Organic nanomaterials are attracting a great deal of interest for use in flexible electronic applications such as logic circuits, displays and solar cells. These technologies have already demonstrated good performances, but flexible organic memories are yet to deliver on all their promise in terms of volatility, operational voltage, write/erase speed, as well as the number of distinct attainable levels. Here, we report a multilevel non-volatile flexible optical memory thin-film transistor based on a blend of a reference polymer semiconductor, namely poly(3-hexylthiophene), and a photochromic diarylethene, switched with ultraviolet and green light irradiation. A three-terminal device featuring over 256 (8 bit storage) distinct current levels was fabricated, the memory states of which could be switched with 3 ns laser pulses. We also report robustness over 70 write-erase cycles and non-volatility exceeding 500 days. The device was implemented on a flexible polyethylene terephthalate substrate, validating the concept for integration into wearable electronics and smart nanodevices.

The integration of photochromic molecules into semiconducting polymer matrices via blending has recently attracted a great deal of attention, as it provides the means to reversibly modulate the output signal of electronic devices by using light as a remote control. However, the structural and electronic interactions between photochromic molecules and semiconducting polymers is far from being fully understood. Here we perform a comparative investigation by combining two photochromic diarylethene moieties possessing similar energy levels yet different propensity to aggregate with five prototypical polymer semiconductors exhibiting different energy levels and structural order, ranging from amorphous to semicrystalline. Our in-depth photochemical, structural, morphological and electrical characterization reveals that the photoresponsive behavior of thin-film transistors (TFTs) including polymer/diarylethenes blends as the active layer is governed by a complex interplay between the relative position of the energy levels and the polymer matrix microstructure. By matching the energy levels and optimizing the molecular packing, high-performance optically switchable organic thin-film transistors were fabricated. These findings represent a major step forward in the fabrication of light-responsive organic devices.

Organic crystals are generated via the bottom-up self-assembly of molecular building blocks which are held together through weak noncovalent interactions. Although they revealed extraordinary charge transport characteristics, their labile nature represents a major drawback toward their integration in optoelectronic devices when the use of sophisticated patterning techniques is required. Here we have devised a radically new method to enable the use of photolithography directly on molecular crystals, with a spatial resolution below 300 nm, thereby allowing the precise wiring up of multiple crystals on demand. Two archetypal organic crystals, i.e., p-type 2,7-diphenyl[1]benzothieno[3,2- b][1]benzothiophene (Dph-BTBT) nanoflakes and n-type N, N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) nanowires, have been exploited as active materials to realize high-performance top-contact organic field-effect transistors (OFETs), inverter and p-n heterojunction photovoltaic devices supported on plastic substrate. The compatibility of our direct photolithography technique with organic molecular crystals is key for exploiting the full potential of organic electronics for sophisticated large-area devices and logic circuitries, thus paving the way toward novel applications in plastic (opto)electronics.

The review article covers the materials and techniques employed to fabricate organic-based inverter circuits and highlights their novel architectures, ground-breaking performances and potential applications.

Dedicated to Professor Franz Effenberger on the occasion of his 90th birthday 1. Introduction Covalently linked donor-acceptor (D-A) dyads, triads, and multiads have been extensively investigated in the context of photoinduced energy and charge transfer (CT) processes, which are fundamental for natural photosynthesis, but as well important for the function of organic solar cells. [1,2] The nature and length of the molecular spacer bridging D and A, flexible nonconjugated or rod-like conjugated, polar or nonpolar, play an important role for the various fundamental processes such as excitation and energy transfer, CT, charge separation, and recombination. [3] CT is also dependent on the environment, [4] which severely comes into play for the photoinduced elementary processes of molecular D-A systems in the solid state, a scenario, encountered in organic electronic devices. In this respect, in thin films, aggregation of the molecules into supramolecular assemblies to form photoactive nanostructures with well-segregated A and D domains and their orientation relative to the substrate play a major role for efficient organic solar cells. [5] As a consequence, the tailoring of molecular properties in D-A systems is an important aspect in the overall structural design for tuning and controlling distance-dependent CT, whereby intermolecular interactions and self-assembly determine charge separation in thin films. The understanding and Single-material organic solar cells (SMOSCs) promise several advantages with respect to prospective applications in printed large-area solar foils. Only one photoactive material has to be processed and the impressive thermal and photochemical long-term stability of the devices is achieved. Herein, a novel structural design of oligomeric donor-acceptor (D-A) dyads 1-3 is established, in which an oligothiophene donor and fullerene acceptor are covalently linked by a flexible spacer of variable length. Favorable optoelectronic, charge transport, and self-organization properties of the D-A dyads are the basis for reaching power conversion efficiencies up to 4.26% in SMOSCs. The dependence of photovoltaic and charge transport parameters in these ambipolar semiconductors on the specific molecular structure is investigated before and after post-treatment by solvent vapor annealing. The inner nanomorphology of the photoactive films of the dyads is analyzed with transmission electron microscopy (TEM) and grazingincidence wide-angle X-ray scattering (GIWAXS). Combined theoretical calculations result in a lamellar supramolecular order of the dyads with a D-A phase separation smaller than 2 nm. The molecular design and the precise distance between donor and acceptor moieties ensure the fundamental physical processes operative in organic solar cells and provide stabilization of D-A interfaces.

WSe2 is a layered ambipolar semiconductor enabling hole and electron transport, which renders it a suitable active component for logic circuitry. However, solid-state devices based on singleand bi-layer WSe2 typically exhibit unipolar transport and poor electrical performances when conventional SiO2 dielectric and Au electrodes are used. Here, we show that silane-containing functional molecules form ordered monolayers on the top of the WSe2 surface, thereby boosting its electrical performance in single-and bi-layer field-effect transistors. In particular, by employing SiO2 dielectric substrates and top Au electrodes, we measure unipolar mobility as high as µh = 150 cm 2 V-1 s-1 and µe = 17.9 cm 2 V-1 s-1 in WSe2 single-layer devices when ad hoc molecular monolayers are chosen. Additionally, by asymmetric double-side functionalization with two different molecules, we provide opposite polarity to the top and bottom layer of bi-layer WSe2, demonstrating nearly balanced ambipolarity at the bi-layer limit. Our results indicate that the controlled functionalization of the two sides of WSe2 mono-and bilayer flakes with highly ordered molecular monolayers offers the possibility to simultaneously achieve energy level engineering and defect functionalization, representing a path towards the deterministic control over charge transport in 2D materials.

2D materials (2DMs), which can be produced by exfoliating bulk crystals of layered materials, display unique optical and electrical properties, making them attractive components for a wide range of technological applications. This review describes the most recent developments in the production of high-quality 2DMs based inks using liquid-phase exfoliation (LPE), combined with the patterning approaches, highlighting convenient and effective methods for generating materials and films with controlled thicknesses down to the atomic scale. Different processing strategies that can be employed to deposit the produced inks as patterns and functional thin-films are introduced, by focusing on those that can be easily translated to the industrial scale such as coating, spraying, and various printing technologies. By providing insight into the multiscale analyses of numerous physical and chemical properties of these functional films and patterns, with a specific focus on their extraordinary electronic characteristics, this review offers the readers crucial information for a profound understanding of the fundamental properties of these patterned surfaces as the millstone toward the generation of novel multifunctional devices. Finally, the challenges and opportunities associated to the 2DMs' integration into working opto-electronic (nano) devices is discussed.

Electrochemically exfoliated graphene (EEG) possesses optical and electronic properties that are markedly different from those of the more explored graphene oxide in both its pristine and reduced forms. EEG also holds a unique advantage compared to other graphenes produced by exfoliation in liquid media: it can be obtained in large quantities in a short time. However, an in-depth understanding of the structure-properties relationship of this material is still lacking. In this work, we report physicochemical characterization of EEG combined with an investigation of the electronic properties of this material carried out both at the single flake level and on the films. Additionally, we use for the first time microwave irradiation to reduce the EEG and demonstrate that the oxygen functionalities are not the bottleneck for charge transport in EEG, which is rather hindered by the presence of structural defects within the basal plane.