Two terminal-chlorinated ortho-benzodipyrrole (o-BDP)-based non-fullerene acceptors (NFAs), CFB-Cl and CMB-Cl, were designed and synthesized by incorporating fluorine or methyl substituents on the o-BDP core, respectively. Compared to their terminal-fluorinated counterparts, both NFAs exhibit red-shifted absorption, higher melting points, and stronger intermolecular interactions, attributed to the introduction of chlorinated end groups. Single-crystal X-ray analysis of CFB-Cl revealed a compact three-dimensional kaleidoscopic packing network stabilized by unique F···Cl halogen interactions between the fluorinated o-BDP core and the chlorinated end group, leading to a short π-π stacking distance of 3.38 Å and enhanced charge transport. Consequently, PM6:CFB-Cl devices achieved a PCE of 16.62% with a fill factor (FF) of 75.54%, outperforming PM6:CMB-Cl (PCE = 16.13%). To further improve device performance, a ternary blend strategy was employed by introducing the fluorinated CMB into PM6:CFB-Cl blends to extend the absorption range and improve the morphology. The resulting PM6:CFB-Cl:CMB inverted device exhibited excellent miscibility (χ = 0.02 K), balanced carrier transport (μe/μh = 1.38), suppressed recombination, and a highest PCE of 17.26% with Jsc = 26.02 mA cm-2 and Voc = 0.892 V. This work highlights the importance of halogen engineering in regulating molecular packing and charge dynamics, providing insights into the structure-morphology-performance relationship of o-BDP-based NFAs for next-generation organic photovoltaics.

The quest for sustainable energy solutions is critical amidst environmental challenges. Thermoelectric (TE) devices present a promising approach by converting waste heat into electricity through the Seebeck effect. These devices are advantageous due to their direct energy conversion, solid-state construction, reliability, scalability, long lifespan, and compatibility. However, their efficiency is often low, and they heavily depend on rare, expensive, and toxic inorganic materials. Carbon-based thermoelectric materials, such as carbon allotropes and organic thermoelectric materials such as conductive polymers, offer a sustainable alternative due to their abundance, low cost, eco-friendliness, and high mechanical flexibility, though their efficiency requires improvement. This study explores two generations of thermoelectric materials combining sulfonated-poly(3,4-ethylenedioxythiophene) (PSEDOT), a water-soluble and self-doped polymer, and single-walled carbon nanotubes (SWCNTs). The first generation optimized SWCNT dispersion and purification conditions, while the second generation improved the performance using better materials, resulting in a flexible film with a high conductivity (2000 S cm-1) and a power factor of 96.8 mu W m-1 K-2.

Photomultiplication organic photodetectors (PM-OPDs) have received substantial interest due to their high sensitivity and tunable spectral response, making them promising candidates for advanced optoelectronic applications. To continuously improve their performance, extensive experimental investigations are imperative. However, computer-aided materials screening could significantly accelerate the development of PM-OPDs. Therefore, we present a comprehensive dataset that encompasses key device performance metrics, the donors and acceptors utilized in active layers, their corresponding codes of simplified molecular input line entry system (SMILES), frontier molecular orbital energy levels, device active areas, applied biases, dark currents, and mass ratios of donors and acceptors. Through data analysis, we identify the essential features of PM-OPDs that are most relevant for training four distinct machine learning (ML) models. The performance of these ML models in predicting external quantum efficiencies (EQE) for PM-OPDs is evaluated using a range of performance metrics. The results indicate that all four ML models exhibit strong correlation coefficients (r > 0.9) in their predictions of the EQE values. Further, PM-OPDs are fabricated from a pair of unseen donor/acceptor materials, and device performance is used to assess the generalization capability of the ML models. This study, to the best of our knowledge, presents the first dataset and ML models specifically focusing on PM-OPDs. We anticipate that the dataset and the ML models will facilitate innovative applications of expert systems in the design and assessment of organic materials for OPDs.

The benzimidazole (BI)-centered acceptor IPF, featuring a perfluorophenyl (C 6 F 5 )-functionalized side chain, leverages fluorine–fluorine interactions to achieve enhanced OPV performance and stability.

ABSTRACT Our group has recently demonstrated the first fully solution‐processed polymeric multilayer piezoelectric devices. The key challenge, that is, the effective control of the redissolution issue, has been overcome using a solvent that offers adequate solubility but extremely slow dissolution for the piezoelectric polymer, poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)]. Several qualified solvents have been identified. Here, we comparatively study the effects of solvents on piezoelectric performance and production yield, for choosing the right solvent for fully solution‐processed multilayer piezoelectric devices. Each solvent exhibits distinct yield dependence on drying temperature, but the maximal yields achieved are independent of processing solvents. The solvents are also found to be interchangeable in terms of piezoelectric performance. The drying temperature and final annealing temperatures are identified to be decisive factors. The former only impacts the yield, and the latter only impacts the performance. The three parameters that define a poling condition are all investigated for the first time. A procedure enabling a fast identification of the right poling condition is proposed. Fully solution‐processed P(VDF‐TrFE) multilayer piezoelectric devices are prepared using the optimized conditions, and the dependence of the performance and yield on the number of layers is demonstrated. This work lays the foundation for producing such devices for practical applications.

The detection of light in the second near-infrared (NIR-II) region of the electromagnetic spectrum is critical for various applications such as bioimaging, environmental sensing and health monitoring. However, the narrow band gaps of organic semiconductors required for NIR-II photodetection increase the probability of charge injection under bias voltages and bulk thermal charge generation in the active layer, leading to a large dark current and low external quantum efficiency which results in poor detectivity. In this study, we introduce a series of low band-gap donor-acceptor type alternating conjugated polymers using thiadiazoloquinoxaline (TQ) as electron-withdrawing units and indacenodithiophene (P1 and P2) or propylenedioxythiophene as electron-donating units (P3-P5) for NIR-II photodetection. Polymers P3-P5 have much lower band gaps than P1 and P2 due to the stronger intrachain D-A interaction in the former. P3 and P5 have excellent solubility in a variety of organic solvents even at room temperature, which greatly facilitates the device fabrication process. The photodiode device based on P5 exhibited the highest specific detectivity of 2.0 x 1010 Jones at 1200 nm under -1 V bias owing to the significantly low dark current.

This study presents a comprehensive dataset that encompasses the indoor device performance of organic photovoltaic (OPV) materials, their corresponding SMILES codes, and frontier molecular orbital (FMO) energy levels. This dataset comprises a total of 128 subsets and features 64 pairs of donors and acceptors. We demonstrate that traditional models, such as the Shockley–Queisser limit and Scharber’s model, are insufficient for accurately predicting the behavior of indoor OPVs based on the molecular orbitals of these materials. In contrast, we explore the predictive capabilities of four machine learning (ML) models for estimating the power conversion efficiencies (PCEs) of indoor OPVs, utilizing molecular structure information and FMO data from the dataset we compiled. The trained ML models exhibit strong predictive performance with high correlation coefficients (r > 0.8) for indoor PCE values; notably, the support vector regression (SVR) model achieves the highest r of 0.878. The generalization capabilities of the models are also assessed using previously unseen materials, and the results demonstrate high accuracy rates. The SVR algorithm reaches the best average accuracy of 92.1

To date, colloidal quantum dots (CQDs) with absorption in the short-wave infrared region (SWIR, 1-2.6 mu m) typically consist of hazardous cadmium, lead, or mercury chalcogenides, which limit commercial acceptance. Environmentally friendly alternatives are therefore required to ensure minimal damage to ecosystems during fabrication, use, and disposal. A promising hazardous-element-free SWIR absorbing nanomaterial candidate is tin chalcogenide. We have developed tin telluride (SnTe) CQDs, with a size ranging from similar to 17 to 26 nm and corresponding absorption peak from similar to 2.3 to 2.5 mu m, indicative of size-dependent quantum confinement. Air-stable tin salts (tin chloride or tin acetate) were employed instead of the typical air-sensitive bis(bis(trimethylsilyl)amino tin(II). The synthesis was systematically investigated by optimizing the ligand type (1-dodecanethiol was used to replace oleic acid to prevent oxidation), injection method, growth temperature, reaction time, and feed molar ratio between tin and tellurium precursors. To improve stability in air, a ZnTe shell was successfully synthesized via cation exchange reaction at 70 degrees C with zinc acetate. The SnTe/ZnTe core-shell nanocrystals were fully characterized, revealing the formation of a protective ZnTe shell with a thickness of two to three monolayers, resulting in long-term stability in air (up to 1 month). These air-stable CQDs may offer a low-toxicity alternative nanomaterial for low-cost solution-processable fabrication of SWIR optoelectronics.

Time-frequency representations such as short-time Fourier transform and wavelet transform of the radar returns capture macro and micro motions of the individuals that facilitate human activity recognition using radars. However, the choice of windows in these transforms constrains the time-frequency resolution and may negatively impact the recognition of human activities. Synchro-squeezed Fourier and synchrosqueezed wavelet transforms are known to provide improved time-frequency resolution and therefore may provide better human activity recognition. This work uses the histogram of gradients (HOG) of the synchro-squeezed transforms as hand-crafted features for radar-based human activity recognition. Two types of synchro-squeezed time-frequency representations, namely, synchro-squeezed Fourier transform (SSFT) and synchro-squeezed wavelet transform (SSWT) are considered in this work. HOG features obtained from the synchrosqueezed transforms, the traditional short-time Fourier transform (STFT), and continuous time wavelet transform (CWT) are used with four well-known machine-learning classifiers, namely stochastic gradient descent (SGD), random forest (RF), K-nearest neighbor (KNN) and support vector machine (SVM). A publicly available dataset consisting of radar signatures of human activities recorded at three different locations is used in this study and a location-wise training/testing strategy is utilized. The performance of radar-based activity recognition is significantly improved with the use of synchro-squeezed time-frequency representations as compared to time-frequency representations without synchro-squeezing.

This paper proposes a Gramian Angular Field (GAF) for detection of fall events using radars. These GAF representations are directly obtained using range-time information and utilize temporal dependency among time samples for enhanced fall event detection. This work compares the performance of a patch-based learning model with attention (improved vision transformer (I-ViT)) and two patch-based learning models without attention (Multi-Layer Perceptron-Mixer (M-mixer) and Convolutional-Mixer (C-Mixer)) for fall detection with GAF plots as input with those obtained with range-time plots as input. Models are evaluated using a publicly available dataset with location-wise testing strategy. Patch-based learning model using GAF plots as input perform significantly better as compared to patch-based learning models using range-time plots at two out of three testing locations.

In this letter we present highly conductive and transparent thin films of single-walled carbon nanotubes (SWCNT) and conductive polymer composite deposited on polyethylene terephthalate film substrates by solution dipping. The initial results show that 66 Omega/square sheet resistance can be achieved with 80% transmission at the wavelength of 550 nm. This result is much superior to the performances of the pure SWCNT thin films deposited using the same technique. The improvement is attributed to the increase of effective electric conductive tube tube junctions in the CNT network. (C) 2009 Elsevier B.V. All rights reserved.

A novel approach for the production of cross-linked and robust hole transport layers for use in multilayer polymeric light-emitting diodes (PLEDs) has been developed. Two alternating triphenylamine–fluorene copolymers (TPAFn, n = 2, 3) with hydroxyl groups on the side chains and tris(4-dihydroxyboranylphenyl)amine (TBPA) as a cross-linker have been designed and synthesized. The mixture of TPAFn and TBPA when subjected to mild reaction conditions (2 h baking at 130 °C under vacuum) undergoes cross-linking reactions to produce cross-linked films (X-TPAFn), due to the formation of boronate ester linkages. The resulting X-TPAFn films have excellent solvent resistance to common organic solvents, such as THF and CHCl3, thereby facilitating the fabrication of multilayer PLEDs. Studies have shown that the cross-linking reaction had no detrimental effects on the photophysical properties of the resulting X-TPAFn films. In addition, the cross-linked X-TPAFn networks have been shown to have much better electron-blocking properties than the widely used PEDOT–PSS. Using X-TPAFn as a hole transport layer, we have investigated the electroluminescent (EL) properties of alternating fluorene–oxadiazole copolymers OxFn (n = 2, 3) and the poly(9,9-dioctylfluorene) (POF) homopolymer. The experimental data indicated that an increase in the oxadiazole content of the polymer lowered the LUMO energy level while decreasing the photoluminescence (PL) quantum yield. Consequently the best device performance was obtained with OxF3 which was found to have a maximum luminance of 2010 cd m−2 at 11.5 V and a maximum luminous efficiency of 1.0 cd A−1 at 820 cd m−2 when used with X-TPAF2 as the hole transport layer and calcium as the cathode.

In this paper, we report on highly efficient red-phosphorescent light-emitting diodes using a series of osmium complexes 1–3 doped into poly(N-vinyl-carbazole) (PVK) matrix as emitters, thermally stable 1,3,5-tris(4′-fluorobiphenyl-4-yl)benzene (F-TBB) as a hole-blocking layer, and Alq3 as an electron injection layer. The CIE 1931 chromaticity coordinates of complexes 1–3 are around (0.650, 0.347), (0.681, 0.317), and (0.696, 0.302), respectively, and remain almost unchanged over a wide range of operation voltages. The maximum luminous efficiencies reached 7.0, 3.5, and 1.2cd/A for devices based on 10wt.% of osmium complexes 1, 2 and 3, respectively, even with air stable aluminum as the cathode. We systematically studied the dependence of device performance on the osmium doping concentrations. It was found that the best device performance was observed at 10wt.% doping concentration for all three osmium complexes. Both maximum luminance and luminous efficiency increased with increasing osmium complex concentrations in the beginning and reached maximum at 10wt.% doping concentration. However, a further increase in the doping level resulted in a reduction in both device brightness and efficiency due to concentration quenching and triplet–triplet annihilation. This is consistent with the absolute photoluminescence quantum yields of PVK thin films doped with different concentration of osmium complexes.

Four dinuclear and trinuclear Cu(I) complexes that contain 2-(2'-pyridyl)benzimidazolyl derivative ligands including 1,4-bis[2-(2'-pyridyl)benzimidazolyl]benzene (1,4-bmb), 1,3-bis[2-(2'-pyridyl)benzimidazolyl]benzene (1,3-bmb), 1,3,5-tris[2-(2'-pyridyl)benzimidazolyl]benzene (tmb), and 4,4'-bis[2-(2'-pyridyl)benzimidazolyl]biphenyl (bmbp) have been synthesized. The formulas of these complexes are [Cu(2)(1,4-bmb)(PPh(3))(4)][BF(4)](2) (1), [Cu(2)(1,3-bmb)(PPh(3))(4)][BF(4)](2) (2), [Cu(3)(tmb)(PPh(3))(6)][BF(4)](3) (3), and [Cu(2)(bmbp)(PPh(3))(4)][BF(4)](2) (4), respectively. The crystal structures of 2-4 have been determined by single-crystal X-ray diffraction analyses. The Cu(I) ions in the complexes have a distorted tetrahedral geometry. For 3, two structural isomers (syn and anti) resulted from two different orientations of the three 2-(2'-pyridyl)benzimidazolyl chelating units were observed in the crystal lattice. Variable-temperature (1)H NMR experiments established the presence of syn and anti isomers for 1-3 in solution which interconvert at ambient temperature. Complexes 1-4 have a weak MLCT absorption band in the 350-450 nm region and display a yellow-orange emission when irradiated by UV light. One unexpected finding is that the yellow-orange emission of complexes 1-4 has a very long decay lifetime (approximately 200 micros) at 77 K. An electroluminescent (EL) device using 4 as the emitter and PVK as the host was fabricated. However, the long decay lifetime of the copper complexes may limit their applications as phosphorescent emitters in EL devices.

A novel series of monodisperse asymmetrically and symmetrically substituted diphenylamino end-capped oligofluorenes, OF(2)-NPhR, R = H or An (An = 9-anthryl) and OF(n)-NPh, n = 2-4, has been synthesized by a convergent approach using palladium-catalyzed Suzuki cross-coupling. End-capping of oligofluorenes with diphenylamino group(s) has been shown to offer advantages in terms of lowering their first ionization potentials, enhancing thermal stability, and inducing good amorphous morphological stability. By tuning the number of diphenylamino end-caps and the chain length, the optimal conjugated length for optical and luminescence properties has been determined. Of all the hitherto reported oligofluorenes capable of serving as non-doped blue emitters, OF(3)-NPh, with an optimal conjugated length, exhibits some of the best hole-transport and blue-emitting properties. A maximum luminance of 7500 cd m(-2) and a luminance efficiency up to 1.8 cd A(-1) have been achieved.

Random and alternating fluorene/carbazole (F/Cz) copolymers with various carbazole contents (20-50 mol %) have been designed and synthesized for use as the hole-transporting as well as light-emitting layer in blue light-emitting diodes (LEDs). DSC analysis has indicated the complete suppression of the crystallizability of these polymers by the introduction of 3,6-carbazole linkages into the polymer backbone, which also results in changes in their optical properties. The absorption maximum has been blue-shifted with an increase in the carbazole content due to the interruption in the main chain conjugation. Meanwhile, the photoluminescent properties have been influenced by the sequence distribution of the fluorene segments as well as the carbazole content. The emission maxima and vibronic features of the alternating copolymers have changed with carbazole content, reflecting the differences in the electronic structures of the repeat units. However, in the case of the random copolymers, the emission spectra remain almost unchanged and are similar to poly(9,9-dioetylfluorene) (PF), despite the fact that the carbazole content increases up to 33 mol %. This feature has been attributed to the existence of longer fluorene segments in the random copolymers, which would be expected to have lower energy gaps, and thus effectively collect excitons from other parts of the polymer backbone. Consequently, the light emitted from these energy traps is similar to that from PF. Electrochemical studies indicate that the introduction of carbazole units effectively raises the HOMO energy levels, thereby facilitating hole injection. Controlling the carbazole content between 20 and 33 mol % results in copolymers with stable and reversible p-doping and n-doping processes. A test for a LED device from P(F3-alt-Cz) indicates that the F/Cz copolymers could be a good candidate for blue light-emitting and hole-transporting materials.

The influences of the carbazole content on the photophysical, electrochemical, and electroluminescent properties of alternating fluorene/carbazole copolymers PFnCz (n = 1, 2, 3) with well-defined chemical structures have been systematically investigated. The incorporation of carbazole units into the polyfluorene (PF) backbone resulted in a blue shift of both the absorption and photoluminescence (PL) emission peaks, improved PL thermal stability, raised HOMO energy levels, and thus facilitated hole injection into the copolymers. Pure deep blue electroluminescence (EL) with narrow fwhms (full width at the half-maximum) (39-52 nm) and negligible low-energy emission bands was successfully achieved from the PFnCz copolymers by using 1,3,5-tris(4'-fluorobiphenyl-4-yl)benzene (F-TBB) as a hole-blocking layer and Alq(3) as an electron injection/transporting layer. This device configuration stabilized the blue emission from the PF derivatives. An efficiency of 0.72 cd/A at a luminance of 100 cd/m(2) was obtained even with aluminum metal as the cathode.

Thermal dehydration of boronic acid groups to form six-membered boronic acid anhydride (boroxine) was employed as a means of immobilizing oligofluorenes. This approach appears to improve the photoluminescenct stability of the cross-linked films compared to polyfluorenes. The emergence of long-wavelength emission upon thermal treatment usually observed in polyfluorenes has been prevented in this system. Initially the fluorene dimer (F2BA), trimer (F3BA), and tetramer (F4BA) containing boronic acid groups were prepared. These compounds were found to be readily soluble in common solvents such as THF, acetone, and DMF. Transparent thin films of these materials could be easily prepared by casting their solutions in THF onto KBr disks or glass substrates. Using mild reaction conditions (60-130degreesC under vacuum for 2 h), these oligomers in the solid sate readily undergo cross-linking reactions by the dehydration of boronic acid groups as evidenced by FT-IR spectroscopy and DSC/TGA studies. The resulting cross-linked amorphous networks exhibit high thermal (T-d at 5% weight loss, 363-420degreesC) and morphological (T-g, 173-202degreesC) stability. Under UV irradiation, these compounds emit bright violet-blue (F2BA) and blue T3BA and F4BA) light both in solution and in the solid state. The cured films exhibited almost identical UV-vis and fluorescence spectra even after heating at 150degreesC for 24 h, showing no long wavelength emission. The fabrication of LED devices using F3BA or F4BA as the light-emitting layer and a carbazole diboronic acid (CzBA) as the hole-transporting layer demonstrated that these thermally curable diboronic acids can be used to achieve double- (or multi-) layered configurations.

Three novel conjugated biphenols 3, 4, and 8 were synthesized by the Pd(OAc)2-catalyzed regioselective carbon−carbon coupling reaction of 2,6-di-tert-butylphenol or 2-phenylphenol with aryl halides. Although poly(arylene ether)s derived from biphenol 3 and arylene difluorides have low solubility in organic solvents, using 4,4‘-(9-fluorenylidene)diphenol or 4,4‘-(hexafluoroisopropylidene)diphenol as a comonomer gave soluble poly(arylene ether)s 6a−c. High molecular weight poly(arylene ether)s 7a‘−c‘ were also prepared from biphenol 4. The biscarbamate-masked monomers 5 and 9 improved the polymerization to give higher molecular weight polymers 7a−e and 10a−e in higher yields. Polymers 7 and 10 possess better film-forming capabilities and are still soluble in organic solvents. Polymers 6, 7, and 10 are all thermally stable with 5% weight loss temperatures higher than 500 °C under nitrogen. The polymers show strong blue light emission ranging from 387 to 478 nm in solution, depending on the conjugated structure.