Search Results (21)

This review provides a comprehensive overview of molecular doping in organic semiconductors (OSCs), with particular emphasis on the mechanistic understanding of doping processes, rational material design strategies, and processing approaches for achieving high doping efficiency and stability. We discuss fundamental doping mechanisms, including integer charge transfer and orbital hybridization models, and highlight how molecular structure, polymer design, and dopant–host interactions influence electrical performance. Recent advances in processing strategies—such as sequential, vapor-phase, and hybrid doping methods—are also summarized in relation to microstructural control and charge transport optimization. In addition, the implications of molecular doping for emerging organic thermoelectric applications are addressed, emphasizing the interplay between dopant distribution, morphology, and device performance. By integrating mechanistic insights, material design principles, and application perspectives, this review aims to provide a unified framework for researchers in organic electronics, materials science, and thermoelectric device engineering seeking to develop highly efficient and stable molecularly doped organic conductors. Full article

Chemical doping is a well-established technique for increasing the electrical conductivity of polyconjugated polymers, and its effectiveness can be assessed through IR spectroscopy, thanks to the rise of the so-called IRAVs (infrared activated vibrations), which prove the formation of polarons on the polymer chain. While the mechanism of the IRAVs activation has been widely explored in the past, several peculiar features remain unclear. Changes in the Raman spectrum of doped polymers (RaAV, Raman activated vibrations) are widely used as well for monitoring the doping process, but the interpretation is often limited to purely empirical correlations. By means of an experimental campaign on doped regio-regular poly(3-hexylthiophene-2,5-diyl) (P3HT) samples in chloroform solution and on the solid samples cast from the same solutions, this paper presents for the first time a thorough comparative analysis of IRAVs and RaAVs, aiming at a unified description of the structure of doped P3HT. In particular, we will discuss the effect of the doping level on the vibrational features of the polymer and the dopant so that spectroscopic markers can be found to be used in the identification of the presence of ICT (integer charge transfer) complexes in different doping regimes. This study demonstrates that combining IR, Raman, and UV-Vis-NIR spectroscopies provides a powerful, complementary set of tools to diagnose not only the doping level but also the detailed molecular and supramolecular structure of the doped P3HT, useful for the development of structure/properties relationships in the perspective of the optimization of the charge transport performances. Full article

In this computational study, we investigate two-sided functionalised MoS₂ with alkali metal atoms as donors and the organic acceptor molecule F₄TCNQ as an acceptor. Characterisation of functionalised MoS₂ involves first-principles calculations within the density functional theory (DFT) framework with a PBE+D3 scheme to investigate the electronic structure and quantify the charge transfer in the two-sided functionalised system in comparison to the one-sided functionalised counterpart. Within the two-sided functionalised systems, there is an increase in the overall charge on MoS₂ as a result of stronger electron transfer from the donor to the monolayer, additionally controlled by the ability of the acceptor to receive electrons. Full article

2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is a molecule widely employed as a very effective p-dopant of semi-conducting polymers, such as poly(3-hexylthiophene-2,5-diyl) (P3HT). The CN stretching transitions of F4TCNQ are exceptionally sensitive to the charge state of the molecule, thus allowing the doping diagnosis via IR spectroscopy. Less pronounced frequency shifts can reveal characteristics of the intermolecular environment. We present a systematic study based on Density Functional Theory (DFT) calculations and on experiments aimed at exploring how different factors, such as the charge state and the environment, modify the vibrational spectra of F4TCNQ. While several effects on the vibrational frequencies are well known and have been thoroughly investigated in the past, this study focuses on the infrared intensities of the CN stretching modes and reveals that they are strongly affected both by the charge state of the molecule and by the surrounding medium: it is then mandatory to consider such remarkable intensity modulation for any quantitative diagnosis based on spectroscopic measurements, e.g., concerning the number of F4TCNQ molecules involved in the formation of charge transfer complexes. Full article

To explore a highly conductive flexible platform, this study develops PIDF-BT@SWCNT by wrapping single-walled carbon nanotubes (SWCNTs) with a conjugated polymer, PIDF-BT, known for its effective doping properties. By evaluating the doping behaviors of various dopants on PIDF-BT, appropriate dopant combinations for cascade doping are selected to improve the doping efficiency of PIDF-BT@SWCNT. Specifically, using F4TCNQ or F6TCNNQ as the first dopant, followed by AuCl₃ as the second dopant, demonstrates remarkable doping efficiency, surpassing that of the individual dopants and yielding an exceptional electrical conductivity exceeding 6000 S/cm. Characterization using X-ray photoelectron spectroscopy and Raman spectroscopy elucidates the doping mechanism, revealing an increase in the proportion of electron-donating atoms and the ratio of quinoid structures upon F4TCNQ/AuCl₃ cascade doping. These findings offer insights into optimizing dopant combinations for cascade doping, showcasing its advantages in enhancing doping efficiency and resulting electrical conductivity compared with single dopant processes. Full article

Hybrid organic–inorganic perovskite solar cells (PSCs) are receiving huge attention owing to their marvelous advantages, such as low cost, high efficiency, and superior optoelectronics characteristics. Despite their promising potential, charge-carrier dynamics at the interfaces are still ambiguous, causing carrier recombination and hindering carrier transport, thus lowering the open-circuit voltages (V_oc) of PSCs. To unveil this ambiguous phenomenon, we intensively performed various optoelectronic measurements to investigate the impact of interfacial charge-carrier dynamics of PSCs under various light intensities. This is because the charge density can exhibit different mobility and charge transport properties depending on the characteristics of the charge transport layers. We explored the influence of the hole transport layer (HTL) by investigating charge transport properties using photoluminescence (PL) and time-resolved (TRPL) to unveil interfacial recombination phenomena and optoelectronic characteristics. We specifically investigated the impact of various thicknesses of HTLs, such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), and poly(triaryl)amine (PTAA), on FA_0.83MA_0.17Pb(Br_0.05I_0.95)₃ perovskite films. The HTLs are coated on perovskite film by altering the HTL’s concentration and using F4-TCNQ and 4-tert-butylpyridine (tBP) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSi) as dopants both for spiro-OMeTAD and PTAA. These HTLs diversified the charge concentration gradients in the absorption layer, thus leading to different recombination rates based on the employed laser intensities. At the same time, the generated charge carriers are rapidly transferred to the interface of the HTL/absorption layer and accumulate holes at the interface because of inefficient capacitance and mobility differences caused by differently doped HTL thicknesses. Notably, the charge concentration gradient is low at lower light intensities and did not accumulate holes at the HTL/absorption layer interface, even though they have high charge mobility. Therefore, this study highlights the importance of interfacial charge recombination and charge transport phenomena to achieve highly efficient and stable PSCs. Full article

A series of xylene charge-transfer complexes with fluorine-substituted tetracyanoquinodimethane (TCNQ) acceptors were studied experimentally and theoretically in order to reveal the role of various intermolecular interactions on stoichiometry and the crystal structure. It was shown that o-xylene face-to-face donor–donor interactions became significant enough to result in the formation of 2:1 cocrystals with F₁TCNQ and F₄TCNQ irrespective of growth conditions. The supramolecular arrangement in these cocrystals is mainly determined by the number of fluorine atoms in the acceptor. Comparative DFT and MP2 calculations of the pairwise intermolecular interactions revealed the overestimation of the dispersion energy for these systems by the DFT-wB97XD approach. Full article

Three new tetraphenylethene (TPE) push–pull chromophores exhibiting strong intramolecular charge transfer (ICT) are described. They were obtained via [2 + 2] cycloaddition–retroelectrocyclization (CA-RE) click reactions on an electron-rich alkyne-tetrafunctionalized TPE (TPE-alkyne) using both 1,1,2,2-tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) as electron-deficient alkenes. Only the starting TPE-alkyne displayed significant AIE behavior, whereas for TPE-TCNE, a faint effect was observed, and for TPE-TCNQ and TPE-F₄-TCNQ, no fluorescence was observed in any conditions. The main ICT bands that dominate the UV–Visible absorption spectra underwent a pronounced red-shift beyond the near-infrared (NIR) region for TPE-F₄-TCNQ. Based on TD-DFT calculations, it was shown that the ICT character shown by the compounds exclusively originated from the clicked moieties independently of the nature of the central molecular platform. Photothermal (PT) studies conducted on both TPE-TCNQ and TPE-F4-TCNQ in the solid state revealed excellent properties, especially for TPE-F4-TCNQ. These results indicated that CA-RE reaction of TCNQ or F₄-TCNQ with donor-substituted are promising candidates for PT applications. Full article

In this study, we developed two novel conjugated polymers that can easily be doped with F4TCNQ organic dopants using a sequential doping method and then studied their organic thermoelectric (OTE) properties. In particular, to promote the intermolecular ordering of OTE polymers in the presence of the F4TCNQ dopant, alkylthiazole-based conjugated building blocks with highly planar backbone structures were synthesized and copolymerized. All polymers showed strong molecular ordering and edge-on orientation in the film state, even in the presence of the F4TCNQ organic dopant. Thus, the sequential doping process barely changed the molecular ordering of the polymer films while making efficient molecular doping. In addition, the doping efficiency was improved in the more π-extended polymer backbones with thienothiophene units due to the emptier space in the polymer lamellar structure to locate ionized F4TCNQ. Moreover, the study of organic thin-film transistors (OTFTs) revealed that higher hole mobility in OTFTs was the key to increasing the electrical conductivity of OTE devices fabricated using the sequential doping method. Full article

Polyaniline (PANI) films are promising candidates for electronic nose-based IoT applications, but device performances are influenced by fabrication parameters and ambient conditions. Affinities of different PANI composites to analytes for gas sensing applications remain elusive. In this study, we investigate the material properties in detail for two different dopant systems: F4TCNQ and carbon black. Using a reproducibility-driven approach, we investigate different dopant concentrations in regard to their sensitivity and specificity towards five relevant markers for breath cancer diagnosis. We benchmark the system using ammonia measurements and evaluate limits of detection. Furthermore, we provide statistical analysis on reproducibility and pave the way towards machine learning discrimination via principal component analysis. The influence of relative humidity on sensor hysteresis is also investigated. We find that F4TCNQ-doped PANI films show improved reproducibility compared to carbon black-doped films. We establish and quantify a tradeoff between sensitivity, reproducibility, and environmental stability by the choice of dopant and concentrations ratios. Full article

We report on the tetraruthenium macrocycles Ru₄-5 and -6 with a π-conjugated pyrene-appended 5,8-divinylquinoxaline ligand and either isophthalate or thiophenyl-2,5-dicarboxylate linkers and their charge-transfer salts formed by oxidation with two equivalents of F₄TCNQ. Both macrocyclic complexes were characterized by NMR spectroscopy, mass spectrometry, cyclic and square-wave voltammetry, and by IR, UV–vis–NIR, and EPR spectroscopy in their various oxidation states. Full article

Organic ultraviolet (UV) phototransistors are promising for diverse applications. However, wide-bandgap organic semiconductors (OSCs) with intense UV absorption tend to exhibit large contact resistance (R_c) because of an energy-level mismatch with metal electrodes. Herein, we discovered that the molecular dopant of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ) was more efficient than the transition metal oxide dopant of MoO₃ in doping a wide-bandgap OSC, although the former showed smaller electron affinity (EA). By efficient contact doping, a low R_c of 889 Ω·cm and a high mobility of 13.89 cm²V⁻¹s⁻¹ were achieved. As a result, UV-sensitive phototransistors showed high photosensitivity and responsivity. Full article

The molecular structure, luminescence behavior, and electronic energy level of an organic optoelectronic materials are important parameters for its synthesis. The electro-optical properties can be changed by modifying the structure of the molecule to make the electronic energy level adjustable. In this article, a series of organic conjugated micro-molecules are successfully synthesized by linking small compound units. This metal-free [2 + 2] click chemistry process generates donor–acceptor chromophore substances with high yield, high solubility, and adjustable energy levels, which can be widely used for sensors and nonlinear optics in different fields. A-TCNE, A-TCNQ, and A-F4-TCNQ molecules are characterized comprehensively via UV-Vis-NIR spectra, ¹H NMR spectra, infrared spectroscopy, and mass spectrometry. The unique nonlinear optical phenomena and powerful intra-molecular charge–transfer interactions of these new materials give them fascinating potential for application as optoelectronic materials. Full article

Near-infrared dyes were developed to be contrast agents due to their ability to improve the productivity of photoacoustic (PA) imaging and photothermal therapy (PTT) treatments. During the article, we described in detail the PA and PT effects of a category of organic molecules. F₄-TCNQ could potentially cause a red-shift in the peak PA intensity. The results show that the PTT intensity of the near-infrared dyes with phenyl groups were higher than near-infrared dyes with thiophene groups. We also investigated the photodynamic treatment effect of C1b to demonstrate that these dyes are highly desirable in biochemistry. The high photoacoustic intensity of the organic molecules and the good yield of reactive oxygen species could indicate that these dyes have good potential for a wide range of imaging applications. Finally, we embedded the dye (C1b) in a liposomal hydrophobic phospholipid bilayer (C1b⊂L) to facilitate the application of hydrophobic dyes in biomedical applications, which can be absorbed by cells with good compatible and high stability for the imaging of cellular PA. Full article

Copper thiocyanate (CuSCN) has been gradually utilized as the hole injection layer (HIL) within optoelectronic devices, owing to its high transparency in the visible range, moderate hole mobility, and desirable environmental stability. In this research, we demonstrate quantum dot light-emitting diodes (QLEDs) with high brightness and current efficiency by doping 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) in CuSCN as the HIL. The experimental results indicated a smoother surface of CuSCN upon F4TCNQ doping. The augmentation in hole mobility of CuSCN and carrier injection to reach balanced charge transport in QLEDs were confirmed. A maximum brightness of 169,230 cd m⁻² and a current efficiency of 35.1 cd A⁻¹ from the optimized device were received by adding 0.02 wt% of F4TCNQ in CuSCN, revealing promising use in light-emitting applications. Full article