Van der Waals heterostructures consisting of graphene and transition metal dichalcogenides have shown great promise for optoelectronic applications. However, an in-depth understanding of the critical processes for device operation, namely, interfacial charge transfer (CT) and recombination, has so far remained elusive. Here, we investigate these processes in graphene-WS2 heterostructures by complementarily probing the ultrafast terahertz photoconductivity in graphene and the transient absorption dynamics in WS2 following photoexcitation. We observe that separated charges in the heterostructure following CT live extremely long: beyond 1 ns, in contrast to ~1 ps charge separation reported in previous studies. This leads to efficient photogating of graphene. Furthermore, for the CT process across graphene-WS2 interfaces, we find that it occurs via photo-thermionic emission for sub-A-exciton excitations and direct hole transfer from WS2 to the valence band of graphene for above-A-exciton excitations. These findings provide insights to further optimize the performance of optoelectronic devices, in particular photodetection.

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 [5]helicene 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.

The current work reports a high power conversion efficiency (PCE) of 9.54% achieved with nonfullerene organic solar cells (OSCs) based on PTB7‐Th donor and 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC) acceptor fabricated by doctor‐blade printing, which has the highest efficiency ever reported in printed nonfullerene OSCs. Furthermore, a high PCE of 7.6% is realized in flexible large‐area (2.03 cm2) indium tin oxide (ITO)‐free doctor‐bladed nonfullerene OSCs, which is higher than that (5.86%) of the spin‐coated counterpart. To understand the mechanism of the performance enhancement with doctor‐blade printing, the morphology, crystallinity, charge recombination, and transport of the active layers are investigated. These results suggest that the good performance of the doctor‐blade OSCs is attributed to a favorable nanoscale phase separation by incorporating 0.6 vol% of 1,8‐diiodooctane that prolongs the dynamic drying time of the doctor‐bladed active layer and contributes to the migration of ITIC molecules in the drying process. High PCE obtained in the flexible large‐area ITO‐free doctor‐bladed nonfullerene OSCs indicates the feasibility of doctor‐blade printing in large‐scale fullerene‐free OSC manufacturing. For the first time, the open‐circuit voltage is increased by 0.1 V when 1 vol% solvent additive is added, due to the vertical segregation of ITIC molecules during solvent evaporation.

Two-dimensional (2D) covalent organic frameworks (COFs) are an emerging class of promising 2D materials with high crystallinity and tunable structures. However, the low electrical conductivity impedes their applications in electronics and optoelectronics. Integrating large π-conjugated building blocks into 2D lattices to enhance efficient π-stacking and chemical doping is an effective way to improve the conductivity of 2D COFs. Herein, two nonplanar 2D COFs with kagome (DHP-COF) and rhombus (c-HBC-COF) lattices have been designed and synthesized from distorted aromatics with different π-conjugated structures (flexible and rigid structure, respectively). DHP-COF shows a highly distorted 2D lattice that hampers stacking, consequently limiting its charge carrier transport properties. Conversely, c-HBC-COF, with distorted although concave–convex self-complementary nodes, shows a less distorted 2D lattice that does not interfere with interlayer π-stacking. Employing time- and frequency-resolved terahertz spectroscopy, we unveil a high charge-carrier mobility up to 44 cm2 V–1 s–1, among the highest reported for 2D COFs.

We report efficient photoconductivity multiplication in few-layer 2H-MoTe 2 as a direct consequence of an efficient steplike carrier multiplication with near unity quantum yield and high carrier mobility (∼45 cm 2 V –1 s –1 ) in MoTe 2 . 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 MoTe 2 to guide future theoretical investigations. The combination of photoconductivity multiplication and the advantageous bandgap renders MoTe 2 as a promising candidate for efficient optoelectronic devices.

of the PO 2 -Nb 4 C 3 electrode was exemplified by assembling the PO 2 -Nb 4 C 3 //NHPC device with both high energy density (55 Wh L −1 ) and large power density (9765 W L −1 ). We hope that our results will encourage increasing efforts devoted to regulating the surface chemistry of MXenes and other 2D materials via terminal group engineering at the molecular level, which would contribute to the development of energy−power-balanced energy-storage devices.Research data are not shared.

Structurally well-defined graphene nanoribbons (GNRs) have emerged as highly promising materials for the next-generation nanoelectronics. The electronic properties of GNRs critically depend on their edge topologies. Here, we demonstrate the efficient synthesis of a curved GNR (cGNR) with a combined cove, zigzag, and armchair edge structure, through bottom-up synthesis. The curvature of the cGNR is elucidated by the corresponding model compounds tetrabenzo­[a,cd,j,lm]­perylene (1) and diphenanthrene-fused tetrabenzo­[a,cd,j,lm]­perylene (2), the structures of which are unambiguously confirmed by the X-ray single-crystal analysis. The resultant multi-edged cGNR exhibits a well-resolved absorption at the near-infrared (NIR) region with a maximum peak at 850 nm, corresponding to a narrow optical energy gap of ∼1.22 eV. Employing THz spectroscopy, we disclose a long scattering time of ∼60 fs, corresponding to a record intrinsic charge carrier mobility of ∼600 cm2 V–1 s–1 for photogenerated charge carriers in cGNR.

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