Organic Semiconductors Research Articles

A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared.

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr-1 m-2.

Dopant-induced Morphology of Organic Semiconductors Resulting in High Doping Performance.

Doping plays a crucial role in modulating and enhancing the performance of organic semiconductor (OSC) devices. In this study, the critical role of dopants is underscored in shaping the morphology and structure of OSC films, which in turn profoundly influences their properties. Two dopants, trityl tetrakis(pentafluorophenyl) (TrTPFB) and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate (DMA-TPFB), are examined for their doping effects on poly(3-hexylthiophene) (P3HT) and PBBT-2T host OSCs. It is found that although TrTPFB exhibits higher doping efficiency, OSCs doped with DMA-TPFB achieve comparable or even enhanced electrical conductivity. Indeed, the electrical conductivity of DMA-TPFB-doped P3HT reaches over 67 S cm-1, which is a record-high value for mixed-solution-doped P3HT. This can be attributed to DMA-TPFB inducing a higher degree of crystallinity and reduced structural disorder. Moreover, the beneficial impact of DMA-TPFB on the OSC films' morphology and structure results in superior thermoelectric performance in the doped OSCs. These findings highlight the significance of dopant-induced morphological and structural considerations in enhancing the film characteristics of OSCs, opening up a new avenue for optimization of dopant performance.

Conjugated Polymer/Recombinant Escherichia coli Biohybrid Systems for Photobiocatalytic Hydrogen Production.

Biohybrid photocatalysts are composite materials that combine the efficient light-absorbing properties of synthetic materials with the highly evolved metabolic pathways and self-repair mechanisms of biological systems. Here, we show the potential of conjugated polymers as photosensitizers in biohybrid systems by combining a series of polymer nanoparticles with engineered Escherichia coli cells. Under simulated solar light irradiation, the biohybrid system consisting of fluorene/dibenzo [b,d]thiophene sulfone copolymer (LP41) and recombinant E. coli (i.e., a LP41/HydA BL21 biohybrid) shows a sacrificial hydrogen evolution rate of 3.442 mmol g-1 h-1 (normalized to polymer amount). It is over 30 times higher than the polymer photocatalyst alone (0.105 mmol g-1 h-1), while no detectable hydrogen was generated from the E. coli cells alone, demonstrating the strong synergy between the polymer nanoparticles and bacterial cells. The differences in the physical interactions between synthetic materials and microorganisms, as well as redox energy level alignment, elucidate the trends in photochemical activity. Our results suggest that organic semiconductors may offer advantages, such as solution processability, low toxicity, and more tunable surface interactions with the biological components over inorganic materials.

Constructing an Asymmetric Covalent Triazine Framework to Boost the Efficiency and Selectivity of Visible-Light-Driven CO2 Photoreduction.

The photocatalytic reduction of CO2 represents an environmentally friendly and sustainable approach for generating valuable chemicals. In this study, a thiophene-modified highly conjugated asymmetric covalent triazine framework (As-CTF-S) is developed for this purpose. Significantly, single-component intramolecular energy transfer can enhance the photogenerated charge separation, leading to the efficient conversion of CO2 to CO during photocatalysis. As a result, without the need for additional photosensitizers or organic sacrificial agents, As-CTF-S demonstrates the highest photocatalytic ability of 353.2µmolg-1 and achieves a selectivity of ≈99.95% within a 4h period under visible light irradiation. This study provides molecular insights into the rational control of charge transfer pathways for high-efficiency CO2 photoreduction using single-component organic semiconductor catalysts.

Strong Acceptors Based on Derivatives of Benzothiadiazoloimidazole

Despite the rapid progression of organic semiconductors, developing high-air-stability n-type organic semiconductors are still challenging. Herein, novel strong acceptors based on benzothiadiazoloimidazole units are reported. The results reveal that the strong acceptor BTI-NDI-BTI-a has good solubility and high electron affinity (3.94 eV), accompanied by 1D slipped-stacking crystals. Notably, the material presents promising potential for developing into air-stable n-type organic semiconductor materials.

Tailoring Cyano Substitutions on Quinoxaline‐based Small‐Molecule Acceptors Enabling Enhanced Molecular Packing for High‐Performance Organic Solar Cells

AbstractCyanation is a common chemical modification strategy to fine‐tune the energy levels and molecular packing of organic semiconductors, especially materials used in organic solar cells (OSCs). Generally, cyanation is used to modify the end groups of high‐performance small‐molecule acceptors (SMAs). However, the cyanation strategy has not been investigated on the central backbone of SMAs, which could introduce stronger intermolecular interaction and enhance the π–π stacking for rapid charge transport. This paper, for the first time, reports a new cyanation strategy on the central benzo‐quinoxaline core and synthesizes two novel A‐DA'D‐A type SMAs, named BQx‐CN and BQx‐2CN, with mono‐ and di‐cyanide groups, respectively. Through tailoring the number of CN groups, the BQx‐CN‐based OSC exhibits the best device performance of 18.8%, which is significantly higher than the non‐cyano BQx‐based one. The reason for the superior performance of BQx‐CN‐based devices can be attributed to the fine‐tuned energy level, stronger packing, and ideal phase segregation, which lead to superior exciton dissociation, faster charge transport, and suppressed recombination, therefore the highest fill factor (FF) and power conversion efficiencies (PCE). The research demonstrates the effectiveness of the cyanation strategy on the central core of SMAs for enhanced molecular packing and better performance of OSCs.

Organic Synaptic Transistors with Environmentally Friendly Core/Shell Quantum Dots for Wavelength-Selective Memory and Neuromorphic Functions.

Organic transistors based on organic semiconductors together with quantum dots (QDs) are attracting more and more interest because both materials have excellent optoelectronic properties and solution processability. Electronics based on nontoxic QDs are highly desired considering the potential health risks but are limited by elevated surface defects, inadequate stability, and diminished luminescent efficiency. Herein, organic synaptic transistors based on environmentally friendly ZnSe/ZnS core/shell QDs with passivating surface defects are developed, exhibiting optically programmable and electrically erasable characteristics. The synaptic transistors feature linear multibit storage capability and wavelength-selective memory function with a retention time above 6000 s. Various neuromorphic applications, including memory enhancement, optical communication, and memory consolidation behaviors, are simulated. Utilizing an established neuromorphic model, accuracies of 92% and 91% are achieved in pattern recognition and complicated electrocardiogram signal processing, respectively. This research highlights the potential of environmentally friendly QDs in neuromorphic applications and health monitoring.

Predicting fundamental gaps accurately from density functional theory with non-empirical local range separation.

We present an exchange-correlation approximation in which the Coulomb interaction is split into long- and short-range components and the range separation is determined by a non-empirical density functional. The functional respects important constraints, such as the homogeneous and slowly varying density limits, leads to the correct long-range potential, and eliminates one-electron self-interaction. Our approach is designed for spectroscopic purposes and closely approximates the piecewise linearity of the energy as a function of the particle number. The functional's accuracy for predicting the fundamental gap in generalized Kohn-Sham theory is demonstrated for a large number of systems, including organic semiconductors with a notoriously difficult electronic structure.

Exciton Delocalization and Polarizability in Perylenetetracarboxylic Diimide Probed Using Electroabsorption and Fluorescence Spectroscopies

Perylenetetracarboxylic diimide (PTCDI) is an n-type organic semiconductor molecule that has been widely utilized in numerous applications such as photocatalysis and field-effect transistors. Polarizability and dipole moment, which are inherent properties of molecules, are important parameters that determine their responses to external electric and optical fields, physical properties, and reactivity. These parameters are fundamentally important for the design of innovative materials. In this study, the effects of external electric fields on absorption and fluorescence spectra were investigated to obtain the PTCDI parameters. The PTCDI substituted by an octyl group (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide) dispersed in a polymethyl methacrylate (PMMA) matrix was studied in this work. The features of vibronic progression in the absorption spectrum were analogous to those observed in solution. The red shift of the absorption band caused by the Stark effect was mainly observed in the presence of an external electric field. Changes in parameters such as the dipole moment and polarizability between the ground and the Franck–Condon excited states of the PTCDI monomer were determined. The fluorescence spectrum shows a contribution from a broad fluorescence band at wavelengths longer than the monomer fluorescence band. This broad fluorescence is ascribed to the excimer-like fluorescence of PTCDI. The effects of the electric field on the fluorescence spectrum, known as the Stark fluorescence or electrofluorescence spectrum, were measured. Fluorescence quenching is observed in the presence of an external electric field. The change in the polarizability of the monomer fluorescence band is in good agreement with that of the electroabsorption spectrum. A larger change in the polarizability was observed for the excimer-like fluorescence band than that for the monomer band. This result is consistent with exciton delocalization between PTCDI molecules in the excimer-like state.

High-speed blade-coating using liquid crystalline organic semiconductor Ph-BTBT-10

Abstract We have investigated the fabrication of crystalline thin films of liquid crystalline organic semiconductor (2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene: Ph-BTBT-10) by high-speed blade-coating at 140 mm/s. Quite uniform crystalline Ph-BTBT-10 films were fabricated at the temperature over 50 ℃, which is the temperature of liquid crystal phase, without inhomogeneous recrystallization despite the high-speed blade-coating. The transistors fabricated with the uniform and flat crystalline thin films showed high average mobility of the 26 devices was 4.8 cm2/Vs and the coefficient of variation was only 7.3 %. We concluded that liquid crystalline organic semiconductors are useful materials for high-speed meniscus-guided-coating for practical use.

Bromine‐Enhanced Organic Materials for X‐ray Sensors: Unveiling the Potential of Small Molecules and Polymers through Material Design and Film Fabrication

AbstractOrganic X‐ray sensors are a promising new class of detectors with the potential to revolutionize medical imaging, security screening, and other applications. However, the development of high‐performance organic X‐ray sensors is challenged by low sensitivity. This paper reports on the development of nine X‐ray sensors based on new organic materials. It is demonstrated that the incorporation of bromine atoms into the sidechains of carbazolyl‐containing organic molecules significantly enhances their X‐ray sensitivity. This research suggests that incorporating a variety of high‐atomic‐number chemical elements into well‐established organic semiconductors is a promising strategy for designing efficient X‐ray sensor materials.

Gate-Tunable Positive and Negative Photoconductance in Near-Infrared Organic Heterostructures for In-Sensor Computing.

The rapid growth of sensor data in the artificial intelligence often causes significant reductions in processing speed and power efficiency. Addressing this challenge, in-sensor computing is introduced as an advanced sensor architecture that simultaneously senses, memorizes, and processes images at the sensor level. However, this is rarely reported for organic semiconductors that possess inherent flexibility and tunable bandgap. Herein, an organic heterostructure that exhibits a robust photoresponse to near-infrared (NIR) light is introduced, making it ideal for in-sensor computing applications. This heterostructure, consisting of partially overlapping p-type and n-type organic thin films, is compatible with conventional photolithography techniques, allowing for high integration density of up to 520 devices cm-2 with a 5µm channel length. Importantly, by modulating gate voltage, both positive and negative photoresponses to NIR light (1050nm) are attained, which establishes a linear correlation between responsivity and gate voltage and consequently enables real-time matrix multiplication within the sensor. As a result, this organic heterostructure facilitates efficient and precise NIR in-sensor computing, including image processing and nondestructive reading and classification, achieving a recognition accuracy of 97.06%. This work serves as a foundation for the development of reconfigurable and multifunctional NIR neuromorphic vision systems.

Realization of an organic semiconductor electroluminescent device with high directionality and color purity

AbstractWe are introducing an innovative organic semiconductor electroluminescent device capable of emitting light with unprecedented characteristics, that is, high directionality with divergence angle of 1.1° and high color purity with the full‐width at half‐maximum of 2.5 nm. This achievement was realized through design techniques aimed at enhancing gain via meticulous recombination zone control and complemented by the reduction of the optical losses. These results demonstrate the simultaneous achievement of a narrow spectrum and high directionality in an organic electroluminescent device.

Design Rules to Optimize the Intermolecular and Long-Range Packing of Organic Semiconductor Crystals

Design Rules to Optimize the Intermolecular and Long-Range Packing of Organic Semiconductor Crystals

Performance Improvement of Formamidinium‐Based Perovskite Photodetector by Solution‐Processed C8‐BTBT Modification

AbstractOrganic–inorganic hybrid perovskite has attracted extensive research due to its excellent optoelectronic properties and is a competitive candidate material for a new generation of photodetectors. However, lateral structure photodetectors based only on perovskite active materials still present moderate performance and poor stability. Herein, lateral structure formamidinium‐based perovskite FA0.9Cs0.1PbI3 photodetectors are reported which are modified by a solution‐processed organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) layer for improved photosensitive performance and ambient/flexibility stability. High‐mobility organic semiconductor C8‐BTBT serves as an efficient hole transport layer that fills the grain boundaries and gaps of the FA0.9Cs0.1PbI3 film, enabling rapid extraction and transport of the photo‐generated carriers from the perovskite to the electrodes, resulting in enhanced photosensitive performance of the photodetector. Compared with the original device, the C8‐BTBT‐modified photodetector exhibits dramatically improved performance with a best responsivity of 1278 mA W−1, specific detectivity of 1.58 × 1012 Jones, external quantum efficiency of 298%, and fall time of 14.09 ms, which is 10.84 times less than 152.76 ms of the pure perovskite device. Moreover, the C8‐BTBT film acts as a protective layer for the FA0.9Cs0.1PbI3 film because of its good air stability and effective coverage, which significantly improves the ambient stability of the perovskite photodetector compared with the original device, increasing photocurrent retention from 2.5% to 61.5% or 81.5% at different humidity after 6 days. Furthermore, the C8‐BTBT‐modified perovskite photodetector exhibits outstanding flexibility performance, with only a 5% reduction in photocurrent under bending and almost no change after 200 bending cycles, while those of the pristine perovskite device have degraded to ≈80% and ≈75% under the same conditions, respectively. This study provides a facile and effective solution‐processed‐based strategy for constructing high‐performance and stable perovskite photodetectors.

Ring Fusion Elevates the Electronic Mobility of Azabenzannulated Perylene Diimide.

The backwardness of n-type organic semiconductors still exists compared with the p-type counterparts. Thus, the development of high-performance n-type organic semiconductors is of great importance for organic electronic devices and their integrated circuits. In recent years, azabenzannulated perylene diimide (PDI), as one of immense bay-region-annulated PDI derivatives, has drawn considerable attentions. However, the electronic mobilities of azabenzannulated PDI derivatives are barely satisfactory. In this contribution, the peripheral benzene ring in azabenzannulated PDI 2 was fused to the ortho position by intermolecular C-H arylation cyclization. This endows the resultant azabenzannulated PDI 4 a planar configuration as well as electron deficient pentagonal ring. As a result, the electronic mobility of 4 is almost two orders of magnitude higher than that of the nonfused azabenzannulated PDI 2. This work shall pave a new avenue in elevating the performance of azabenzannulated PDI in organic electronics.

Room temperature excitonic coupling in self-assembled copper – fullerene hybrid films exposed to ambient air

Analytically sound combination of organic and inorganic semiconductors in designing functional hybrid nanomaterials promises new advances in nanoscience and in creation of next-generation optoelectronic devices. In this work, we report on combining two contrasting semiconductors (inorganic and organic) possessing attractive optical and electronic properties, namely Cu2O (in form of small single-crystalline nanoparticles, NPs) and C60-fullerene (as a medium supporting the NP ensemble), which were formed within the well-controlled Cux(Oy)C60 hybrid films through self-assembling and ambient air exposure of the vapour-deposited Cu and C60 mixture. The controllability of the hybrid film nanostructure was established and verified through systematic study of the films using Rutherford backscattering spectrometry, transmission electron microscopy, X-ray diffraction, Raman spectrometry and spectroscopic ellipsometry. The remarkable coincidence of the optical absorption peaks around 3.5 eV, reported for the Wannier-Mott (WM) excitons in a Cu2O crystal and detected for the Frenkel (F) excitons in the pristine C60 film, allowed us to observe room temperature polaritons as a product of the F-WM excitonic strong coupling. Quite high coupling energy of the FWM hybrid exciton estimated for the Cux(Oy)C60 films in the x interval of 5<x<15 (from 390 meV to 610 meV) implies the mediated effect of nanocavity photons and quantum confinement effect, strongly enhancing the hybrid exciton coupling energy. The implemented study discloses the self-assembled Cux(Oy)C60 hybrid films as promising material for application in optoelectronics and nonlinear optics.

Regulation on photocatalytic debromination by the reconfiguration of carbonyl groups on the covalent organic frameworks

Covalent organic frameworks (COFs) as promising organic semiconductor photocatalysts have become a research hotspot in the field of photocatalytic organic synthesis. Herein, a series of imine-linked EN-COF-x were synthesized by condensation reaction of amine monomer with triformylbenzene monomer. Then, β-ketoamine-linked KE-COF-y were obtained by the reconstruction of EN-COF-x in alkaline solution. The photocatalytic performance of COFs before and after the isomerization from enols to ketones were investigated. The characterization results and density functional theory calculations clearly demonstrated that the carbonyl groups not only make the conduction band energy level more negative, but also lead to a more inhomogeneous charge distribution in the molecule, which improved the separation efficiency of the photogenerated electrons. In addition, the increase in the number of hydroxyl groups on triformylbenzene monomer contributed to the formation of more carbonyl groups in the COF frameworks, which is beneficial to improving its photocatalytic performance. KE-COF-3 synthesized from 2,4,6-Trihydroxy-1,3,5-benzenetricarbaldehyde has more carbonyl group units and more suitable redox potential, which effectively promoted the debromination reaction with 99% yield under light irradiation. Meanwhile, it can be reused at least five times without loss of catalytic activity. This work provides insights for the rational design of functionalized β-ketoamine COFs for photocatalytic organic transformations.

Nonradical-dominated peroxymonosulfate activation by perylenetetracarboxylic acid nanosheet photocatalyst for efficient degradation of bisphenol a under visible-light irradiation

As a green, highly efficient, and sustainable technology, photocatalytic peroxymonosulfate (PMS) activation is a promising strategy for wastewater treatment. Moreover, the development of photocatalysts with excellent PMS activation performance is highly desirable for removing refractory organic contaminants from wastewater. Herein, perylenetetracarboxylic acid (PTA) nanosheets obtained using a facile method were explored as a highly efficient photocatalyst with a high PMS activation ability for bisphenol A (BPA) removal. Experimental results indicated that BPA can be removed within 16 min using PTA under optimal conditions. As confirmed through radical quenching, electron paramagnetic resonance spectroscopy, galvanic-oxidation-process experiments, and density functional theory calculations, photoinduced electrons and holes from PTA trigger PMS activation and thereby convert the reaction routes of BPA degradation from radical- to nonradical-dominated. The BPA degradation pathway was also studied using intermediate analysis and Fukui functions. Overall, the findings of this study shed light on organic semiconductor photocatalysts for nonradical-dominated PMS activation with regard to recalcitrant-organic-pollutant removal.

Tunable Solid‐State Properties and Anisotropic Charge Mobility in Hydrogen‐Bonded Diketopyrolopyrrole Polymers via Automated Device Fabrication and Characterization

AbstractThe optoelectronic properties of semiconducting polymers and device performance rely on a delicate interplay of design and processing conditions. However, screening and optimizing the relationships between these parameters for reliably fabricating organic electronics can be an arduous task requiring significant time and resources. To overcome this challenge, Polybot is developed—a robotic platform within a self‐driving lab that can efficiently produce organic field‐effect transistors (OFETs) from various semiconducting polymers via high‐throughput blade coating deposition. Polybot not only handles the fabrication process but also can conduct characterization tests on the devices and autonomously analyze the data gathered, thus facilitating the rapid acquisition of data on a large scale. This work leverages the capabilities of this platform to investigate the fabrication of OFETs using hydrogen bonding‐containing semiconducting polymers. Through high‐throughput fabrication and characterization, various data trends are analyzed, and large extents of anisotropic charge mobility are observed in devices. The materials are thoroughly characterized to understand the role of processing conditions in solid state and electronic properties of these organic semiconductors. The findings demonstrate the effectiveness of automated fabrication and characterization platforms in uncovering novel structure–property relationships, facilitating refinement of rational chemical design, and processing conditions, ultimately leading to new semiconducting materials.