Imperial College London

ProfessorThomasAnthopoulos

Faculty of Natural SciencesDepartment of Physics

Visiting Professor
 
 
 
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Contact

 

+44 (0)20 7594 6669thomas.anthopoulos Website

 
 
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Assistant

 

Mrs Carolyn Dale +44 (0)20 7594 7579

 
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Location

 

1111Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

314 results found

Tetzner K, Isakov I, Regoutz A, Payne DJ, Anthopoulos TDet al., 2016, The impact of post-deposition annealing on the performance of solution-processed single layer In2O3 and isotype In2O3/ZnO heterojunction transistors, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 5, Pages: 59-64, ISSN: 2050-7526

JOURNAL ARTICLE

Nam S, Han H, Seo J, Song M, Kim H, Anthopoulos TD, McCulloch I, Bradley DDC, Kim Yet al., 2016, Ambipolar Organic Phototransistors with p-Type/n-Type Conjugated Polymer Bulk Heterojunction Light-Sensing Layers, ADVANCED ELECTRONIC MATERIALS, Vol: 2, ISSN: 2199-160X

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Fallon KJ, Wijeyasinghe N, Manley EF, Dimitrov SD, Yousaf SA, Ashraf RS, Duffy W, Guilbert AAY, Freeman DME, Al-Hashimi M, Nelson J, Durrant JR, Chen LX, McCulloch I, Marks TJ, Clarke TM, Anthopoulos TD, Bronstein Het al., 2016, Indolo-naphthyridine-6,13-dione Thiophene Building Block for Conjugated Polymer Electronics: Molecular Origin of Ultrahigh n-Type Mobility, CHEMISTRY OF MATERIALS, Vol: 28, Pages: 8366-8378, ISSN: 0897-4756

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Nam S, Seo J, Han H, Kim H, Hahm SG, Ree M, Gal Y-S, Anthopoulos TD, Bradley DDC, Kim Yet al., 2016, > 10% Efficiency Polymer: Fullerene Solar Cells with Polyacetylene-Based Polyelectrolyte Interlayers, ADVANCED MATERIALS INTERFACES, Vol: 3, ISSN: 2196-7350

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Casey A, Han Y, Gann E, Green JP, McNeill CR, Anthopoulos TD, Heeney Met al., 2016, Vinylene-linked oligothiophene–difluorobenzothiadiazole copolymer for transistor applications, ACS Applied Materials & Interfaces, Vol: 8, Pages: 31154-31165, ISSN: 1944-8244

The synthesis of the novel donor-acceptor monomer 4,7-bis[(E)-2-(5-bromo-3-dodecylylthiophen-2-yl)ethenyl]-5,6-difluoro-2,1,3-benzothiadiazole (FBT-V2T2) is reported. Polymerization with 4,4'-ditetradecyl-5,5'-bistrimethylstannyl-2,2'-bithiophene afforded a highly crystalline polymer that aggregated strongly in solution. Polymer films were well ordered resulting in high performance field-effect transistors with low onset voltages, negligible hysteresis, high channel current on/off ratios and peak hole mobilities of up to 0.5 cm2V-1s-1. Notably the transistors exhibited close to ideal behavior with extracted mobilities almost independent of gate of voltage.

JOURNAL ARTICLE

Han Y, Barnes G, Lin Y-H, Martin J, Al-Hashimi M, AlQaradawi SY, Anthopoulos TD, Heeney Met al., 2016, Doping of large ionization potential indenopyrazine polymers via Lewis acid complexation with tris(pentafluorophenyl)borane: a simple method for improving the performance of organic thin-film transistors, Chemistry of Materials, Vol: 28, Pages: 8016-8024, ISSN: 1520-5002

Molecular doping, under certain circumstances, can be used to improve the charge transport in organic semiconductors through the introduction of excess charge carriers which can in turn negate unwanted trap states often present in organic semiconductors. Here, two Lewis basic indenopyrazine copolymers with large ionization potential (5.78 and 5.82 eV) are prepared to investigate the p-doping efficiency with the Lewis acid dopant, tris(pentafluorophenyl)borane, using organic thin-film transistors (OTFTs). The formation of Lewis acid–base complex between the polymer and dopant molecules is confirmed via optical spectroscopy and electrical field-effect measurements, with the latter revealing a dopant-concentration-dependent device performance. By adjusting the amount of p-dopant, the hole mobility can be increased up to 11-fold while the OTFTs’ threshold voltages are reduced. The work demonstrates an alternative doping mechanism other than the traditional charge transfer model, where the energy level matching principle can limit the option of dopants.

JOURNAL ARTICLE

Mukhopadhyay T, Puttaraju B, Senanayak SP, Sadhanala A, Friend RH, Faber HA, Anthopoulos TD, Salzner U, Meyer A, Patil Set al., 2016, Air-Stable n-type Diketopyrrolopyrrole-Diketopyrrolopyrrole Oligomers for High Performance Ambipolar Organic Transistor, ACS Applied Materials & Interfaces, Vol: 8, Pages: 25415-25427, ISSN: 1944-8244

N-type organic semiconductors are prone to oxidation upon exposed to ambient conditions. Herein, we report design and synthesis of diketopyrrolopyrrole (DPP) based oligomers for ambipolar organic thin film transistors (OFETs) with excellent air and bias stability at ambient conditions. The cyclic voltammetry measurements reveal exceptional electrochemical stability during the redox cycle of oligomers. Structural properties including aggregation, crystallinity and morphology in thin film were investigated by UV-visible spectroscopy, atomic force microscopy (AFM), thin film X-ray diffraction (XRD) and grazing incidence small angle X-ray scattering (GISAXS) measurements. AFM reveals morphological changes induced by different processing conditions whereas GISAXS measurements show increase in the population of face-on oriented crystallites in films subjected to a combination of solvent and thermal treatments. These measurements also highlight the significance of chalcogen atom from sulphur to selenium on the photophysical, optical, electronic and solid-state properties of DPP-DPP oligomers. Charge carrier mobilities of the oligomers were investigated by fabricating top-gate bottom-contact (TG-BC) thin-film transistors by annealing the thin films under various conditions. Combined solvent and thermal annealing of DPP-DPP oligomer thin films results in consistent electron mobilities as high as ~0.2 cm2V-1s-1 with an on/off ratio exceeding 104. Field-effect behaviour was retained for up to ~ 4 week which illustrates remarkable air and bias stability. This work paves the way towards the development of n-type DPP-DPP based oligomers exhibiting retention of field effect behaviour with superior stability at ambient conditions.

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Kryvchenkova O, Abdullah I, Macdonald JE, Elliott M, Anthopoulos TD, Lin YH, Igić P, Kalna K, Cobley RJet al., 2016, Nondestructive Method for Mapping Metal Contact Diffusion in In2O3 Thin-Film Transistors, ACS Applied Materials & Interfaces, ISSN: 1944-8244

The channel width-to-length ratio is an important transistor parameter for integrated circuit design. Contact diffusion in to the channel during fabrication or operation alters the channel width and this important parameter. A novel methodology combining atomic force microscopy and scanning Kelvin probe microscopy (SKPM) with self-consistent modelling is developed for the non-destructive detection of contact diffusion on active devices. Scans of the surface potential are modelled using physically-based Technology Computer Aided Design (TCAD) simulations when the transistor terminals are grounded and under biased conditions. The simulations also incorporate the tip geometry to investigate its effect on the measurements due to electrostatic tip-sample interactions. The method is particularly useful for semiconductor- and metal- semiconductor interfaces where the potential contrast resulting from dopant diffusion is below that usually detectable with scanning probe microscopy.

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Fei Z, Han Y, Martin J, Scholes FH, Al-Hashimi M, AlQaradawi SY, Stingelin N, Anthopoulos TD, Heeney Met al., 2016, Conjugated Copolymers of Vinylene Flanked Naphthalene Diimide, Macromolecules, Vol: 49, Pages: 6384-6393, ISSN: 0024-9297

We report the synthesis of a novel naphthalene diimide (NDI) monomer containing two (tributylstannyl)vinyl groups. The utility of this building block is demonstrated by its copolymerization with five different electron-rich comonomers under Stille conditions. The resulting high molecular weight polymers show red-shifted optical absorptions in comparison to the analogous polymers without the vinylene spacer and a significant increase in the intensity of the low-energy intramolecular charge transfer band. The polymers all exhibit ambipolar behavior in bottom-gate, top-contact organic thin-film transistors. The insertion of a solution-processed barium hydroxide layer between the polymer and the gold electrode led to unipolar behavior with improved electron mobilities.

JOURNAL ARTICLE

Semple J, Rossbauer S, Anthopoulos TD, 2016, Analysis of Schottky Contact Formation in Coplanar Au/ZnO/Al Nanogap Radio Frequency Diodes Processed from Solution at Low Temperature, ACS Applied Materials & Interfaces, Vol: 8, Pages: 23167-23174, ISSN: 1944-8244

Much work has been carried out in recent years in fabricating and studying the Schottky contact formed between various metals and the n-type wide bandgap semiconductor zinc oxide (ZnO). In spite of significant progress, reliable formation of such technologically interesting contacts remains a challenge. Here, we report on solution-processed ZnO Schottky diodes based on a coplanar Al/ZnO/Au nanogap architecture and study the nature of the rectifying contact formed at the ZnO/Au interface. Resultant diodes exhibit excellent operating characteristics, including low-operating voltages (±2.5 V) and exceptionally high current rectification ratios of >106 that can be independently tuned via scaling of the nanogap’s width. The barrier height for electron injection responsible for the rectifying behavior is studied using current–voltage–temperature and capacitance–voltage measurements (C–V) yielding values in the range of 0.54–0.89 eV. C–V measurements also show that electron traps present at the Au/ZnO interface appear to become less significant at higher frequencies, hence making the diodes particularly attractive for high-frequency applications. Finally, an alternative method for calculating the Richardson constant is presented yielding a value of 38.9 A cm–2 K–2, which is close to the theoretically predicted value of 32 A cm–2 K–2. The implications of the obtained results for the use of these coplanar Schottky diodes in radio frequency applications is discussed.

JOURNAL ARTICLE

Bovo G, Bräunlich I, Caseri WR, Stingelin N, Anthopoulos TD, Sandeman KG, Bradley DDC, Stavrinou PNet al., 2016, Room temperature dielectric bistability in solution-processed spin crossover polymer thin films, Journal of Materials Chemistry C, Vol: 4, Pages: 6240-6248, ISSN: 2050-7534

The spin crossover (SCO) phenomena are a remarkable example of spin-state switching at the molecular level. The low- and high-spin states can be reversibly selected through application of external stimulus-often simply a variation in temperature. Since the particular spin-state embodies optical, electronic and structural characteristics, the spin switching can be readily detected or probed using a variety of techniques. In this regard, SCO phenomena show great promise for a range of devices. The key to this uptake is the preparation of high-quality, thin-films capable of retaining SCO properties, and solution-based materials, in particular, provide further opportunities for integration or blending with other functional materials. The present work examines SCO behaviour from two iron(ii)-triazole polymers, with short and long side chains, prepared and investigated in a variety of formats-from bulk powders to thick and thin films. Magnetic, optical and electronic techniques all verify the SCO behaviour is faithfully maintained for all formats. The two materials serve to highlight the impact on key properties arising from the different density of Fe atoms. The results, all from solution-based materials, are extremely promising and clearly emphasise the growing capabilities and processing advances associated with SCO compounds.

JOURNAL ARTICLE

Hunter S, Mottram AD, Anthopoulos TD, 2016, Temperature and composition-dependent density of states in organic small-molecule/polymer blend transistors, Journal of Applied Physics, Vol: 120, ISSN: 1089-7550

The density of trap states (DOS) in organic p-type transistors based on the small-molecule 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES ADT), the polymer poly(triarylamine) and blends thereof are investigated. The DOS in these devices are measured as a function of semiconductor composition and operating temperature. We show that increasing operating temperature causes a broadening of the DOS below 250 K. Characteristic trap depths of ∼15 meV are measured at 100 K, increasing to between 20 and 50 meV at room-temperature, dependent on the semiconductor composition. Semiconductor films with high concentrations of diF-TES ADT exhibit both a greater density of trap states as well as broader DOS distributions when measured at room-temperature. These results shed light on the underlying charge transport mechanisms in organic blend semiconductors and the apparent freezing-out of hole conduction through the polymer and mixed polymer/small molecule phases at temperatures below 225 K.

JOURNAL ARTICLE

Bottacchi F, Bottacchi S, Späth F, Namal I, Hertel T, Anthopoulos TDet al., 2016, Nanoscale Charge Percolation Analysis in Polymer-Sorted (7,5) Single-Walled Carbon Nanotube Networks, Small, Vol: 12, Pages: 4211-4221, ISSN: 1613-6810

The current percolation in polymer-sorted semiconducting (7,5) single-walled carbon nanotube (SWNT) networks, processed from solution, is investigated using a combination of electrical field-effect measurements, atomic force microscopy (AFM), and conductive AFM (C-AFM) techniques. From AFM measurements, the nanotube length in the as-processed (7,5) SWNTs network is found to range from ≈100 to ≈1500 nm, with a SWNT surface density well above the percolation threshold and a maximum surface coverage ≈58%. Analysis of the field-effect charge transport measurements in the SWNT network using a 2D homogeneous random-network stick-percolation model yields an exponent coefficient for the transistors OFF currents of 16.3. This value is indicative of an almost ideal random network containing only a small concentration of metallic SWNTs. Complementary C-AFM measurements on the other hand enable visualization of current percolation pathways in the xy plane and reveal the isotropic nature of the as-spun (7,5) SWNT networks. This work demonstrates the tremendous potential of combining advanced scanning probe techniques with field-effect charge transport measurements for quantification of key network parameters including current percolation, metallic nanotubes content, surface coverage, and degree of SWNT alignment. Most importantly, the proposed approach is general and applicable to other nanoscale networks, including metallic nanowires as well as hybrid nanocomposites.

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Paterson AF, Treat ND, Zhang W, Fei Z, Wyatt-Moon G, Faber H, Vourlias G, Patsalas PA, Solomeshch O, Tessler N, Heeney M, Anthopoulos TDet al., 2016, Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm V−1 s−1, Advanced Materials, Vol: 28, Pages: 7791-7798, ISSN: 1521-4095

A ternary organic semiconducting blend composed of a small-molecule, a conjugated polymer, and a molecular p-dopant is developed and used in solution-processed organic transistors with hole mobility exceeding 13 cm(2) V(-1) s(-1) (see the Figure). It is shown that key to this development is the incorporation of the p-dopant and the formation of a vertically phase-separated film microstructure.

JOURNAL ARTICLE

Casey A, Dimitrov SD, Shakya-Tuladhar P, Fei Z, Nguyen M, Han Y, Anthopoulos TD, Durrant JR, Heeney Met al., 2016, Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance, Chemistry of Materials, Vol: 28, Pages: 5110-5120, ISSN: 0897-4756

We report a systematic study into the effects of cyano substitution on the electron accepting ability of the common acceptor 4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT). We describe the synthesis of DTBT monomers with either 0, 1, or 2 cyano groups on the BT unit and their corresponding copolymers with the electron rich donor dithienogermole (DTG). The presence of the cyano group is found to have a strong influence on the optoelectronic properties of the resulting donor–acceptor polymers, with the optical band gap red-shifting by approximately 0.15 eV per cyano substituent. We find that the polymer electron affinity is significantly increased by ∼0.25 eV upon addition of each cyano group, while the ionization potential is less strongly affected, increasing by less than 0.1 eV per cyano substituent. In organic photovoltaic (OPV) devices power conversion efficiencies (PCE) are almost doubled from around 3.5% for the unsubstituted BT polymer to over 6.5% for the monocyano substituted BT polymer. However, the PCE drops to less than 1% for the dicyano substituted BT polymer. These differences are mainly related to differences in the photocurrent, which varies by 1 order of magnitude between the best (1CN) and worst devices (2CN). The origin of this variation in the photocurrent was investigated by studying the charge generation properties of the photoactive polymer–fullerene blends using fluorescence and transient absorption spectroscopic techniques. These measurements revealed that the improved photocurrent of 1CN in comparison to 0CN was due to improved light harvesting properties while maintaining a high exciton dissociation yield. The addition of one cyano group to the BT unit optimized the position of the polymer LUMO level closer to that of the electron acceptor PC71BM, such that the polymer’s light harvesting properties were improved without sacrificing either the exciton dissociation yield or device VOC. We also identify that the dr

JOURNAL ARTICLE

Petti L, Muenzenrieder N, Vogt C, Faber H, Buethe L, Cantarella G, Bottacchi F, Anthopoulos TD, Troester Get al., 2016, Metal oxide semiconductor thin-film transistors for flexible electronics, Applied Physics Reviews, Vol: 3, ISSN: 1931-9401

The field of flexible electronics has rapidly expanded over the last decades, pioneering novelapplications, such as wearable and textile integrated devices, seamless and embedded patch-likesystems, soft electronic skins, as well as imperceptible and transient implants. The possibility torevolutionize our daily life with such disruptive appliances has fueled the quest for electronic deviceswhich yield good electrical and mechanical performance and are at the same time light-weight,transparent, conformable, stretchable, and even biodegradable. Flexible metal oxide semiconductorthin-film transistors (TFTs) can fulfill all these requirements and are therefore considered the mostpromising technology for tomorrow’s electronics. This review reflects the establishment of flexiblemetal oxide semiconductor TFTs, from the development of single devices, large-area circuits, up toentirely integrated systems. First, an introduction on metal oxide semiconductor TFTs is given,where the history of the field is revisited, the TFT configurations and operating principles are presented,and the main issues and technological challenges faced in the area are analyzed. Then, therecent advances achieved for flexible n-type metal oxide semiconductor TFTs manufactured byphysical vapor deposition methods and solution-processing techniques are summarized. In particular,the ability of flexible metal oxide semiconductor TFTs to combine low temperature fabrication,high carrier mobility, large frequency operation, extreme mechanical bendability, together withtransparency, conformability, stretchability, and water dissolubility is shown. Afterward, a detailedanalysis of the most promising metal oxide semiconducting materials developed to realize thestate-of-the-art flexible p-type TFTs is given. Next, the recent progresses obtained for flexible metaloxide semiconductor-based electronic circuits, realized with both unipolar and complementarytechnology, are reported. In particular, the realizatio

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Shaw JE, Perumal A, Bradley DDC, Stavrinou PN, Anthopoulos TDet al., 2016, Nanoscale current spreading analysis in solution-processed graphene oxide/silver nanowire transparent electrodes via conductive atomic force microscopy, Journal of Applied Physics, Vol: 119, ISSN: 1089-7550

JOURNAL ARTICLE

Ruzie C, Karpinska J, Laurent A, Sanguinet L, Hunter S, Anthopoulos TD, Lemaur V, Cornil J, Kennedy AR, Fenwick O, Samori P, Schweicher G, Chattopadhyay B, Geerts YHet al., 2016, Design, synthesis, chemical stability, packing, cyclic voltammetry, ionisation potential, and charge transport of [1]benzothieno[3,2-b][1]benzothiophene derivatives, Journal of Materials Chemistry C, Vol: 4, Pages: 4863-4879, ISSN: 2050-7534

Five new molecular semiconductors that differ from dioctylbenzothienobenzothiophene, by the introduction of ether or thioether side chains, have been synthesized and obtained in good yields. Their availability in sufficient quantities has allowed investigation of their electrochemical behaviour in solution and their electronic properties in solid state. Both ether and thioether compounds oxidise rather easily in solution, but nevertheless, they exhibit rather high ionisation potentials. This is a consequence of their crystal structure. Dioctylthioetherbenzothienobenzothiophene is rather sensitive to oxidation and degrades easily in close to ambient conditions. Dioctyletherbenzothienobenzothiophene is more stable. Its charge carrier mobility remains however rather moderate, on the order of 0.5 cm2 V−1 s−1, whereas that of dioctylbenzothienobenzothiophene reached 4 cm2 V−1 s−1, in the same conditions. The difference is explained by intrinsic factors as shown by a theoretical modelling.

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Green J, Han Y, Kilmurray R, McLachlan M, Anthopoulos T, Heeney MJet al., 2016, An Air-Stable Semiconducting Polymer Containing Dithieno[3,2-b:2′,3′-d]arsole, Angewandte Chemie - International Edition, Vol: 55, Pages: 7148-7151, ISSN: 1433-7851

Arsole-containing conjugated polymers are a practically unexplored class of materials despite the high interest in their phosphole analogues. Herein we report the synthesis of the first dithieno[3,2-b;2′,3′-d]arsole derivative, and demonstrate that it is stable to ambient oxidation in its +3 oxidation state. A soluble copolymer is obtained by a palladium-catalyzed Stille polymerization and demonstrated to be a p-type semiconductor with promising hole mobility, which was evaluated by field-effect transistor measurements.

JOURNAL ARTICLE

Green JP, Han Y, Kilmurray R, McLachlan MA, Anthopoulos TD, Heeney Met al., 2016, An air-stable semiconducting polymer containing Dithieno[3,2- b :2′,3′- d ]arsole, Angewandte Chemie, Vol: 128, Pages: 7264-7267, ISSN: 0044-8249

Arsole-containing conjugated polymers are a practically unexplored class of materials despite the high interest in their phosphole analogues. Herein we report the synthesis of the first dithieno[3,2-b;2′,3′-d]arsole derivative, and demonstrate that it is stable to ambient oxidation in its +3 oxidation state. A soluble copolymer is obtained by a palladium-catalyzed Stille polymerization and demonstrated to be a p-type semiconductor with promising hole mobility, which was evaluated by field-effect transistor measurements.

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Lin YH, Thomas SR, Faber H, Li R, McLachlan MA, Patsalas PA, Anthopoulos TDet al., 2016, Al-Doped ZnO Transistors Processed from Solution at 120 °C, Advanced Electronic Materials, Vol: 2, ISSN: 2199-160X

A simple Al-doping method that is used to significantly enhance the operating characteristics of ZnO thin-film transistors processed from solution at temperatures down to 120 °C is reported. The two-step doping process relies on the dissolution of zinc oxide hydrate in ammonia hydroxide to form an aqueous Zn-ammine complex solution and the subsequent immersion of Al pellets into it at room temperature. The pellets are then removed, and the doped precursor solution is spin-coated onto the substrate followed by thermal annealing in air to form the n-doped ZnO:Al layers. By controlling the immersion time of the Al pellets in the precursor solution, the free electron concentration in ZnO can be tuned. The resulting ZnO:Al layers are shown to be polycrystalline with tuneable electrical properties. ZnO:Al-based transistors processed at 180 °C exhibit enhanced electron mobility when compared to intrinsic ZnO devices with the maximum values exceeding 5 cm2 V−1 s−1. Even when the process temperature is reduced to 120 °C, the ZnO:Al transistors retain their excellent operating characteristics with a maximum electron mobility of 3 cm2 V−1 s−1. This is amongst the highest values reported to date for soluton-deposited ZnO transistors processed at 120 °C in air.

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Pitsalidis C, Pappa AM, Hunter S, Laskarakis A, Kaimakamis T, Payne MM, Anthony JE, Anthopoulos TD, Logothetidis Set al., 2016, High mobility transistors based on electrospray-printed small-molecule/polymer semiconducting blends, Journal of Materials Chemistry C, Vol: 4, Pages: 3499-3507, ISSN: 2050-7534

Spray-coating techniques have recently emerged as especially effective approaches for the deposition of small semiconducting molecules toward the fabrication of organic field-effect transistors (OFETs). Despite the promising mobility values and the industrial implementation capability of such techniques, the resultant devices still face challenges in terms of morphology control and performance variation. In this work, the efficient process control of electrostatic spraying deposition (ESD) and the excellent film forming properties of polymer:small molecule blends were successfully combined to develop reliable and high performance transistors. Specifically, a highly efficient blended system of 2,8-difluoro-5,11-bis(triethylsilylethynyl)-anthradithiophene (diF-TES-ADT) and poly(triarylamine) (PTAA) was employed in order to realize top-gate OFETs under ambient conditions, both on rigid and on flexible substrates. The films revealed extensive crystallization and microstructural organization implying distinct phase separation in the electrosprayed blend. Furthermore, we investigated the effect of processing temperature on film continuity and the presence of grain boundaries. Remarkably, the electrosprayed OFETs exhibited field-effect mobilities as high as 1.7 cm2 V−1 s−1 and enhanced performance consistency when compared to conventional gas-sprayed transistors. Additionally, the transistors showed excellent electrical and environmental stability, indicative of the good interface quality and the self-encapsulation capability of the top-gate structure. These results highlight the great potential of electrohydrodynamic atomization techniques for implementation in large-area processing for OFET fabrication.

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Semple J, Rossbauer S, Burgess CH, Zhao K, Jagadamma LK, Amassian A, McLachlan MA, Anthopoulos TDet al., 2016, Radio Frequency Coplanar ZnO Schottky Nanodiodes Processed from Solution on Plastic Substrates., Small, Vol: 12, Pages: 1993-2000, ISSN: 1613-6829

Coplanar radio frequency Schottky diodes based on solution-processed C60 and ZnO semiconductors are fabricated via adhesion-lithography. The development of a unique asymmetric nanogap electrode architecture results in devices with a high current rectification ratio (10(3) -10(6) ), low operating voltage (<3 V), and cut-off frequencies of >400 MHz. Device fabrication is scalable and can be performed at low temperatures even on plastic substrates with very high yield.

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Mottram AD, Lin YH, Pattanasattayavong P, Zhao K, Amassian A, Anthopoulos TDet al., 2016, Quasi two-dimensional dye-sensitized In2O3 phototransistors for ultrahigh responsivity and photosensitivity photodetector applications, ACS Applied Materials & Interfaces, Vol: 8, Pages: 4894-4902, ISSN: 1944-8244

We report the development of dye-sensitized thin-film phototransistors consisting of an ultrathin layer (<10 nm) of indium oxide (In2O3) the surface of which is functionalized with a self-assembled monolayer of the light absorbing organic dye D102. The resulting transistors exhibit a preferential color photoresponse centered in the wavelength region of ∼500 nm with a maximum photosensitivity of ∼10(6) and a responsivity value of up to 2 × 10(3) A/W. The high photoresponse is attributed to internal signal gain and more precisely to charge carriers generated upon photoexcitation of the D102 dye which lead to the generation of free electrons in the semiconducting layer and to the high photoresponse measured. Due to the small amount of absorption of visible photons, the hybrid In2O3/D102 bilayer channel appears transparent with an average optical transmission of >92% in the wavelength range 400-700 nm. Importantly, the phototransistors are processed from solution-phase at temperatures below 200 °C hence making the technology compatible with inexpensive and temperature sensitive flexible substrate materials such as plastic.

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Zhao K, Wodo O, Ren D, Khan HU, Niazi MR, Hu H, Abdelsamie M, Li R, Li EQ, Yu L, Yan B, Payne MM, Smith J, Anthony JE, Anthopoulos TD, Thoroddsen ST, Ganapathysubramanian B, Amassian Aet al., 2016, Vertical phase separation in small molecule: polymer blend organic thin film transistors can be dynamically controlled, Advanced Functional Materials, Vol: 26, Pages: 1737-1746, ISSN: 1616-3028

Blending of small-molecule organic semiconductors (OSCs) with amorphous polymers is known to yield high performance organic thin film transistors (OTFTs). Vertical stratification of the OSC and polymer binder into well-defined layers is crucial in such systems and their vertical order determines whether the coating is compatible with a top and/or a bottom gate OTFT configuration. Here, we investigate the formation of blends prepared via spin-coating in conditions which yield bilayer and trilayer stratifications. We use a combination of in situ experimental and computational tools to study the competing effects of formulation thermodynamics and process kinetics in mediating the final vertical stratification. It is shown that trilayer stratification (OSC/polymer/OSC) is the thermodynamically favored configuration and that formation of the buried OSC layer can be kinetically inhibited in certain conditions of spin-coating, resulting in a bilayer stack instead. The analysis reveals here that preferential loss of the OSC, combined with early aggregation of the polymer phase due to rapid drying, inhibit the formation of the buried OSC layer. The fluid dynamics and drying kinetics are then moderated during spin-coating to promote trilayer stratification with a high quality buried OSC layer which yields unusually high mobility >2 cm2 V−1 s−1 in the bottom-gate top-contact configuration.

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Labram JG, Treat ND, Lin Y-H, Burgess CH, McLachlan MA, Anthopoulos TDet al., 2016, Energy quantization in solution-processed layers of indium oxide and their application in resonant tunneling diodes, Advanced Functional Materials, Vol: 26, Pages: 1656-1663, ISSN: 1616-3028

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Seo J, Nam S, Kim H, Anthopoulos TD, Bradley DDC, Kim Yet al., 2016, Strong molecular weight effects of gate-insulating memory polymers in low-voltage organic nonvolatile memory transistors with outstanding retention characteristics, NPG Asia Materials, Vol: 8, ISSN: 1884-4057

Organic nonvolatile memory transistors, featuring low-voltage operation (less than or equal to5 V) and high retention characteristics (>10 000 cycles), are demonstrated by introducing high molecular weight poly(vinyl alcohol) (PVA) as a gate insulating layer. PVA polymers with four different molecular weights (9.5–166 kDa) are examined for organic memory devices with poly(3-hexylthiophene) channel layers. All devices show excellent p-type transistor behavior and strong hysteresis in the transfer curves, but the lower molecular weight PVA delivers the higher hole mobility and the wider memory window. This has been attributed to the higher ratio of hydroxyl group dipoles that align in the out-of-plane direction of the PVA layers, as supported by impedance spectroscopy (dielectric constants), polarized Fourier transform-infrared spectroscopy and synchrotron radiation grazing incidence X-ray diffraction measurements. However, outstanding retention characteristics (<4% current variation after 10 000 cycles) have been achieved with the higher molecular weight PVA (166 kDa) rather than the lower molecular weight PVA (9.5 kDa).

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Arumugam S, Cortizo-Lacalle D, Rossbauer S, Hunter S, Kanibolotsky AL, Inigo AR, Lane PA, Anthopoulos TD, Skabarat PJet al., 2015, An Air-Stable DPP-thieno-TTF Copolymer for Single-Material Solar Cell Devices and Field Effect Transistors, ACS APPLIED MATERIALS & INTERFACES, Vol: 7, Pages: 27999-28005, ISSN: 1944-8244

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Porte Y, Maller R, Faber H, Alshareef H, Anthopoulos T, McLachlan MAet al., 2015, Exploring and controlling intrinsic defect formation in SnO2 thin films, Journal of Materials Chemistry C, Vol: 4, Pages: 758-765, ISSN: 2050-7534

By investigating the influence of key growth variables on the measured structural and electrical properties of SnO2 prepared by pulsed laser deposition (PLD) we demonstrate fine control of intrinsic n-type defect formation. Variation of growth temperatures shows oxygen vacancies (VO) as the dominant defect which can be compensated for by thermal oxidation at temperatures >500 °C. As a consequence films with carrier concentrations in the range 1016–1019 cm−3 can be prepared by adjusting temperature alone. By altering the background oxygen pressure (PD) we observe a change in the dominant defect – from tin interstitials (Sni) at low PD (<50 mTorr) to VO at higher PD with similar ranges of carrier concentrations observed. Finally, we demonstrate the importance of controlling the composition target surface used for PLD by exposing a target to >100 000 laser pulses. Here carrier concentrations >1 × 1020 cm−3 are observed that are associated with high concentrations of Sni which cannot be completely compensated for by modifying the growth parameters.

JOURNAL ARTICLE

Ullah M, Lin Y-H, Muhieddine K, Lo S-C, Anthopoulos TD, Namdas EBet al., 2015, Hybrid Light-Emitting Transistors Based on Low-Temperature Solution-Processed Metal Oxides and a Charge-Injecting Interlayer, Advanced Optical Materials, Vol: 4, Pages: 231-237, ISSN: 2195-1071

The performance of solution and low-temperature processed hybrid light-emitting field-effect transistors is enahnced by a new development strategy. The manipulation of the work function at the oxide/polymer interface is presented for achieving high all-round performance in these devices.

JOURNAL ARTICLE

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