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The deposition of organic semiconductors (OSCs) using solution shearing deposition techniques is highly appealing for device implementation. However, when using high deposition speeds, it is necessary to use very concentrated OSC solutions. The OSCs based on the family of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) have been shown to be excellent OSCs due to their high mobility and stability. However, their limited solubility hinders the processing of these materials at high speed. Here, we report the conditions to process alkylated DNTT and the S-shaped π-core derivative S-DNTT by bar-assisted meniscus shearing (BAMS) at high speed (i.e., 10 mm s-1). In all the cases, homogeneous thin films were successfully prepared, although we found that the gain in solubility achieved with the S-DNTT derivative strongly facilitated solution processing, achieving a field-effect mobility of 2.1 cm2 V-1 s-1, which is two orders of magnitude higher than the mobility found for the less soluble linear derivatives., This work was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 811284 (UHMob), the Spanish Ministry (project GENESIS PID2019-111682RB-I00 and through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S)) and the Generalitat de Catalunya (2017-SGR-918). L. F. and J. L. are enrolled in the UAB Materials Science PhD program. J. L. acknowledges the Scholarship from the Chinese Council. 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). Y. H. G. is thankful to FNRS for financial support through research projects Pi-Fast (No T.0072.18), Pi-Chir (No T.0094.22), and DIFFRA (No U.G001.19)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Organic semiconductors with distinct molecular properties and large carrier mobilities are constantly developed in attempt to produce highly-efficient electronic materials. Recently, designer molecules with unique structural modifications have been expressly developed to suppress molecular motions in the solid state that arise from low-energy phonon modes, which uniquely limit carrier mobilities through electron-phonon coupling. However, such low-frequency vibrational dynamics often involve complex molecular dynamics, making comprehension of the underlying electronic origins of electron-phonon coupling difficult. In this work, we first generate a mode-resolved picture of electron-phonon coupling in a series of materials that were specifically designed to suppress detrimental vibrational effects. From this foundation, we develop a method based on the crystalline orbital Hamiltonian population analyses to resolve the origins -- down to the single atomic-orbital scale -- of surprisingly large electron-phonon coupling constants of particular vibrations, explicitly detailing the manner in which the intermolecular wavefunction overlap is perturbed. Overall, this approach provides a comprehensive explanation into the unexpected effects of less-commonly studied molecular vibrations, revealing new aspects of molecular design that should be considered for creating improved organic semiconducting materials.

Synthesis, polymorph investigation, crystallographic study, and fabrication of OFETs in solution-processed thin films of C7-BTBT-C7.

The deposition of organic semiconductors (OSCs) using solution shearing deposition techniques is highly appealing for device implementation. However, when using high deposition speeds, it is necessary to use very concentrated OSC solutions. The OSCs based on the family of dinaphtho[2,3

The lattice dynamics of organic semiconducting crystals has a significant role in determining their electronic and mechanical properties. A common technique to control these macroscopic properties is chemically modifying the molecular structure. These modifications are known to change the molecular packing, but their effect on the lattice dynamics is relatively unexplored though it can be equally important to their performance at finite temperatures. Therefore, we investigate how chemical modifications to a core [1]benzothieno[3,2-b]benzothiophene (BTBT) semiconducting crystal affect the evolution of the crystal structural dynamics with temperature. Our study combines temperature-dependent polarization-orientation (PO) low-frequency Raman measurements with first-principles calculations and single-crystal XRD measurements. We show that the chemical modifications can indeed suppress expressions of vibrational anharmonicity in the lattice dynamics. Specifically, we detect in BTBT a gradual change in the PO Raman response with temperature, indicating a unique expression of anharmonicity. This anharmonic expression is suppressed in all examined chemically modified crystals (ditBu-BTBT and diC8-BTBT, diPh-BTBT, and DNTT). Our findings indicate that π-conjugated chemical modifications suppress anharmonic effects more effectively than alkyl chains.

Many molecular crystals (approximately one third) grow as twisted, helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance, charge-transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a monocomponent organic semiconductor, 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT), that forms twisted crystals with varied helicoidal pitches and makes possible a correlation of twist strength with carrier mobility. Films are analyzed by X-ray scattering and Mueller matrix polarimetry to characterize the microscale organization of the polycrystalline ensembles. Carrier mobilities of organic field-effect transistors are five times higher when the crystals are grown with the smallest pitches (most twisted), compared to those with the largest pitches, along the fiber elongation direction. A tenfold increase is observed along the perpendicular direction. Simulation of electrical potential based on scanning electron microscopy images and density functional theory suggests that the twisting-enhanced mobility is mainly controlled by the fiber organization in the film. A greater number of tightly packed twisted fibers separated by numerous smaller gaps permit better charge transport over the film surface compared to fewer big crystallites separated by larger gaps.

We study by scanning thermal microscopy the nanoscale thermal conductance of films (40-400 nm thick) of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8). We demonstrate that the out-of-plane thermal conductivity is significant along the interlayer direction, larger for BTBT (0.63 ± 0.12 W m-1 K-1) compared to C8-BTBT-C8 (0.25 ± 0.13 W m-1 K-1). These results are supported by molecular dynamics calculations (approach to equilibrium molecular dynamics method) performed on the corresponding molecular crystals. The calculations point to significant thermal conductivity (3D-like) values along the 3 crystalline directions, with anisotropy factors between the crystalline directions below 1.8 for BTBT and below 2.8 for C8-BTBT-C8, in deep contrast with the charge transport properties featuring a two-dimensional character for these materials. In agreement with the experiments, the calculations yield larger values in BTBT compared to C8-BTBT-C8 (0.6-1.3 W m-1 K-1versus 0.3-0.7 W m-1 K-1, respectively). The weak thickness dependence of the nanoscale thermal resistance is in agreement with a simple analytical model. This journal is, M. G., D. G., S. L. and D. V. thank the ANR for financial support (ANR-16-CE05-0029). Y. G. is thankful to the Belgian National Fund for Scientific Research (FNRS) for financial support through research projects BTBT (# 2.4565.11), Phasetrans (# T.0058.14), Pi-Fast (# T.0072.18), 2D to 3D (# 30489208), and DIFFRA (# U.G001.19). Financial supports from the French Community of Belgian (ARC # 20061) is also acknowledged. G. S. acknowledges postdoctoral fellowship support from the FNRS. The work in the Laboratory for Chemistry of Novel Materials was supported by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under grant # 2.5020.11. J.C. and A.V. are FNRS research fellows.

Thin films of the organic semiconductor Ph-BTBT-10 and blends of this material with polystyrene have been deposited by a solution shearing technique at low (1 mm s−1) and high (10 mm s−1) coating velocities and implemented in organic field-effect transistors. Combined X-ray diffraction and electrical characterisation studies prove that the films coated at low speed are significantly anisotropic. The highest mobility is found along the coating direction, which corresponds to the crystallographic a-axis. In contrast, at high coating speed the films are crystallographically less ordered but with better thin film homogeneity and exhibit isotropic electrical characteristics. Best mobilities are found in films prepared at high coating speeds with the blended semiconductor. This work demonstrates the interplay between the crystal packing and thin film morphology and uniformity and their impact on the device performance., The authors also thank the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 811284 (UHMob), the Spanish Ministry project GENESIS PID2019-111682RB-I00, the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE, CEX2019-000917-S), the Generalitat de Catalunya (2017-SGR-918) and the Austrian Science Fund (FWF): [P30222]. A. T. thanks his enrolment in the Materials Science PhD program of Universitat Autònoma de Barcelona and acknowledges FPU fellowship from the Spanish Ministry. We thank the synchrotron Elettra, Trieste for provision of synchrotron radiation and Luisa Barba for her support to use the beamline XRD1. G.S. acknowledges postdoctoral fellowship support from the Belgian National Fund for Scientific Research (FNRS). We acknowledge support of the publication fee from the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

The development of systems capable of responding to environmental changes, such as humidity, requires the design and assembly of highly sensitive and efficiently transducing elements. Such a challenge can be mastered only by disentangling the role played by each component of the responsive system, thus ultimately achieving high performance by optimizing the synergistic contribution of all functional elements. Here, we designed and synthesized a novel [1]benzothieno[3,2

Funder: Consortium des Équipements de Calcul Intensif, Funder: The Leverhulme Trust, While the charge transport properties of organic semiconductors have been extensively studied over the recent years, the field of organics‐based thermoelectrics is still limited by a lack of experimental data on thermal transport and of understanding of the associated structure–property relationships. To fill this gap, a comprehensive experimental and theoretical investigation of the lattice thermal conductivity in polycrystalline thin films of dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (Cn‐DNTT‐Cn with n = 0, 8) semiconductors is reported. Strikingly, thermal conductivity appears to be much more isotropic than charge transport, which is confined to the 2D molecular layers. A direct comparison between experimental measurements (3ω–Völklein method) and theoretical estimations (approach‐to‐equilibrium molecular dynamics (AEMD) method) indicates that the in‐plane thermal conductivity is strongly reduced in the presence of the long terminal alkyl chains. This evolution can be rationalized by the strong localization of the intermolecular vibrational modes in C8‐DNTT‐C8 in comparison to unsubstituted DNTT cores, as evidenced by a vibrational mode analysis. Combined with the enhanced charge transport properties of alkylated DNTT systems, this opens the possibility to decouple electron and phonon transport in these materials, which provides great potential for enhancing the thermoelectric figure of merit ZT.

Thermoelectric effect is a physical phenomenon which intricately relates the thermal energy of charge carriers to their charge transport. Understanding the mechanism of this interaction in different systems lies at the heart of inventing novel materials which can revolutionize thermoelectric power generation technology. Despite the recent surge of interest in organic thermoelectric materials, the community has had difficulties in formulating the charge transport mechanism in the presence of a significant degree of disorder. Here, we analyze the thermoelectric properties of various conducting polymers doped by solid-state diffusion of dopant molecules based on a transport model with a power law energy dependence of transport function. A fine control of the degree of doping via postdoping annealing provides an accurate empirical evidence of a strong energy dependence of the carrier mobility in the conducting polymers. A superior thermoelectric power factor of conducting polymers doped by solid-state diffusion to that of other doping methods can be attributed to a resulting higher intrinsic mobility and higher free carrier concentration.

A directional crystallization of the compound 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8) based on a temperature gradient approach has been used as a post-deposition process to control the crystalline morphology of thin films. C8-BTBT-C8 films of arbitrary thicknesses have been fabricated by spin-coating and subjected to the directional crystallization process. Dewetting is prevented by the liquid crystal phase of C8-BTBT-C8, allowing the formation of flat and rather uniform thin films with large crystalline domains. Spin-coating concentration, gradient magnitude, and cooling rate have been varied to explore a large set of crystallization conditions and to correlate them with the thin film morphology. The latter has been characterized by a combined use of optical profilometry, polarized optical microscopy, X-ray reflectometry, and X-ray diffraction measurements. The characterization results confirm that the roughness and crystalline order of the thin films are improved after the temperature gradient treatments: (1) high cooling rate treatments (≥9 °C min−1) significantly reduce the roughness of high thickness films, leading to good continuity and uniformity of the films; (2) dendritic growth dominates not only the films with low thickness but also films with high thickness treated at low cooling rates (, info:eu-repo/semantics/published

The molecule 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) is an organic semiconductor with outstanding performance in thin-film transistors. The asymmetric shape of the molecule causes an unusual phase behavior, which is a result of a distinct difference in the molecular arrangement between the head-to-head stacking of the molecules versus head-to-tail stacking. Thin films are prepared at elevated temperatures by crystallization from melt under controlled cooling rates, thermal-gradient crystallization, and bar coating at elevated temperatures. The films are investigated using X-ray diffraction techniques. Unusual peak-broadening effects are found, which cannot be explained using standard models. The modeling of the diffraction patterns with a statistic variation of the molecules reveal that a specific type of molecular disorder is responsible for the observed peak-broadening phenomena: the known head-to-head stacking within the crystalline phase is disturbed by the statistic integration of reversed (or flipped) molecules. It is found that 7–15% of the molecules are integrated in a reversed way, and these fractions are correlated with cooling rates during the sample preparation procedure. Temperature-dependent in situ experiments reveal that the defects can be healed by approaching the transition from the crystalline state to the smectic E state at a temperature of 145 °C. This work identifies and quantifies a specific crystalline defect type within thin films of an asymmetric rodlike conjugated molecule, which is caused by the crystallization kinetics., This work was supported by the Fonds de la Recherche Scientifique (FNRS) and the Fonds voor Wetenschappelijk Onderzoek – Vlanderen (FWO) under EOS project 30489208 and the Austrian Science Fund (FWF): [P30222]. YG is also thankful to FNRS for financial support through research projects BTBT n° 2.4565.11, Phasetrans n° T.0058.14, Pi-Fast n° T.0072.18, and 2D to 3D No. 30489208. Financial supports from the French Community of Belgian (ARC n° 20061) and by the Walloon Region (WCS No. 1117306, SOLIDYE n° 1510602) are also acknowledged. G.S. acknowledges postdoctoral fellowship support from the FNRS. M.M. thanks the Spanish Ministry project GENESIS PID2019-111682RB-I00, the “Severo Ochoa” Programme for the Centers of Excellence in R&D (FUNFUTURE, CEX2019-000917-S), and the Generalitat de Catalunya (2017-SGR-918). A.T. is enrolled in the Materials Science PhD program of Universitat Autònoma de Barcelona and acknowledges FPU fellowship from the Spanish Ministry. The large-scale facility Elettra, Trieste, Italy, provided synchrotron radiation for grazing incidence X-ray diffraction experiments at the beamline XRD1.

We present a nanospectroscopic device platform allowing simple and spatially resolved thermoelectric detection of molecular fingerprints of soft materials. Our technique makes use of a locally generated thermal gradient converted into a thermoelectric photocurrent that is read out in the underlying device. The thermal gradient is generated by an illuminated atomic force microscope tip that localizes power absorption onto the sample surface. The detection principle is illustrated using a concept device that contains a nanostructured strip of polymethyl methacrylate (PMMA) defined by electron beam lithography. The platform’s capabilities are demonstrated through a comparison between the spectrum obtained by on-chip thermoelectric nanospectroscopy with a nano-FTIR spectrum recorded by scattering-type scanning near-field optical microscopy at the same position. The subwavelength spatial resolution is demonstrated by a spectral line scan across the edge of the PMMA layer., info:eu-repo/semantics/published

Conjugated polymers and molecular semiconductors are emerging as a viable semiconductor technology in industries such as displays, electronics, renewable energy, sensing and healthcare. A key enabling factor has been significant scientific progress in improving their charge transport properties and carrier mobilities, which has been made possible by a better understanding of the molecular structure–property relationships and the underpinning charge transport physics. Here we aim to present a coherent review of how we understand charge transport in these high-mobility van der Waals bonded semiconductors. Specific questions of interest include estimates for intrinsic limits to the carrier mobilities that might ultimately be achievable; a dis- cussion of the coupling between charge and structural dynamics; the importance of molecular conformations and mesoscale structural features; how the transport physics of conjugated polymers and small molecule semiconductors are related; and how the incorporation of counterions in doped films—as used, for example, in bioelectronics and thermoelectric devices—affects the electronic structure and charge transport properties., info:eu-repo/semantics/published

Hysteresis-free operational stable perovskite FETs is demonstrated through ionic passivation and crystal modification., Despite sustained research, application of lead halide perovskites in field-effect transistors (FETs) has substantial concerns in terms of operational instabilities and hysteresis effects which are linked to its ionic nature. Here, we investigate the mechanism behind these instabilities and demonstrate an effective route to suppress them to realize high-performance perovskite FETs with low hysteresis, high threshold voltage stability (ΔVt < 2 V over 10 hours of continuous operation), and high mobility values >1 cm2/V·s at room temperature. We show that multiple cation incorporation using strain-relieving cations like Cs and cations such as Rb, which act as passivation/crystallization modifying agents, is an effective strategy for reducing vacancy concentration and ion migration in perovskite FETs. Furthermore, we demonstrate that treatment of perovskite films with positive azeotrope solvents that act as Lewis bases (acids) enables a further reduction in defect density and substantial improvement in performance and stability of n-type (p-type) perovskite devices.

Three thiophene ring-terminated benzothieno[3,2-b]benzothiophene (BTBT) derivatives, C-C6-DBTTT, C-C12-DBTTT, and L-C12-DBTTT, were designed and synthesized, differing in the isomerization of alkyl...

There is a growing interest in utilizing the distinctive material properties of organic semiconductors for spintronic applications. Here, we explore the injection of pure spin current from Permalloy into a small molecule system based on dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) at ferromagnetic resonance. The unique tunability of organic materials by molecular design allows us to study the impact of interfacial properties on the spin injection efficiency systematically. We show that both the spin injection efficiency at the interface and the spin diffusion length can be tuned sensitively by the interfacial molecular structure and side chain substitution of the molecule., info:eu-repo/semantics/published

The field of organic electronics has been prolific in the last couple of years, leading to the design and synthesis of several molecular semiconductors presenting a mobility in excess of 10 cm2 V-1 s-1. However, it also started to recently falter, as a result of doubtful mobility extractions and reduced industrial interest. This critical review addresses the community of chemists and materials scientists to share with it a critical analysis of the best performing molecular semiconductors and of the inherent charge transport physics that takes place in them. The goal is to inspire chemists and materials scientists and to give them hope that the field of molecular semiconductors for logic operations has not engaged into a dead end. To the contrary, it offers plenty of research opportunities in materials chemistry., info:eu-repo/semantics/published

Carbon-based semiconductors such as conjugated organic polymers are of potential use in the development of spintronic devices and spin-based information processing. In particular, these materials offer a low spin–orbit coupling strength due to their relatively light constituent chemical elements, which should, in principle, favour long spin diffusion lengths. However, organic polymers are relatively disordered materials and typically have a carrier mobility that is orders of magnitude lower than crystalline inorganic materials. As a result, small spin diffusion lengths of around 50 nm have typically been measured using vertical organic spin valves. Here, we report measuring spin diffusion lengths in doped conjugated polymers using a lateral spin transport device architecture, which is based on spin pumping injection and inverse spin Hall detection. The approach suggests that long spin diffusion lengths of more than 1 μm and fast spin transit times of around 10 ns are possible in conjugated polymer systems when they have a sufficiently high spin density (around 1020 cm−3). We explain these results in terms of an exchange-based spin diffusion regime in which the exchange interactions decouple spin and charge transport., info:eu-repo/semantics/published

Molecular vibrations play a critical role in the charge transport properties of weakly van der Waals bonded organic semiconductors. To understand which specific phonon modes contribute most strongly to the electron – phonon coupling and ensuing thermal energetic disorder in some of the most widely studied high mobility molecular semiconductors, we have combined state-of-the-art quantum mechanical simulations of the vibrational modes and the ensuing electron phonon coupling constants with experimental measurements of the low-frequency vibrations using inelastic neutron scattering and terahertz time-domain spectroscopy. In this way we have been able to identify the long-axis sliding motion as a ‘killer’ phonon mode, which in some molecules contributes more than 80% to the total thermal disorder. Based on this insight, we propose a way to rationalize mobility trends between different materials and derive important molecular design guidelines for new high mobility molecular semiconductors., Royal Society German Research Foundation European Research Council Engineering and Physical Sciences Research Council ARCHER UK National Supercomputing Service Belgian National Fund for Scientific Research Leverhulme Trust Wiener-Anspach Foundation Belgian Walloon Region GENCI-CINES/IDRIS

In this study, the nature and characteristics of the intramolecular and intermolecular interactions in crystal structures of the fluoro-substituted 7,7,8,8-tetracyanoquinodimethane (TCNQ) family of molecules, i.e. F x -TCNQ (x = 0, 2, 4), are explored. The molecular geometry of the reported crystal structures is directly dependent on the degree of fluorination in the molecule, which consequently also results in the presence of an intramolecular N[triple-bond]C...F—C π-hole tetrel bond. Apart from this, the energy framework analysis performed along the respective transport planes provides new insights into the energetic distribution in this class of molecules.

The lack of long‐term stability in thin films of organic semiconductors can often be caused by the low structural stability of metastable phases that are frequently formed upon deposition on a substrate surface. Here, thin films of 2,7‐dioctyloxy[1]benzothieno[3,2‐b]benzothiophene (C8O‐BTBT‐OC8) and blends of this material with polystyrene by solution shearing are fabricated. Both types of films exhibit the metastable surface‐induced herringbone phase (SIP) in all the tested coating conditions. The blended films reveal a higher device performance with a field‐effect mobility close to 1 cm2 V−1 s−1, a threshold voltage close to 0 V, and an on/off current ratio above 107. In situ lattice phonon Raman microscopy is used to study the stability of the SIP polymorph. It is found that films based on only C8O‐BTBT‐OC8 slowly evolve to the Bulk cofacial phase, significantly impacting device electrical performance. In contrast, the blended films stabilize the SIP phase, leading to devices that maintain a high performance over 1.5 years. This work demonstrates that blending small‐molecule organic semiconductors with insulating binding polymers can trap metastable polymorphs, which can lead to devices with both improved performance and long‐term stability., T.S. and A.C. contributed equally to this work. This work was funded by the Spanish Ministry projects (FANCY CTQ2016‐80030‐R, GENESIS PID2019‐111682RB‐I00, PID2019‐110907GB‐I00, MICIUN/FEDER RTI2018‐095460‐B‐I00 and MAT2016‐77852‐C2‐1‐R (AEI/FEDER, UE)) the Generalitat de Catalunya (2017‐SGR13, 2017‐SGR‐918 and 2017‐SGR668) and the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centers of Excellence in R&D (SEV‐2015‐0496) and “María de Maeztu” program for Spanish Structures of Excellence (MDM‐2017‐0767). The authors also thank the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska‐Curie grant agreement No 811284 (UHMob). They also acknowledge access to supercomputer resources as provided through grants from the Red Española de Supercomputación. T.S. acknowledges the H2020‐MSCA‐COFUND‐2014 Programme (P‐SPHERE, Grant agreement 665919). A.B. thanks the Spanish Government financial support through BES‐2016‐077519 FPI fellowship. This work was carried out within the framework of the doctoral program (Ph.D.) of Material Science (Department of Physics and Chemistry) of the Universitat Autonoma de Barcelona (UAB). Y.G. is thankful to the Belgian National Fund for Scientific Research (FNRS) for financial support through research projects BTBT no. 2.4565.11, Phasetrans no. T.0058.14, Pi‐Fast no T.0072.18, and 2D to 3D no. 30489208. Financial support from the French Community of Belgian (ARC no. 20061) is also acknowledged. G.S. acknowledges postdoctoral fellowship support from the FNRS. The authors acknowledge Dr. Gemma Rius and CNM‐IMB for the access to the Raman facility.

A novel trap mitigation mechanism using molecular additives, which relieves a characteristic early turn-on voltage in a high-mobility p-type acene-based small-molecule organic semiconductor, when processed from hydrous solvents, is reported. The early turn-on voltage is attributed to photo-induced trapping, and additive incorporation is found to be very effective in suppressing this effect. Remarkably, the molecular additive does not disturb the charge transport properties of the small-molecule semiconductor, but rather intercalates in the crystal structure. This novel technique allows for the solution-processing of small molecular semiconductors from hydrous solvents, greatly simplifying manufacturing processes for large-area electronics. Along with various electric and spectroscopic characterization techniques, simulations have given a deeper insight into the trap mitigation effect induced by the additive.

Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy. The main characteristics are low transition barrier, ultrafast kinetics, and structural reversibility. They are rarely observed in molecular crystals, and hence the origin and mechanism are largely unexplored. Here we report the discovery of martensitic transition in single crystals of two different organic semiconductors. In situ microscopy, single-crystal X-ray diffraction, Raman and nuclear magnetic resonance spectroscopy, and molecular simulations combined indicate that the rotating bulky side chains trigger cooperative transition. Cooperativity enables shape memory effect in single crystals and function memory effect in thin film transistors. We establish a molecular design rule to trigger martensitic transition in organic semiconductors, showing promise for designing next-generation smart multifunctional materials., Martensitic transition is commonly seen in steel and shape memory alloys but rarely in organic materials. Chung et al. discover martensitic transitions in organic electronics and utilize it in designing field-effect transistors, leading to shape memory effect that in return modifies charge transport properties.

A series of bulky end-capped [1]benzothieno[3,2-b]benzothiophenes (BTBTs) are developed in order to tune the packing structure via terminal substitution. A coupled theoretical and experimental study allows us to identify 2,7-di-tert-butylBTBT as a new high-performance organic semiconductor with large and well-balanced transfer integrals, as evidenced by quantum-chemical calculations. Single-crystal field-effect transistors show a remarkable average saturation mobility of 7.1 cm(2) V(-1) s(-1) .

Terahertz electromodulation spectroscopy provides insight into the material-inherent transport properties of charge carriers in organic semiconductors. Experiments on didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C12-BTBT-C12) devices yield for holes an intraband mobility of 9 cm2 V–1 s–1. The short duration of the THz pulses advances the understanding of the hole transport on the molecular scale. The efficient screening of Coulomb potentials leads to a collective response of the hole gas to external fields, which can be well described by the Drude model. Bias stress of the devices generates deep traps that capture mobile holes. Although the resulting polarization across the device hinders the injection of mobile holes, the hole mobilities are not affected.

Poly(ethylene oxide) (PEO) thin films of different thicknesses (220, 450, and 1500 nm) and molecular masses (4000, 8000, and 20 000 g/mol) have been fabricated by spin-coating of methanol solutions onto glass substrates. All these samples have been recrystallized from the melt using a directional thermal gradient technique. Millimeter-size domains with crystallites uniformly oriented in the direction of the thermal gradient are observed. Futhermore, the crystallites size and orientation distribution are enhanced (e.g., increases and decreases, respectively) when film thickness is decreased, ultimately leading to a single-crystal-like behavior for 220 nm thick PEO films of mass 8000 g/mol. Interestingly, this fine microstructure is partially retained after melting and subsequent cooling back to ambient temperature for the highest molecular weight polymer allowing, in this particular case, to significantly decrease the distribution of crystal orientation obtained after crystallization using the thermal grad...

Organic semiconductors (OSC) such as conjugated polymers/molecules are enabling flexible, large area optoelectronic devices, such as organic light-emitting diodes, transistors, and solar cells.

Film forming properties of semiconducting organic molecules comprising alkyl-chains combined with an aromatic unit have a decisive impact on possible applications in organic electronics. In particular, knowledge on the film formation process in terms of wetting or dewetting, and the precise control of these processes, is of high importance. In the present work, the subtle effect of temperature on the morphology and structure of dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) films deposited on silica surfaces by spin coating is investigated in situ via X-ray diffraction techniques and atomic force microscopy. Depending on temperature, bulk C8-BTBT exhibits a crystalline, a smectic A and an isotropic phase. Heating of thin C8-BTBT layers at temperatures below the smectic phase transition temperature leads to a strong dewetting of the films. Upon approaching the smectic phase transition, the molecules start to rewet the surface in the form of discrete monolayers with a defined number of monolayers being present at a given temperature. The wetting process and layer formation is well defined and thermally stable at a given temperature. On cooling the reverse effect is observed and dewetting occurs. This demonstrates the full reversibility of the film formation behavior and reveals that the layering process is defined by an equilibrium thermodynamic state, rather than by kinetic effects., info:eu-repo/semantics/published

Charge carrier mobility is a central property that characterizes the performances of organic semiconductors and is mostly measured in field-effect transistors. High mobility values are sought by many research teams. This article, that provides an overview of best performing molecular semiconductors is constructed on the question: What currently limits charge carrier mobility in crystals of molecular semiconductors? With this in mind, we confront, in a critical way, the current theoretical understanding to the most salient experimental results with the hope to reach a deeper understanding based on first principles and order of magnitudes of the main physical parameters.

Owing to a technical error, the ‘Published online’ date of this Article originally mistakenly appeared as ‘15 March 2019’, but should have been ‘18 March 2019’.

The order in molecular monolayers is a crucial aspect for their technological application. However, the preparation of defined monolayers by spin-coating is a challenge, since the involved processes are far from thermodynamic equilibrium. In the work reported herein, the dynamic formation of dioctyl-benzothienobenzothiophene monolayers is explored as a function of temperature by using X-ray scattering techniques and atomic force microscopy. Starting with a disordered monolayer after the spin-coating process, post-deposition self-reassembly at room temperature transforms the initially amorphous layer into a well-ordered bilayer structure with a molecular herringbone packing, whereas at elevated temperature the formation of crystalline islands occurs. At the temperature of the liquid-crystalline crystal–smectic transition, rewetting of the surface follows resulting in a complete homogeneous monolayer. By subsequent controlled cooling to room temperature, cooling-rate-dependent kinetics is observed; at rapid cooling, a stable monolayer is preserved at room temperature, whereas slow cooling causes bilayer structures. Increasing the understanding and control of monolayer formation is of high relevance for achieving ordered functional monolayers with defined two-dimensional packing, for future applications in the field of organic electronics., SCOPUS: ar.j, FLWNA, info:eu-repo/semantics/published

International audience; Five new molecular semiconductors that differ from dioctylbenzothienobenzothiophene, by the introduction of ether or thioether side chains, have been synthesized and obtained in good yields. Their availability in sufficient quantities has allowed investigation of their electrochemical behaviour in solution and their electronic properties in solid state. Both ether and thioether compounds oxidise rather easily in solution, but nevertheless, they exhibit rather high ionisation potentials. This is a consequence of their crystal structure. Dioctylthioetherbenzothienobenzothiophene is rather sensitive to oxidation and degrades easily in close to ambient conditions. Dioctyletherbenzothienobenzothiophene is more stable. Its charge carrier mobility remains however rather moderate, on the order of 0.5 cm2 V−1 s−1, whereas that of dioctylbenzothienobenzothiophene reached 4 cm2 V−1 s−1, in the same conditions. The difference is explained by intrinsic factors as shown by a theoretical modelling.

Both high gain and transconductance at low operating voltages are essential for practical applications of organic field-effect transistors (OFETs). Here, we describe the significance of the double-layer capacitance effect in polar rubbery dielectrics, even when present in a very low ion concentration and conductivity. We observed that this effect can greatly enhance the OFET transconductance when driven at low voltages. Specifically, when the polar elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) was used as the dielectric layer, despite a thickness of several micrometers, we obtained a transconductance per channel width 30 times higher than that measured for the same organic semiconductors fabricated on a semicrystalline PVDF-HFP with a similar thickness. After a series of detailed experimental investigations, we attribute the above observation to the double-layer capacitance effect, even though the ionic conductivity is as low as 10–10 S/cm. Different from previously reported OFETs with double-layer capacitance effects, our devices showed unprecedented high bias-stress stability in air and even in water., info:eu-repo/semantics/published

A new phase of a known discotic liquid crystal is observed at the interface with a rigid substrate. The structure of the substrate-induced phase has been characterized by atomic force microscopy, specular X-ray diffraction, and small-angle and wide-angle grazing incidence X-ray diffraction. The substrate-induced phase, which has a thickness of ∼30 nm and a tetragonal symmetry, differs notably from the bulk phase. The occurrence of such phase casts a new light on alignment of discotic liquid crystals. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A method for the preparation of uniaxially oriented thin films of terthiophene (20–50 μm thick) is introduced. It relies on the crystal growth with a Bridgman-type process that decouples nucleation and growth phenomena. An effective thermal gradient of 6–11.6 °C/mm has been used in which the sample (terthiophene powder deposited on either glass or fluorinated glass substrates) is displaced from a hot zone to a cold zone at a constant rate of 2.5–5 μm/s. The size and orientation of crystals have been investigated by polarized optical microscopy and X-ray diffraction measurements. A coexistence of two polymorphs of terthiophene has been observed, but optimal gradient conditions enabling the selective crystallization of only the room temperature stable polymorph have been found. Terthiophene films deposited on fluorinated glass substrates and crystallized using the thermal gradient technique show a stronger tendency to polymorphism and random orientation of crystallites for all gradient conditions tested. Th...

The exploration of a wide range of molecular structures has led to the development of high-performance conjugated polymer semiconductors for flexible electronic applications including displays, sensors, and logic circuits. Nevertheless, many conjugated polymer field-effect transistors (OFETs) exhibit nonideal device characteristics and device instabilities rendering them unfit for industrial applications. These often do not originate in the material's intrinsic molecular structure, but rather in external trap states caused by chemical impurities or environmental species such as water. Here, a highly efficient mechanism is demonstrated for the removal of water-induced traps that are omnipresent in conjugated polymer devices even when processed in inert environments; the underlying mechanism is shown, by which small-molecular additives with water-binding nitrile groups or alternatively water-solvent azeotropes are capable of removing water-induced traps leading to a significant improvement in OFET performance. It is also shown how certain polymer structures containing strong hydrogen accepting groups will suffer from poor performances due to their high susceptibility to interact with water molecules; this allows the design guidelines for a next generation of stable, high-performing conjugated polymers to be set forth.

Blends of two metal-free phthalocyanine mesogens exhibiting different mesophases (Colr phase from room temperature to isotropization for the first one, and Colr at room temperature then Colh from around 60 °C to isotropization for the second one) have been studied in order to determine the relationship between the type of mesophase and the alignment behavior. The phase diagram of this system has been built and evidence of full solid-state miscibility of the two pure constituents in all proportions and temperatures is presented. Investigation of phase alternation at room temperature as a function of composition revealed that border compositions exhibit Colr phases similar to the pure constituents, whereas Colh mesophase was stabilized for intermediate compositions. Combined polarized optical microscopy observations and X-ray diffraction measurements showed that homeotropic alignment is adopted only for mixed samples exhibiting Colh mesophase, thus demonstrating that the presence of a Colh mesophase is a ne...

The fabrication of multifunctional high-performance organic thin-film transistors as key elements in future logic circuits is a major research challenge. Here we demonstrate that a photoresponsive bi-functional field-effect transistor with carrier mobilities exceeding 0.2 cm(2) V(-1) s(-1) can be developed by incorporating photochromic molecules into an organic semiconductor matrix via a single-step solution processing deposition of a two components blend. Tuning the interactions between the photochromic diarylethene system and the organic semiconductor is achieved via ad-hoc side functionalization of the diarylethene. Thereby, a large-scale phase-segregation can be avoided and superior miscibility is provided, while retaining optimal π-π stacking to warrant efficient charge transport and to attenuate the effect of photoinduced switching on the extent of current modulation. This leads to enhanced electrical performance of transistors incorporating small conjugated molecules as compared with polymeric semiconductors. These findings are of interest for the development of high-performing optically gated electronic devices., SCOPUS: ar.j, info:eu-repo/semantics/published

Two thienoacene dimers based on the thieno[3,2-b]thiophene moiety were efficiently synthesized, characterized and evaluated as active hole-transporting layers in organic thin-film field-effect transistors. Both compounds behaved as active p-channel organic semi-conductors showing averaged hole mobility of up to 1.33 cm2 V−1 s−1.

High-mobility organic semiconductors such as [1]benzothieno[3,2-b]benzothiophene (BTBT) derivatives are potential candidates for ultrasensitive biosensors. Here 2,7-dioctyl BTBT (C8-BTBT-C8)-based liquid-gated organic electronic devices are demonstrated with two device architectures, viz. electrolyte-gated organic field-effect transistor (EGOFET) and electrolyte-gated organic synapstor (EGOS), and different electrode materials, viz. gold and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). EGOFETs exhibit a mean transconductance of about 45 µS, on a par with literature, and a max value up to 256 µS at the state-of-the-art in aqueous electrolyte, with a mean product of charge mobility and effective capacitance of about 0.112 and 0.044 µS V−1 for gold and PEDOT:PSS electrodes, respectively. EGOSs exhibit a dynamic response with 15 ms characteristic timescale with Au electrodes and about twice with PEDOT:PSS electrodes. These results demonstrate a promising route for sensing applications in physiological environment based on fully solution-processed whole-organic electronic devices featuring ultrahigh sensitivity and fast response.