Synergistic Effect of Solvent Vapor Annealing and Chemical Doping for Achieving High-Performance Organic Field-Effect Transistors with Ideal Electrical Characteristics

Contact resistance and charge trapping are two key obstacles, often intertwined, that negatively impact on the performance of organic field-effect transistors (OFETs) by reducing the overall device mobility and provoking a nonideal behavior. Here, we expose organic semiconductor (OSC) thin films based on blends of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8) with polystyrene (PS) to (i) a CH3CN vapor annealing process, (ii) a doping I2/water procedure, and (iii) vapors of I2/CH3CN to simultaneously dope and anneal the films. After careful analysis of the OFET electrical characteristics and by performing local Kelvin probe force microscopy studies, we found that the vapor annealing process predominantly reduces interfacial shallow traps, while the chemical doping of the OSC film is responsible for the diminishment of deeper traps and promoting a significant reduction of the contact resistance. Remarkably, the devices treated with I2/CH3CN reveal ideal electrical characteristics with a low level of shallow/deep traps and a very high and almost gate-independent mobility. Hence, this work demonstrates the promising synergistic effects of performing simultaneously a solvent vapor annealing and doping procedure, which can lead to trap-free OSC films with negligible contact resistance problems

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

High throughput processing of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) organic semiconductors

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).Peer reviewe

Charge transfer complexes of a benzothienobenzothiophene derivative and their implementation as active layer in solution-processed thin film organic field-effect transistors

Single crystals of novel (C 8 O-BTBT-OC 8 )(F x TCNQ) charge complexes (CT) are prepared and fully characterised. Solution processed films of the (C 8 O-BTBT-OC 8 )(F 4 TCNQ) CT are implemented in organic field-effect transistors giving an n-type behaviour.info:eu-repo/semantics/publishe

Charge transfer complexes of a benzothienobenzothiophene derivative and their implementation as active layer in solution-processed thin film organic field-effect transistors

Herein, we report on the synthesis and structural characterization of novel charge transfer (CT) complexes of the benzothienobenzothiophene derivative C8O-BTBT-OC8 with the series of FxTCNQ derivatives (x = 2, 4). The degree of charge transfer and HOMO–LUMO gap energies were evaluated by spectroscopic means and by DFT calculations. Thin films of the (C8O-BTBT-OC8)(F4TCNQ) complex were prepared by a simple solution shearing technique and by blending the active materials with polystyrene. X-Ray diffraction and IR/Raman spectroscopy techniques were instrumental for the structural identification of the films, which belonged to the same phase as the resolved single crystal. The films were implemented as an active layer in organic field-effect transistor (OFET) devices, which exhibited an n-type behavior in ambient conditions in agreement with the theoretical calculations.This work was funded by European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 811284 (UHMob), the Spanish Ministry with the project GENESIS PID2019-111682RB-I00 and through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S), the Generalitat de Catalunya (2017-SGR-918) and the Consortium des Equipements de Calcul Intensif (CECI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S. – FNRS) under grant no. 2.5020.11. A. T. acknowledges his FPU fellowship. A. T and L. F. are enrolled in the UAB Materials Science PhD program. Y. G. is thankful to the Belgian National Fund for Scientific Research (FNRS) for financial support through research projects, Pi-Fast No. T.0072.18, and 2D to 3D No. 30489208. Financial supports from the French Community of Belgium (ARC No. 20061) is also acknowledged. DB is a FNRS research director, CQ is a FNRS research associate. S. D. acknowledges financial support from the University of Bologna (RFO-Scheme). TS thanks the European co-financing project FSE REACT EU – PON R&I 2014–2020.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Impact of Hydrophilic Side Chains on the Thin Film Transistor Performance of a Benzothieno-Benzothiophene Derivative

Side-chain engineering in molecular semiconductors provides a versatile toolbox for precisely manipulating the material’s processability, crystallographic properties, as well as electronic and optoelectronic characteristics. This study explores the impact of integrating hydrophilic side chains, specifically oligoethylene glycol (OEG) units, into the molecular structure of the small molecule semiconductor, 2,7-bis(2(2-methoxy ethoxy)ethoxy) benzo[b]benzo[4,5] thieno[2,3-d] thiophene (OEG-BTBT). The investigation includes a comprehensive analysis of thin film morphology and crystallographic properties, along with the optimization of deposition parameters for improving the device performance. Despite the anticipated benefits, such as enhanced processability, our investigation into OEG-BTBT-based organic field-effect transistors (OFETs) reveals suboptimal performance marked by a low effective charge carrier mobility, a low on/off ratio, and a high threshold voltage. The study unveils bias stress effects and device degradation attributed to the high ionization energy of OEG-BTBT alongside the hydrophilic nature of the ethylene-glycol moieties, which lead to charge trapping at the dielectric interface. Our findings underscore the need for a meticulous balance between electronic properties and chemical functionalities in molecular semiconductors to achieve stable and efficient performance in organic electronic devices

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

Synthesis, polymorph investigation, crystallographic study, and fabrication of OFETs in solution-processed thin films of C7-BTBT-C7 .info:eu-repo/semantics/publishe