Showing papers on "Absorption (electromagnetic radiation) published in 2018"

A Voltage-Boosting Strategy Enabling a Low-Frequency, Flexible Electromagnetic Wave Absorption Device.

Abstract: Nowadays, low-frequency electromagnetic interference (<2.0 GHz) remains a key core issue that plagues the effective attenuation performance of conventional absorption devices prepared via the component-morphology method (Strategy I). According to theoretical calculations, one fundamental solution is to develop a material that possesses a high e' but lower e″. Thus, it is attempted to control the dielectric values via applying an external electrical field, which inducts changes in the macrostructure toward a performance improvement (Strategy II). A sandwich-structured flexible electronic absorption device is designed using a carbon film electrode to conduct an external current. Simultaneously, an absorption layer that is highly responsive to an external voltage is selected via Strategy I. Relying on the synergistic effects from Strategies I and II, this device demonstrates an absorption value of more than 85% at 1.5-2.0 GHz with an applied voltage of 16 V while reducing the thickness to ≈5 mm. In addition, the device also shows a good absorption property at 25-150 °C. The method of utilizing an external voltage to break the intrinsic dielectric feature by modifying a traditional electronic absorption device is demonstrated for the first time and has great significance in solving the low-frequency electromagnetic interference issue.

Direct Growth of Edge-Rich Graphene with Tunable Dielectric Properties in Porous Si3N4 Ceramic for Broadband High-Performance Microwave Absorption

Abstract: High-performance graphene microwave absorption materials are highly desirable in daily life and some extreme situations. A simple technique for the direct growth of graphene as absorption fillers in wave-transmitting matrices is of paramount importance to bring it to real-world application. Herein, a simple chemical vapor deposition (CVD) route for the direct growth of edge-rich graphene (ERG) with tailored structures and tunable dielectric properties in porous Si3N4 ceramics using only methyl alcohol (CH3OH) as precursor is reported. The large O/C atomic ratio of CH3OH helps to build a mild oxidizing atmosphere and leads to a unique structure featuring open graphite nanosteps and freestanding nanoplanes, endowing the ERG/Si3N4 hybrid with an appropriate balance between good impedance matching and strong loss capacity. Accordingly, the prepared materials exhibit superior electromagnetic wave absorption, far surpassing that of traditional CVD graphene and reduced graphene oxide-based materials, achieving an effective absorption bandwidth of 4.2 GHz covering the entire X band, with a thickness of 3.75 mm and a negligibly low loading content of absorbents. The results provide new insights for developing novel microwave absorption materials with strong reflection loss and wide absorption frequency range.

Saturable Absorption in 2D Ti₃C₂ MXene Thin Films for Passive Photonic Diodes

Abstract: MXenes comprise a new class of 2D transition metal carbides, nitrides, and carbonitrides that exhibit unique light-matter interactions. Recently, 2D Ti3 CNTx (Tx represents functional groups such as OH and F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences, which is useful for mode locking in fiber-based femtosecond lasers. However, the fundamental origin and thickness dependence of SA behavior in MXenes remain to be understood. 2D Ti3 C2 Tx thin films of different thicknesses are fabricated using an interfacial film formation technique to systematically study their nonlinear optical properties. Using the open aperture Z-scan method, it is found that the SA behavior in Ti3 C2 Tx MXene arises from plasmon-induced increase in the ground state absorption at photon energies above the threshold for free carrier oscillations. The saturation fluence and modulation depth of Ti3 C2 Tx MXene is observed to be dependent on the film thickness. Unlike other 2D materials, Ti3 C2 Tx is found to show higher threshold for light-induced damage with up to 50% increase in nonlinear transmittance. Lastly, building on the SA behavior of Ti3 C2 Tx MXenes, a Ti3 C2 Tx MXene-based photonic diode that breaks time-reversal symmetry to achieve nonreciprocal transmission of nanosecond laser pulses is demonstrated.

Application of yolk–shell Fe 3 O 4 @N-doped carbon nanochains as highly effective microwave-absorption material

Abstract: Yolk–shell Fe3O4@N-doped carbon nanochains, intended for application as a novel microwave-absorption material, have been constructed by a three-step method. Magnetic-field-induced distillation-precipitation polymerization was used to synthesize nanochains with a one-dimensional (1D) structure. Then, a polypyrrole shell was uniformly applied to the surface of the nanochains through oxidant-directed vapor-phase polymerization, and finally the pyrolysis process was completed. The obtained products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and thermogravimetric analyses (TGA) to confirm the compositions. The morphology and microstructure were observed using an optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The N2 absorption–desorption isotherms indicate a Brunauer–Emmett–Teller (BET) specific surface area of 74 m2/g and a pore width of 5–30 nm. Investigations of the microwave absorption performance indicate that paraffin-based composites loaded with 20 wt.% yolk–shell Fe3O4@N-doped carbon nanochains possess a minimum reflection loss of −63.09 dB (11.91 GHz) and an effective absorption bandwidth of 5.34 GHz at a matching layer thickness of 3.1 mm. In addition, by tailoring the layer thicknesses, the effective absorption frequency bands can be made to cover most of the C, X, and Ku bands. By offering the advantages of stronger absorption, broad absorption bandwidth, low loading, thin layers, and intrinsic light weight, yolk–shell Fe3O4@N-doped carbon nanochains will be excellent candidates for practical application to microwave absorption. An analysis of the microwave absorption mechanism reveals that the excellent microwave absorption performance can be explained by the quarter-wavelength cancellation theory, good impedance matching, intense conductive loss, multiple reflections and scatterings, dielectric loss, magnetic loss, and microwave plasma loss.

Bio-gel derived nickel/carbon nanocomposites with enhanced microwave absorption

Abstract: A bio-gel derived strategy was used to construct Ni/C nanocomposites consisting of three-dimensional (3-D) carbon networks with embedded nickel nanoparticles. The amorphous carbon prevents agglomeration of the nickel nanoparticles and thus contributes to a good impedance match. The microwave absorption properties of the Ni/C nanocomposites were optimized according to percolation theory for good impedance matching. As a result, microwave absorbing coatings, which have the advantages of thin thickness (1.75 and 1.5 mm) and light weight (25 and 30 wt%), were achieved with excellent absorbing properties (90% microwave absorption) and a broad bandwidth (13.6–18 GHz and 13.2–18 GHz). The absorbing properties were mainly attributed to the dielectric relaxation processes at 2–18 GHz from the multilevel interface, porous carbon materials and nanoscale nickel nanoparticles in the Ni/C nanocomposites. It is believed that this work not only helps to elucidate the mechanism of absorption but also provides a new design paradigm for determining the optimal content of absorbers using percolation theory. The bio-gel derived strategy paves a possible way for the mass synthesis of microwave absorbers.

An Unusual Strong Visible-Light Absorption Band in Red Anatase TiO2 Photocatalyst Induced by Atomic Hydrogen-Occupied Oxygen Vacancies.

Abstract: Increasing visible light absorption of classic wide-bandgap photocatalysts like TiO2 has long been pursued in order to promote solar energy conversion. Modulating the composition and/or stoichiometry of these photocatalysts is essential to narrow their bandgap for a strong visible-light absorption band. However, the bands obtained so far normally suffer from a low absorbance and/or narrow range. Herein, in contrast to the common tail-like absorption band in hydrogen-free oxygen-deficient TiO2 , an unusual strong absorption band spanning the full spectrum of visible light is achieved in anatase TiO2 by intentionally introducing atomic hydrogen-mediated oxygen vacancies. Combining experimental characterizations with theoretical calculations reveals the excitation of a new subvalence band associated with atomic hydrogen filled oxygen vacancies as the origin of such band, which subsequently leads to active photo-electrochemical water oxidation under visible light. These findings could provide a powerful way of tailoring wide-bandgap semiconductors to fully capture solar light.

Facile synthesis of ultrasmall Fe3O4 nanoparticles on MXenes for high microwave absorption performance

Abstract: Although two dimensional (2D) materials have already been studied as promising microwave absorption materials due to fascinating layered structure, it is hard to achieve both thin coating and excellent absorbing capability. Herein, 2D hierarchical composites of nano-sized Fe3O4 particles on MXenes (TiO2/Ti3C2Tx/Fe3O4) with different [TiO2/Ti3C2Tx]/[Fe3O4] ratios were synthesized by using a moderate chemical hydrothermal reaction. Scanning electron microscope and transmission electron microscope techniques indicated that the surfaces of MXenes were densely covered with Fe3O4 nanoparticles of ∼4.9 nm in diameter and TiO2 particles. By tuning the ratio of [TiO2/Ti3C2Tx]/[Fe3O4], microwave absorption capabilities in terms of the maximum reflection loss (RL) value and absorber thickness could be readily optimized. Specifically, the sample TiO2/Ti3C2Tx/Fe3O4-5 exhibited a remarkable absorption performance, with a maximum reflectivity of −57.3 dB at 10.1 GHz and a band range below −10 dB to over 9.1–11.1 GHz at a thickness of 1.9 mm. Therefore, our 2D MXene composites are expected to be promising candidates as ultrathin and lightweight absorbing materials.

Prussian blue analogues derived magnetic FeCo alloy/carbon composites with tunable chemical composition and enhanced microwave absorption.

Abstract: A series of magnetic FeCo alloy/carbon composites have been successfully prepared through in situ pyrolysis of Prussian blue analogues (PBAs) with different Fe/Co ratios. The Fe/Co ratio can affect the crystalline phase, particle size, and magnetic property of the FeCo alloy particles, as well as the relative graphitization degree of the carbon frameworks. As a result, the electromagnetic functions of these composites will be highly associated with the Fe/Co ratio, where high Co content is beneficial to the formation of strong dielectric loss and moderate Co content can facilitate the magnetic loss. When Fe/Co ratio reaches 1:1, the as-obtained composite (sample S4) displays excellent reflection loss characteristics with powerful absorption in a very broad frequency range (over −10 dB in 3.2–18.0 GHz), which is superior to those of single magnetic metal (Fe or Co)/carbon composite derived from PBAs, as well as many previously reported FeCo alloy/carbon composites. Electromagnetic analysis reveals that the excellent microwave absorption of sample S4 benefits from its preferable matching of characteristic impedance and good attenuation ability toward incident electromagnetic waves. These results provide new insight into the fabrication of carbon-based magnetic composites with enhanced microwave absorption by rationally manipulating the chemical composition of magnetic components.

Heterostructured Nanorings of Fe-Fe3O4@C Hybrid with Enhanced Microwave Absorption Performance.

Abstract: Microwave absorption is a critical challenge with progression in electronics, where fine structural designing of absorbent materials plays an effective role in optimizing their microwave absorption properties. Here, we have developed Fe3O4@C (FC) and Fe-Fe3O4@C (FFC) hybrid nanorings via a hydrothermal method coupled with a chemical catalytic vapor deposition technique. FC and FFC hybrid nanorings have fine carbon coating while their size can easily be tunable in a certain range from 80-130 to 90-140 nm. The optimized FC and FFC hybrid nanorings bear minimum reflection loss (RL) values of -39.1 dB at 15.9 GHz and -32.9 dB at 17.1 GHz, respectively, whereas FFC shows an effective absorption bandwidth (RL values < -10 dB) ranged from 5.2 to 18 GHz. Such an enhanced microwave absorption performance of hybrid nanorings is mainly due to the suitable impedance characteristics, multilevel interfaces, and polarization features in nanorings. This work provides an approach to design hybrid materials having a complex structure to enhance the microwave absorption properties.

Super Broadband Near-Infrared Phosphors with High Radiant Flux as Future Light Sources for Spectroscopy Applications

Abstract: The near-infrared (NIR) light source is desirable for real-time nondestructive examination applications, which include the analysis of foodstuffs, health monitoring, iris recognition, and infrared cameras. The emission spectra of such an infrared light source should also be as broad as possible for effective performance, in view of the fact that the broad absorption and reflection of light by the organic elements present in foodstuffs and human health fall in the blue and NIR regions of the electromagnetic spectrum, respectively. In this letter, a blue light-emitting diode (LED) excitable super broadband NIR phosphor light source is developed with a high fwhm of 330 nm and radiant flux of 18.2 mW for the first time. The observation of super-broad-band luminescence from two distinct luminescence centers is studied and evidenced by electron paramagnetic resonance, X-ray absorption near-edge structure, steady-state luminescence, and time-resolved luminescence at ambient and high-pressure environments. Finall...

Hollow N-Doped Carbon Polyhedron Containing CoNi Alloy Nanoparticles Embedded within Few-Layer N-Doped Graphene as High-Performance Electromagnetic Wave Absorbing Material.

Abstract: Magnetic metal nanostructures have exhibited good electromagnetic wave (EMW) absorption properties. However, the surface of the nanostructures is easily oxidized upon exposure to air, leading to the bad stability of the EMW absorption properties. We use metal–organic framework structure as a template to fabricate hollow N-doped carbon polyhedron containing CoNi alloy nanoparticles embedded within N-doped graphene (CoNi@NG-NCPs). The atomic ratio of Co/Ni can be tuned from 1:0.54 to 1:0.91 in the hollow CoNi@NG-NCPs. Experimental results demonstrate that the EMW absorption properties of the CoNi@NG-NCPs can be improved through the Ni introduction and increased with an increase of the Ni content. Typically, the minimal reflection loss of the optimal CoNi@NG-NCP can reach −24.03 dB and the effective absorption bandwidth (reflection loss below −10 dB) is as large as 4.32 GHz at the thickness of 2.5 mm. Furthermore, our CoNi@NG-NCPs exhibit favorably comparable or superior EMW absorption properties to other ma...

Sunlight-driven water-splitting using two-dimensional carbon based semiconductors

Abstract: The overwhelming challenge of depleting fossil fuels and anthropogenic carbon emissions has driven research into alternative clean sources of energy. To achieve the goal of a carbon neutral economy, the harvesting of sunlight by using photocatalysts to split water into hydrogen and oxygen is an expedient approach to fulfill the energy demand in a sustainable way along with reducing the emission of greenhouse gases. Even though the past few decades have witnessed intensive research into inorganic semiconductor photocatalysts, their quantum efficiencies for hydrogen production from visible photons remain too low for the large scale deployment of this technology. Visible light absorption and efficient charge separation are two key necessary conditions for achieving the scalable production of hydrogen from water. Two-dimensional carbon based nanoscale materials such as graphene oxide, reduced graphene oxide, carbon nitride, modified 2D carbon frameworks and their composites have emerged as potential photocatalysts due to their astonishing properties such as superior charge transport, tunable energy levels and bandgaps, visible light absorption, high surface area, easy processability, quantum confinement effects, and high photocatalytic quantum yields. The feasibility of structural and chemical modification to optimize visible light absorption and charge separation makes carbonaceous semiconductors promising candidates to convert solar energy into chemical energy. In the present review, we have summarized the recent advances in 2D carbonaceous photocatalysts with respect to physicochemical and photochemical tuning for solar light mediated hydrogen evolution.

Gradient Structure Design of Flexible Waterborne Polyurethane Conductive Films for Ultraefficient Electromagnetic Shielding with Low Reflection Characteristic

Abstract: Highly efficient electromagnetic shielding materials entailing strong electromagnetic wave absorption and low reflection have become an increasing requirement for next-generation communication technologies and high-power electronic instruments. In this study, a new strategy is employed to provide flexible waterborne polyurethane composite films with an ultra-efficient electromagnetic shielding effectiveness (EMI SE) and low reflection by constructing gradient shielding layers with a magnetic ferro/ferric oxide deposited on reduced graphene oxide (rGO@Fe3O4) and silver-coated tetraneedle-like ZnO whisker (T-ZnO/Ag) functional nanoparticles. Because of the differences in density between rGO@Fe3O4 and T-ZnO/Ag, a gradient structure is automatically formed during the film formation process. The gradient distribution of rGO@Fe3O4 over the whole thickness range forms an efficient electromagnetic wave absorption network that endows the film with a strong absorption ability on the top side, while a thin layer of high-density T-ZnO/Ag at the bottom constructs a highly conductive network that provides an excellent electromagnetic reflection ability for the film. This specific structure results in an "absorb-reflect-reabsorb" process when electromagnetic waves penetrate into the composite film, leading to an excellent EMI shielding performance with an extremely low reflection characteristic at a very low nanofiller content (0.8 vol % Fe3O4@rGO and 5.7 vol % T-ZnO/Ag): the EMI SE reaches 87.2 dB against the X band with a thickness of only 0.5 mm, while the shielding effectiveness of reflection (SER) is only 2.4 dB and the power coefficient of reflectivity ( R) is as low as 0.39. This result means that only 39% of the microwaves are reflected in the propagation process when 99.9999998% are attenuated, which is the lowest value among the reported references. This composite film with remarkable performance is suitable for application in portable and wearable smart electronics, and this method offers an effective strategy for absorption-dominated EMI shielding.

Design Strategy for Improving Optical and Electrical Properties and Stability of Lead-Halide Semiconductors

Abstract: Broad absorption, long-lived photogenerated carriers, high conductance, and high stability are all required for a light absorber toward its real application on solar cells Inorganic–organic hybrid lead-halide materials have shown tremendous potential for applications in solar cells This work offers a new design strategy to improve the absorption range, conductance, photoconductance, and stability of these materials We synthesized a new photochromic lead-chloride semiconductor by incorporating a photoactive viologen zwitterion into a lead-chloride system in the coordinating mode This semiconductor has a novel inorganic–organic hybrid structure, where 1-D semiconducting inorganic lead-chloride nanoribbons covalently bond to 1-D semiconducting organic π-aggregates It shows high stability against light, heat, and moisture After photoinduced electron transfer (PIET), it yields a long-lived charge-separated state with a broad absorption band covering the 200–900 nm region while increasing its conductance

Boosting Two-Dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation

Abstract: Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices because of their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate all-inorganic perovskite CsPbBr3 nanosheets with MoS2 atomic layers and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMD-based photodetectors. Significantly, the interfacial charge transfer from the CsPbBr3 to the MoS2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS2/CsPbBr3. Resultantly, such a hybrid MoS2/CsPbBr3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5 × 1010 Jones because of the high efficient photoexcited carrier separation at the interface of MoS2 a...

Frontiers of Mid-IR Lasers Based on Transition Metal Doped Chalcogenides

Abstract: Enabling broad tunability, high peak and average power, ultrashort pulse duration, and all known modes of laser operation—transition-metal (TM)-doped II–VI chalcogenides are the materials of choice for direct lasing in the mid-IR. The host materials feature broad infrared transparency, high thermal conductivity, low phonon cutoff, low optical losses, and are available as either single crystals or polycrystalline ceramics. Doped with TM ions, these media exhibit a four-level energy structure, the absence of excited state absorption, as well as broad absorption and emission bands. Doped single-crystals of high optical quality are difficult to grow; however, the advent of postgrowth diffusion doped ceramics has resulted in significant progress in laser development. Here, we summarize recent experimental laser results on Cr and Fe doped II–VI chalcogenides providing access to the 1.8–6 μm spectral range with a high (>60%) efficiency, multi-Watt-level [140 W in continuous wave (CW)] output powers, tunability of >1000 nm, short-pulse (<16 fs) multi-Watt oscillation, and multi-Joule output energies in free running and gain-switched regimes. We also review recent results on hybrid fiber-bulk (Er-fiber/Er:YAG, Tm-fiber: Ho:YAG/YLF) systems combining high efficiency of CW fiber lasers with high pulse energies of bulk materials and serving as pump sources of gain-switched Cr:II-VI lasers.

How to determine optical gaps and voltage losses in organic photovoltaic materials

Abstract: The best performing organic solar cells (OSC) efficiently absorb photons and convert them to free charge carriers, which are subsequently collected at the electrodes However, the energy lost in this process is much larger than for inorganic and perovskite solar cells, currently limiting the power conversion efficiency of OSCs to values slightly below 14% To quantify energy losses, the open-circuit voltage of the solar cell is often compared to its optical gap The latter is, however, not obvious to determine for organic materials which have broad absorption and emission bands, and is often done erroneously Nevertheless, a deeper understanding of the energy loss mechanisms depends crucially on an accurate determination of the energies of the excited states involved in the photo-conversion process This perspective therefore aims to summarize how the optical gap can be precisely determined, and how it relates to energy losses in organic photovoltaic materials

Ultralight MXene-Coated, Interconnected SiCnws Three-Dimensional Lamellar Foams for Efficient Microwave Absorption in the X-Band

Abstract: Two-dimensional (2D) few-layered Ti3C2TX MXene (f-Ti3C2TX) has been proved to be one of the most promising electromagnetic interference (EMI) materials, but its electromagnetic (EM) absorption properties and loss mechanism have not been studied so far Herein, for the first time, ordered lamellar f-Ti3C2TX/SiCnws hybrid foams with ultralow density are synthesized by a combination of self-assembly and bidirectional freezing processes The freestanding foams exhibit excellent EM absorption properties superior to most of the current foam-based counterparts The effective absorption bandwidth is always able to cover the whole X-band, when the sample thicknesses of f-Ti3C2TX/SiCnws hybrid foams distribute in any value between 35 and 38 mm, and the minimum reflection coefficient reaches −557 dB at an ultralow density of only about 0029 g·cm–3 The fundamental mechanism associated with optimized impedance matching, enhanced polarization loss, and conductive loss is discussed in detail Our results evidence t

Laminated Hybrid Junction of Sulfur-Doped TiO2 and a Carbon Substrate Derived from Ti3C2 MXenes: Toward Highly Visible Light-Driven Photocatalytic Hydrogen Evolution.

Abstract: TiO2 is an ideal photocatalyst candidate except for its large bandgap and fast charge recombination. A novel laminated junction composed of defect-controlled and sulfur-doped TiO2 with carbon substrate (LDC-S-TiO2/C) is synthesized using the 2D transition metal carbides (MXenes) as a template to enhance light absorption and improve charge separation. The prepared LDC-S-TiO2/C catalyst delivers a high photocatalytic H2 evolution rate of 333 µmol g-1 h-1 with a high apparent quantum yield of 7.36% at 400 nm and it is also active even at 600 nm, resulting into a 48 time activity compared with L-TiO2/C under visible light irradiation. Further theoretical modeling calculation indicates that such novel approach also reduces activation energy of hydrogen production apart from broadening the absorption wavelength, facilitating charge separation, and creating a large surface area substrate. This synergic effect can also be applied to other photocatalysts' modification. The study provides a novel approach for synthesis defective metal oxides based hybrids and broaden the applications of MXene family.

A Halogenation Strategy for over 12% Efficiency Nonfullerene Organic Solar Cells

Abstract: DOI: 10.1002/aenm.201702870 acceptor end-groups,[12,13,15,28–36] aiming to tune the energy levels, absorption, and even packing modes in the active layers. In contrast to the various core units for the A–D–A-type NFAs, only a few endgroups such as 2-(2,3-dihydro-3-oxo-1Hinden-1-ylidene)propanedinitrile (INCN) and rhodanine and their derivatives have been reported.[11,32,34–37] The optimization of end-groups, especially delicate modification of the successful end-group INCN has been proved to exert great influence not only on the energy levels, but also on the intraand intermolecular packing states of the NFAs.[9,37–39] Halogens have been widely used in the organic semiconductors.[40,41] The roles of fluorine (F) atom in OSCs materials have been well studied.[42–45] It has been found that the electronegativity of the substituted sites could be improved and the bathochromic absorption would be obtained after introducing the F atom. In addition, the possible internal F–S and F–H noncovalent interaction might be beneficial to improve the intermolecular packing and thus promoting charge transport properties.[9,12,43,45] Also, few studies have addressed on the materials incorporating the Cl and Br in bulk-heterojunction OSCs. Just recently, Li and co-workers have reported a series of halogenation NFAs based on 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC) and PCE over 9% has been achieved.[37] Recently, our group has reported an NFA named 2,9-bis(2methylene(3(1,1dicyanomethylene)indanone))7,12-dihydro4,4,7,7,12,12-hexaoctyl-4H-cyclopenta[2′′,1′′:5,6;3′′,4′′:5′,6′]diindeno[1,2-b:1′,2′-b′]dithiophene (FDICTF) (F–H) (Figure 1a).[15] When blended with the wide bandgap polymer poly[(2,6-(4,8bis(5-(2-ethylhexyl) thiophen-2-yl) -benzo[1,2-b:4,5-b ′ ] dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl) benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T), its based device demonstrated a PCE of 10.06%. Taking account of the unique advantages of halogenated molecules, in this work, three NFAs, namely, F–F, F–Cl, and F–Br (Figure 1a), using the same conjugated core of F–H and introducing F, Cl, and Br onto the end-capping group INCN, respectively, have been designed and synthesized. Compared with F–H, the lowest unoccupied molecular orbital (LUMO) levels of the three molecules decreased with different degrees, owing to the electron-withdrawing difference of the halogen atoms. When blended with PBDB-T as the donor material, the F–F-, F–Cl-, and F–Br-based Three acceptor–donor–acceptor type nonfullerene acceptors (NFAs), namely, F–F, F–Cl, and F–Br, are designed and synthesized through a halogenation strategy on one successful nonfullerene acceptor FDICTF (F–H). The three molecules show red-shifted absorptions, increased crystallinities, and higher charge mobilities compared with the F–H. After blending with donor polymer PBDB-T, the F–F-, F–Cl-, and F–Br-based devices exhibit power conversion efficiencies (PCEs) of 10.85%, 11.47%, and 12.05%, respectively, which are higher than that of F–H with PCE of 9.59%. These results indicate that manipulating the absorption range, crystallinity and mobilities of NFAs by introducing different halogen atoms is an effective way to achieve high photovoltaic performance, which will offer valuable insight for the designing of high-efficiency organic solar cells.

Synthesis of synergetic phosphorus and cyano groups (CN) modified g-C3N4 for enhanced photocatalytic H2 production and CO2 reduction under visible light irradiation

Abstract: Graphitic carbon nitride (g-C3N4) has become an attractive photocatalyst for solar energy conversion owing to its numerous advantages. Due to insufficient solar-light absorption and fast photogenerated carriers recombination, the photocatalytic activity of traditional g-C3N4 material is unsatisfactory. In this work, P element and cyano groups ( C N) incorporated into the g-C3N4 framework is successfully fabricated by heat treatment of the mixed g-C3N4 and NaH2PO2. The cyano groups ( C N) originated from the de-protonation of C NH2 can enhance the light absorption and act as strong electron-withdrawing groups, which can promote the efficient separation of photo-generated electron-hole pairs. The P element doping can enhance the visible light absorption, shorten the band gap and suppress the recombination of photo-induced carriers. The synergistic effect of C N functional groups and P element doping results in a 6.7 times enhanced photocatalytic H2 production activity and 1.58 times enhanced photocatalytic CO2 reduction activity than that of pristine g-C3N4. Experimental analysis indicates that the enhanced photocatalytic performance is mainly attributed to the enhanced light absorption and charge separation. Our work provides a new thought to design other high performance and low-cost g-C3N4-based photocatalytic materials for solar energy conversion.