We report efficient photoconductivity multiplication in few-layer 2H-MoTe2 as a direct consequence of an efficient steplike carrier multiplication with near unity quantum yield and high carrier ...mobility (∼45 cm2 V–1 s–1) in MoTe2. This photoconductivity multiplication is quantified using ultrafast, excitation-wavelength-dependent photoconductivity measurements employing contact-free terahertz spectroscopy. We discuss the possible origins of efficient carrier multiplication in MoTe2 to guide future theoretical investigations. The combination of photoconductivity multiplication and the advantageous bandgap renders MoTe2 as a promising candidate for efficient optoelectronic devices.
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IJS, KILJ, NUK, PNG, UL, UM
Bottom-up-synthesized graphene nanoribbons (GNRs) with excellent electronic properties are promising materials for energy storage systems. Herein, we report bottom-up-synthesized GNR films employed ...as electrode materials for micro-supercapacitors (MSCs). The micro-device delivers an excellent volumetric capacitance and an ultra-high power density. The electrochemical performance of MSCs could be correlated with the charge carrier mobility within the differently employed GNRs, as determined by pump–probe terahertz spectroscopy studies.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
Developing efficient artificial photocatalysts for the biomimetic photocatalytic production of molecular materials, including medicines and clean energy carriers, remains a fundamentally and ...technologically essential challenge. Hydrogen peroxide is widely used in chemical synthesis, medical disinfection, and clean energy. However, the current industrial production, predominantly by anthraquinone oxidation, suffers from hefty energy penalties and toxic byproducts. Herein, we report the efficient photocatalytic production of hydrogen peroxide by protonation-induced dispersible porous polymers with good charge-carrier transport properties. Significant photocatalytic hydrogen peroxide generation occurs under ambient conditions at an unprecedented rate of 23.7 mmol g
–1
h
–1
and an apparent quantum efficiency of 11.3% at 450 nm. Combined simulations and spectroscopies indicate that sub-picosecond ultrafast electron “localization” from both free carriers and exciton states at the catalytic reaction centers underlie the remarkable photocatalytic performance of the dispersible porous polymers.
Bottom‐up synthesized graphene nanostructures, including 0D graphene quantum dots and 1D graphene nanoribbons, have recently emerged as promising candidates for efficient, green optoelectronic, and ...energy storage applications. The versatility in their molecular structures offers a large and novel library of nanographenes with excellent and adjustable optical, electronic, and catalytic properties. In this minireview, recent progress on the fundamental understanding of the properties of different graphene nanostructures, and their state‐of‐the‐art applications in optoelectronics and energy storage are summarized. The properties of pristine nanographenes, including high emissivity and intriguing blinking effect in graphene quantum dots, superior charge transport properties in graphene nanoribbons, and edge‐specific electrochemistry in various graphene nanostructures, are highlighted. Furthermore, it is shown that emerging nanographene‐2D material‐based van der Waals heterostructures provide an exciting opportunity for efficient green optoelectronics with tunable characteristics. Finally, challenges and opportunities of the field are highlighted by offering guidelines for future combined efforts in the synthesis, assembly, spectroscopic, and electrical studies as well as (nano)fabrication to boost the progress toward advanced device applications.
The recent progress on the fundamental properties of different bottom‐up synthesized nanographenes, and the collective properties upon forming nanographene‐2D material‐based van der Waals heterostructures, toward their state‐of‐the‐art applications in optoelectronics and energy storage is summarized. Forthcoming challenges and opportunities of this emerging field are highlighted, and perspectives in boosting the progress toward advanced device applications are offered.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
As a new family of semiconductors, graphene nanoribbons (GNRs), nanometer-wide strips of graphene, have appeared as promising candidates for next-generation nanoelectronics. Out-of-plane deformation ...of π-frames in GNRs brings further opportunities for optical and electronic property tuning. Here we demonstrate a novel fjord-edged GNR (FGNR) with a nonplanar geometry obtained by regioselective cyclodehydrogenation. Triphenanthro-fused teropyrene 1 and pentaphenanthro-fused quateropyrene 2 were synthesized as model compounds, and single-crystal X-ray analysis revealed their helically twisted conformations arising from the 5helicene substructures. The structures and photophysical properties of FGNR were investigated by mass spectrometry and UV–vis, FT-IR, terahertz, and Raman spectroscopic analyses combined with theoretical calculations.
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IJS, KILJ, NUK, PNG, UL, UM
Semiconductor nanoplatelets exhibit spectrally pure, directional fluorescence. To make polarized light emission accessible and the charge transport effective, nanoplatelets have to be collectively ...oriented in the solid state. We discovered that the collective nanoplatelets orientation in monolayers can be controlled kinetically by exploiting the solvent evaporation rate in self-assembly at liquid interfaces. Our method avoids insulating additives such as surfactants, making it ideally suited for optoelectronics. The monolayer films with controlled nanoplatelets orientation (edge-up or face-down) exhibit long-range ordering of transition dipole moments and macroscopically polarized light emission. Furthermore, we unveil that the substantial in-plane electronic coupling between nanoplatelets enables charge transport through a single nanoplatelets monolayer, with an efficiency that strongly depends on the orientation of the nanoplatelets. The ability to kinetically control the assembly of nanoplatelets into ordered monolayers with tunable optical and electronic properties paves the way for new applications in optoelectronic devices.
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Graphene nanoribbons (GNRs) with atomically precise width and edge structures are a promising class of nanomaterials for optoelectronics, thanks to their semiconducting nature and high mobility of ...charge carriers. Understanding the fundamental static optical properties and ultrafast dynamics of charge carrier generation in GNRs is essential for optoelectronic applications. Combining THz spectroscopy and theoretical calculations, we report a strong exciton effect with binding energy up to ∼700 meV in liquid-phase-dispersed GNRs with a width of 1.7 nm and an optical band gap of ∼1.6 eV, illustrating the intrinsically strong Coulomb interactions between photogenerated electrons and holes. By tracking the exciton dynamics, we reveal an ultrafast formation of excitons in GNRs with a long lifetime over 100 ps. Our results not only reveal fundamental aspects of excitons in GNRs (strong binding energy and ultrafast exciton formation etc.) but also highlight promising properties of GNRs for optoelectronic devices.
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Synthesis of covalent organic frameworks (COFs) with desirable organic units furnishes advanced materials with unique functionalities. As an emerging class of two‐dimensional (2D) COFs, ...sp2‐carbon‐conjugated COFs provide a facile platform to build highly stable and crystalline porous polymers. Herein, a 2D olefin‐linked COF was prepared by employing nanographene, namely, dibenzohi,stovalene (DBOV), as a building block. The DBOV‐COF exhibits unique ABC‐stacked lattices, enhanced stability, and charge‐carrier mobility of ≈0.6 cm2 V−1 s−1 inferred from ultrafast terahertz photoconductivity measurements. The ABC‐stacking structure was revealed by the high‐resolution transmission electron microscopy and powder X‐ray diffraction. DBOV‐COF demonstrated remarkable photocatalytic activity in hydroxylation, which was attributed to the exposure of narrow‐energy‐gap DBOV cores in the COF pores, in conjunction with efficient charge transport following light absorption.
Dibenzohi,stovalene‐based covalent organic frameworks form 2D ABC stacking sp2 carbon lattices with robust olefin linkage. The resulting 2D unique structure exhibits high photoconductivity, charge‐carrier mobility and photocatalytic activity in hydroxylation attributed to the narrow‐energy‐gap nanographene cores as active sites.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The role of solution aggregates on the charge transport process of conjugated polymers in electronic devices has gained increasing attention; however, the correlation of the charge carrier mobilities ...between the solution aggregates and the solid‐state films remains elusive. Herein, three polymers, FBDOPV‐2T, FBDOPV‐2F2T, and FBDOPV‐4F2T, are designed and synthesized with distinct aggregation behavior in solution. By combining contact‐free ultrafast terahertz (THz) spectroscopy and field‐effect transistor measurements, we track the charge carrier mobility of the aggregates of these polymers from the solution to the thin‐film state. Remarkably, the mobility of these three polymers is found to follow nearly the same trend (FBDOPV‐2T>FBDOPV‐2F2T≫FBDOPV‐4F2T) in both solutions and thin‐film states. The quantitative mobility correlation indicates that the charge transport properties of solution aggregates play a critical role in determining the thin‐film charge transport properties and final device performance. Our results highlight the importance of investigating and controlling solution aggregation structures towards efficient organic electronic devices.
Different aggregation structures of three BDOPV‐based polymers in solution were obtained via subtle adjustment of the molecular structures. By employing contact‐free ultrafast terahertz (THz) spectroscopy, we directly reveal that the correlation of the charge carrier mobilities between the solution aggregates and the solid‐state films remains highly consistent.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The precise bottom‐up synthesis of graphene nanoribbons (GNRs) with controlled width and edge structures may compensate for graphene's limitations, such as the absence of an electronic bandgap. At ...the same time, GNRs maintain graphene's unique lattice structure in one dimension and provide more open‐edge structures compared to graphene, thus allowing faster ion diffusion, which makes GNRs highly promising for energy storage systems. However, the current solution‐synthesized GNRs suffer from severe aggregation due to the strong π–π interactions, which limits their potential applications. Thus, it is indispensable to develop a facile and scalable approach to exfoliate the GNRs from the postsynthetic aggregates, yielding individual nanoribbons. Here, a high‐shear‐mixing approach is demonstrated to untie the GNR bundles into practically individual GNRs, by introducing suitable molecular interactions. The micro‐supercapacitor (MSC) electrode based on solution‐processed GNR film exhibits an excellent volumetric capacitance of 355 F cm−3 and a high power density of 550 W cm−3, reaching the state‐of‐the‐art performance of graphene and related carbon materials, and thus demonstrating the great potential of GNRs as electrode materials for future energy storage.
A high‐shear‐mixing approach is demonstrated to untie the bundles of graphene nanoribbons. The micro‐supercapacitor electrode based on solution‐processed graphene nanoribbons film delivers promising electrochemical performance, which is comparable to state‐of‐the‐art performance based on graphene‐related materials, thus demonstrating the great potential of graphene nanoribbons as candidate materials for future energy storage.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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