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Hybrid quantum wells are electronic structures where charge carriers are confined along stacked inorganic planes, separated by insulating organic moieties. 2D quantum-confined hybrid materials are of great interest from a solid-state physics standpoint because of the rich many-body phenomena they host, their tunability and easy synthesis, allowing the creation of material libraries. In addition, from a technological point of view, 2D hybrids are promising candidates for efficient, tunable, low-cost materials impacting a broad range of optoelectronic devices. Different approaches and materials have, therefore, been investigated, with the notable example of 2D metal halide hybrid perovskites. Despite the remarkable properties of such materials, the presence of toxic elements like lead is not desirable in applications and their ionic lattices may represent a limiting factor for stability under operating conditions. Therefore, non-ionic 2D materials made with non-toxic elements are preferable. In order to expand the library of possible hybrid quantum well materials, herein, we consider an alternative platform based on non-toxic, self-assembled, metal-organic chalcogenides. While the optical properties have been recently explored and some unique excitonic characters highlighted, photo-generation of carriers and their transport in these lamellar inorganic/organic nanostructures and critical optoelectronic aspects remain totally unexplored. We hereby report the first investigation on the electrical properties of the air-stable [AgSePh]∞ 2D coordination polymer in the form of nanocrystal (NC) films readily synthesized in situ and at low temperature, compatible with flexible plastic substrates. The wavelength-dependent photo-response of the NC films suggests the possible use of this material as a near-UV photodetector. We therefore built a lateral photo-detector, achieving a sensitivity of 0.8 A W-1 at 370 nm, thanks to a photoconduction mechanism, and a cut-off frequency of ∼400 Hz, and validated its reliability as an air-stable UV detector on flexible substrates.

The use of printing technologies is widely recognized to be a major advantage for the deployment of large-area organic electronics and there is still plenty of room for exploring new strategies to exploit printing of solution processable conductors and semiconductors. In this paper, we show for the first time how an additive layer-by-layer deposition, achieved through inkjet printing, enables the fabrication of broadband organic photodetectors with a flat responsivity spectrum extending to the near-infrared (NIR). The use of narrow bandgap polymers enables light detection up to 1.1 μm. By controlling the photoactive layer thickness in a range between 150 nm and 4 μm, we could filter the contribution from UV and Vis absorption to the photocurrent, while keeping light detection in the NIR. The visible detection efficiency decreases of a 70% at 425 nm for thicknesses going from 250 nm up to 2 μm, while the NIR detection decreases only of 31% at 950 nm, and increases of 26% at 1020 nm. This photoactive layer thickness dependent UV–vis optical filtering enables the control over the shape of the responsivity spectra.

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.

This chapter introduces basic concepts of organic electronics, with the aim to provide an accessible, phenomenological introduction to the more advanced content discussed in detail in the following chapters. First, we deal with the basic optoelectronic properties of organic semiconductors, with emphasis on charge carrier transport phenomena, and then we discuss how to change the charge carrier concentration, by means of photogeneration and capacitive coupling phenomena. After addressing the subject of metal/semiconductor interfaces, we show how to exploit these physical properties in order to realize the main building blocks of electronics, such as (photo)-diodes and field-effect transistors. Purpose of this chapter is to offer a critical view, with a clear understanding of pros and cons of organic electronics, of the main differences with respect to traditional, inorganic electronics, and of the inherent trade-off between processability and performances.

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.

The increasing diffusion of portable and wearable technologies results in a growing interest in electronic devices having features such as flexibility, lightness-in-weight, transparency, and wireless operation. Organic electronics is proposed as a potential candidate to fulfill such needs, in particular targeting pervasive radio-frequency (RF) applications. Still, limitations in terms of device performances at RF, particularly severe when large-area and scalable fabrication techniques are employed, have largely precluded the achievement of such an appealing scenario. In this work, the rectification of an electromagnetic wave at 13.56 MHz with a fully inkjet printed polymer diode is demonstrated. The rectifier, a key enabling component of future pervasive wireless systems, is fabricated through scalable large-area methods on plastic. To provide a proof-of-principle demonstration of its future applicability, its adoption in powering a printed integrated polymer circuit is presented. The possibility of harvesting electrical power from RF waves and delivering it to a cheap flexible substrate through a simple printed circuitry paves the way to a plethora of appealing distributed electronic applications.

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.

In Africa et al. (Sci Rep 7(1):3803, 2017) a step-by-step procedure was presented that enables to determine the density of states width, the carrier mobility and the injection barrier height of an OTFT! structure by fitting data from simple measurements to suitable numerical simulations. At each step of the procedure only one parameter value is determined, thus highly simplifying the fitting procedure and enhancing its robustness. In this study we apply such procedure to p-type organic polymers. A very satisfactory fitting of experimental measurements is obtained, and physically meaningful values for the aforementioned parameters are extracted thus further confirming the soundness of the parameter extraction method.

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.

The reduction of dark current is required to enhance the signal-to-noise ratio and decrease the power consumption in photodetectors. This is typically achieved by introducing additional functional layers to suppress carrier injection, a task that proves to be challenging especially in printed devices. Here we report on the successful reduction of dark current below 100 nA cm −2 (at −1 V bias) in an inkjet printed photodetector by the insertion of an electron blocking layer based on poly[3-(3,5-di-tert-butyl-4-methoxyphenyl)-thiophene], while preserving a high quantum yield. Furthermore, the electron blocking layer strongly increases the surface energy of the hydrophobic photoactive layer, therefore simplifying the printing of transparent top electrodes from water based formulations without the addition of surfactants.

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]

Bulk-heterojunction based organic photodetectors are fabricated by means of drop-on-demand inkjet printing with vertical topology, inverted structure, and small footprint (about 100 μm x 100 μm). Due to optimization of the deposition technique, an external quantum efficiency in excess of 80% at 525 nm and a -3dB bandwidth of a few tens of kHz is achieved.

Deformable mirrors are key optical elements in modern astronomical telescopes and instrumentation both for active and adaptive optical systems. Different technological approaches have been exploited for the realization of the deformable mirrors, especially for adaptive optics devices. A new approach is here presented, namely the photo-controlled deformable mirrors, where the size and density of actuators is set by an illumination pattern projected on the back side of a photoconductor. The working principle and an electric model are presented highlighting the features of the material that affect the performances of the mirror in terms of dynamic range and response time. Based on these results, a prototype exploiting ZnSe as photoconductor is reported together with its characterization.

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.

Organic photodetectors represent an emerging field of organic electronics. The peculiarities of organic semiconductors make them attractive for various, innovative and disruptive optoelectronic applications. By means of chemical tailoring they can be tuned to absorb light from ultraviolet to near-infrared. They are strong absorbers, which means that organic optoelectronics is a thin-film technology, amenable to yield lightweight and even non-planar devices. In addition the processing thermal budget is limited, and many materials can be processed from solution: as a consequence devices can be realized in principle on any substrate, large areas can be addressed and high throughput techniques, adapted from graphical arts, can be employed as convenient deposition protocols. We resume the basics of organic semiconductors, focusing on the physics of charge photogeneration and illustrating the main processing options, and we discuss the peculiar regimes of device operation, related to the fact that organic semiconductors are intrinsic and low-mobility materials. Notable realizations from the scientific literature are reported and discussed, classified according to their photoaction spectrum. Emphasis is given to devices completely developed by means of scalable, solution-based processes. Finally organic optoelectronics systems, addressing integrated transreceivers and imagers are reviewed. Very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, in some cases approaching and rivaling inorganic-based commercial devices. Even though the simultaneous optimization of all the relevant parameters is demonstrated in a limited number of papers, it clearly emerges that real applications are within reach for this technology.

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.

The paper presents an organic-based photodiode coupled to a CsI(Tl) scintillator to realize an X-ray detector. A suitable blend of an indolic squaraine derivative and of fullerene derivative has been used for the photodiode, thus allowing external quantum efficiency in excess of 10% at a wavelength of 570 nm, well matching the scintillator output spectrum. Thanks to the additional deposition of a 15 nm thin layer of a suitable low electron affinity polymer, carriers injection from the metal into the organic semiconductor has been suppressed, and dark current density as low as 1 nA/cm 2 has been obtained, which is comparable to standard Si-based photodiodes. By using a collimated X-ray beam impinging onto the scintillator mounted over the photodiode we have been able to measure current variations in the order of 150 pA on a dark current floor of less than 50 pA when operating the X-ray tube in switching mode, thus proving the feasibility of indirect X-ray detection by means of organic semiconductors. © 2012 IEEE.

In search for an organic material suitable for the detection of near-infrared electromagnetic radiation and at the same time capable of air stable operation of related devices, so to address the many applications envisaged with this technology (remote control, chemical/biological sensing, optical communication, spectroscopic and medical instruments), we explore the performance of a blend of hydrazone end-capped symmetric squaraines and phenyl C61 butyric acid methyl ester. We succeed in developing air stable solution-processed devices with external quantum efficiency in the NIR as high as 3.5% and response times of few hundreds of nanoseconds. Essential to these achievements has been a detailed characterization of the devices performed by correlating the optoelectronic performances to the morphology of the layers (extracted from AFM measurements) and to the charge carrier mobility (extracted from transistor structures), enabling their optimization at the chemical level, by tailoring the squaraine substitution pattern, and at the device level, by tuning the blend composition. We show that a good balance between holes and electrons mobility is essential for high EQE and fast response speed, and that a smooth morphology is mandatory to achieve long term air stability and operability with no need for encapsulation. © 2009 Elsevier B.V. All rights reserved.

A solid-state memory based on a hindered phenol substituted bithiophene is reported, showing conductance switching behaviour between three discrete states among which it is possible to cycle repeatedly on the basis of three characteristic threshold voltages. The experimental measurements show that the addressing of the three states is independent of the programming time, that the retention time for each state is longer than 15 h and that the devices endure current–voltage cycles well in excess of 50. Considerations based on density functional theory calculations are made to provide hints on the mechanism behind this memory effect.

We studied organic thin film transistors based on poly-(3-hexylthiophene) having as gate dielectric Al 2 O 3 , which was prepared by atomic layer deposition (ALD) technique, that provides films with very good electrical properties, roughness below 1 nm and compatibility with virtually any type of substrate, including polymeric ones. High-k gate oxides such as Al 2 O 3 are advantageous since they enable a reduction of operating voltages, but when used in conjunction with organic semiconductors, they induce worse transport properties if compared to low-k dielectrics. To address this issue, we focused on the interface between the gate dielectric and the active material and we explored the effects of functionalizing the Al 2 O 3 surface by means of self-assembled monolayers (SAM). We studied and compared a set of SAMs differing in the ligand groups and in the chain lengths. We show that the most important parameter is the SAM chain length, the longer SAM being more effective in giving better charge carrier mobility. The microscopical origins of this finding are analyzed exploiting and comparing the dependence of the mobility on the gate voltage in the transistors based on the variously functionalized Al 2 O 3 . With n-octadecyltrichlorosilane (OTS) the mobility reaches the value of 10−2 cm2/V s, comparable to the mobility on transistors with properly functionalized SiO 2 gate dielectric.

The strong sensitivity of organic/polymeric semiconductors to the exposure to O-2 and H2O atmospheres makes the use of capping layers mandatory for the realization of stable devices based on such materials. In this paper we explore the realization of inorganic capping layers by atomic layer deposition (ALD) that provides smooth and pinhole-free films with a great potential as passivation layer for organic based devices. We show that the deposition of Al2O3 on transistors based on poly-3 hexyltiophene (P3HT) allows to obtain air stable devices. Whereas the growth of Al2O3 directly on the P3HT layer leads to a rough interface and significant intermixing between the oxide and the polymer, which results in a deterioration of transistor performances, an interlayer of a poly-alcohol such as poly-vinylphenot interposed between the Al2O3 and the P3HT gives a well defined Al2O3/polymer interface without degradation of the hole mobility. Transistors capped with Al2O3/PVP are very stable in air, with no appreciable differences in the electrical characteristics when measured in vacuum or in air. In addition no significant degradation of the transistors electrical properties was detected even after one month of air exposure. (c) 2007 Elsevier B.V. All rights reserved.

We report on the first example of a light signal photodetecting device based on the new class of neutral bis(1,2-dithiolene) complexes [M(R-dmet) 2 ], whose ligand is intermediate between those belonging to the classes dmit 2− and R,R′-timdt 2− (dmit 2− = 2-thioxo-1,3-dithiole-4,5-dithiolato; R,R′-timdt 2− = N , N ′-disubstituted 2-thioxoimidazoline-4,5-dithiolato; R-dmet 2− = N -substituted 2-thioxothiazoline-4,5-dithiolato). The device, hosting the active material [Ni(Et-dmet) 2 ] ( 1 ) casted on a quartz substrate, acts as a photodetector responsive in a wide spectral range, reaching the appealing near-IR region, and features the highest efficiency values as compared to those based on the dithiolene complexes [Ni(Me,Non-timdt) 2 ] ( 2 ) and [Pt(Et,Pent-timdt) 2 ] ( 3 ).

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.

We report on the electrochromic behavior of a dinuclear ruthenium complex, which provides high environmental stability together with an intense absorption maximum at 1237 nm in solution in its +3 oxidation state. To verify its optoelectronic properties, we used this complex as the photoactive material in a planar photodetector prototype for near-infrared light pulses, succeeding in the detection of a train of light pulses at a wavelength of 1280 nm.

We report on the detection of near infrared (NIR) radiation in the range 900–1600 nm by means of coordination complexes such as [M(R t R’timdt) 2 ] x− (M = Ni, Pd, Pt; R,R’timdt = formally monoreduced disubstituted imidazolidine-2,4,5-trithione; x = 0, 1), and [{Ru(bipy) 2 } 2 (μ-L)] x+ (H 3 L = 9-phenyl-2,3,7-trihydroxy-6-fluorone; x = 1, 3). By exploiting these stable coordination complexes absorbing in the visible and NIR region, the poor stability to air and light usually found in low band-gap organic semiconductors can be overcome. [M(R,R’timdt) 2 ] and [{Ru(bipy) 2 } 2 (μ-L)] 1+ complexes show π-π* transitions in the range 700-1000 nm, which can be bathochromically shifted by changing their oxidation state. Taking profit of this feature, we prepared photodetecting devices operating in the NIR region up to 1600 nm, thus reaching the appealing spectral range of telecommunications. NIR quantum efficiencies of these preliminary photodetectors, made by simple casting from solution, are comparable to those in the visible of most devices based on pristine organic materials. We succeeded in detecting train pulses with a repetition frequency of about 200 kHz at 960 nm and 80 kHz at 1450 nm, to our knowledge an unprecedented result that demonstrates the possibility to enter the NIR region by organic molecular-based devices.

In the framework of one-carrier space-charge-limited currents, exact equations are derived for the evaluation of arbitrary field-dependent mobility. A differential method, which simply needs the first and second derivatives of measured current–voltage (I–V) curves, is presented for a trap-free case. Extension to a mixed case of exponentially distributed traps and field-dependent mobility is also outlined. In addition, a tool based on a combination of capacitance–voltage and I–V measurements was developed to certify the applicability of this method by checking whether the device tested is actually in the space-charge-limited regime. The extraction of the mobility from measurements can be a valuable tool for use in the theory: theoretical predictions of mobility field dependence can be easily compared to experimental results, thus permitting improvement of the models and fostering the development of transport theories. This method can also be of particular relevance for organic semiconductors whose field-dependent mobility has recently attracted so much theoretical and experimental work.

The unusual NIR-photoconducting properties of [M(Et,Pent-timdt)2] neutral dithiolenes (M=Ni, Pd, Pt; Et,Pent-timdt=monoreduced N-ethyl,N′-pentylimidazolidine-2,4,5-trithione) have been investigated with the aim of developing wavelength-selective air-stable photodetectors. In addition, the ps time-resolved dynamics of the absorption saturation has been studied on the Pd-complex by means of pump–probe experiments.

Noise spectroscopy is presented to be a powerful tool to investigate the current flowing in organic light emitting diodes (oLEDs) with high sensitivity. Measurements can be performed over the whole bias range of interest, from reverse bias up to high values of forward bias voltage. From these measurements one can gain insight into the microscopic conduction processes dominating the device current and obtain valuable information for improved device modeling. In particular it is shown that the low frequency power spectrum of the tested oLEDs has a power law dependence around 1/f 1.3 almost irrespective of device characteristics and of measurement conditions. Additionally, noise spectra are also proposed as a means to sense the initial state and the growth of degradation phenomena in these devices. The onset of degradation is shown to be signaled by current spikes that reflect on a net increase of the white noise component of about three orders of magnitude in the power spectral density, when degradation is just hardly beginning to be visible as dark spots on the emitting surface.

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.