323 results found
Lin YH, Thomas SR, Faber H, et 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.
Pitsalidis C, Pappa AM, Hunter S, et 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.
Semple J, Rossbauer S, Burgess CH, et 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.
Mottram AD, Lin YH, Pattanasattayavong P, et 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.
Zhao K, Wodo O, Ren D, et 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.
Labram JG, Treat ND, Lin Y-H, et 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
Seo J, Nam S, Kim H, et 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).
Arumugam S, Cortizo-Lacalle D, Rossbauer S, et 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
Porte Y, Maller R, Faber H, et 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.
Ullah M, Lin Y-H, Muhieddine K, et 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.
Pattanasattayavong P, Mottram AD, Yan F, et al., 2015, Study of the Hole Transport Processes in Solution-Processed Layers of the Wide Bandgap Semiconductor Copper(I) Thiocyanate (CuSCN), Advanced Functional Materials, Vol: 25, Pages: 6802-6813, ISSN: 1616-3028
Wide bandgap hole-transporting semiconductor copper(I) thiocyanate (CuSCN) has recently shown promise both as a transparent p-type channel material for thin-film transistors and as a hole-transporting layer in organic light-emitting diodes and organic photovoltaics. Herein, the hole-transport properties of solution-processed CuSCN layers are investigated. Metal–insulator–semiconductor capacitors are employed to determine key material parameters including: dielectric constant [5.1 (±1.0)], flat-band voltage [−0.7 (±0.1) V], and unintentional hole doping concentration [7.2 (±1.4) × 1017 cm−3]. The density of localized hole states in the mobility gap is analyzed using electrical field-effect measurements; the distribution can be approximated invoking an exponential function with a characteristic energy of 42.4 (±0.1) meV. Further investigation using temperature-dependent mobility measurements in the range 78–318 K reveals the existence of three transport regimes. The first two regimes observed at high (303–228 K) and intermediate (228–123 K) temperatures are described with multiple trapping and release and variable range hopping processes, respectively. The third regime observed at low temperatures (123–78 K) exhibits weak temperature dependence and is attributed to a field-assisted hopping process. The transitions between the mechanisms are discussed based on the temperature dependence of the transport energy.
Jeong J, Seo J, Nam S, et al., 2015, Significant stability enhancement in high-efficiency polymer:fullerene bulk heterojunction solar cells by blocking ultraviolet photons from solar light, Advanced Science, Vol: 3, ISSN: 2198-3844
Al-Hashimi M, Han Y, Smith J, et al., 2015, Influence of the heteroatom on the optoelectronic properties and transistor performance of soluble thiophene-, selenophene- and tellurophene-vinylene copolymers, Chemical Science, Vol: 7, Pages: 1093-1099, ISSN: 2041-6539
We report the first soluble poly(3-dodecyl tellurophenylene-vinylene) polymer (P3TeV) by Stille copolymerization and compare its properties to the analogous thiophene and selenophene containing polymers. The optical band gap of the polymers is shown to systematically decrease as the size of the heteroatom is increased, mainly as a result of a stabilization of the LUMO energy, resulting in a small band gap of 1.4 eV for P3TeV. Field effect transistors measurements in variety of architectures demonstrate that the selenophene polymer exhibits the highest mobility, highlighting that increasing the size of the heteroatom is not always beneficial for charge transport.
Heeney MJ, Han Y, Fei Z, et al., 2015, A Novel Alkylated Indacenodithieno[3,2-b]thiophene-based Polymer for High-performance Field Effect Transistors, Advanced Materials, Vol: 28, Pages: 3922-3927, ISSN: 1521-4095
A novel rigid donor monomer, indacenodithieno[3,2-b]thiophene (IDTT), containing linear alkyl chains is reported. Its copolymer with benzothiadiazole is an excellent p-type semiconductor, affording a mobility of 6.6 cm² V⁻¹ s⁻¹ in top-gated field-effect transistors with pentafluorobenzenethiol-modified Au electrodes. Electrode treatment with solution-deposited copper(I) thiocyanate (CuSCN) has a beneficial hole-injection/electron-blocking effect, further enhancing the mobility to 8.7 cm² V⁻¹ s⁻¹.
Boufflet P, Han Y, Fei Z, et al., 2015, Using Molecular Design to Increase Hole Transport: Backbone Fluorination in the Benchmark Material Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]-thiophene (pBTTT), Advanced Functional Materials, Vol: 25, Pages: 7038-7048, ISSN: 1616-3028
The synthesis of a novel 3,3'-difluoro-4,4'-dihexadecyl-2,2'-bithiophene monomer and its copolymerisation with thieno[3,2-b]thiophene to afford the fluorinated analogue of the well-known poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]-thiophene) (PBTTT) polymer is reported. Fluorination is found to have a significant influence on the physical properties of the polymer, enhancing aggregation in solution and increasing melting point by over 100 °C compared to non-fluorinated polymer. On the basis of DFT calculations these observations are attributed to inter- and intra-molecular S…F interactions. As a consequence, the fluorinated polymer PFBTTT exhibits a four-fold increase in charge carrier mobility compared to the non-fluorinated polymer and excellent ambient stability for a non-encapsulated transistor device.
Casey A, Han Y, Wyatt MF, et al., 2015, Novel soluble thieno[3,2-b]thiophene fused porphyrazine, RSC Advances, Vol: 5, Pages: 90645-90650, ISSN: 2046-2069
The synthesis of the first soluble thieno[3,2-b]thiophene based porphyrazine (ZnTTPz) is reported from the cyclisation of 2,3-dicyano-5-octylthieno[3,2-b]thiophene. ZnTTPz can be considered the all thiophene analogue of naphthalocyanine. ZnTTPz exhibits a red-shifted absorption in solution and thin film, as well as a reduced band gap in comparison to the thiophene analogue due to an increased conjugation length. Films of ZnTTPz processed from solution exhibit p-type semiconducting behaviour in field-effect transistors with low hysteresis and reasonable charge carrier mobility.
Mendaza ADDZ, Melianas A, Rossbauer S, et al., 2015, High-entropy mixtures of pristine fullerenes for solution-processed transistors and solar cells, Advanced Materials, Vol: 27, Pages: 7325-7331, ISSN: 1521-4095
Schießl SP, Faber H, Lin YH, et al., 2015, Hybrid modulation-doping of solution-processed ultrathin layers of ZnO using molecular dopants, Advanced Materials, Vol: 28, Pages: 3952-3959, ISSN: 1521-4095
An alternative doping approach that exploits the use of organic donor/acceptor molecules for the effective tuning of the free electron concentration in quasi 2D ZnO transistor channel layers is reported. The method relies on the deposition of molecular dopants/formulations directly onto the ultrathin ZnO channels. Through careful choice of materials combinations, electron transfer from the dopant molecule to ZnO and vice versa is demonstrated.
Labram JG, Lin YH, Anthopoulos TD, 2015, Exploring Two-Dimensional Transport Phenomena in Metal Oxide Heterointerfaces for Next-Generation, High-Performance, Thin-Film Transistor Technologies., Small, Vol: 11, Pages: 5472-5482, ISSN: 1613-6810
In the last decade, metal oxides have emerged as a fascinating class of electronic material, exhibiting a wide range of unique and technologically relevant characteristics. For example, thin-film transistors formed from amorphous or polycrystalline metal oxide semiconductors offer the promise of low-cost, large-area, and flexible electronics, exhibiting performances comparable to or in excess of incumbent silicon-based technologies. Atomically flat interfaces between otherwise insulating or semiconducting complex oxides, are also found to be highly conducting, displaying 2-dimensional (2D) charge transport properties, strong correlations, and even superconductivity. Field-effect devices employing such carefully engineered interfaces are hoped to one day compete with traditional group IV or III-V semiconductors for use in the next-generation of high-performance electronics. In this Concept article we provide an overview of the different metal oxide transistor technologies and potential future research directions. In particular, we look at the recent reports of multilayer oxide thin-film transistors and the possibility of 2D electron transport in these disordered/polycrystalline systems and discuss the potential of the technology for applications in large-area electronics.
Dhar J, Mukhopadhay T, Yaacobi-Gross N, et al., 2015, Effect of Chalcogens on Electronic and Photophysical Properties of Vinylene-Based Diketopyrrolopyrrole Copolymers, JOURNAL OF PHYSICAL CHEMISTRY B, Vol: 119, Pages: 11307-11316, ISSN: 1520-6106
Wijeyasinghe N, Anthopoulos TD, 2015, Copper(I) thiocyanate (CuSCN) as a hole-transport material for large-area opto/electronics, Semiconductor Science and Technology, Vol: 30, ISSN: 1361-6641
Recent advances in large-area optoelectronics research have demonstrated the tremendous potential of copper(I) thiocyanate (CuSCN) as a universal hole-transport interlayer material for numerous applications, including transparent thin-film transistors, high-efficiency organic and hybrid organic-inorganic photovoltaic cells, and organic light-emitting diodes. CuSCN combinesintrinsic hole-transport (p-type) characteristics with a large bandgap (>3.5 eV) which facilitates optical transparency across the visible to near infrared part of the electromagnetic spectrum.Furthermore, CuSCN is readily available from commercial sources while it is inexpensive and can be processed at low-temperatures using solution-based techniques. This unique combination of desirable characteristics makes CuSCN a promising material for application in emerging large-area optoelectronics. In this review article, we outline some important properties of CuSCN and examine its use in the fabrication of potentially low-cost optoelectronic devices. The meritsof using CuSCN in numerous emerging applications as an alternative to conventional holetransport materials are also discussed.
Fallon KJ, Wijeyasinghe N, Yaacobi-Gross N, et al., 2015, A Nature-Inspired Conjugated Polymer for High Performance Transistors and Solar Cells, MACROMOLECULES, Vol: 48, Pages: 5148-5154, ISSN: 0024-9297
Zhong H, Han Y, Shaw J, et al., 2015, Fused ring cyclopentadithienothiophenes as novel building blocks for high field effect mobility conjugated polymers, Macromolecules, Vol: 48, Pages: 5605-5613, ISSN: 0024-9297
Treat ND, Yaacobi-Gross N, Faber H, et al., 2015, Copper thiocyanate: An attractive hole transport/extraction layer for use in organic photovoltaic cells, Applied Physics Letters, Vol: 107, ISSN: 1077-3118
We report the advantageous properties of the inorganic molecular semiconductor copper(I)thiocyanate (CuSCN) for use as a hole collection/transport layer (HTL) in organic photovoltaic(OPV) cells. CuSCN possesses desirable HTL energy levels [i.e., valence band at 5.35 eV,0.35 eV deeper than poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS)], whichproduces a 17% increase in power conversion efficiency (PCE) relative to PEDOT:PSS-baseddevices. In addition, a two-fold increase in shunt resistance for the solar cells measured in dark conditionsis achieved. Ultimately, CuSCN enables polymer:fullerene based OPV cells to achievePCE > 8%. CuSCN continues to offer promise as a chemically stable and straightforward replacementfor the commonly used PEDOT:PSS.
Schroeder BC, Nielsen CB, Westacott P, et al., 2015, Effects of alkyl chain positioning on conjugated polymer microstructure and field-effect mobilities, MRS Communications, Vol: 5, Pages: 435-440, ISSN: 2159-6867
Peng Y, Yaacobi-Gross N, Perumal AK, et al., 2015, Efficient organic solar cells using copper(I) iodide (CuI) hole transport layers, Applied Physics Letters, Vol: 106, ISSN: 1077-3118
We report the fabrication of high power conversion efficiency (PCE) polymer/fullerene bulkheterojunction (BHJ) photovoltaic cells using solution-processed Copper (I) Iodide (CuI) as hole transportlayer (HTL). Our devices exhibit a PCE value of 5.5% which is equivalent to that obtained forcontrol devices based on the commonly used conductive polymer poly(3,4-ethylenedioxythiophene):polystyrenesulfonate as HTL. Inverted cells with PCE>3% were also demonstrated using solutionprocessedmetal oxide electron transport layers, with a CuI HTL evaporated on top of the BHJ. Thehigh optical transparency and suitable energetics of CuI make it attractive for application in a range ofinexpensive large-area optoelectronic devices.
Hunter BS, Ward JW, Payne MM, et al., 2015, Low-voltage polymer/small-molecule blend organic thin-film transistors and circuits fabricated via spray deposition, Applied Physics Letters, Vol: 106, ISSN: 1077-3118
Organic thin-film electronics have long been considered an enticing candidate in achieving highthroughput manufacturing of low-power ubiquitous electronics. However, to achieve this goal, more work is required to reduce operating voltages and develop suitable mass-manufacture techniques.Here, we demonstrate low-voltage spray-cast organic thin-film transistors based on a semiconductor blend of 2,8-difluoro- 5,11-bis (triethylsilylethynyl) anthradithiophene and poly(triarylamine). Both semiconductor and dielectric films are deposited via successive spray deposition in ambient conditions(air with 40%–60% relative humidity) without any special precautions. Despite the simplicity of the deposition method, p-channel transistors with hole mobilities of >1 cm2 /Vs are realized at 4 V operation, and unipolar inverters operating at 6 V are demonstrated.
Lin Y-H, Faber H, Labram JG, et al., 2015, High Electron Mobility Thin-Film Transistors Based on Solution-Processed Semiconducting Metal Oxide Heterojunctions and Quasi-Superlattices, Advanced Science, Vol: 2, ISSN: 2198-3844
High mobility thin-film transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thin-film transistors is reported that exploits the enhanced electron transport properties of low-dimensional polycrystalline heterojunctions and quasi-superlattices (QSLs) consisting of alternating layers of In2O3, Ga2O3, and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180–200 °C). Optimized prototype QSL transistors exhibit band-like transport with electron mobilities approximately a tenfold greater (25–45 cm2 V−1 s−1) than single oxide devices (typically 2–5 cm2 V−1 s−1). Based on temperature-dependent electron transport and capacitance-voltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gas-like systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, roll-to-roll, etc.) and can be seen as an extremely promising technology for application in next-generation large area optoelectronics such as ultrahigh definition optical displays and large-area microelectronics where high performance is a key requirement.
Bottacchi F, 2015, Polymer-sorted (6,5) single-walled carbon nanotubes for solution-processed low-voltage flexible microelectronics, Applied Physics Letters, Vol: 106, ISSN: 0003-6951
We report on low operating voltage transistors based on polymer-sorted semiconducting (6,5) single-walled carbon nanotube (SWNT) networks processed from solution at room temperature. The (6,5) SWNTs were separated from the as-received carbon nanotubes mixture using a polyfluorene-based derivative as the sorting and dispersing polymer agent. As-prepared devices exhibit primarily p-type behavior with channel current on/off ratio >103 and hole mobility ≈2 cm2 V−1 s−1. These transistor characteristics enable realization of low-voltage unipolar inverters with wide noise margins and high signal gain (>5). Polymer/(6,5) SWNT transistors were also fabricated on free-standing polyimide foils. The devices exhibit even higher hole mobility (≈8 cm2 V−1 s−1) and on/off ratios (>104) while remaining fully functional when bent to a radius of 4 mm.
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