Search

Although the power conversion efficiency of organic solar cells has recently exceeded 19% benefiting from the development of non-fullerene acceptors (NFAs), the electron affinity and electron mobility of NFAs still lag behind those of fullerene acceptors. Therefore, it is necessary to investigate a design rule that can break the currently used A–D–A linear strategy. In our early study, we have proposed a kind of two-dimensional (2D) NFA containing four electron-withdrawing end groups, which exhibited better electron affinity and electron mobility than those of typical linear NFAs. As we know, isomerism is one of the major factors affecting the properties of materials. Herein, three isomeric 2D NFAs based on a 2D fused-ring core (naphthalene) and four electron-withdrawing end groups, 2D-ICH, d-2D-ICH and b-2D-ICH, are reported, which exhibited a similar chemical structure but different symmetries. The molecular structures, intramolecular interactions, energy level, electron affinity, electrostatic potential, absorption spectra, exciton binding energy, electron mobility, solubility and chemical stability of these isomers were investigated. The results indicated that the isomerism of the conjugated backbone is an efficient method to turn the optoelectronic properties of NFA materials. d-2D-ICH shows an appropriate LUMO energy of –3.99 eV, a high electron affinity of 3.34 eV, higher integrated absorption intensity and smaller exciton binding energy than those of Y6, good solubility of 52 mg mL−1 in chlorobenzene, the highest chemical stability, and high electron mobility of 9.42 × 10−4 cm2 V−1 s−1. This demonstrated that numerous critical factors including absorption intensity, exciton separation, chemical stability, and charge mobility of d-2D-ICH are superior to those of widely used Y6. We propose that d-2D-ICH will be an excellent candidate for the development of next-generation NFAs for high-performance organic solar cells. [ABSTRACT FROM AUTHOR]

Solubility prediction is important in developing high-performance optoelectronic materials for organic solar cells, and can assist the synthetic route and chemical process design of optoelectronic materials, and control the morphology of bulk-heterojunctions. Here we report a successful approach that can effectively predict the solubility of optoelectronic materials in any solvents by using a combination of machine learning and quantum chemistry descriptors. Temperature combined with quantum chemistry calculated molecular vdW surface area (area), positive electrostatic potential (ESP) variance (σ+2) and negative ESP variance (σ−2) were used as a small set of descriptors containing only 7 bits of data. It is the smallest set of descriptors currently used and shows good predictive performance to predict the solubility. This small set of descriptors enables us to predict the solubility of any small molecule in various solvents with a small number of quantum chemical calculations. The solubility of PCBM and Y6 in 42 common solvents used in organic chemistry was predicted, and 10 solvents with the highest solubility are screened out from the dataset. This model can be applied to other small-molecule systems to rapidly predict their solubility in any solvent and provide an important parameter for designing promising high-performance optoelectronic materials for organic solar cells. [ABSTRACT FROM AUTHOR]

The development of pure deep-blue emitters with excellent optoelectronic and electroluminescence (EL) properties is full of challenges due to limited molecular designs. Herein, three novel color-tunable phenylcarbazole derivative based emitters from deep-blue to blue pCz-DPS, pCz-BTO and pCz-BP were demonstrated, which were designed by incorporating different short conjugation length building blocks as electron-accepting moieties and twisted rigid electron-donating carbazole derivatives. These emitters show deep-blue to blue emission, thanks to the deep highest occupied molecular energy level of the carbazole derivative donor units. In addition, pCz-BP exhibits aggregation-induced emission (AIE) properties, while pCz-BTO exhibits AIE and thermally activated delayed fluorescence (TADF) properties simultaneously. Nondoped organic light-emitting diodes (OLEDs) using these emitters as emission layers were fabricated, along with a maximum external quantum efficiency (EQE) and Commission Internationale de l'Éclairage (CIE) color coordinates of 7.1% and (0.15, 0.10) for pCz-BTO devices. The pCz-BTO emitter can also function robustly in doped OLEDs with an impressive maximum current efficiency (CE) and EQE of 23.3 cd A−1 and 9.5%, respectively, along with ultrapure blue color CIE coordinates of (0.15, 0.09). The significantly excellent performance of pCz-BTO could be ascribed to excellent photoluminescence quantum yield (PLQY), high reverse intersystem crossing rate constant (kRISC) and high fluorescence decay rate constant (kF) values. The excellent performance, ultrahigh color purity and extremely low efficiency roll-off of pCz-BTO are among the state-of-the-art deep-blue emitters, indicating the great potential of these materials in the application of ultrapure deep-blue OLEDs. [ABSTRACT FROM AUTHOR]

The synergistic effect between metal and acid sites has been considered to be of great importance to n-alkane hydroisomerization catalyzed by bifunctional catalysts. Herein, we report a facile mercaptosilane-assisted in situ synthesis approach to achieve stable and highly dispersed small Pt nanoparticles supported on HL zeolite catalysts (Pt/HL-SH) for n-hexane hydroisomerization. In comparison with the catalysts (Pt/HL-C) synthesized by a traditional ion-exchange method, the Pt/HL-SH catalysts show both high activity and excellent catalytic stability and also no obvious sintering of Pt nanoparticles is observed during the reaction due to the fact that the Pt/HL-SH catalysts possess both higher dispersion of Pt particles within the HL nanocrystals and more mesopores produced by mercaptosilane. Moreover, the regeneration stability of n-hexane hydroisomerization over Pt/HL-SH catalysts was also examined by five continuous cycles, demonstrating excellent regeneration properties. Thus, the mercaptosilane-assisted in situ synthesis approach is a promising way to prepare bifunctional catalysts for enhancing their catalytic performance in n-alkane hydroisomerization. [ABSTRACT FROM AUTHOR]

Incorporating mesopores into ZSM-5 zeolite to form a hierarchical structure has been regarded as an important approach to enhance the diffusivity and catalyst lifetime for light alkane aromatization. Herein, hierarchical ZSM-5 nano-aggregated microspheres were simply and directly synthesized and characterized using TPAOH as a single template without any mesoporous templates or zeolite seeds. The size of the ZSM-5 microspheres and the distribution of mesopores could be regulated by controlling the alkalinity of the synthesis gel. A possible self-assembly mechanism was proposed based on tracing the formation process of ZSM-5 microspheres with crystallization time. The ZSM-5 microspheres modified with Zn were applied in n-hexane aromatization and exhibited better catalytic stability than conventional mono-dispensed microporous ZSM-5 due to the existence of accessible mesopores. [ABSTRACT FROM AUTHOR]

Hollow zeolites have been considered as promising materials due to their unique porosity. Although some progress has been made in the synthesis of hollow zeolites, there are still few reports on the one-step synthesis of high-quality hollow ZSM-5 zeolites. In this work, we used a simple one-step strategy to synthesize high-quality bowl-like hollow ZSM-5 zeolites without additional templates. The strategy involves two key factors including the hydrolysis temperature of TEOS (tetraethoxysilane) and the amount of NaOH. During the preparation of the synthesis gel, the hydrolysis temperature of TEOS was carefully controlled to tune the spatial distribution of Al and Si throughout the micelle/nucleus, creating Al-zoning and a Si-rich core for the formation of intracrystalline macropores. The amount of Na+ was adjusted to change the competitive electrostatic interactions with TPA+ for negatively charged groups on the surface of crystals, producing bowl-like macropores on the shell of crystals. Various characterizations were made and the formation mechanism of bowl-like hollow ZSM-5 zeolites was proposed. [ABSTRACT FROM AUTHOR]

In recent years, non-fullerene acceptors, especially fused-ring electron acceptors (FREAs), have been successfully applied to develop high-performance bulk-heterojunction organic solar cells (OSCs). FREAs are typically composed of two strongly electron-withdrawing end groups connected by a planar fused-ring core. Through variation of the fused-ring core and electron-withdrawing end groups, OSCs based on these materials exhibit a higher power conversion efficiency than those based on fullerenes, and the highest power conversion efficiency exceeds 14%. However, the optimum thickness of the active layer of FREAs remains limited to ∼100 nm, which is mainly due to the low electron mobility of traditional FREAs. Therefore, developing new FREAs with higher electron mobility is of great significance. Here, we proposed two novel FREAs, namely, BFTT-N and BFTT-TN. These FREAs consist of four strongly electron-withdrawing end groups linked by a two-dimensional fused-ring core, forming a structure similar to a quad-rotor helicopter. These two FREAs not only exhibit higher electron mobility than the widely used non-fullerene acceptor ITIC but also have lower frontier molecular orbital energy levels, greater electron affinity, higher absorption coefficients and smaller exciton binding energies. Compared with that of ITIC, the absorption spectrum of BFTT-TN is red shifted approximately 100 nm, and its integrated intensity is 2.4 times that of ITIC. These numbers indicate that BFTT-TN features strong absorption in the visible and near-infrared region and produces more excitons. Simultaneously, the exciton binding energy of BFTT-TN (1.47 eV) is smaller than that of ITIC (2.04 eV), which can facilitate the separation of excitons into free charges. In addition, the electron mobility of BFTT-TN (5.32 × 10−3 cm2 V−1 s−1) is 6.5 times that of ITIC (8.20 × 10−4 cm2 V−1 s−1), which can accelerate the transmission of electrons to improve the short-circuit current. All these results imply that the quad-rotor-shaped FREAs are more suitable as electron acceptors for high-performance OSCs. The quad-rotor-shaped FREAs are expected to be an important candidate for the development of next-generation FREAs for high-performance OSCs. [ABSTRACT FROM AUTHOR]

Bipolar host materials can achieve excellent charge-transport balance and enhance device performance in phosphorescent organic light-emitting diodes (PhOLEDs). In this work, we designed three Ge-based bipolar host materials, (4-((4-(9H-carbazol-9-yl)phenyl)diphenylgermyl)phenyl)diphenylphosphine oxide (CzGeTpo), 2-(4-((4-(9H-carbazol-9-yl)phenyl)diphenylgermyl) phenyl)-5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazole (CzGeOdz), and 9-(4-(diphenyl(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)germyl)phenyl)-9H-carbazole (CzGePbzd), for blue PhOLEDs. These Ge-based bipolar hosts incorporate both the electron-donating group and electron-withdrawing group into the Ge-based core moiety (tetraphenylgermane) at the same time. The frontier molecular orbital energy levels of these materials suggest that all these Ge-based hosts are not only facilitated to obtain holes but also electrons. A multiscale simulation of charge transport in the amorphous thin film was developed to investigate the charge-transport properties of these materials. The simulation was based on quantum chemical calculations, molecular dynamics simulations, and Monte Carlo calculations. The results showed that all these materials exhibited both good electron and hole transport properties. CzGeTpo showed balanced charge-transport properties with a hole/electron ratio of 8 (the electron and hole mobilities were 1.6 × 10−3 and 1.2 × 10−2 cm2 V−1 s−1, respectively). At the same time, the lowest triplet energy of CzGeTpo was 3.31 eV, which is higher than that of most blue phosphorescent materials. The findings suggest that CzGeTpo would be a promising candidate for Ge-based bipolar small molecular hosts for highly efficient blue PhOLEDs. [ABSTRACT FROM AUTHOR]

In the last decade, fluorination has been successfully applied to organic semiconductor materials, especially to donor or acceptor materials for non-fullerene organic solar cells (OSCs). Currently, the power conversion efficiency based on these fluorinated materials is higher than that of the fullerene-based ones. Thus fluorination can down-shift the frontier molecular orbits, enhance inter/intramolecular interactions and reduce the Coulombic potential between holes and electrons. However, the key role of fluorine in improving the charge mobility of electron acceptors has yet to be systematically investigated. Here, we comprehensively explore the intermolecular interactions and electron mobilities in amorphous ITOIC and ITOIC-2F films by multiscale simulations. The simulations indicate that the electrostatically driven fluorine–π (F–π) interaction can exhibit a key role in increasing the intermolecular interactions and reducing the distance between the terminal groups of the fluorinated material ITOIC-2F. This phenomenon ultimately increases the intermolecular transfer integral and leads to an increase in electron mobility. Our work suggests that adding fluorine to the appropriate position of the phenyl ring can effectively inverse the electrostatic potential and produce intermolecular F–π interactions, which will be an effective way to improve the electron mobilities of the fluorinated electron acceptors for non-fullerene OSCs. [ABSTRACT FROM AUTHOR]

Being incompatible with host materials in a physically blended emitting layer, phosphorescent dyes are prone to form aggregates induced by Joule heat in devices under work. In this work, a new and efficient blue phosphorescent dye Cz-C8-FIrpic was designed and synthesised by incorporating 9-phenyl-9H-carbazole into a commonly used blue emissive iridium complex bis(4,6-(difluorophenyl)pyridine-N,C2′)picolinate (FIrpic) via an alkyl chain linkage. This phosphorescent dye exhibits similar photophysical properties to the units of FIrpic and 9-phenyl-9H-carbazole in solutions. In solid films of Cz-C8-FIrpic, the energy transfer from 9-phenyl-9H-carbazole to FIrpic units is effective. The Cz-C8-FIrpic doped emissive layer was investigated by AFM, STEM-EDS, transient photoluminescence decay curves and molecular dynamics simulations. The results show that in the Cz-C8-FIrpic doped film the phase aggregation of FIrpic units is less severe than that in the typically used FIrpic film. In addition, the optimized Cz-C8-FIrpic based device achieved a maximum luminance of 25 142 cd m−2, a maximum EQE of 8.5% and a maximum current efficiency of 22.5 cd A−1 which is about 15% higher than that of the control device based on FIrpic. We conclude that grafting a typically used dye to functional groups with alkyl chains is useful to restrict phase separation in physically blended emitting layers, and thus can achieve high electroluminescence performances. [ABSTRACT FROM AUTHOR]

Organic semiconductor materials with one-dimensional (1D) radial (core–shell) heterojunction structures are highly desired for their expected excellent optoelectronic properties. However, currently, such structures are still in a fledgling period for optoelectronic applications due to the absence of both good materials and suitable preparation methods. Here we have synthesized a p-type organic semiconductor based on a new electron-donating unit (dithienopyrazine) and utilized it as a shell material to construct organic 1D radial p–n heterojunctions. This p-type compound shows a higher oxidation potential and is more resistant to photooxidation in air than its analogs with the commonly-used benzodithiophene unit. Moreover, we prepared organic microwires with radial heterojunctions via a solution-processed method by self-assembly of our p-type material on the surface of n-type cores. Thus, photoconductive devices based on an individual microwire with the radial heterojunction can be fabricated and demonstrate a high photoconductivity. Our work provides a path for preparing 1D radial heterojunctions suitable for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Two kinds of host materials, 4,4′-(diphenylgermanediyl)bis(N,N-diphenylaniline) and bis(4-(9H-carbazol-9-yl)phenyl)diphenylgermane (DCzGe), for blue phosphorescent organic light emitting diodes (PhOLEDs) were designed by incorporating electron donating groups (carbazole and triphenylamine) into tetraphenylgermane, which is a new type of core moiety that has never been studied for use in this field. This molecular structure endows the compounds with a wide energy bandgap, high thermal/morphological stability and good solution processability. Based on the theoretic calculations, DCzGe was selected and synthesized as a host material which demonstrates a wide bandgap (Eg: 3.56 eV) and a high triplet energy (ET: 3.02 eV). It also exhibits a high glass transition temperature (110 °C), which is beneficial for resisting the Joule heat in devices. All solution processed, blue emitting PhOLEDs were fabricated by using a mixed host combining DCzGe and an electron-transporting material, with a maximum luminance of 10 000 cd m−2 and a maximum current efficiency of 15.2 cd A−1. Furthermore, the devices showed a very low current efficiency roll-off, which remained as high as 15.2 cd A−1 at the luminance of 1000 cd m−2, and the roll-off is only 2.6% even at the higher luminance of 2000 cd m−2. [ABSTRACT FROM AUTHOR]

Two blue-emitting fluorescent polymers PTPATPPO and PTPATPP with small singlet–triplet splitting comprising triphenylamine and triphenylphosphine/triphenylphosphine oxide moieties have been designed and synthesized. An appropriate overlap between the HOMO and the LUMO in these compounds was realized. This design strategy endows the two blue-emitting polymers with a high triplet energy of 2.45 and 2.46 eV, a shallow HOMO level of −5.21 and −5.23 eV, and a bipolar feature to act as good host materials. Monochromic organic light-emitting devices (OLEDs) using these polymers as emitters show sky-blue emissions with Commission Internationale de l'Eclairage (CIE) coordinates of (0.24, 0.32) and (0.24, 0.31) together with a maximum current efficiency of 3.63 cd A−1. Moreover, the single-emitting-layer two-element fluorescent–phosphorescent (F–P) hybrid white OLEDs based on PTPATPPO or PTPATPP as both hosts and blue-emitting fluorophores were fabricated by a solution process. Among the two polymers, PTPATPPO-based F–P hybrid white OLEDs show better performance with a maximum current efficiency of 10.5 cd A−1, a maximum external quantum efficiency of 6.1%, CIE coordinates of (0.40, 0.34), and a maximum luminance of 11 962 cd m−2. [ABSTRACT FROM AUTHOR]

By attaching two electron-withdrawing trifluoromethyl (CF3) groups to the 2-phenylbenzothiazole cyclo-metalated ligand, a bis-trifluoromethyl-functionalized orange-emitting phosphorescent iridium(iii) complex bis-(6-(trifluoromethyl)-2-(4-(trifluoromethyl)phenylbenzothiozolato))iridium(acetylacetonate) [(F3BT-CF3P)2Ir(acac)] was successfully synthesized. The optical, electrochemical and electroluminescence (EL) properties of this new complex were studied. The experimental results support the theoretical expectation that incorporating electron-withdrawing trifluoromethyl groups at the 4-site of the phenyl ring directly bonded to the metal center, and at the 6-site of 2-phenylbenzothiazole, cause a bathochromic shift in the emission peak and bring the emission color much closer to long-wavelength orange light. Moreover, such trifluoromethyl substituents can hinder the π–π stacking or self-polarization effect occurring from the aggregation of the molecules. The new iridium complex gives an unchanged luminescence spectrum, regardless of whether it is in solution, in untreated film or in film doped at different concentrations. Using this iridium complex as a dopant emitter, solution-processed single emissive layer orange and two-element white OLEDs with good performance can be obtained. Highly efficient orange electroluminescence was obtained with a maximum efficiency of 10.5 cd A−1 and CIE coordinates (0.48, 0.51). When combined with a commercial sky-blue phosphorescent emitter, (CF3BT–CF3P)2Ir(acac) can be utilized to achieve two-element white OLEDs that exhibited a high efficiency of 28.3 cd A−1. Such OLEDs retain high efficiency at a luminance suitable for lighting (e.g. 5000 cd m−2). [ABSTRACT FROM AUTHOR]

Correction for ‘Quad-rotor-shaped non-fullerene electron acceptor materials with potential to enhance the photoelectric performance of organic solar cells’ by Chuang Yao et al., J. Mater. Chem. A, 2019, DOI: URL10.1039/c9ta04084f/URL. [ABSTRACT FROM AUTHOR]

Metal organic framework (MOF)-derived nanostructures display remarkable characteristics and have broad application potential. Os@ZIF-8 nanocomposites were prepared by a depositional method. The Os nanoparticles distributed on the surface of ZIF-8. The nanocomposites displayed enhanced peroxidase-like activity with smaller K m for both 3,3',5,5'-tetramethylbenzidine (TMB) and H 2 O 2 compared to Os NPs due to the confinement effect and large surface area that ZIF-8 provided. From the average reaction rate constants obtained from three different temperatures, the activation energy values were determined. The kinetic data indicated that the Os@ZIF-8 NCs are catalytically more active than Os NPs. In addition, quantitative measurement of Hg 2+ was performed based on the formation of Os-Hg alloy. Os@ZIF-8 NCs had a wide detection range between 0 μM and 71.43 μM for Hg 2+ with a limit of detection (LOD) of 2.29 μM. Using a MOF with a large surface area to load Os nanoparticles to achieve enhanced nanozyme activity is the novelty of this work., Competing Interests: The authors declared that they have no conflicts of interest to this work., (This journal is © The Royal Society of Chemistry.)

In this study, fcSe@TiO 2 and [Cu 2 I 2 (fcSe) 2 ] n @TiO 2 nanosystems based on ferrocenylselenoether and its cuprous cluster were developed and characterized by X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX), and electron paramagnetic resonance (EPR). Under optimized conditions, 0.2 g L -1 catalyst, 20 mM H 2 O 2 , and initial pH 7, good synergistic visible light photocatalytic tetracycline degradation and Cr(vi) reduction were achieved, with 92.1% of tetracycline and 64.5% of Cr(vi) removal efficiency within 30 minutes. Mechanistic studies revealed that the reactive species ˙OH, ˙O 2 - , and h + were produced in both systems through the mutual promotion of Fenton reactions and photogenerated charge separation. The [Cu 2 I 2 (fcSe) 2 ] n @TiO 2 system additionally produced 1 O 2 from Cu + and ˙O 2 - . The advantages of the developed nanosystems include an acidic surface microenvironment provided by Se⋯H + , resourceful product formation, tolerance of complex environments, and excellent adaptability in refractory N-cyclic organics., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

The cyano-group (-C[triple bond, length as m-dash]N) is an electron-withdrawing group, which has been widely used to construct high-performance fused-ring electron acceptors (FREAs). Benefiting from these FREAs, the power conversion efficiency of organic solar cells has recently exceeded 18%. However, malononitrile is a highly toxic substance used to introduce -C[triple bond, length as m-dash]N during the synthesis of these FREAs. Therefore, the synthesis processes of most high-performance FREAs are typically harmful to the environment. Our previous work demonstrated that the electron-withdrawing ability of -C[triple bond, length as m-dash]N is necessary for FREAs. Thus, the use of other electron-withdrawing groups instead of -C[triple bond, length as m-dash]N to design environmentally friendly FREAs is feasible. We utilized seven electron-withdrawing groups, namely, -C[double bond, length as m-dash]NH, -N[double bond, length as m-dash]O, -CH[double bond, length as m-dash]O, -CO-CH3, -CO-OH, -CO-Cl, and -CO-Br, to replace -C[triple bond, length as m-dash]N in the commonly used acceptor Y6 to design new FREAs (Y6-CNH, Y6-NO, Y6-CHO, Y6-COCH3, Y6-COOH, Y6-COCl, and Y6-COBr). Multi-scale theoretical calculation methods were used to investigate the photoelectronic properties of these new FREAs, including energy level, absorption spectrum, exciton binding energy, and electron mobility. The results showed that Y6-CNH, Y6-COCH3 and Y6-COOH are unsuitable for use as acceptor materials because of their high frontier molecular orbital energy level and weak electron affinity. The strong absorption intensity and weak exciton binding energy of Y6-CHO, Y6-COCl, and Y6-COBr indicated that they can absorb more solar energy than Y6 and excitons are easier to separate into free charges. The electron mobility of Y6-CHO (3.53 × 10 -4 cm 2 V -1 s -1 ) was found to be approximately 28 times that of Y6-COCl (1.24 × 10 -5 cm 2 V -1 s -1 ) and Y6-COBr (1.28 × 10 -5 cm 2 V -1 s -1 ). The possible synthetic routes to Y6-CHO are environmentally friendly. Therefore, -CH[double bond, length as m-dash]O is the most suitable electron-withdrawing group for constructing high-performance environmentally friendly FREAs. This work can provide a new molecular design perspective in experimental science for developing high-performance environmentally friendly FREAs.