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A working prototype of integrated fiber/receiver system for optical data transmission is realized. The prototype is made by directly depositing an organic photodetector onto a plastic optical fiber. For the deposition of the organic layers, spray coating is successfully exploited. Operation over four orders of magnitude range of light intensities as well as photoresponse to pulsed stimulation are demonstrated.

While organic electronics is mostly dominated by light-emitting diodes, photovoltaic cells and transistors, optoelectronics properties peculiar to organic semiconductors make them interesting candidates for the development of innovative and disruptive applications also in the field of light signal detection. In fact, organic-based photoactive media combine effective light absorption in the region of the spectrum from ultraviolet to near-infrared with good photogeneration yield and low-temperature processability over large areas and on virtually every substrate, which might enable innovative optoelectronic systems to be targeted for instance in the field of imaging, optical communications or biomedical sensing. In this review, after a brief resume of photogeneration basics and of devices operation mechanisms, we offer a broad overview of recent progress in the field, focusing on photodiodes and phototransistors. As to the former device category, very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, and even though the simultaneous optimization of all these relevant parameters is demonstrated in a limited number of papers, real applications are within reach for this technology, as it is testified by the increasing number of realizations going beyond the single-device level and tackling more complex optoelectronic systems. As to phototransistors, a more recent subject of study in the framework of organic electronics, despite a broad distribution in the reported performances, best photoresponsivities outperform amorphous silicon-based devices. This suggests that organic phototransistors have a large potential to be used in a variety of optoelectronic peculiar applications, such as a photo-sensor, opto-isolator, image sensor, optically controlled phase shifter, and opto-electronic switch and memory.

Here we show how Stark spectroscopy, coupled with confocal microscopy, is able to directly map the electric field in an n-type Copper-Fluorinated Phthalocyanine Thin-Film Transistor (TFT) under different operating conditions. To this extent, we locally probe Electro-Reflectance, with a nominal spatial resolution better than 500 nm, exploiting the fact that the detected signal is directly proportional to the square of the local field on the probe volume. This electric field imaging technique has unique advantages because it is non-invasive, since it exploits low incident power and because it probes the existing field in the bulk rather than the surface. Combining the experimental data with numerical modeling, it is possible not only to reconstruct the space charge profile in the few-nanometer thick accumulation layer, but also to extract the AC electron mobility.

We propose a system where an Organic PhotoDetector (OPD) is realized directly onto the cleaved surface of a standard polymethylmethacrylate (PMMA)-based Plastic Optical Fiber (POF). The OPD photoactive layer is based on the bulk-heterojunction of [6,6]-phenyl-C61-butyric acid methyl ester with a squaraine dye, whose absorption spectrum well matches the POF minimum loss window in the red (around 650nm). The device is realized by consecutively depositing the solution-processed transparent anode on the fiber surface, the solution-processed active layer and the evaporated aluminum cathode. When tested with monochromatic pulsed light at a wavelength of 660nm, the POF-OPD system showed the capability of operating up to a 10MHz repetition frequency, not far from the POF intrinsic bandwidth limitation. This promising result represents a first step towards the development of all-organic integrated optical data links.

Photoconductivity in organic semiconductors is modeled taking into account the hopping nature of charge transport in an exponential density of states and exploiting the transport energy concept. Explicit and analytical expressions describing device behavior are obtained, and a robust procedure is outlined to extract from experimental measurements relevant material parameters, including the charge density dependent bulk mobility, as we show on a prototypical all-organic photoconductor. This qualifies the photoconductor not only as a technologically relevant device but also as a test bed for the optoelectronic characterization of disordered materials. © 2012 American Institute of Physics.

A model for polymer Solar Cells is presented consisting of a system of nonlinear diffusion-reaction PDEs with electrostatic convection, coupled to a kinetic ODE. A proof of the existence of both stationary and transient solutions is given and an algorithm for computing them is proposed and numerically validated by comparison with experimentally measured data for a photovoltaic cell.

A high-mobility organic semiconductor employed as the active material in a field-effect transistor does not guarantee per se that expectations of high performance are fulfilled. This is even truer if a downscaled, short channel is adopted. Only if contacts are able to provide the device with as much charge as it needs, with a negligible voltage drop across them, then high expectations can turn into high performances. It is a fact that this is not always the case in the field of organic electronics. In this review, we aim to offer a comprehensive overview on the subject of current injection in organic thin film transistors: physical principles concerning energy level (mis)alignment at interfaces, models describing charge injection, technologies for interface tuning, and techniques for characterizing devices. Finally, a survey of the most recent accomplishments in the field is given. Principles are described in general, but the technologies and survey emphasis is on solution processed transistors, because it is our opinion that scalable, roll-to-roll printing processing is one, if not the brightest, possible scenario for the future of organic electronics. With the exception of electrolyte-gated organic transistors, where impressively low width normalized resistances were reported (in the range of 10 Ω·cm), to date the lowest values reported for devices where the semiconductor is solution-processed and where the most common architectures are adopted, are ∼10 kΩ·cm for transistors with a field effect mobility in the 0.1-1 cm(2)/Vs range. Although these values represent the best case, they still pose a severe limitation for downscaling the channel lengths below a few micrometers, necessary for increasing the device switching speed. Moreover, techniques to lower contact resistances have been often developed on a case-by-case basis, depending on the materials, architecture and processing techniques. The lack of a standard strategy has hampered the progress of the field for a long time. Only recently, as the understanding of the rather complex physical processes at the metal/semiconductor interfaces has improved, more general approaches, with a validity that extends to several materials, are being proposed and successfully tested in the literature. Only a combined scientific and technological effort, on the one side to fully understand contact phenomena and on the other to completely master the tailoring of interfaces, will enable the development of advanced organic electronics applications and their widespread adoption in low-cost, large-area printed circuits.

We demonstrate an organic photodetector showing high detectivity (3.4× 1012Hz0.5cm/W) at a wavelength of 700 nm, based on squaraine/phenyl- C61-butyric-acid-methyl-ester bulk-heterojunction active material. This result is achieved by suppressing the device dark currents while simultaneously preserving its external quantum efficiency, as high as 15% at 700 nm. To this aim, a thin cross-linked film based on poly[2-methoxy-5-(2′ -ethyl-hexyloxy)-1,4-phenylene-vinylene] is exploited to suppress electron injection from the device anode into the organic blend, thus reducing the dark currents by a factor of 30, to the extremely low value of 2 nA/cm2. Also, the detector bandwidth (∼1 MHz) is unaffected by the introduction of a blocking layer. © 2011 American Institute of Physics.

We demonstrate efficient electron injection from a high work function metal in staggered transistors based on the high mobility poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}. Channel length scaling shows that the linear mobility for electrons remains higher than 0.1 cm2/V s when reducing the channel length to a few micrometers. Field-enhanced injection favors downscaling at a fixed lateral voltage and reduces the contact resistance to 11 kΩ cm at high gate voltages for channels of only a few micrometers. The contacts are asymmetric, with the source contribution dominating the overall resistance, consistent with an injection limited regime rather than bulk-limited as generally found in staggered transistors.

X- and Γ-rays sensing application might benefit from the development of detectors based on organic semiconductors. Their processing from solution and at room temperature envisages large area coverage of, in principle, any substrate. The intrinsic low yield in the photogeneration of free charge pairs, due to the low intermolecular interaction resulting in localized excited states, has been reasonably overcome by suitable donor/acceptor molecule blends. Instead, as a consequence of the presence of two mixed moieties in the active layers, efficient transport and collection of photogenerated charges and, at the same time, suppression of dark injected charge are still subject of intense research. In this paper we show that the entangled issues regarding leakage currents, quantum efficiency, response speed, and device lifetime can be effectively addressed: at a chemical level by suitably tailoring the organic molecules, and at a device level by optimizing the metal–semiconductor interface and the morphology of photosensitive blend layer. Leakage current 10% and stability to air and moisture in more than one year can be achieved. Radiation hardness (>500 Gy) for such devices has also been demonstrated.

To the aim of developing an X-ray imager based on a scintillator coupled to an organic photodetector, we fabricated and tested a detector pixel whose active material is a blend of squaraine dyes and Phenyl-C61-Butyric-Acid-Methyl-Ester (PCBM), processed to obtain a detector thickness of 2μm and a leakage current, at the operating voltage, below 10nA/cm2. The detector was coupled to a CsI(Tl) scintillator crystal obtaining, upon collimated 30keV x-ray beam, clear current signals of few hundreds of pA for a dose less than 5μGray/s, both in QCW and under 500μs long pulses. In addition, the development of the pixel on a flexible and transparent substrate leads to a better scintillator light collection.

A novel encapsulation structure to protect organic thin film transistors against oxygen and moisture contaminations is presented. The sealing architecture is comprised of three-layers: aluminum oxide deposited by means of Atomic Layer Deposition is the actual capping layer, while cross-linked poly-vinylphenol and poly-vinylphenol prevent the contamination/damage of the underlying organic semiconductor during the oxide growth. The process has negligible impact on device mobility but it enables poly-3-hexylthiophene based transistors to operate with an on/off ratio in excess of 103 even after 100 days of continuous ambient air exposure.

A new co-oligomer constituted by both a thiophene sequence bearing a 3,4-dialkyl substitution, imparting processability, and by end-capping fluorenone moieties, has been synthesised. The molecule, potentially suitable for close-packing aptness, has been characterized by means of combined optical, thermal, structural, and morphological analyses, showing that, despite the O–H intermolecular interaction favoured by fluorenone presence, the large steric hindrance specific to the dialkyl 3,4-disubstitution strongly limits the intermolecular interaction. Hence it makes such substitution pattern unsuitable for field effect transistor application, as it is confirmed by the electrical performances measured on prototype devices.

Planar organic detectors for the near infrared region of the light spectrum have been realized, processing from solution the quinoid molecule 5,5'-bis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadiene-1-ylidene )-5,5'-dihydro-2,2'-bithiophene (QBT), which shows a peculiar absorption at 680 nm. Sensitization of the active material was obtained by creating a bulk donor-acceptor interface with poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene], which acts as hole acceptor. Photoexcitation and relaxation dynamics in pristine materials and bulk heterojunction have been investigated by means of pump-probe measurements, revealing charge transfer from QBT to polymer and efficient energy transfer the other way round. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3033376]

The role of the silanization of silicon oxide (SiO x ) with different alkyl-silane molecules, in determining the morphology and structure of the overlying poly(3-hexylthiophene) (P3HT) layer has been studied by atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. Particular attention has been paid to the first thin layers close to the interface P3HT/SiO x . For each case the effect of the annealing temperature has been studied. For all the considered silanizations XRD investigations on the P3HT layers, 5–20 nm thick, reveal an edge-on configuration of the thiophene rings. However, a strong morphology dependence has been observed on the length and polarity of the silanizer. By using silanizer with substituents of short length (dimethyldichlorosilane (DMDS) and hexamethyldisilazane (HDMS)) and of significant polarity (3-aminopropyl-trietoxysilane (APS)), P3HT layer organizes into filaments where the macromolecular backbones, perpendicular to the surface, form Π–Π interaction. By moving to a longer alkyl substituents (octadecyltrichlorosilane (OTS) and propyltrichlorosilane (PTS)), a different globular morphology occurs where the same Π–Π edge-on stacking gives rise to shorter and thinner needle-like fundamental structures. The morphological features have been demonstrated to be highly related to the electron mobility of field effect transistors, having as acting layer P3HT film deposited over the two most significant silanized surfaces.

The paper analyses the interrelation between the signal frequency response in an organic planar photodetector and the distribution of traps of the active material playing a fundamental role in the transport of charge carriers. In particular, the response of a dithiolene-based photodetector spectrally matched to the near infrared has been acquired under optical pulses ranging from 10 Hz to 1 MHz in frequency. By means of modulated photocurrent spectroscopy, the trap density distribution of the dithiolene in the solid state has been extracted. The capture and release of photogenerated carriers exerted by a Gaussian density of trapping states, located 0.42 eV below the transport energy, is shown to be the responsible for the observed device frequency response.

The paper studies the role of electrons and holes mobility in determining the external quantum efficiency (EQE) in photodetectors based on a 1:1 in weight blend of poly(3-hexylthiophene) (P3HT) and C61-butyric acid methyl ester (PCBM). In order to fairly correlate the optoelectronic properties (efficiency and transient photocurrent) measured on photodetectors with the transport properties measured on field effect transistors, the photodetectors and the transistors have been produced with an identical planar geometry, where in both cases the charges flow occurs in the same direction with respect to the substrate. The measurements have been performed on devices based on pristine P3HT, on pristine PCBM, and on P3HT:PCBM 1:1 blend, before and after annealing, and have revealed the importance of a balanced carrier transport, showing that quantum efficiency increases as long as the mobility of electrons, which are the slowest carrier, increases. On the other end, the response time is mainly affected by the extension of the effective area.

We report on oriented thin films of poly[3-(5-methoxypentyl)-thiophene] (P 5 OMe) obtained by compressing a monolayer of P 5 OMe formed at the air/water interface of a Langmuir trough. By using this film as the active layer of a Thin Film Transistor a mobility anisotropy ratio in the range of 10 was measured, which is an unprecedented result for a Langmuir–Blodgett (LB) film.

In this work we study a co-oligomer based on fluorenone and thiophene moieties, whose chemical design aimed at a molecule suitable for application as active material in organic field effect transistors. The molecule has been fully characterized in terms of its electrochemical, structural, morphological and electrical properties. Combining these measurements, it has been possible to address the role of the film morphology and of the crystal structure, due to the polymorphic behaviour of the molecule, in determining the mobility of films obtained by vacuum deposition on substrates held at different temperatures. © 2005 Elsevier B.V. All rights reserved.

Derivatives of both oligo- and polythiophene-based FET were recently considered for low cost electronic applications. In the device optimization, factors like redox reversibility of the molecule/polymer, electronic level compatibility with source/drain electrodes, packing closeness, and orientation versus the electrodes, can determine the overall performance. In addition, a gate insulator with a high dielectric constant, a low leakage current, and capability to promote ordering in the semiconductor is required to increase device performances and to lower the FET operating voltage. In this view, Al 2 O 3 appears a good candidate, although its widespread adoption is limited by the disorder that such oxide induces on the semiconductor with detrimental consequences on semiconductor electrical properties. In this contribution, an overview of recent results obtained on thiophene-derivative-based FET devices, fabricated by different growth techniques, and using both thermally grown SiO 2 and Al 2 O 3 from atomic layer deposition gate insulators will be reported and discussed with particular reference to organic solid state aggregation, morphology, and organic–inorganic interface.

The progress in the field of organic photodetectors has recently led to the development of very fast and efficient devices, but their spectral sensitivity is mainly limited to the visible, without covering the regions of the spectrum of greater interest for telecommunications. One of the major issues when dealing with long wavelength organic photodetectors is the usually poor environmental stability of low bandgap organic semiconductors. A possible exception to this scenario is represented by coordination complexes with organic ligands. We employ as photosensitive materials transition metal dithiolene and dioxolene complexes which combine high thermal and photochemical stabilities with high molar extinction coefficients in the near infrared. Taking advantage of the broad tuning of electronic absorption spectra which can be exerted by changing the oxidation state of the complexes, we develop planar metal-semiconductor-metal phostodetectors which are spectrally matched to the optical fiber windows and which can detect light pulses with repetition rates in the range of hundreds of kbit/s. This investigation demonstrates the existence of organic materials of potential telecom interest and that the detection of infrared light pulses is feasible, thus representing a first step toward organic photodetectors for telecommunications.

The transport properties of three fluorenone derivatives used as active layers in organic field effect transistor (OFET) have been studied. A full structural characterization, evidencing the packing features due to the fluorenone moiety, has been carried out. To rationalize the charge carrier mobility values, it is shown that in addition to structural considerations the redox behavior of molecules has to be taken into account. Structure-property relationships are identified, which might drive the future development of oligomers suitable for OFET applications. © 2004 Elsevier B.V. All rights reserved.

A new class of photodetectors, whose active material is an organic semiconductor, has been developed. Thanks to the ease of deposition on any dielectric surface, the device may be built directly on the cleaved surface of an optical fiber, therefore realizing an on-fiber-detector (OFD). The photodetector is based on an organic semiconductor belonging to a new general class of neutral dithiolenes deposited onto a quartz substrate with microlithographically defined gold electrodes so to realize a metal-semiconductor-metal surface structure. First experimental results on a photodiode made of (monoreduced imidazolidine-2,4,5-trithione) having peak responsivity at 1014nm, have shown a time response down to 100microseconds, at present limited by the leakage current noise due to the poorly rectifying contacts. Differently from the vast majority of organic semiconductor materials, dithiolenes have shown extremely high chemical and thermal stability. The photoresponse of the dithiolenes in the liquid phase is shown to be wavelength selective with an absorption peak about 150nm wide that can be chemically tailored so to shift from almost 1000nm to 1700nm. Experimental measurements to prove that the absorption property is maintained in the solid state also at wavelengths around 1500nm, thus covering with a photodetector the spectrum of possible telecom applications, are under way.

The paper describes the use of noise current analysis to sense variations of the microscopic conduction process in organic Light Emitting Diodes and to track their evolution through time. The monitoring of current fluctuations has been made both in time and frequency domain and is of great value when one wants to correlate the conduction properties of the charge carriers and the changes in current flow with the corresponding changes in the microscopic morphology of the organic layers. The method reveals itself to be very effective also in sensing the initial state and the growth of catastrophic degradation of oLEDs in large advance with respect to current monitoring or other techniques. Microscopic damages within the device, as a result of microshorts and/or thermal breakdown, are shown to reveal a neat increase of the white noise component of about three orders of magnitude in the power spectral density, that can therefore be detected with very good time precision. This would allow to study the sources that may give reason of degradation, through structural or spectroscopic investigations for example, before the microscopic damages have sum up to a visible and irreversible macroscopic failure.

In the framework of trap-free steady-state space-charge-limited single-carrier currents, exact equations are derived for the evaluation of arbitrary field-dependent mobility. A differential method, which simply needs first and second derivatives of measured current-voltage (I-V) curves, is put forward. No a priori assumptions are required, other than those which are typical for space-charge-limited currents. An extension to the mixed case of exponentially distributed traps and field-dependent mobility is briefly outlined. The extraction of mobility from measurements can be a valuable tool for the theoretician: theoretical predictions on mobility field-dependence can be easily compared to the real field-dependence, thus permitting an improvement of the model and stimulating the development of transport theory. This method can be of particular relevance for organic semiconductors, whose field-dependent mobility has recently attracted so much theoretical and experimental work.

The paper will describe a new photodetector based on a metal-organic semiconductor material sensitive to the near IR region of the electromagnetic spectrum. The detector has a planar metal-semiconductor-metal structure with the active material deposited from liquid phase over a quartz substrate. Together with the fabrication process and the time response to light pulses, emphasis will be given to the intrinsic wavelength selectivity of the semiconductor material, of about 100nm around its peak sensitivity. The ease of deposition may enable to directly develop optical devices on passive optical component or on electronic substrates.

Ambipolar semiconducting polymers, characterized by both high electron (μe) and hole (μh) mobility, offer the advantage of realizing complex complementary electronic circuits with a single semiconducting layer, deposited by simple coating techniques. However, to achieve complementarity, one of the two conduction paths in transistors has to be suppressed, resulting in unipolar devices. Here, we adopt charge injection engineering through a specific interlayer in order to tune injection into frontier energy orbitals of a high mobility donor-acceptor co-polymer. Starting from field-effect transistors with Au contacts, showing a p-type unbalanced behaviour with μh = 0.29 cm2/V s and μe = 0.001 cm2/V s, through the insertion of a caesium salt interlayer with optimized thickness, we obtain an n-type unbalanced transistor with μe = 0.12 cm2/V s and μh = 8 × 10−4 cm2/V s. We applied this result to the development of the basic pass-transistor logic building blocks such as inverters, with high gain and good noise ma...

Noise current analysis, both in time and frequency, is proposed as a means to sense variations of the microscopic conduction in organic light emitting diodes and to track their time evolution. The sensitivity of the technique would allow to correlate the carriers conduction properties with the corresponding changes in the microscopic morphology of the organic layers as obtained with structural or spectroscopic investigations. The method is shown to be very effective also in sensing the initial state and the growth of organic diodes catastrophic degradation in large advance to current monitoring or other techniques.

Electrochemically monoreduced [M(R,R'timdt)(2)](-) dithiolenes, showing unprecedented wavelength selective photoconducting properties in the third optical fiber window (1500-1800 nm), fine-tunable through modifications in the chemical structure, allowed for the fabrication of a test photodetector with a bit rate of about 85 kbit s(-1).

Based on a new general class [M(R,R'timdt) 2 ] of neutral dithiolenes, an innovative photodetector has been developed. By casting the organ material onto an opportunely configured quartz substrate a planar metal-semiconductor-meta structure has been obtained. Thanks to the strikingly intense absorption in the near infrared of these compounds, the device photoconductivity is enhanced when the irradiating wavelength belongs to this region of the spectrum. The device therefore acts as an intrinsically wavelength-selective photodetector.

Squaraine compounds are currently investigated as high performance active components in both organic and hybrid photovoltaic devices as well as in photodetectors. Their most valuable features include a particularly efficient optical absorption in the Vis-NIR region, high polarizability, and a remarkable chemical stability. Their full exploitation is somewhat limited by a negligible absorption in the UV-Vis region (prototypical squaraines basically do not absorb below 500 nm). The aim of the present paper is the design and synthesis of truly panchromatic squaraines to be effectively employed as the photoactive materials in Vis operating optoelectronic devices. Our strategy involves the design of squaraines that are both nonsymmetric and core-substituted with suitable electron-withdrawing groups. We show the effect of such a design strategy by means of UV-Vis spectroscopy, cyclic voltammetry and prototypical device performances rationalization. © The Royal Society of Chemistry 2012.

We present a study performed on organic thin film transistors based on poly(3-hexylthiophene) with molecular weights ranging from 20 to 80 kDa as active material. Besides having a strong influence on the absolute value of the mobility, we show that the molecular weight also drastically affects the mobility functional dependence on the gate voltage and on the longitudinal electric field. While the medium range of molecular weight (37–53 kDa) yields a high (about 10−2 cm2/V s) and practically constant mobility, the low and high ranges yield a lower mobility, which in addition shows a strong dependence on both the charge density and the electric field. By means of a detailed analysis of experimental transfer characteristics of transistors, this behavior is traced back to the broadness of the density of states, which turns out to be higher for low mobility polymers. Finally, consequences on transistor modeling due to the simultaneous dependence of the mobility on charge density and electric field are discussed.

Planar organic photodetectors represent a simple, cheap, and versatile alternative to devices built in sandwich configuration. The nonuniform electric field distribution in these structures has significant consequences on the extent of the device active region, because photogeneration of free carriers in organic semiconductors is a field-assisted phenomenon. By means of microscopy mapping of the photocurrent in a poly(p-phenylene vinylene) based planar device, we show that due to the deep trapping of photogenerated electrons leading to negative space charge accumulation, exciton dissociation occurs only close to the positively biased electrode. The effect of large leakage currents in defining the device active region is also analyzed and discussed.

Field effect transistors require an Ohmic source contact and an Ohmic drain contact for ideal operation. In many real situations, however, and specifically in organic devices, the injection of charge carriers from metals into semiconductors can be an inefficient process that is non-Ohmic. This has an adverse impact on the performance of thin film transistors and makes the analysis of electrical measurements a complex task because contact effects need to be disentangled from transistor properties. This paper deals with the effects of non-Ohmic contacts on the modeling of organic transistors and gives specific rules on how to extract the real transistor parameters (mobility, threshold voltage, and contact resistances) using only electrical measurements. The method consists of a differential analysis of the transfer characteristic curves (current versus gate voltage) and exploits the different functional dependences of current on gate voltage which is induced by the presence of contact resistances. This paper fully covers the situations from constant carrier mobility to power law gate-voltage-dependent mobility, from constant contact resistance to gate-voltage-dependent contact resistance, and in the linear and in the saturation regime of the operation of the transistor. It also gives important criteria for the validation of the extracted parameters to assess whether the conditions for the application of the method are fulfilled. Examples of application to organic transistors showing various behaviors are given and discussed.

A conductance-switching memory cell based on 3,3′-bis-(3,5-di-tert-butyl-4-methoxyphenyl)-2,2′-bithiophene, showing long time retention, very high endurance to electrical stress, and operation in ambient air condition, is presented and the switching mechanism is investigated by comparing cells with aluminum and mercury top metal contacts. Write and erase cycles in excess of 200 and long term information retention of both states without refresh in excess of 48h are demonstrated. The memory cell is also operating in air with only a small increase in threshold voltage values.

Non volatile memory devices have been developed using diphenyl bithiophene derivatives (DPBT) as active layer. The devices, developed with a two terminal vertical structure where the spin cast organic layer is sandwiched between two electrodes, behave as bistable conductance switching memory cells; the modification of the electrodes material and of the organic layer composition introduces significant changes in the electrical behaviour, that give some indications on the molecular origin of the electrical bistability. These data are enriched by in-situ spectroscopic experiments.