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Deformable mirrors are becoming more and more important elements in the astronomical field, both for development of active and adaptive optics. PCDMs behave in a completely different way respect to the traditional ones, since a pattern of light creates virtual actuators, whose size and density can be freely modulated. PCDMs consist in a slab of photoconductive material with a reflective membrane placed at a certain distance from the photoconductor, creating a capacitor. In this paper will be presented the mechanical solution adopted in order to realize a prototype and the setup used in order to start the characterization of the different component. A critical analysis will be performed on the sensitivity of the system to the different dimension that characterize the system itself, like the distance between the membrane and the photoconductor and the membrane tension. The result presented will be relate to the static deformation of the membrane using the DC current.

The photoconducting properties of platinum diimine-dithiolate complex [Pt(bipy)(Naph-edt)] (1; bipy = 2,2′-bipyridine; Naph-edt2− = 2-naphthylethylene-1,2-dithiolate) were investigated. DFT calculations on a model assembly with four complex units suggest that the high external quantum efficency measured on a prototype photodetector correlates with the intermolecular character of electronic excitations in the visible region.

Metal bis(1,2-dithiolene) complexes belonging to the class [Ni(Ar-edt)2]x- [Ar-edt2- = arylethylene-1,2-dithiolate; Ar = phenyl, (1x-), 2-naphthyl (2x-); x = 0 and 1] were fully characterized by NMR, UV-visible-near-infrared (UV-vis-NIR), diffuse reflectance, and FT-IR spectroscopy, as well as cyclic voltammetry and single-crystal X-ray diffraction analysis. These complexes have emerged as new photoconducting materials that allowed for the development of a prototype of photodetectors with response in the vis-NIR region. The photodetecting devices showed in some cases quantum efficiencies orders of magnitude higher than those of previously reported 1,2-dithiolene systems.

The predictive accuracy of state–of–the–art continuum models for charge transport in organic semiconductors is highly dependent on the accurate tuning of a set of parameters whose values cannot be effectively estimated either by direct measurements or by first principles. Fitting the complete set of model parameters at once to experimental data requires to set up extremely complex multi–objective optimization problems whose solution is, on the one hand, overwhelmingly computationally expensive and, on the other, it provides no guarantee of the physical soundness of the value obtained for each individual parameter. In the present study we present a step–by–step procedure that enables to determine the most relevant model parameters, namely the density of states width, the carrier mobility and the injection barrier height, by fitting experimental data from a sequence of relatively simple and inexpensive measurements to suitably devised numerical simulations. At each step of the proposed procedure only one parameter value is sought for, thus highly simplifying the numerical fitting and enhancing its robustness, reliability and accuracy. As a case study we consider a prototypical n-type organic polymer. A very satisfactory fitting of experimental measurements is obtained, and physically meaningful values for the aforementioned parameters are extracted.

This paper investigates with a statistical analysis the issue of performance reproducibility and optimization in fully inkjet-printed organic photodetectors on flexible substrates. The most crucial process step to obtain reproducible, well performing devices with a high process yield turns out to be the printing of the thin polyethylenimine interlayer used as a surface modifier for the bottom electrode. Controlling solution composition and deposition parameters for this layer, a 57 nA cm–2 mean reverse dark current was achieved, with an outstanding standard deviation as low as 15 nA cm–2, with dramatic improvements in process yield (from less than 20% to over 90%). Device performance in terms of dark currents, EQE (from 50% up to 90% at 525 nm, depending on process), and rectification (ratio between forward current and reverse current over 104 and reaching 105 in the best cases) is among the best for fully printed detectors. Furthermore, the importance of relative humidity control in the deposition enviro...

A light-driven deformable mirror based on an organic photoconductive layer is designed and realized. The requirements for the photoconductive organic material are reported showing their effect on the mirror performances. The production and characterization of the photoconductive thick layer consisting in a polystyrene matrix doped with P3HT:PCBM and an arylamine (4,4',4 ''-tris[phenyl(m-tolyl)amino]triphenylamine) are reported. A prototype of the mirror with a clear aperture of 12 mm is built and its performance measured in terms of reflective surface displacement. Moreover, a light valve device based on this mirror is built and characterized.

In this paper a UV sensor is demonstrated, operating at less than 1 V bias and showing a switching range as high as 60 dB for seconds of exposure. To this achievement, light-induced conductance switching in solution processed TiO2 is exploited. Information retention can be tuned from few seconds to almost permanent according to processing conditions. In addition, processing involves a limited thermal budget, which in perspective makes the device compatible with plastic substrates. Prototypical detector arrays, developed as simple crossbar thanks to the peculiar light-matter interaction mechanism, are tested as imagers.

Nanometer-thick Langmuir-Schafer monolayers of an electron transporting polymer display charge transport, optical and electro-optical properties that do not depend on the number of layers deposited one above the other. This phenomenon can be rationalized with the micro-structure of the specific multi-layers, which introduces an interlayer hopping penalty confining transport to a neat 2D regime, with a channel not extending beyond a single similar to 3 nm thick polymer strand, as confirmed by kinetic Monte Carlo simulations. Such findings are critical to establish a quantitative structure-property nexus in high mobility polymer semiconductors and in the control of charge transport at a molecular scale. Funding Agencies|European Research Council (ERC) under the European Unions Horizon research and innovation programme HEROIC [638059]; Knut och Alice Wallenbergs stiftelse; Advanced Functional Materials Center at Linkoping University [2009-00971]; VINNOVA [2015-04859]

A suitably designed fulleropyrrolidine-squaraine dyad enables the preparation of efficient single component organic photodiodes.

Photo Controlled Deformable Mirrors (PCDMs) are electro-static membrane mirrors where a photoconductive material replaces the conventional electrode pads, so that the mirror surface deforms according to a light pattern projected on the photoconductor, leading to a simplified control system. A proper device design and manufacturing has to take into account many different issues and the material choice is of primary importance. After a brief description of PCDM working principles we consider an equivalent electrical model, deriving the photoconductor’s parameters that most influence the device performances and show some examples among currently available photoconductors. Finally, we propose a complete electro-opto-mechanical model that allows to optimize the system and to enhance the mirror performances.

Interdependence of chemical structure, thin-film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high-mobility, solution-processed polymers for large-area and flexible electronics applications. There is a specific need to achieve >1 cm2 V−1 s−1 field-effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron-transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene-diimide based donor–acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field-effect transistors show maximum μ of 2.4 cm2 V−1 s−1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface-segregated prevalently edge-on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high-electron-mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure–property nexus in semiconducting polymer thin films.

In this contribution we demonstrate an integrated photoactive switch employing a fully-printed planar photodetector and complementary Schmitt trigger. A photoactive switch is fundamental to several light driven systems, such as twilight sensors or industrial machinery control devices. This paper explores a fabrication methodology that enables reliable complementary logic building blocks and photodetectors with a fully-printed, all-polymer approach, resulting in a semi-transparent integrated system on a single plastic foil.

The Density of States (DOS) is an ingredient of critical importance for the accurate physical understanding of the optoelectronic properties of organic semiconductors. The disordered nature of this class of materials, though, renders the task of determining the DOS far from trivial. Its extraction from experimental measurements is often performed by driving the semiconductor out of thermal equilibrium and therefore requires making assumptions on the charge transport properties of the material under examination. This entanglement of DOS and charge transport models is unfavorable since transport mechanisms in organic semiconductors are themselves still subject of debate. To avoid this, we propose an alternative approach which is based on populating and probing the DOS by means of capacitive coupling in Metal Insulator Semiconductors (MIS) structures while keeping the semiconductor in thermal equilibrium. Assuming a Gaussian shape, we extract the DOS width by numerical fitting of experimental Capacitance–Voltage curves, exploiting the fact that the DOS width affects the spatial distribution of accumulated charge carriers which in turn concurs to define the MIS capacitance. The proposed approach is successfully tested on two benchmark semiconducting polymers, one of n-type and one of p-type and it is validated by verifying the robustness of the extraction procedure with respect to varying the insulator electrical permittivity. Finally, as an example of the usefulness and effectiveness of our approach, we study the static characteristics of thin film transistors based on the aforementioned polymers in the framework of the Extended Gaussian Disorder transport model. Thanks to the extracted DOS widths, the functional dependence of current on the gate voltage is nicely predicted and physical insight on transistor operation is achieved.

Thanks to their strong absorption in the near infrared, squaraine dyes have raised interest in the field of organic photovoltaics and photodetection. We develop photodetectors based on the bulk heterojunction of an indolic squaraine and of a fullerene derivative, obtaining an external quantum efficiency as high as 12% at 590 nm. To gain insight into carrier transport and recombination phenomena, devices are characterized in the dark by means of admittance spectroscopy. At low applied voltages carrier transport is dominated by holes, which show dispersive transport and an electric field dependent mobility of about 10−5–10−4 cm2 V−1 s−1. At higher voltages electron injection occurs as well and a bipolar, recombination-limited regime sets in. The modeling of the low-frequency negative capacitance contribution suggests a trap-mediated carrier recombination mechanism.

Naphthalenediimide (NDI)-based polymers co-polymerized with thienyl units are an interesting class of polymer semiconductors because of their good electron mobilities and unique fi lm microstructure. Despite these properties, understanding how the extension of the thienyl co-monomer affects charge transport properties remains unclear. With this goal in mind, we have synthesized a series of NDI derivatives of the parent poly{[ N,N -bis(2octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5-(2,2bithiophene) (P(NDI2OD-T2)), which exhibited excellent electron mobility. The strategy comprises both the extension of the donor o -conjugation length and the heteroatomic fusion of the thiophene rings. These newly synthesized compounds are characterized experimentally and theoretically vis-a-vis with P(NDI2OD-T2) as the reference. UV-vis data and cyclic-voltammetry are adopted to assess the effect of the donor modifi cation on the frontier energy levels and on the bandgap. Intra-molecular polaronic effects are accounted for by computing the internal reorganization energy with density functional theory (DFT) calculations. Finally electrons and holes transport is experimentally investigated in fitransistors (FETs), by measuring currentvoltage characteristics at variable temperatures. Overall we have identifi ed a regime where inter-molecular effects, such as the wavefunction overlap and the degree of energetic disorder, induced by the different donor group prevail over polaronic effects and are the leading factors in determining electrons mobility.

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.

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.

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.

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.

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.

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.