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Vibrational spectroscopy allows the investigation of structural properties of pristine and doped poly(3-hexylthiophene-2,5-diyl) (P3HT) in highly anisotropic materials, such as electrospun micro- and nanofibers. Here, we compare several approaches for doping P3HT fibers. We have selected two different electron acceptor molecules as dopants, namely iodine and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). In the case of iodine, we have explored the doping of the fibers according to several different procedures, i.e., by sequential doping both in vapors and in solution, and with a novel promising one-step method, which exploits the mixing of the dopant to the electrospinning feed solution. Polarized infrared (IR) spectroscopy experiments prove the orientation of P3HT chains, with the polymer backbone mainly running parallel to the fiber axis. After doping, P3HT fibers show very strong and polarized doping-induced IR active vibrations (IRAVs), which are the spectroscopic signature of the structure relaxation induced by the charged defects (polarons), thus providing an unambiguous proof of the effective doping. Raman spectroscopy complements the IR evidence: The Raman spectrum shows a clearly recognizable shift of the main band, the so-called effective conjugation coordinate band, in the doped samples. A simple protocol, which quantifies the evolution of the IRAV bands with time, allows monitoring of the doping stability over time and confirms that F4TCNQ is by far superior to iodine. [ABSTRACT FROM AUTHOR]

Thermoelectric materials with high electrical conductivity and low thermal conductivity (e.g., Bi2Te3) can efficiently convert waste heat into electricity; however, in spite of favorable theoretical predictions, individual Bi2Te3 nanostructures tend to perform less efficiently than bulk Bi2Te3. We report a greater-than-order-of-magnitude enhancement in the thermoelectric properties of suspended Bi2Te3 nanoribbons, coated in situ to form a Bi2Te3/F4-TCNQ core-shell nanoribbon without oxidizing the core-shell interface. The shell serves as an oxidation barrier but also directly functions as a strong electron acceptor and p-type carrier donor, switching the majority carriers from a dominant n-type carrier concentration (∼1021 cm-3) to a dominant p-type carrier concentration (∼1020 cm-3). Compared to uncoated Bi2Te3 nanoribbons, our Bi2Te3/F4-TCNQ core-shell nanoribbon demonstrates an effective chemical potential dramatically shifted toward the valence band (by 300-640 meV), robustly increased Seebeck coefficient (∼6× at 250 K), and improved thermoelectric performance (10-20× at 250 K).

Regulating the charge-related properties in materials is highly valuable in the field of electronic devices. Charge transfer doping received significant attention as an efficient method of modulation. Graphene oxide (GO) is often used for regulation due to its abundance of oxygen-containing groups. However, the conventional operations to perform charge transfer doping for GO are complex, expensive and environmentally unfriendly. Here, we propose a charge transfer doping strategy by simply mixing GO suspension with 5 mg/ml 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F 4 TCNQ), together with ultrasonic treatment. Notably, the F 4 TCNQ-GO flexible photodetector exhibits outstanding responsivity (R) of up to 1.57 × 103 A/W in the 650 nm regime, surpassing most of the GO/graphene-based photodetectors reported in the past decade. Moreover, the photodetector successfully realizes in-sensor computing for complex pattern imaging, enabling clear and efficient multi-directional edge extraction. Experiments employing X-ray photoelectron spectra (XPS), X-ray diffraction spectra (XRD), Raman spectra, Ultraviolet–visible (UV–vis) spectra and scanning electron microscopy (SEM) reveal the stable non-covalent binding between GO and F 4 TCNQ through π-π interactions, as well as the electron transfer from GO to the F 4 TCNQ molecule, resulting in the formation of electron accumulation and depletion layers on the F 4 TCNQ molecule and GO, respectively. This finding holds great potential for regulating the electronic properties of a wide range of π-electron-rich two-dimensional materials in the fields of energy, biomedicine, environmental technology, and materials science. [Display omitted] [ABSTRACT FROM AUTHOR]

Summary: Organic electrode material has advantages of renewable, low cost, and environmentally friendly, which are promising for application in lithium‐ion batteries (LIBs). However, most organic cathode materials demonstrate low redox potentials and are easy to dissolve in conventional liquid electrolytes that retard the development of organic lithium batteries (OLBs). In this paper, 2,3,5,6‐Tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), a novel organic electrode with a high‐voltage of 3.4 V is reported as cathode material for OLBs. To suppress the flow out of active materials and improve cycling performance, solid‐state PEO‐LLZTO is used as an electrolyte. Through adjusting the molecular weight of PEO, optimizing electrochemical windows, and using electrolyte additive, we finally fabricated an organic solid‐state lithium battery which delivered a capacity of 80 mAh g−1 at a current density of 10 mA g−1, and maintained 77% capacity after 50 cycles. Our work provides a new material option for high‐voltage OLBs, and gives instructions for fabrication of solid‐state OLBs with high‐stability. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) hold great potential in thermoelectric (TE) applications, thanks to their regular and soft lattice in nature. However, the poor electrical conductivity caused by low charge carrier density (<1014 cm−3 for lead‐based MHPs) strongly impedes its TE development. In this scenario, tin halide perovskites (THPs) emerge as promising TE candidates owing to their high background hole densities (>1019 cm−3). However, further electrical doping remains challenging, originating from the limited capability of accommodating heterogeneous dopants and the heavy compensation in THPs. Herein, a novel diffusion‐mediated doping approach is demonstrated to prominently increase the p‐type doping level of THPs by a sequence of air exposure and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) surface treatments. In paradigm photovoltaic THP materials—CH(NH2)2SnI3 (namely FASnI3), the electrical conductivity is dramatically increased by 300× from 0.06 to 18 S cm−1 in thin films, leading to a remarkable enhancement of power factor by 25× up to 53 μW m−1 K−2. In contrast, only a slight variation of thermal conductivity is observed after F4TCNQ deposition, which is in accordance with the increase in electrical conductivity, indicating that the lattice structures of FASnI3 remain intact after doping. This study paves an illuminating way to ameliorate TE properties in halide perovskites. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) hold great potential in thermoelectric (TE) applications, thanks to their regular and soft lattice in nature. However, the poor electrical conductivity caused by low charge carrier density (1019 cm−3). However, further electrical doping remains challenging, originating from the limited capability of accommodating heterogeneous dopants and the heavy compensation in THPs. Herein, a novel diffusion‐mediated doping approach is demonstrated to prominently increase the p‐type doping level of THPs by a sequence of air exposure and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) surface treatments. In paradigm photovoltaic THP materials—CH(NH2)2SnI3 (namely FASnI3), the electrical conductivity is dramatically increased by 300× from 0.06 to 18 S cm−1 in thin films, leading to a remarkable enhancement of power factor by 25× up to 53 μW m−1 K−2. In contrast, only a slight variation of thermal conductivity is observed after F4TCNQ deposition, which is in accordance with the increase in electrical conductivity, indicating that the lattice structures of FASnI3 remain intact after doping. This study paves an illuminating way to ameliorate TE properties in halide perovskites.

In this study, the kinetics of the adsorption of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been intensively investigated, as molecular doping is known to play a crucial role in organic electronic devices. Based on the results obtained from UV–visible (vis)–near-infrared (NIR) absorption spectroscopy, cryogenic transmission electron microscopy, scanning nanobeam electron diffraction, and electron energy loss spectroscopy, a two-step interaction kinetics has been proposed for the Ag NPs and F4TCNQ molecules, which includes the first step of electron transfer from Ag NPs to F4TCNQ indicated by the ionization of F4TCNQ and the second step of the formation of a Ag–F4TCNQ complex. The whole process has been followed via UV–vis–NIR absorption spectroscopy, which reveals distinct kinetics at two stages: the instantaneous ionization and the long-term complex formation. The kinetics and the influence of the molar ratio of Ag NPs/F4TCNQ molecules on the interaction between Ag NPs and F4TCNQ molecules in an organic solution are reported herein for the first time. Furthermore, the control experiment with silica-coated Ag NPs manifests that the charge transfer at the surface between Ag NPs and F4TCNQ molecules is prohibited by a silica layer of 18 nm. [ABSTRACT FROM AUTHOR]

In the research field on materials for energy solutions, the exploitation of organic compounds and polymers is of great interest, especially in view of a more eco-sustainable development. In this context, the 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) molecule actively participates in the optimization of many optoelectronic devices based on such elements, thanks to its electrical properties. In this paper, we report a study on its optical properties, in particular demonstrating fluorescence emission from solutions containing F4TCNQ. This phenomenon is equally relevant, together with the effects on electrical conductivity, in the design of systems for energy technology. The results we present here offer new insights in the phenomenological picture of this molecule and can sharpen its applicability.

During the course of research into the structure of 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), C12F4N4, an important compound in charge‐transfer and organic semiconductor research, a previously unreported polymorph of F4TCNQ was grown concomitantly with the known polymorph from a saturated solution of dichloromethane. The structure was elucidated using single‐crystal X‐ray diffraction and it was found that the new polymorph packs with molecules in parallel layers, in a similar manner to the layered structure of F2TCNQ. The structure was analysed using Hirshfeld surface analysis, fingerprint plots and pairwise interaction energies, and compared to existing data. The structure of a toluene solvate of F4TCNQ is also reported. [ABSTRACT FROM AUTHOR]

The copper phthalocyanine and 2,3,5,6‐tetrafluoro‐tetracyano‐quino‐dimethane molecules adsorbed on the copper and single‐layer graphene‐modified copper surfaces have been investigated using Raman and X‐ray photoelectron spectroscopy. The adsorbed amounts for both molecules on the two different substrates are almost comparable as confirmed by the C 1s and N 1s core level X‐ray photoelectron spectra. Raman signal enhancement has been observed for both molecules when they are adsorbed on the graphene surface. The strongest chemical interaction is observed between the 2,3,5,6‐tetrafluoro‐tetracyano‐quino‐dimethane and copper substrate. Based on the Raman and X‐ray photoelectron spectroscopic data, the mechanism of the graphene‐enhanced Raman scattering is discussed, which might greatly rely on the unique electronic properties of graphene. [ABSTRACT FROM AUTHOR]

Thermoelectric materials with high electrical conductivity and low thermal conductivity (e.g., Bi 2 Te 3 ) can efficiently convert waste heat into electricity; however, in spite of favorable theoretical predictions, individual Bi 2 Te 3 nanostructures tend to perform less efficiently than bulk Bi 2 Te 3 . We report a greater-than-order-of-magnitude enhancement in the thermoelectric properties of suspended Bi 2 Te 3 nanoribbons, coated in situ to form a Bi 2 Te 3 /F 4 -TCNQ core-shell nanoribbon without oxidizing the core-shell interface. The shell serves as an oxidation barrier but also directly functions as a strong electron acceptor and p-type carrier donor, switching the majority carriers from a dominant n-type carrier concentration (∼10 21 cm -3 ) to a dominant p-type carrier concentration (∼10 20 cm -3 ). Compared to uncoated Bi 2 Te 3 nanoribbons, our Bi 2 Te 3 /F 4 -TCNQ core-shell nanoribbon demonstrates an effective chemical potential dramatically shifted toward the valence band (by 300-640 meV), robustly increased Seebeck coefficient (∼6× at 250 K), and improved thermoelectric performance (10-20× at 250 K).

The commercial mass production of perovskite solar cells requires full compatibility with roll-to-roll processing with enhanced device stability. In line with this, the present work addresses following issues simultaneously from multiple fronts: (i) low temperature processed (140 °C) ZnO is used as electron transport layer (ETL) for fabricating the mixed organic cation based perovskite solar cells, (ii) the expensive hole transporting layer (HTL) spiro-OMeTAD is replaced with F4TCNQ doped P3HT and (iii) the fabrication method does not incorporate the dopant TBP which is known to induce degradation processes in perovskite layer. All the devices under study were fabricated in ambient conditions. The F4TCNQ doped P3HT (HTL) based devices exhibits 14 times higher device stability compared to the conventional Li-TFSI/TBP doped P3HT devices. The underlying mechanism behind the enhanced device lifetime in F4TCNQ doped P3HT (HTL) based devices was investigated via in-depth electronic, ionic and polaronic characterization. The enhanced polaronic property in F4TCNQ doped P3HT HTL device ascertains its superior hole extraction and electron blocking capability; and consequently higher stability retained even after a month of ageing. [ABSTRACT FROM AUTHOR]

The CH 3 NH 3 PbI 3 -based perovskite solar cells using α, α′-diethoxyethyl-oligothiophenes (DEPT-SC) doped with 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquino-dimethane (F4TCNQ) as hole transport material (HTM) exhibited a power conversion efficiency of 11.52%. Compared to the pristine devices, the perovskite solar cells using the new synthesized HTM showed an increased efficiency by about 18% and exhibited better photo-stability, indicating that the organic dopant is an effective method for DEPT-SC toward stable perovskite solar cells. [ABSTRACT FROM AUTHOR]

In this paper, the top-contact (TC) pentacene-based organic thin-film transistor (OTFT) with a tetrafluorotetracyanoquinodimethane (F4TCNQ)-doped pentacene interlayer between the source/drain electrodes and the pentacene channel layer were fabricated using the co-evaporation method. Compared with a pentacene-based OTFT without an interlayer, OTFTs with an F4TCNQ:pentacene ratio of 1:1 showed considerably improved electrical characteristics. In addition, the dependence of the OTFT performance on the thickness of the F4TCNQ-doped pentacene interlayer is weaker than that on a Teflon interlayer. Therefore, a molecular doping-type F4TCNQ-doped pentacene interlayer is a suitable carrier injection layer that can improve the TC-OTFT performance and facilitate obtaining a stable process window. [ABSTRACT FROM AUTHOR]

Electron acceptors are classes of molecules that are important in organic devices as they help to improve the conductivity of organic semiconducting molecules by formingp-type complexes or anion radical complexes. These molecules can be doped into hole transporting materials to provide good ohmic contact with the anode and to improve the carrier density of the hole transport layer. This results in organic light-emitting devices with low driving voltages and high power efficiencies. In this study, we investigate a series of tetracyano-p-quinodimethane derivatives with substituents expected to facilitate the electron-acceptor capabilities of the quinones using density functional theory (DFT) and time-dependent DFT (TDDFT). As expected, the cyano substitution stabilises both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and increases the adiabatic electron affinity of the dopants. The stabilisation effect on the LUMO levels is greater, and as a result the narrowing of the HOMO–LUMO gap is seen. This fact was further confirmed by TDDFT studies, energy of the computed S1 ← S0transition red shifted upon CN substitution. However, perturbation to the ground-state geometry is negligible, and all anionic structures exhibit aromatisation independent of substitution. Our study suggests that the substituted derivatives reported herein show promise as conductivity dopants. [ABSTRACT FROM AUTHOR]

We have already reported a nanowire structure of bis-tetrathiafulvalenb(bis-TTF)annelated macrocycle–tetrafluorotetracyanoquinodimethane(F 4 TCNQ)charge transfer complex formed by Langmuir-Blodgett(LB)technique. Nanowires oriented on the mica substrates forming an angle of 60 degree to each other recognizing hexagonal potassium array of mica surface. In the present study, we examined the conditions for obtaining well oriented nanowiresand found that the nanowire orientation was quite sensitive to the temperature and potassium-ion concentration of subphase as well as the deposition speeds. By a slight change in conditions, a variety of nanowire morphology was observed on mica surface. [ABSTRACT FROM AUTHOR]

During the course of research into the structure of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ), C 12 F 4 N 4 , an important compound in charge-transfer and organic semiconductor research, a previously unreported polymorph of F 4 TCNQ was grown concomitantly with the known polymorph from a saturated solution of dichloromethane. The structure was elucidated using single-crystal X-ray diffraction and it was found that the new polymorph packs with molecules in parallel layers, in a similar manner to the layered structure of F 2 TCNQ. The structure was analysed using Hirshfeld surface analysis, fingerprint plots and pairwise interaction energies, and compared to existing data. The structure of a toluene solvate of F 4 TCNQ is also reported., (open access.)

Organic charge-transfer complexes (CTCs) formed by strong electron acceptor and strong electron donor molecules are known to exhibit exotic effects such as superconductivity and charge density waves. We present a low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) study of a two-dimensional (2D) monolayer CTC of tetrathiafulvalene (TTF) and fluorinated tetracyanoquinodimethane (F 4 TCNQ), self-assembled on the surface of oxygen-intercalated epitaxial graphene on Ir(111) (G/O/Ir(111)). We confirm the formation of the charge-transfer complex by d I /d V spectroscopy and direct imaging of the singly occupied molecular orbitals. High-resolution spectroscopy reveals a gap at zero bias, suggesting the formation of a correlated ground state at low temperatures. These results point to the possibility to realize and study correlated ground states in charge-transfer complex monolayers on weakly interacting surfaces.

Graphene as one of the most promising transparent electrode materials has been successfully applied in organic light-emitting diodes (OLEDs). However, traditional poly(methyl methacrylate) (PMMA) transfer method usually results in hardly removed polymeric residues on the graphene surface, which induces unwanted leakage current, poor diode behavior, and even device failure. In this work, we proposed a facile and efficient two-in-one method to obtain clean graphene and fabricate OLEDs, in which the poly(9,9-di-n-octylfluorene-alt-(1,4-phenylene-(4-sec-butylphenyl)imino)-1,4-phenylene) (TFB) layer was inserted between the graphene and PMMA film both as a protector during the graphene transfer and a hole-injection layer in OLEDs. Finally, green OLED devices were successfully fabricated on the PMMA-free graphene/TFB film, and the device luminous efficiency was increased from 64.8 to 74.5 cd/A by using the two-in-one method. Therefore, the proposed two-in-one graphene transfer method realizes a high-efficient graphene transfer and device fabrication process, which is also compatible with the roll-to-roll manufacturing. It is expected that this work can enlighten the design and fabrication of the graphene-based optoelectronic devices.

π-conjugated organic molecules tend to adsorb in a planar configuration on graphene irrespective of their charge state. In contrast, here we demonstrate charging-induced strong structural relaxation of tetrafluorotetracyanoquinodimethane (F 4 TCNQ) on epitaxial graphene on Ir(111) (G/Ir(111)). The work function modulation over the graphene moiré unit cell causes site-selective charging of F 4 TCNQ. Upon charging, the molecule anchors to the face-centered cubic sites of the G/Ir(111) moiré through one or two cyano groups. The reaction is reversible and can be triggered on a single molecule by moving it between different adsorption sites. We introduce a model taking into account the trade-off between tilt-induced charging and reduced van der Waals interactions, which provides a general framework for understanding charging-induced structural relaxation on weakly interacting substrates. In addition, we argue that the partial sp 3 rehybridization of the underlying graphene and the possible bonding mechanism between the cyano groups and the graphene substrate are also relevant for the complete understanding of the experiments. These results provide insight into molecular charging on graphene, and they are directly relevant for potential device applications where the use of molecules has been suggested for doping and band structure engineering.