From synthesis to device fabrication: elucidating the structural and electronic properties of C7-BTBT-C7

We report the polymorph investigation, crystallographic study and fabrication of organic field-effect transistors (OFETs) in solution-processed thin films of a prototypical organic semiconductor, i.e., 2,7-diheptylbenzo[b]benzo[4,5]thieno[2,3-d]thiophene (C7-BTBT-C7). We found that this molecule self-assembles solely into one type of stable crystal form, regardless of the experimental conditions employed when using conventional and non-conventional methods of crystallization. The integration of blends of C7-BTBT-C7 with polystyrene as active materials in OFETs fabricated using a solution shearing technique led to a field-effect mobility of 1.42 ± 0.45 cm2 V−1 s−1 in the saturation regime when a coating speed of 10 mm s−1 was employed. The intrinsic structural properties control the overlap of the frontier orbitals, thereby affecting the device performance. The interplay between the crystal packing, thin film morphology and uniformity and its impact on the device performance are reported.We acknowledge the Paul Scherrer Institut, Villigen, Switzerland, for the provision of synchrotron radiation beam time at the beamline MS-X04SA of the SLS (ID proposal 20201790). P. P., L. F., N. M., N. T., J. C., P. S., M. M. T., Y. G., E. M., and L. M., contributors of the paper, are the members of the UHMob project. This work has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant no. 811284. G. S. is a FNRS Research Associate (Belgian National Fund for Scientific Research). G. S. acknowledges financial support from the Francqui Foundation (Francqui Start-Up Grant). G. S. thanks the FNRS for financial support through the research project COHERENCE2 (no. F.4536.23). M. M. T. and L. F. also acknowledge MCIN through the project GENESIS PID2019 and the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S), and the Generalitat de Catalunya (2017-SGR-918).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Dinaphthotetrathienoacenes : synthesis, characterization, and applications in organic field-effect transistors

The charge transport properties of organic semiconductors are limited by dynamic disorder that tends to localize charges in organic crystals. It is the main hurdle to overcome in order to significantly increase charge carrier mobility. We propose an innovative design that combines a chemical structure based on sulfur-rich thienoacene with a solid-state herringbone packing and present the synthesis, physicochemical characterization and charge transport properties of two new thienoacenes bearing a central tetrathienyl core fused with two external naphthyl rings: DN4T and isoDN4T. Both compounds crystallize with a herringbone pattern structure and present transfer integrals ranging from 33 to 99 meV (for the former) within the herringbone plane of charge transport. Molecular dynamics simulations point towards an efficient resilience of the transfer integrals to the intermolecular sliding motion commonly responsible for strong variations of the electronic coupling in the crystal. Best device performances were reached with DN4T with hole mobility up to μ = 2.1 cm² V-1 s-1 in polycrystalline OFETs, showing the effectiveness of the electronic coupling enabled by the new aromatic core. These promising results pave the way to the design of high-performing materials based on this new thienoacene, notably through the introduction of alkyl side-chains

Auto-assemblage et caractérisation multi-échelle des surfaces et des interfaces

Understanding charge transport is the base for the development of functional optoelectronic devices based on organic semiconductors, namely small molecules or polymers. The thesis begins with a brief introduction on organic semiconductors focusing on the structural aspects that are key to understanding charge transport in organic electronics. Tied to this first chapter, a practical introduction concerning the different experimental techniques that have been employed throughout my work as a PhD student is presented in a comparative way. The three following chapters each refer to a particular functional device: 1 - Humidity sensors based on a hydrophilic small organic molecule, 2 - Optically switchable organic electrochemical transistors based on a polymer blend with a photochromic molecule, 3 - Study of the out-of-plane charge transport in organic field effect transistors based on small organic molecules.La compréhension du transport de charge est une condition indispensable du développement de dispositifs optoélectroniques fonctionnels basés sur des semi-conducteurs organiques (petites molécules ou polymères). La thèse commence par une brève introduction sur les semi-conducteurs organiques et les aspects structurels essentiels pour comprendre le transport de charge en électronique organique. Liée à ce premier chapitre, une introduction pratique concernant les différentes techniques expérimentales qui ont été utilisées dans la thèse est présentée de manière comparative. Les trois chapitres suivants se réfèrent chacun à un dispositif fonctionnel particulier : 1 - Capteurs d'humidité basés sur une petite molécule organique hydrophile, 2 - Transistors électrochimiques organiques optiquement commutables basés sur un mélange de polymères avec une molécule photochromique, 3 - Etude du transport de charge hors plan dans des transistors organiques basés sur de petites molécules organiques

Self-assembly and multiscale characterization of structures and interfaces

La compréhension du transport de charge est une condition indispensable du développement de dispositifs optoélectroniques fonctionnels basés sur des semi-conducteurs organiques (petites molécules ou polymères). La thèse commence par une brève introduction sur les semi-conducteurs organiques et les aspects structurels essentiels pour comprendre le transport de charge en électronique organique. Liée à ce premier chapitre, une introduction pratique concernant les différentes techniques expérimentales qui ont été utilisées dans la thèse est présentée de manière comparative. Les trois chapitres suivants se réfèrent chacun à un dispositif fonctionnel particulier : 1 - Capteurs d'humidité basés sur une petite molécule organique hydrophile, 2 - Transistors électrochimiques organiques optiquement commutables basés sur un mélange de polymères avec une molécule photochromique, 3 - Etude du transport de charge hors plan dans des transistors organiques basés sur de petites molécules organiques.Understanding charge transport is the base for the development of functional optoelectronic devices based on organic semiconductors, namely small molecules or polymers. The thesis begins with a brief introduction on organic semiconductors focusing on the structural aspects that are key to understanding charge transport in organic electronics. Tied to this first chapter, a practical introduction concerning the different experimental techniques that have been employed throughout my work as a PhD student is presented in a comparative way. The three following chapters each refer to a particular functional device: 1 - Humidity sensors based on a hydrophilic small organic molecule, 2 - Optically switchable organic electrochemical transistors based on a polymer blend with a photochromic molecule, 3 - Study of the out-of-plane charge transport in organic field effect transistors based on small organic molecules

Au (111) Surface Contamination in Ambient Conditions: Unravelling the Dynamics of the Work Function in Air

Gold is an inert noble metal displaying superior chemical stability that renders it a suitable component for the manufacturing of electrodes for various types of devices. Despite being widely employed, the variation of gold surface properties occurring upon the material's exposure to ambient conditions have been often disregarded. While it is well-known that the contamination of a metallic surface can have a dramatic impact on its properties, the process of contamination itself is poorly understood. Changes of the work function by fractions of an electron-volt are commonly observed in gold surfaces that are processed at ambient laboratory conditions, but an exhaustive comprehension and control of this phenomenon are still lacking. Here, a multiscale characterization of Au(111) surfaces aiming to unravel the surface dynamics underlying the air contamination is presented. The visualization of the adventitious carbon contamination on Au(111) surface by atomic force microscopy is key to rationalize the mechanisms of surface reorganization ruling the change of Au work function between 5.25 and 4.75 eV by solely changing the storage conditions. Such a huge variation must be taken into account when optimizing the Au surface for both controlling its fundamental surface and interfacial physical processes, as well as its functional applications

A photo-responsive organic electrochemical transistor

The design of novel organic electrochemical transistor (OECT) channel materials that can be controlled by a whole range of external stimuli is key towards the emergence of unprecedented technologies in bioelectronics. Like the established multiresponsive field-effect transistors, multiresponsive OECTs can in principle be realised via blending, by combining multiple components with each one imparting a specific function to the device. Here we report the first example of an optically switchable OECT which is capable of undergoing a reversible modulation of its ON current by up to 30% upon irradiation with UV and visible light. By investigating the electrical characteristics of the channel material, in conjunction with the electronic characterisation performed by a macroscopic Kelvin probe technique and photoemission yield spectroscopy in air, we gained distinct insight into the electrochemical doping process occurring within the blend upon light irradiation. Such a proof-of-concept work opens perspectives towards the implementation of complex neuromorphic operations and algorithms in OECTs

A robust vertical nanoscaffold for recyclable, paintable, and flexible light-emitting devices

International audienceOrganic light-emitting devices are key components for emerging opto- and nanoelectronics applications including health monitoring and smart displays. Here, we report a foldable inverted polymer light-emitting diode (iPLED) based on a self-suspended asymmetrical vertical nanoscaffold replacing the conventional sandwich-like structured LEDs. Our empty vertical-yet-open nanoscaffold exhibits excellent mechanical robustness, proven by unaltered leakage current when applying 1000 cycles of 40-kilopascal pressure loading/unloading, sonication, and folding, with the corresponding iPLEDs displaying a brightness as high as 2300 candela per square meter. By using photolithography and brush painting, arbitrary emitting patterns can be generated via a noninvasive and mask-free process with individual pixel resolution of 10 μm. Our vertical nanoscaffold iPLED can be supported on flexible polyimide foils and be recycled multiple times by washing and refilling with a different conjugated polymer capable of emitting light of different color. This technology combines the traits required for the next generation of high-resolution flexible displays and multifunctional optoelectronics

Molecular Doping of 2D Indium Selenide for Ultrahigh Performance and Low‐Power Consumption Broadband Photodetectors

International audienceTwo-dimensional (2D) photodetecting materials have shown superior performances over traditional materials (e.g., silicon, perylenes), which demonstrate low responsivity (R) (<1 AW−1), external quantum efficiency (EQE) (<100%), and limited detection bandwidth. Recently, 2D indium selenide (InSe) emerged as high-performance active material in field-effect transistors and photodetectors, whose fabrication required expensive and complex techniques. Here, it is shown for the first time how molecular functionalization with a common surfactant molecule (didodecyldimethylammonium bromide) (DDAB) represents a powerful strategy to boost the (opto)electronic performances of InSe yielding major performance enhancements in phototransistors, Schottky junctions, and van der Waals heterostructures via a lithography-compatible fabrication route. The functionalization can controllably dope and heal vacancies in InSe, resulting in ultrahigh field-effect mobility (10^3 cm2 V−1 s−1) and photoresponsivity (10^6 A W−1), breaking the record of non-graphene-contacted 2D photodetectors. The strategy towards the molecular doping of 2D photodetecting materials is efficient, practical, up-scalable, and operable with ultra-low power input, ultimately paving the way to next-generation 2D opto-electronics

2D MXene–Molecular Hybrid Additive for High-Performance Ambipolar Polymer Field-Effect Transistors and Logic Gates

International audienceMXenes are highly conductive layered materials that are attracting a great interest for high-performance opto-electronics, photonics, and energy applications.. Their non-covalent functionalization with ad hoc molecules enables the production of stable inks of 2D flakes to be processed in thin-films. Here, the formation of stable dispersions via the intercalation of Ti3C2Tx with didecyldimethyl ammonium bromide (DDAB) yielding Ti3C2Tx–DDAB, is demonstrated. Such functionalization modulates the properties of Ti3C2Tx, as evidenced by a 0.47 eV decrease of the work function. It is also shown that DDAB is a powerful n-dopant capable of enhancing electron mobility in conjugated polymers and 2D materials. When Ti3C2Tx–DDAB is blended with poly(diketopyrrolopyrrole-co-selenophene) [(PDPP–Se)], a simultaneous increase by 170% and 152% of the hole and electron field-effect mobilities, respectively, is observed, compared to the neat conjugated polymer, with values reaching 2.0 cm2 V−1 s−1. By exploiting the balanced ambipolar transport of the Ti3C2Tx–DDAB/PDPP–Se hybrid, complementary metal–oxide–semiconductor (CMOS) logic gates are fabricated that display well-centered trip points and good noise margin (64.6% for inverter). The results demonstrate that intercalant engineering represents an efficient strategy to tune the electronic properties of Ti3C2Tx yielding functionalized MXenes for polymer transistors with unprecedented performances and functions