic semiconductors and devices
This work focuses on the development and study of ambipolar organic semiconductors - i.e. compounds that are capable of conducting both types of charge carriers (electrons & holes). The work is also concerned with the use of ambipolar organic semiconductors in various technology applications including integrated microelectronic circuits and optical sensors. The figure below shows the electronic structure of a squarylium (SQ) dye and the output operating characteristics of an ambipolar SQ-based field-effect transistor.
Fullere-based semiconductors and devices
Aim of this work is the development of fullerene derivatives with high electron mobility and useful environmental stability and their subsequent application in organic microelectronics and particularly complementary circuits i.e. the equivalent of CMOS technology in Si microelectronics. This work is a collaboration between our group and various academic as well as industrial partners around the world. The figure below displays the chemical structure of four fullerene derivatives and the operating characteristics of a unipolar multi-stage ring oscillator based on a solution processed C60 derivative.
The development of high-performance light-sensing thin-film transistors (LS-TFTs) and electro-optical circuits is the primary objective of this work. Use of ambipolar organic semiconductors enables the detection of light with fast response time and high responsivity. Integration of LS-TFTs with ordinary transistors allows the fabrication of novel electro-optical circuits. Such circuits are capable of processing optical as well as electronic signals. The figure below displays the schematic circuitry and the operating characteristics for an electro-optical NOT gate based on a light-sensing ambipolar organic transistor (T2) and a unipolar organic (i.e. driving) transistor (T1). Here the input is an optical signal (AIN) while the output is an electrical signal (VOUT).
Aim of this work is the development of molecular self-assembling monolayer (SAM) nanodielectrics. Such materials could enable the fabrication of low-voltage, low-power transistors and electronic circuits required for application in future ubiquitous electronics. Most importantly, SAM nanodielectrics can be processed from solution at room temperature employing simple and large-area compatible techniques. The figure below shows the chemical structure of three SAM nanodielectrics studied in our laboratory and their electrical characteristics when employed in metal/SAM/metal device structures.
Low-power organic electronics
Implementation of organic devices in ubiquitous electronics will not only require organic transistors with high carrier mobility but also low-voltage, low-power operation. Aim of our work is to address this major technological bottleneck through the development of solution processable low-power organic transistors and integrated circuits. To achieve this we combine novel SAM nanodielectrics with state-of-the-art organic semiconductors. The figure below displays few of the organic semiconductors (PCB M and diF-TESADT) and SAM dielectrics studied together with the operating characteristics of two low-voltage organic transistors - i.e. a p- and an n-channel - b ased on the solution processable organic semiconductors PCBM and diF-TESADT, respectively.
We aim to develop high-performance, large-area, flexible, and transpare nt e lectronics fabricated using novel high-throughput manufacturing paradigms. Our approach is based on the use of spray pyrolysis, a known method that until recently had not been considered for the manufacturing of large-area, high-performance oxide-based microelectronics. Very recently we demonstrated (Bashir et al., Adv. Mat. 2009) the suitability of spray pyrolysis for the deposition of oxide semiconductors onto large-area substrates and the fabrication of high mobility (>20 cm2 /Vs) ZnO thin-film transistors. The figure below displays the schematic of the spray pyrolysis apparatus together with the operating characteristics of a low-voltage ZnO transistor fabricated by spray pyrolysis.
Organic semiconducting blends
Aim of this project is the development of high-performance organic devices base d on organic semiconductor bl ends. B y mixin g solutions of small-molec ule organics with polymer s we are able to fabricate hole transporting transistors with reco rd carrier mobilities and excellent environmental stability. A key finding of this wo rk is the distinct vertical phase separation that occurs between the small-molecule and the polymer matrix used. The latter is responsible for the formation of large crystalline domains at the surface of the film and for the high carrier mobilities measured. The figure below shows: i) examples of small-molecule (diF-TESADT) an d polymer (PTAA) semiconductors, ii) the morphology of a diF-TESADT:PT AA fil m imaged using polarised light microscopy, and iii) the operating characteristics of a transistor based on this blend.
An excellent range of state-of-the-art equipment dedicated to device fabrication and characterization exists. This includes a large area cleanroom (100 m2, ISO class 6) equipped with a variety of fabrication tools and all relevant inspection and measurement facilities. Major equipment available includes: several spin coaters, two vacuum evaporators (e-beam and resistive), one optical microscope, one atomic-force microscope (AFM), numerous fume-hoods, wet-benches, profilometers, a mask aligner, several high-temperature ovens, and plasma etchers. The AMD group is equipped with a glove-box integrated with a vacuum sublimation system dedicated to research on advanced materials and devices. The system also includes a spin-coater and a 6-arm probe-station used for electrical characterisation of devices. Our laboratories are also equipped with two state-of-the-art cryogenic probe stations, dedicated to fundamental studies on charge transport processes in novel materials and devices, and a multi-mode AFM system.
European Research Council (ERC)
Dutch Polymer Institute (DPI)
Plastic logic ltd.
cambridge display technology ltd
centre for process innovation (cpi)
EU-FP7: Life Long Learning (LLP) Erasmus Project “Organic Electronics & Applications (OREA)
Objectives: The main objective of the Life Long Learning (LLP) Erasmus Project “Organic Electronics & Applications (OREA)” is the development of a MSc curriculum in the field of organic electronics.
Project Partners: TEI of Crete (coordinator), Imperial College London (UK), University of Oxford (UK), Politechnico di Milan (IT), University of St-Andrews (UK), Cyprus University of Technology (CY), Johannes Keppler University of Linz (AT), University of Groningen (HOL), Friedrich-Alexander Universitat Erlangen -Nurnberg (GER), Institute of Electronic Structure and Laser – IESL (GR), Technion Israel Institute of Technology (ISR), NanoForce Ltd (UK), Solvay S.A. (BEL), Ceradrop (FR), Beneq (FIN), Aixtron (GER).
Personnel Involved: The coordinator of the project at Imperial College London is Prof. Thomas Anthopoulos
Module to be developed: Optical Displays: Science and Device Technology
Link to the OREA website: http://orea.chania.teicrete.gr