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In recent years there has been an increasing interest to integrate optical sensing in mobile displays, for instance, for biometric fingerprint scanning functionality. There are several routes to incorporate optical fingerprint functionality within the full display area, each with their own benefits and challenges. Here we investigate the different integration routes using large-area, ultra-thin imagers based on organic photodiodes.

Solution-processed photodetectors could be of use in large-area light-sensing applications because they can be fabricated at low cost on plastic substrates and their absorption spectra can be tuned by chemical design. However, fabricating photodetectors with low dark currents and integrating them into high-resolution backplanes remains challenging. Here we show that solution-processed metal halide perovskite photodiodes on top of an amorphous indium gallium zinc oxide transistor backplane can be used to create a flexible image sensor that is ~100 μm thick and has a resolution of 508 pixels per inch. We have developed a pixel edge cover layer for the system that reduces electrode current leakage and thus dark current density. The low noise current in combination with high external quantum efficiency results in high photodetectivity at wavelengths from 550 nm to 770 nm. We show that our imager can be used for document scanning and biometric fingerprinting and that it can be wrapped around objects with radii as small as 0.6 cm. Low-dark-current perovskite photodetectors can be integrated with an oxide transistor backplane to create a high-resolution optical scanning array capable of imaging flat and curved surfaces.

To realize the potential of artificial intelligence in medical imaging, improvements in imaging capabilities are required, as well as advances in computing power and algorithms. Hybrid inorganic–organic metal halide perovskites, such as methylammonium lead triiodide (MAPbI3), offer strong X-ray absorption, high carrier mobilities (µ) and long carrier lifetimes (τ), and they are promising materials for use in X-ray imaging. However, their incorporation into pixelated sensing arrays remains challenging. Here we show that X-ray flat-panel detector arrays based on microcrystalline MAPbI3 can be created using a two-step manufacturing process. Our approach is based on the mechanical soft sintering of a freestanding absorber layer and the subsequent integration of this layer on a pixelated backplane. Freestanding microcrystalline MAPbI3 wafers exhibit a sensitivity of 9,300 µC Gyair–1 cm–2 with a μτ product of 4 × 10–4 cm2 V–1, and the resulting X-ray imaging detector, which has 508 pixels per inch, combines a high spatial resolution of 6 line pairs per millimetre with a low detection limit of 0.22 nGyair per frame.

A curved image sensor on plastic foil has been developed for cone beam computed tomography (CBCT) X-ray imaging. The image sensor of about 6 × 8 cm2 size has been built on a thin polyimide foil with an indium gallium zinc oxide (IGZO) backplane and an organic photodetectors (OPD) frontplane. A flexible cesium iodide (CsI) scintillator has been attached to the optical sensor with 480 × 640 pixels of 126 µm size. Dark current density of the OPD was low with less than 10−7 mA/cm2 at −2 V, while an external quantum efficiency (EQE) of about 50% was reached in the visible wavelength range matched to the scintillator output. The image quality of the digital X-ray detector allowed for 3D reconstruction images of a bone phantom on a rotating stage with a lab setup. The curved detector with 32 cm curvature radius opens up the path for very compact CBCT gantries with largely reduced footprint.

We combine a low dark current and high-detectivity near-infrared (NIR)-sensitive organic photodetector with a high-resolution 508 pixels per inch (ppi) oxide thin-film transistor (TFT) backplane to create a large-area thin NIR detector, using processes that are compatible with flat-panel display fabrication. The detector is characterized showing high uniformity and linearity. With the use of a NIR light source, the detector is capable of imaging the (pattern of) veins under the skin in reflection, leading to improved biometric authentication.

To develop a detailed understanding about halide perovskite processing from solution, the crystallization processes are investigated during spin coating and slot-die coating of MAPbI3 at different evaporation rates by simultaneous in situ photoluminescence, light scattering, and absorption measurements. Based on the time evolution of the optical parameters it is found that for both processing methods initially solvent-complex-structures form, followed by perovskite crystallization. The latter proceeds in two stages for spin coating, while for slot-die coating only one perovskite crystallization phase occurs. For both processing methods, it is found that with increasing evaporation rates, the crystallization kinetics of the solvent-complex structure and the perovskite crystallization remain constant on a relative time scale, whereas the duration of the second perovskite crystallization in spin coating increases. This second perovskite crystallization appears restricted due to differences in solvent-complex phase morphologies from which the perovskite forms. The work emphasizes the importance of the exact precursor state properties on the perovskite formation. It further demonstrates that detailed analyses of multimodal optical in situ spectroscopy allows gaining a fundamental understanding of the crystallization processes that take place during solution processing of halide perovskites, independent from the specific processing method.

Quality Assurance (QA) in hadron therapy is crucial to ensure safe and accurate dose delivery to patients. This can be achieved with fast, reliable and high-resolution detectors. In this paper, we present a novel solution that combines a triple Gas Electron Multiplier (GEM) and a highly pixelated readout based on a matrix of organic photodiodes fabricated on top of an oxide-based thin-film transistor backplane. The first LaGEMPix prototype with an active area of 60 × 80 mm2 was developed and characterized using low energy X-rays. The detector comprises a drift gap of 3.5 mm, a triple-GEM stack for electron amplification, and a readout featuring 480 × 640 pixels at a 126 µm pitch. Here, we describe the measurements and results in terms of spatial resolution for various experimental configurations. A comparison with GAFCHROMIC® films and the GEMPix detector used in the charge readout mode was performed to better understand the contribution to the spatial resolution from both the electron diffusion and the isotropic emission of photons. The measurements were compared to Monte Carlo simulations, using the FLUKA code. The simulation predictions are in good agreement with the GEMPix results. Future plans with respect to applications in hadron therapy are discussed.

Patterning organic materials by photolithography enables not only high-resolution, side-by-side RGB OLED arrays, but also the introduction of organic photodetector in the same frontplane. We show patterned active matrix displays processed on flexible backplane. Furthermore, we demonstrate OPD patterning proof-of-concept. These are the building blocks allowing in-cell optical fingerprint sensor.

Reflectance oximeters based on organic photodiode (OPD) arrays offer the potential to map blood pulsation and oxygenation via photoplethysmography (PPG) over a large area and beyond the traditional sensing locations. Here, an organic reflectance PPG array based on 16 × 16 OPD pixels is developed. The individual pixels exhibit near-infrared sensitivity up to ≈950 nm and low dark current density in the order of 10−6 mA cm−2. This results in high-quality PPG signals. Analysis of the full PPG waveform yields insight on the artery stiffness and the quality of blood circulation, demonstrating the potential of these arrays beyond pulse oximetry and heart-rate calculation.

We show a thin, flexible and large 500 dpi fingerprint sensor for security applications providing better usability than existing sensors with a similar performance. A new process flow, using PVDF-TrFE pyroelectric capacitors on top of an IGZO TFT backplane on a flexible polyimide (PI) foil is implemented to create an active thermal fingerprint sensor. The system measurements fit well with the simulation of the thermal operation.

We made and characterized an X-ray detector on a 25- $\mu \text{m}$ -thick plastic substrate that is capable of medical-grade performance. As an indirect conversion flat panel detector, it combined a standard scintillator with an organic photodetector (OPD) layer and oxide thin-film transistor backplane. Using solution-processed organic bulk heterojunction photodiode rather than the usual amorphous silicon, process temperature is reduced to be compatible with plastic film substrates, and a number of costly lithography steps are eliminated, opening the door to lower production costs. With dark currents as low as 1 pA/mm $^{2}$ and sensitivity of 0.2 A/W the OPD also meets functional requirements: the proof-of-concept detector delivers high-resolution, dynamic images at 10 frames/s, and 200 pixels/in using X-ray doses as low as $3~\mu $ Gy/frame.

We present recent developments on flexible a-IGZO TFT technology scaling in terms of TFT channel length and operating voltage, as well as manufacturing cost optimization with a focus on R2R processing compatibility. We present progress on the relevant technology building blocks; (i) R2R compatible TFT architecture, (ii) (multilevel) nanoimprint lithography and (iii) S-ALD deposited TFT materials. Additionally, we show a developing application that drives scaling of the technology, namely a monolithically integrated flexible AMOLED display with in-display fingerprint detection.

Organic photodetectors (OPDs) have attracted much attention in recent years, due to their promise in large-area light sensing applications. Here, high-resolution slot-die-coated large-area bulk heterojunction organic photodiode (OPD) arrays are reported. The OPD uses a novel electron transport layer, indium gallium zinc oxide in combination with a molybdenum oxide top-electrode. Together, these effectively reduce dark current densities to very low levels of ≈10−7 mA cm−2 at −2 V. The OPDs show linear behavior in a wide range of light intensities and high detectivity values under reverse bias conditions. When coated on a 508 ppi TFT backplane, a high-quality optical fingerprint scanner capable of imaging in reflection is realized. The optical and electrical properties of the fingerprint sensor are characterized and high-resolution fingerprint images are obtained.

Ferroelectric materials are important components of sensors, actuators and non-volatile memories. However, possible device configurations are limited due to the need to provide screening charges to ferroelectric interfaces to avoid depolarization. Here we show that, by alternating ferroelectric and semiconducting nanowires over an insulating substrate, the ferroelectric dipole moment can be stabilized by injected free charge carriers accumulating laterally in the neighboring semiconducting nanowires. This lateral electrostatic coupling between ferroelectric and semiconducting nanowires offers new opportunities to design new device architectures. As an example, we demonstrate the fabrication of an elementary non-volatile memory device in a transistor-like configuration, of which the source-drain current exhibits a typical hysteretic behavior with respect to the poling voltage. The potential for size reduction intrinsic to the nanostructured hybrid layer offers opportunities for the development of strongly miniaturized ferroelectric and piezoelectric devices., SCOPUS: ar.j, info:eu-repo/semantics/published

Solution-processed organic ferroelectric resistive switches could become the long-missing non-volatile memory elements in organic electronic devices. To this end, data retention in these devices should be characterized, understood and controlled. First, it is shown that the measurement protocol can strongly affect the apparent retention time and a suitable protocol is identified. Second, it is shown by experimental and theoretical methods that partial depolarization of the ferroelectric is the major mechanism responsible for imperfect data retention. This depolarization occurs in close vicinity to the semiconductor-ferroelectric interface, is driven by energy minimization and is inherently present in this type of phase-separated polymer blends. Third, a direct relation between data retention and the charge injection barrier height of the resistive switch is demonstrated experimentally and numerically. Tuning the injection barrier height allows to improve retention by many orders of magnitude in time, albeit at the cost of a reduced on/off ratio. (c) 2016 Elsevier B.V. All rights reserved. Funding Agencies|European Community [248092]

Organic electronics is becoming more and more important because the low level of fabrication and deposition complexity even at large scale makes it a good candidate for future low cost technological product development. P(VDF-TrFE) is a co-polymer of special interest due its ferroelectric property enabling usage in re-programmable non-volatile organic memory and magnetoelectric sensors. Piezo force microscopy (PFM) provides access to the technologically relevant ferroelectric polarisability and its remanent polarization via imaging of the piezoelectric property. Here we use PFM to show that piezoelectric response of a P(VDF-TrFE) film can be enhanced by up to 260 % after soft X-ray irradiation. This enhancement correlates with morphological change of part of the film, from amorphous to crystalline. An optimal irradiation dose is found above which the film gets eroded and the piezoelectric response gets lowered.

We demonstrate high performance X-ray imaging detectors on foil suitable for medical grade X-ray imaging applications. The detectors are based on solution-processed organic photodiodes forming bulk-heterojunctions from photovoltaic donor and acceptor blend. The organic photodiodes are deposited using an industrially compatible slot die coating technique with end of line processing temperature below 100° C. These photodiodes have extremely low dark leakage current density of 10-7 mA/cm2 at -2V bias with very high yield and have peak absorption around 550 nm wavelength. We combine these organic photodiodes with high mobility metal oxide semiconductor based thin film transistor arrays with high pixel resolution of 200ppi on thin plastic substrate. When combined with a typical CsI(TI) scintillator material on top, they are well suited for low dose X-ray imaging applications. The optical crosstalk is insignificant upto resolution of 200 ppi despite the fact that the photodiode layer is one continuous layer and is non-pixelated. Low processing temperatures are another key advantage since they can be fabricated on plastic substrate. This implies that we can make X-ray detectors on flexible foil. Those detectors can be mechanically more robust and light weight when compared to amorphous Si based detectors fabricated on glass substrate.

This article describes a combined experimental and theoretical study on nanophase structure development as a result of liquid phase demixing in solution-cast blends of the organic semiconductor poly(9,9'-dioctyl fluorene) (PFO) and the ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)). Blend layers (200 nm) are prepared by spin coating a 1:9 (w/w) PFO:P(VDF-TrFE) blend solution in a common solvent on a poly(ethylenedioxy thiophene)/poly(styrene sulfonate) substrate. Owing to the pronounced incompatibility between the two polymers, a strong phase-separated morphology is obtained, characterized by disk-like nanodomains of PFO embedded in a P(VDF-TrFE) matrix, as revealed by scanning electron microscopy. By varying the processing conditions, we find the average domain size and standard deviation to increase with spinning time. The considerable increase in domain size suggests the coarsening process not to be impeded by a steep rise in viscosity. This indicates solvent evaporation to be only moderate within the experimental time frame. The evolution of the observed phase morphology is modeled using ternary diffuse interface theory integrated with a modified Flory-Huggins (FH) treatment of the homogeneous (bulk) free energy of mixing, to account for significant molecular differences between the active blend components. Using calculated FH interaction parameters, the model confirms the phase separation to occur via spinodal decomposition of the blend solution during spin coating, as suggested by experimental observations. The simulated phase morphologies as well as the modeled trends in domain growth and standard deviation compare favorably with the experimental data. © 2011 Wiley Periodicals, Inc.

(Figure Presented) Controlling the morphology of soluble small molecule organic semiconductors is crucial for the application of such materials in electronic devices. Using a simple dip-coating process we systematically vary the film drying speed to produce a range of morphologies, including oriented needle-like crystals. Structural characterization as well as electrical transistor measurements show that intermediate drying velocities produce the most uniformly aligned films. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.

The anisotropic conductivity of spin-coated poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films by temperature-dependent conductivity measurements, has been analyzed. A detailed 3D morphological model was derived from topographic scanning tunneling microscopy (STM) and cross-sectional atomic force microscopy (AFM) images, which correlated the anisotropy, both in conductivity magnitude and in the conduction mechanism. Spin coated films of PEDOT:PSS formed a reasonably homogenous material in terms of electrical conductivity. It was observed that the vertical conductivity that is perpendicular to the substrate, can be up to three orders of magnitude lower than the lateral conductivity in the plane of the film. The macroscopic in-plane conductivity was found to be completely isotropic, and the ordering was found to be confined to randomly oriented micrometer-size domains.

Ferroelectric polarization switching of poly(vinylidene difluoride-trifluoroethylene) is investigated in different thin-film device structures, ranging from simple capacitors to dual-gate thin-film transistors (TFT). Indium gallium zinc oxide, a high mobility amorphous oxide material, is used as semiconductor. We find that the ferroelectric can be polarized in both directions in the metal-ferroelectric-semiconductor (MFS) structure and in the dual-gate TFT under certain biasing conditions, but not in the single-gate thin-film transistors. These results disprove the common belief that MFS structures serve as a good model system for ferroelectric polarization switching in thin-film transistors. cop. 2015 AIP Publishing LLC.

Ferroelectric polymers and amorphous metal oxide semiconductors have emerged as important materials for re-programmable non-volatile memories and high-performance, flexible thin-film transistors, respectively. However, realizing sophisticated transistor memory arrays has proven to be a challenge, and demonstrating reliable writing to and reading from such a large scale memory has thus far not been demonstrated. Here, we report an integration of ferroelectric, P(VDF-TrFE), transistor memory arrays with thin-film circuitry that can address each individual memory element in that array. n-type indium gallium zinc oxide is used as the active channel material in both the memory and logic thin-film transistors. The maximum process temperature is 200 °C, allowing plastic films to be used as substrate material. The technology was scaled up to 150 mm wafer size, and offers good reproducibility, high device yield and low device variation. This forms the basis for successful demonstration of memory arrays, read and write circuitry, and the integration of these. cop. 2015 IOP Publishing Ltd.

In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase-separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. (c) 2015 Wiley Periodicals, Inc. Funding Agencies|European Communitys Seventh Framework Programme under MOMA project [248092]

Highly ordered thin films of organic materials are receiving a great deal of attention as active layers in a new generation of plastic electronic devices, particularly in organic field-effect transistors (OFETs). [1] Numerous organic-film preparation technologies have been tested over the past few decades. For commercial organic electronics, solution-processed, low-cost technologies such as spin-coating, inkjet printing, and screenprinting are preferred. [2] Mostly, these methods produce thin films with moderate structural order from soluble polymers and oligomers. The relevant physical parameters (e.g., chargecarrier mobilities) of thin organic films are strongly affected by the orientation, distribution, and size of the domains and domain boundaries, [3] and, more generally, by the degree of structural order. The endeavor to improve molecular alignment in active organic layers has led to the implementation of high-quality organic single crystals in OFETs with optimized performance. [4] However, recent methods for the fabrication of single-crystal devices are rather complex and inappropriate for practical applications. [5] Therefore, suitable organic compounds and preparation methods that yield highly ordered thin films are quite essential for progress in this field. In this paper, we present highly ordered thin films of 5,5″bis(5-hexyl-2-thienylethynyl)-2,2′:5′,2″-terthiophene (TR5-C6) prepared from solution by spin-coating and subsequent thermal treatment, and studied using X-ray diffraction (XRD) techniques. The calamitic TR5-C6 molecule consists of a central terthiophene unit with acetylene linkages connecting two terminal thiophene rings with hexyl end groups (Fig. 1a). The thermotropic liquid crystalline behavior of TR5-C6 has been studied by differential scanning calorimetry (DSC), and the mesophases have been assigned by polarized optical microscopy. During cooling, exothermic phase transitions from the nematic to the smectic C phase at 115°C, from the smectic C to the smectic B phase at 109°C, and from the smectic B

We demonstrate the design of a multifunctional organic layer by the rational combination of nanosized regions of two functional polymers. Instead of relying on a spontaneous and random phase separation process or on the tedious synthesis of block copolymers, the method involves the nanomolding of a first component, followed by the filling of the resulting open spaces by a second component. We apply this methodology to fabricate organic nonvolatile memory diodes of high density. These are built by first creating a regular array of ferroelectric nanodots by nanoimprint lithography, followed by the filling of the trenches separating the ferroelectric nanodots with a semiconducting polymer. The modulation of the current in the semiconductor by the polarization state of the ferroelectric material is demonstrated both at the scale of a single semiconductor channel and in a microscopic device measuring about 80.000 channels in parallel, for voltages below ca. 2 V. The fabrication process, which combines synergetically orthogonal functional properties with a fine control over their spatial distribution, is thus demonstrated to be efficient over large areas.

Carbon-nanotube top-gate transistors with fluorinated dielectrics are presented. With PTrFE as the dielectric, the devices have absent or small hysteresis at different sweep rates and excellent bias-stress stability under ambient conditions. Ambipolar single-walled carbon nanotube (SWNT) transistors are observed when P(VDF-TrFE-CTFE) is utilized as a topgate dielectric. Furthermore, continuous tuning of the threshold voltages of both unipolar and ambipolar SWNT thin-film transistors (TFTs) is demonstrated for the first time. cop. 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this paper, we demonstrate a scalable and low-cost memory technology using a phase separated blend of a ferroelectric polymer and a semiconducting polymer as data storage medium on thin, flexible polyester foils of only 25μm thickness. By sandwiching this polymer blend film between rows and columns of metal electrode lines where each intersection makes up one memory cell, we obtained 1 kbit cross bar arrays with bit densities of up to 10 kbit/cm2. © 2014 The Japan Society of Applied Physics

In this paper, we successfully fabricated and operated passive matrix P(VDF-TrFE) transistor arrays, i.e. memory arrays in which no pass-transistors or other additional electronic components are used. Because of the smaller cell, a higher integration density is possible. We demonstrate arrays up to a size of 16 × 16, processed on thin (25 μm) poly(ethylene naphthalate) substrates, using Indium-Gallium-Zinc-Oxide (IGZO) as the semiconductor and 200 nm-thick P(VDF-TrFE) as a ferroelectric gate dielectric. The memory transistors have remnant current modulations of ∼105 with a retention time of more than 12 days. They can be switched in less than 1 μs at operating voltages of 25 V. Switching speed is strongly decreased with decreasing voltage: at ∼10 V the transistors do not switch within 10 s. This difference in switching speed of more than 4 orders in magnitude when changing the electric field by a factor of only 2.5 makes these memories robust towards disturb voltages, and forms the basis of integration of these transistors in passive matrix-addressable transistor arrays that contains only one (memory) transistor per cell. It is shown that with current technology and memory characteristics it is possible to scale up the array size in the future. © 2013 Elsevier B.V. All rights reserved.

Using a concept of asymmetric side gate and main gate, it is shown that it is possible to realize unipolar transport (both p-type and n-type) in a thin-film transistor with a high-performance ambipolar polymer semiconductor. In a complementary inverter, this results in higher noise margin and DC gain.

We present a voltage programmable polymer light emitting field-effect transistor (LEFET), consisting of a green emitting polymer (F8BT), and a ferroelectric polymer, P(VDF-TrFE), as the gate dielectric. We show by both experimental observations and numerical modeling that, when the ferroelectric gate dielectric is polarized in opposite directions at the drain and source sides of the channel, respectively, both electron and hole currents are enhanced, resulting in more charge recombination and ∼10 times higher light emission in a ferroelectric LEFET, compared to the device with non-ferroelectric gate. As a result of the ferroelectric poling, our ferroelectric LEFETs exhibit repeated programmability in light emission, and an external quantum efficiency (EQE) of up to 1.06%. Numerical modeling reveals that the remnant polarization charge of the ferroelectric layer tends to ‘pin’ the position of the recombination zone, paving the way to integrate specific optical out-coupling structures in the channel of these devices to further increase the brightness.

Multibit memory devices based on the ferroelectric copolymer P(VDF-TrFE) (poly-(vinylidenefluoride-trifluoroethylene)) are presented. Multilevel microstructures are fabricated by thermal imprinting of spin-coated ferroelectric polymer film using a rigid Si template. Multibit storage in capacitors and thin-film transistor memory is realized by implementing imprinted ferroelectric polymer films as the insulator and gate dielectric layers, respectively. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Miniaturization of biosensors is envisaged by the development of biochips consisting of parallel microarray patterns of binding sites on rigid substrates, such as glass or silicon. Thin plastic substrates are promising flexible alternatives because of the possibility for large-area roll-to-roll manufacturing of disposable chips at lower costs. Mature optical lithography technology faces many challenges when used to pattern flexible foils as a result of the substrate instabilities, especially at higher temperatures. In this work, flexible biochips with gold electrode patterns were fabricated on thin polyethylene naphthalate (PEN) foils using photolithography. The gold electrode structures of the chips were manufactured by direct metal patterning and by lift-off processing. Both methodologies resulted in well-defined electrode patterns as concluded from optical microscopy and scanning electron microscopy (SEM) characterization and resistance measurements. The biochips were successfully employed for the electrical and optical detection of DNA molecules. The DNA detection was based on the immobilization of capture DNA between electrode gaps, hybridization with biotin-labeled target DNA, and enzymatic silver enhancement. © 2009 American Chemical Society.

The morphology of spin-cast films of poly(p-phenylenevinylene) (PPV) derivatives is studied as a function of the substitution pattern of the conjugated backbone. Moreover, the influence of concentration in the casting solution, annealing, the choice of solvent, and the role of defects are addressed. By using a recently developed scanning-probe technique, we are able to visualize individual polymer chains and aggregates on the surface of spin-cast films. We find that a symmetric substitution pattern strongly promotes interchain aggregation in the surface layer, whereas an unsymmetric pattern in some cases leads to intrachain or self-aggregation. The nature of these intrachain aggregates is further investigated using molecular dynamics simulations. The observed molecular morphologies can in most cases be qualitatively related to macroscopic electrooptical properties. Therefore, our results strongly suggest that the surface morphology may be regarded as indicative of the morphology of the entire film. © 2005 American Chemical Society.

The influence of the substitution pattern (unsymmetrical or symmetrical), the nature of the side chain (linear or branched), and the processing of several solution processable alkoxy-substituted poly(p-phenylene vinylene)s (PPVs) on the charge-carrier mobility in organic field-effect transistors (OFETs) is investigated. We have found the highest mobilities in a class of symmetrically substituted PPVs with linear alkyl chains (e.g., R1, R2 = n-C11H23, R3 = n-C18H37). We have shown that the mobility of these PPVs can be improved significantly up to values of 10-2 cm2 V-1 s-1 by annealing at 110°C. In addition, these devices display an excellent stability in air and dark conditions. No change in the electrical performance is observed, even after storage for thirty days in humid air.

We demonstrate the fabrication of an organic Ferroelectric Field Effect Transistor (FeFET) incorporating a ferroelectric gate dielectric made of nanostripes obtained by nanoimprinting poly(vinylidene fluoride-co-trifluoroethylene) over a layer of semiconducting poly(triarylamine). The imprinting process results in a decreased switching voltage for the ferroelectric, by a factor of ca. 1.5, resulting in a decreased operating voltage compared to a reference FeFET with a continuous ferroelectric layer. The transistor consists of a large number of nanostripe-gated transistors placed in parallel, which also offers interesting possibilities for a strong size reduction of organic FeFETs.

An I-line photolithography process for ferroelectric polymers is developed. It is based on photocrosslinking using a bisazide photoinitiator. Patterned layers were realized down to 1-2 mu m resolution. Crosslinking yields a close-to-insoluble ferroelectric polymer network that counter intuitively has similar ferroelectric properties as a noncrosslinked film. The negative process is used to stack ferroelectric films on top of each other to make three-dimensional cross-bar arrays of nonvolatile ferroelectric capacitor memories. (C) 2011 American Institute of Physics. [doi:10.1063/1.3571284]

We present a systematic study of the influence of the processing conditions on the charge-carrier mobility in hole-only diodes and field-effect transistors (FETs) based on alkoxy-substituted poly(p-phenylene vinylene) (PPV). It is demonstrated that by chemical modification from asymmetrically to fully symmetrically substituted PPVs the mobility in both types of devices can be significantly improved. Furthermore, for symmetrical PPVs the mobility is strongly dependent on processing conditions, such as choice of solvents and annealing conditions. The increase in mobility is accompanied by a strong enhancement of the anisotropy in the charge transport. Ultimately, mobility of up to 10(-2) cm(2)/Vs in FETs and 10(-5) cm(2)/Vs in hole-only diodes have been achieved.

Dye-doped semiconducting polymers are used as active layers in polymer light-emitting diodes (polyLEDs). The emission color can be tuned by doping the active polymer with certain dyes. This concept of energy transfer is demonstrated for a green matrix doped with a red-emitting dye, suitable for use in LEDs. An absolute PL efficiency of 39% is observed for this system. Another very attractive development is taking place in the area of all-polymer transistors. This may lead to a (partial) replacement of the driving electronics by all-plastic circuits. A new precursor route toward poly(thienylenevinylene)s (PTVs), suitable as active material in all-polymer integrated circuits, is presented. Synthesis of the precursors is reproducible and fast, and can readily be scaled for manufacture. Quantitative conversion of the precursor polymer can be accomplished by heating at 150°C for 20 min. The resulting mobility (6 × 10 -3 cm 2 /V-sec) and ON-OFF ratio (4 × 10 4 ) makes this material a suitable candidate for the development and large-scale manufacturing of all-polymer integrated circuits.

The handling of grey levels by these large displays paves the way for electronic paper. The main advantages of using soluble semiconductive polymers in microelectronic devices are ease of processing1,2,3 and mechanical flexibility4. Here we describe an active-matrix display with 64 × 64 pixels, each driven by a thin-film transistor with a solution-processed polymer semiconductor. In a significant step towards low-cost flexible displays, this polymer-dispersed liquid-crystal arrangement gives a reflective, low-power display with paper-like contrast, which can handle 256 grey levels while being refreshed at video speed.