Rapid progress on the fabrication of lead halide perovskite has led to the development of high performance optoelectronic devices, particularly in the field of solar cell technologies. This initial success has subsequently inspired investigations into layered 2D-halide perovskite structures, motivated in part by their good environmental stability, but more significantly by their intriguing fundamental photo-physics. They have recently been used to improve the photoresponsivity of monolayer transition metal dichalcogenides in hybrid heterostructures. In this paper, we report on the synthesis of the (PEA)2(MA)n−1PbnI3n+1 series (with n = 1, 2, 3) of 2D-halide perovskites, in order to develop a platform that provides ultra-thin layers for the fabrication of hybrid heterostructures. The crystal synthesis method and its basic structural and optical characterization are shown, highlighting the differences in the crystal synthesis processes. Furthermore, we explore the preparation of 2D halide perovskite ultra-thin flakes using the mechanical exfoliation method, and few-layer-areas of n = 1 member of the series are identified using atomic force microscopy. Finally, we study the deposition of thin and ultra-thin films using the spin coating technique to provide an alternative process to the exfoliation.

We analyzed the dynamic response to the light of organic field-effect transistors in bottom-gate/top-contact configuration. We fabricated Al/Al2O3/SAM/DNTT/Au phototransistors by evaporating thin film layers through shadow masks on flexible PEN (polyethylene naphthalate) substrates. The structure is composed of Al layer as the gate electrode, and Au used both for Source and Drain electrodes. DNTT (Dinaphtho[2,3-b: 2 ' , 3 ' -f]thieno[3,2-b]thiophene) is the active organic semiconductor layer and Al(2)O(3)is the dielectric material, chosen for the high value of the dielectric constant. SAM (self-assembled monolayer) was used to improve adhesion and interface properties between Al(2)O(3)and DNTT. The transistors, sensitive to blue light, were biased at low-voltage (Vgs and Vds from 0 to 3.5 V). Devices showed low Igs leakage currents, of the order of 5x10(-10) A, and a clear electro-optical response to the light. The maximum responsivity value was about 0.21 A/W in the static regime, while the lowest irradiance producing a measurable response in dynamic regime was 13 mu W/cm(2). Fast time components of the rise time of the light response for the analyzed phototransistors, of the order of few hundreds of ms, turned out to be among the fastest reported in literature for Al/AlOx/DNTT/Au organic phototransistor. These preliminary results are encouraging for developing organic phototransistors for visible light communication.

We report here on the synthesis and characterization of three novel isoindigo (II)-based organic semiconductors. The three dyes are based on an electron acceptor II core, symmetrically linked to two 3-octylthiophene donor rings; this common fragment, easily synthesizable, is end-capped with three different auxiliary electron acceptor groups, 1,1-Dicyanomethylene-3-Indanone (IDM) and two derivatives of it, bearing a bromine atom in position 5 or 6 of the IDM ring. The effect of the bromination and of the position of the bromine atom on the chemical–physical and electrical properties of the compounds were examined by means of thermal, optical, and electrochemical analysis; the electronic properties were investigated in more details at the DFT level. The novel compounds were used as active layers in organic field effect transistors: all the II derivatives were n-type unipolar semiconductors with electron mobilities ranging between 10−3 and 10−4 cm2/V∙s.

In the last 15 years, DNTT-based compounds have emerged as a new generation of hole-transporting (p-type) organic semiconductors with superior charge transport properties. Even today, indeed, this class of derivatives is under intense scrutiny for the achievement of high-performance field-effect transistors to be applied in the development of advanced organic circuitry. Here, we analyze the growth of evaporated C8-DNTT films on HMDS-treated SiO2 surfaces, highlighting the dependence of the related morphological and electrical properties on the substrate temperature (T-sub) held during film condensation. In this way, we identified a T-sub range able to guarantee high mobility values (larger than 2.5 cm(2) V-1 s(-1)) and morphological features being more compatible for the growth of additional layers on their top surfaces. This finding was the basic point to investigate the deposition of n-type PDIF-CN2 films on bottom C8-DNTT layers for the fabrication of heterojunction field-effect transistors. The electrical characterization of these devices, providing a shift of the threshold voltages and a minor sensitivity to the bias stress effect in comparison with the single-layer C8-DNTT counterparts, suggests the formation of a charge accumulation region at the organic/organic interface. This scenario was confirmed by additional electrical analyses performed on complementary double-layer structures.

The diketopyrrolopyrrole (DPP) unit represents one of the building blocks more widely employed in the field of organic electronics; in most of the reported DPP-based small molecules, this unit represents the electron acceptor core symmetrically coupled to donor moieties, and the solubility is guaranteed by functionalizing lactamic nitrogens with long and branched alkyl tails. In this paper, we explored the possibility of modulating the solubility by realizing asymmetric DPP derivatives, where the molecular structure is extended in just one direction. Four novel derivatives have been prepared, characterized by a common dithyenil-DPP fragment and functionalized on one side by a thiophene unit linked to different auxiliary electron acceptor groups. As compared to previously reported symmetric analogs, the novel dyes showed an increased solubility in chloroform and proved to be soluble in THF as well. The novel dyes underwent a thorough optical and electrochemical characterization. Electronic properties were studied at the DFT levels. All the dyes were used as active layers in organic field effect transistors, showing balanced charge transport properties.

Eight novel isoindigo (iI) based small molecules have been successfully synthesized. Their molecular structure consists of an electron acceptor iI core symmetrically linked to two furan (F-series) or thiophene (T-series) rings and end-functionalized with four auxiliary electron withdrawing groups (EWGs) of different strength. The optical properties of the dyes in chloroform solution are uniformly modulated by the terminal EWGs so that absorption maxima wavelengths move to higher values as the EWG's strength increases. A computational (DFT level) analysis provides useful information on the electronic structure of the dyes: upon photoexcitation, the electron density moves away from iI core or towards it according to the different EWG considered. Optical analysis is performed on dyes' thin films as well and a general broadening and red shift of the absorption is observed as compared to the behaviour in solution; all the dye's thin films are characterized by narrow bandgaps (<1.60 eV) and diffused absorption of most of the visible light. From XRD diffraction analysis performed on drop casted films of the dyes, it is possible to observe a lamellar organization in the solid phase with lamellae width clearly linked to the nature of the terminal EWG. HOMO and LUMO energies of the dyes, determined by cyclic voltammetry analysis performed on dyes' thin films, show very stable LUMO and HOMO energy levels, suggesting, respectively, a tendency to act as n-type semiconductors and a very good thermo-oxidative stability. The dyes are finally employed as active layers in organic field-effect transistors to study their charge transport properties: all of them display unipolar n-type charge transport with the presence of the electron accumulation phenomenon under the application of positive gate voltages. For one of the dye, mobility (mu) up to 10-2 cm2/V center dot s was measured, whereas values around 10-3 cm2/V center dot s were found for the others.

The effect of chalcogen bonding interaction led to the interesting crystal packing and coordination geometry of copper(II) in novel organic-inorganic hybrids. The reactions of organic bridging ligands 1,2,5-benzothiadiazole (btd) and 1,2,5-benzoselenazadiazole (bsed) with CuCl2 and CuBr2 by slow diffusion of two miscible solvents afforded three isomorphic 2D-network polymers, [CuCl2 (btd)](r) (1), [CuBr2(btd)](n) (2), and (CuCl2(bsed)](n) (3), and one molecular hybrid, CuBr2(bsed)(2) (4). The crystal structures of these novel hybrids were determined by single X-ray crystallography. The three isomorphic hybrids consist of 2-D sheets in which (Cu(mu-X)(2)](n) infinite linear chains running along the a axis are linked through N-coordinated molecules of btd and bsed along the b axis. On the other hand, the crystal packing of 4 is strongly influenced by the presence of the (Se center dot center dot center dot N](2) supramolecular synthon and Se- short interactions, all based on chalcogen bonding, that link the dimeric complex molecules into two-dimensional arrays parallel to the ac plane.

Electronic devices relying on the combination of different conjugated organic materials are considerably appealing for their potential use in many applications such as photovoltaics, light emission, and digital/analog circuitry. In this study, the electrical response of field-effect transistors achieved through the evaporation of picene and PDIF-CN2 molecules, two well-known organic semiconductors with remarkable charge transport properties, was investigated. With the main goal to get a balanced ambipolar response, various device configurations bearing double-layer, triple-layer, and codeposited active channels were analyzed. The most suitable choices for the layer deposition processes, the related characteristic parameters, and the electrode position were identified to this purpose. In this way, ambipolar organic field-effect transistors exhibiting balanced mobility values exceeding 0.1 cm(2) V-1 s(-1) for both electrons and holes were obtained. These experimental results highlight also how the combination between picene and PDIF-CN2 layers allows tuning the threshold voltages of the p-type response. Scanning Kelvin probe microscopy (SKPM) images acquired on picene/PDIF-CN2 heterojunctions suggest the presence of an interface dipole between the two organic layers. This feature is related to the partial accumulation of space charge at the interface being enhanced when the electrons are depleted in the underlayer.

Four novel diketopyrrolopyrrole (DPP) derivatives have been synthesized and characterized: the dyes are based on a DPP electron acceptor core symmetrically functionalized with donor bi-furyl moieties and end capped with four different auxiliary electron-acceptor groups. Because of the alternation along the molecular backbone of electron acceptor and donor groups, all the dyes are characterized by optical absorption maxima approaching or exceeding 700 nm. In the solid state, this optical behavior determines for all the dyes a very low optical bandgap ranging from 1.57 eV to 1.29 eV, while electrochemical characterization shows a clear dependence of the LUMO energies on the strength of the auxiliary electron-acceptor groups. All the dyes are characterized by stable LUMO energies suitable for their application as n-type semiconductors. Organic field-effect transistors based on the reported compounds display actually n-type behavior and, in three cases, a very interesting and balanced ambipolar charge transport behavior was moreover observed.

Correction for ‘Space-charge accumulation and band bending at conductive P3HT/PDIF-CN2 interfaces investigated by scanning-Kelvin probe microscopy’ by Federico Chianese et al., J. Mater. Chem. C, 2021, DOI: 10.1039/d1tc04840f.

Charge transfer processes and space charge accumulation phenomena are fundamental topics concerning the technological applications of organic heterointerfaces.

Correction for 'Space-charge accumulation and band bending at conductive P3HT/PDIF-CN2 interfaces investigated by scanning-Kelvin probe microscopy' by Federico Chianese et al., J. Mater. Chem. C, 2021, DOI: 10.1039/d1tc04840f.

The new frontier for spintronics is the realization of devices in which the spin can be controlled by electric fields. Multiferroics, materials exhibiting strong interplay between spin and orbital degrees of freedom, are candidates for the realization of such a paradigm. In this work, we study the magnetoelectric coupling in epitaxial BiMnO_3 thin films which exhibit a large saturation magnetization. By combining X-ray absorption spectroscopy data and theoretical modeling, we demonstrate that BiMnO_3 thin films have an improper magnetoelectric behavior, characterized by competing antiferromagnetic and ferromagnetic correlations. As a consequence, we show that in these materials the Mn-3d orbital and magnetic orders can be tuned via the ferroelectric polarization, opening perspectives for the realization of novel spintronic devices.

Contact effects occurring at organic-semiconductor/graphene-electrode interfaces are directly analyzed in unprecedented detail in n-type OFETs via scanning Kelvin probe force microscopy.

In the last few decades there has been growing interest in studying Mott insulators due to their ability to host novel quantum phenomena when the system is perturbed by various stimuli. Recently the antiferromagnetic Mott insulator Ca2RuO4 has received considerable attention due to superconductivity and metal-insulator transition induced by pressure and electric field respectively. Here we report the details of the synthesis of a novel systems made by Ca2RuO4 and Ru metal inclusions. Samples with lamellae, rods and globules of Ru embedded in Ca2RuO4 single crystals were successfully synthesized by floating zone technique with an excess of Ru in the starting material. The morphology and structural studies revealed a randomly orientated distribution of the shining Ru inclusions with an average size of few microns. Magnetic and electrical properties showed a behavior similar to the one observed in single crystals with the only Ca2RuO4 phase. We also measured the current-voltage characteristics of the whole Ca2RuO4–Ru system and of a single Ru rod by electric micro-contacts estimating the room temperature resistivity of the Ru embedded inclusions. This study shows that physical properties of Ca2RuO4–Ru metal system are related to the properties of the constituent phases, similarly to the case of Sr2RuO4–Ru metal.

Core-cyanated perylene diimide (PDI_CY) derivatives are molecular compounds exhibiting an uncommon combination of appealing properties, including remarkable oxidative stability, high electron affinities, and excellent self-assembling properties. Such features made these compounds the subject of study for several research groups aimed at developing electron-transporting (n-type) devices with superior charge transport performances. After about fifteen years since the first report, field-effect transistors based on PDI_CY thin films are still intensely investigated by the scientific community for the attainment of n-type devices that are able to balance the performances of the best p-type ones. In this review, we summarize the main results achieved by our group in the fabrication and characterization of transistors based on PDI8-CN2 and PDIF-CN2 molecules, undoubtedly the most renowned compounds of the PDI_CY family. Our attention was mainly focused on the electrical properties, both at the micro and nanoscale, of PDI8-CN2 and PDIF-CN2 films deposited using different evaporation techniques. Specific topics, such as the contact resistance phenomenon, the bias stress effect, and the operation in liquid environment, have been also analyzed.

In this paper, we report on the fabrication of n-type bottom-gate bottom-contact transistors, based on evaporated films of a perylene diimide derivative (PDI8-CN2), displaying electrical performances comparable to their top-contact counterparts. By combining very thin (20 nm) electrodes and a cleaning process with oxygen plasma, indeed, bottom-contact devices with maximum mobility approaching 0.2 cm2/V s and a contact resistance lower than 35 kΩ cm at low VDS values have been achieved. AFM analyses reveal that the improved electrical responses are accompanied by the optimized PDI8-CN2 film morphology which, very significantly, exhibits similar features on the gold and dielectric (i.e., SiO2) surfaces.

Here, electron-transporting semiconducting organic channels made of N,N′-1H, 1H-perfluorobutyl dicyanoperylenecarboxydiimmide (PDIF-CN2) molecules were thermally evaporated on flexible polyethylene-naphtalate (PEN) plastic substrates equipped with gold (Au) electrodes. This multilayer structure represents the basic component for the fabrication of staggered top-gate n-type organic thin-film transistors (OTFTs) to be completed with the addition of a polymeric dielectric layer and an aluminum gate electrode. PEN substrate was treated with hexamethyldisilazane (HMDS) in order to make it more hydrophobic. Indeed, the hydrophobized surface of the plastic substrate was shown to induce a more ordered supramolecular structure of the semiconductor layer during the evaporation process. The hybrid organic/inorganic formally trilayer non-passivated OTFT structure was successfully profiled in a single run through ToF-SIMS depth profiling experiments with low energy cesium ions. High mass molecular fragment ions were obtained and used as indicators of interfaces, leading to an increase of information on molecular specificity. The HMDS surface modification was clearly detected and spatially located. Finally, a chemometric approach was also adopted to evaluate depth profiling data. In particular, principal component analysis (PCA) and K-means algorithm were tested as innovative method for the identification of molecular fragments useful for the OTFT multi-layer structure characterization and the determination of the number of OTFT layers, respectively.

The impact of the processing method in controlling the polymorphism and field-effect charge mobility of 2,3-thienoimide-based oligothiophenes semiconductors was investigated.