Van der Waals Coupled Organic Molecules with Monolayer MoS2 for Fast Response Photodetectors with Gate-Tunable Responsivity

Ultrafast Formation of Charge Transfer Trions at Molecular-Functionalized 2D MoS2 Interfaces

In this work, we investigate trion dynamics occurring at the heterojunction between organometallic molecules and a monolayer transition metal dichalcogenide (TMD) with transient electronic sum frequency generation (tr-ESFG) spectroscopy. By pumping at 2.4 eV with laser pulses, we have observed an ultrafast hole transfer, succeeded by the emergence of charge-transfer trions. This observation is facilitated by the cancellation of ground state bleach and stimulated emission signals due to their opposite phases, making tr-ESFG especially sensitive to the trion formation dynamics. The presence of charge-transfer trion at molecular functionalized TMD monolayers suggests the potential for engineering the local electronic structures and dynamics of specific locations on TMDs and offers a potential for transferring unique electronic attributes of TMD to the molecular layers.

Ab Initio Modeling of Mixed-Dimensional Heterostructures: A Path Forward

Understanding the electronic structure of mixed-dimensional heterostructures is essential for maximizing their application potential. However, accurately modeling such interfaces is challenging due to the complex interplay between the subsystems. We employ a computational framework integrating first-principles methods, including GW, density functional theory (DFT), and the polarizable continuum model, to elucidate the electronic structure of mixed-dimensional heterojunctions formed by free-base phthalocyanines and monolayer molybdenum disulfide. We assess the impact of dielectric screening across various scenarios, from isolated molecules to organic films on a substrate-supported monolayer. Our findings show that while polarization effects cause significant renormalization of molecular energy levels, band energies and alignments in the most relevant setup can be accurately predicted through DFT simulations of the individual subsystems. Additionally, we analyze orbital hybridization, revealing potential pathways for interfacial charge transfer. This study offers new insights into hybrid inorganic/organic interfaces and provides a practical computational protocol suitable for scaled-up studies.

Insulating 6,6-Phenyl-C61-butyric Acid Methyl Ester on Transition-Metal Dichalcogenides: Impact of the Hybrid Materials on the Optical and Electrical Properties

In this study we develop a strategy to insulate 6,6 -Phenyl C61 butyric acid methyl ester (PCBM) on the basal plane of transition metal dichalcogenides (TMDs). Concretely single layers of MoS2, MoSe2, MoTe2, WS2, WSe2 and WTe2 and ultrathin MoO2 and WO2 were grown via chemical vapor deposition (CVD). Then, the thiol group of a PCBM modified with cysteine reacts with the chalcogen vacancies on the basal plane of TMDs, yielding PCBM-MoS2, PCBM-MoSe2, PCBM-WS2, PCBM-WSe2, PCBM-WTe2, PCBM-MoO2 and PCBM-WO2. Afterwards, all the hybrid materials were characterized using several techniques, including XPS, Raman spectroscopy, TEM, AFM, and cyclic voltammetry. Furthermore, PCBM causes a unique optical and electrical impact in every TMDs. For MoS2 devices, the conductivity and photoluminescence (PL) emission achieve a remarkable enhancement of 1700 % and 200 % in PCBM-MoS2 hybrids. Similarly, PCBM-MoTe2 hybrids exhibit a 2-fold enhancement in PL emission at 1.1 eV. On the other hand, PCBM-MoSe2, PCBM-WSe2 and PCBM-WS2 hybrids exhibited a new interlayer exciton at 1.29-1.44, 1.7 and 1.37-154 eV along with an enhancement of the photo-response by 2400, 3200 and 600 %, respectively. Additionally, PCBM-WTe2 and PCBM-WO2 showed a modest photo-response, in sharp contrast with pristine WTe2 or WO2 which archive pure metallic character.

Solution-Processable Large-Area Black Phosphorus/Reduced Graphene Oxide Schottky Junction for High-Temperature Broadband Photodetectors

2D materials-based broadband photodetectors have extensive applications in security monitoring and remote sensing fields, especially in supersonic aircraft that require reliable performance under extreme high-temperature conditions. However, the integration of large-area heterostructures with 2D materials often involves high-temperature deposition methods, and also limited options and size of substrates. Herein, a liquid-phase spin-coating method is presented based on the interface engineering to prepare larger-area Van der Waals heterojunctions of black phosphorus (BP)/reduced graphene oxide (RGO) films at room temperature on arbitrary substrates of any required size. Importantly, this method avoids the common requirement of high-temperature, and prevents the curling or stacking in 2D materials during the liquid-phase film formation. The BP/RGO films-based devices exhibit a wide spectral photo-response, ranging from the visible of 532 nm to infrared range of 2200 nm. Additionally, due to Van der Waals interface of Schottky junction, the array devices provide infrared detection at temperatures up to 400 K, with an outstanding photoresponsivity (R) of 12 A W-1 and a specific detectivity (D*) of ≈2.4 × 109 Jones. This work offers an efficient approach to fabricate large-area 2D Schottky junction films by solution-coating for high-temperature infrared photodetectors.

Exciton Dynamics of TiOPc/WSe2 Heterostructure

The van der Waals (vdW) heterostructures composed of two-dimensional (2D) transition metal dichalcogenides (TMDs) and organic semiconductors demonstrate numerous compelling optoelectronic properties. However, the influence of the vdW epitaxial effect and temperature on the optoelectronic properties and interface exciton dynamics of heterostructures remains unclear. This study systematically investigates the fluorescence properties of TiOPc/WSe2 heterostructure. Comprehensive spectral characterization elucidates that the emission behavior of the TiOPc/WSe2 heterostructure arises from charge/energy transfer at the heterostructure interfaces and the structural ordering of the organic layer on the 2D monolayer WSe2 induced by vdW epitaxy. The interface exciton dynamic features probed by ultrafast transient spectroscopy reveal that the face-to-face molecular stacking configuration of TiOPc exhibits ultrafast exciton dynamics. In particular, we observe picosecond-scale absorption of organic molecular dimer cations, providing direct evidence of interface charge transfer at room temperature. Moreover, energy transfer from the TiOPc to WSe2 may exist based on the tunability in the fluorescence emission of the TiOPc/WSe2 heterostructure as the temperature changes. This study unveils the critical role of vdW epitaxy and temperature in the exciton dynamics of organic/2D TMDs hybrid systems and provides guidance for studying interlayer charge and energy transfer in organic/inorganic heterostructures.

Recent progress in emerging two-dimensional organic-inorganic van der Waals heterojunctions

Two-dimensional (2D) materials have attracted significant attention in recent decades due to their exceptional optoelectronic properties. Among them, to meet the growing demand for multifunctional applications, 2D organic-inorganic van der Waals (vdW) heterojunctions have become increasingly popular in the development of optoelectronic devices. These heterojunctions demonstrate impressive capability to synergistically combine the favourable characteristics of organic and inorganic materials, thereby offering a wide range of advantages. Also, they enable the creation of innovative device structures and introduce novel functionalities in existing 2D materials, avoiding the need for lattice matching in different material systems. Presently, researchers are actively working on improving the performance of devices based on 2D organic-inorganic vdW heterojunctions by focusing on enhancing the quality of 2D materials, precise stacking methods, energy band regulation, and material selection. Therefore, this review presents a thorough examination of the emerging 2D organic-inorganic vdW heterojunctions, including their classification, fabrication, and corresponding devices. Additionally, this review offers profound and comprehensive insight into the challenges in this field to inspire future research directions. It is expected to propel researchers to harness the extraordinary capabilities of 2D organic-inorganic vdW heterojunctions for a wider range of applications by further advancing the understanding of their fundamental properties, expanding the range of available materials, and exploring novel device architectures. The ongoing research and development in this field hold potential to unlock captivating advancements and foster practical applications across diverse industries.

High-performance MoS2phototransistors with Hf1-xAlxO back-gate dielectric layer grown by plasma enhanced atomic layer deposition

Molybdenum sulfide (MoS2) as an emerging optoelectronic material, shows great potential for phototransistors owing to its atomic thickness, adjustable band gap, and low cost. However, the phototransistors based on MoS2have been shown to have some issues such as large gate leakage current, and interfacial scattering, resulting in suboptimal optoelectronic performance. Thus, Al-doped hafnium oxide (Hf1-xAlx) is proposed to be a dielectric layer of the MoS2-based phototransistor to solve this problem because of the relatively higher crystallization temperature and dielectric constant. Here, a high-performance MoS2phototransistor with Hf1-xAlxO gate dielectric layer grown by plasma-enhanced atomic layer deposition has been fabricated and studied. The results show that the phototransistor exhibits a high responsivity of 2.2 × 104A W-1, a large detectivity of 1.7 × 1017Jones, a great photo-to-dark current ratio of 2.2 × 106%, and a high external quantum efficiency of 4.4 × 106%. The energy band alignment and operating mechanism were further used to clarify the reason for the enhanced MoS2phototransistor. The suggested MoS2phototransistors could provide promising strategies in further optoelectronic applications.

Enthalpy-uphill exciton dissociation in organic/2D heterostructures promotes free carrier generation

Despite the large binding energy of charge transfer (CT) excitons in type-II organic/2D heterostructures, it has been demonstrated that free carriers can be generated from CT excitons with a long lifetime. Using a model fluorinated zine phthalocyanine (F8ZnPc)/monolayer-WS2 interface, we find that CT excitons can dissociate spontaneously into free carriers despite it being an enthalpy-uphill process. Specifically, it is observed that CT excitons can gain an energy of 250 meV in 50 ps and dissociate into free carriers without any applied electric field. This observation is surprising because excited electrons typically lose energy to the environment and relax to lower energy states. We hypothesize that this abnormal enthalpy-uphill CT exciton dissociation process is driven by entropy gain. Kinetically, the entropic driving force can also reduce the rate for the reverse process - the conversion of free electron-hole pairs back to CT excitons. Hence, this mechanism can potentially explain the very long carrier lifetime observed in organic/2D heterostructures.

Origin of photoinduced DC current and two-level population dynamics in a single molecule

Studying the photoinduced changes of materials with atomic-scale spatial resolution can provide a fundamental understanding of light-matter interaction. A long-standing impediment has been the detrimental thermal effects on the stability of the tunneling gap from intensity-modulated laser irradiation of the scanning tunneling microscope junction. Photoinduced DC current transduces photons to an electric current and is widely applied in optoelectronics as switches and signal transmission. Our results revealed the origin of the light-induced DC current and related it to the two-level population dynamics and related nonlinearity in the conductance of a single molecule. Here, we compensated for the near-visible laser-induced thermal effects to demonstrate photoinduced DC current spectroscopy and microscopy and to observe the persistent photoconductivity of a two-level pyrrolidine molecule. The methodology can be generally applied to the coupling of light to scan probes to investigate light-matter interactions at the atomic scale.

Lung cancer cells detection by a photoelectrochemical MoS2 biosensing chip

This research aims to explore the potential application of this approach in the production of biosensor chips. The biosensor chip is utilized for the identification and examination of early-stage lung cancer cells. The findings of the optical microscope were corroborated by the field emission scanning electron microscopy, which provided further evidence that the growth of MoS2 is uniform and that there is minimal disruption in the electrode, hence minimizing the likelihood of an open circuit creation. Furthermore, the bilayer structure of the produced MoS2 has been validated through the utilization of Raman spectroscopy. A research investigation was undertaken to measure the photoelectric current generated by three various types of clinical samples containing lung cancer cells, specifically the CL1, NCI-H460, and NCI-H520 cell lines. The findings from the empirical analysis indicate that the coefficient of determination (R-Square) for the linear regression model was approximately 98%. Furthermore, the integration of a double-layer MoS2 film resulted in a significant improvement of 38% in the photocurrent, as observed in the device's performance.

van der Waals 2D transition metal dichalcogenide/organic hybridized heterostructures: recent breakthroughs and emerging prospects of the device

The near-atomic thickness and organic molecular systems, including organic semiconductors and polymer-enabled hybrid heterostructures, of two-dimensional transition metal dichalcogenides (2D-TMDs) can modulate their optoelectronic and transport properties outstandingly. In this review, the current understanding and mechanism of the most recent and significant breakthrough of novel interlayer exciton emission and its modulation by harnessing the band energy alignment between TMDs and organic semiconductors in a TMD/organic (TMDO) hybrid heterostructure are demonstrated. The review encompasses up-to-date device demonstrations, including field-effect transistors, detectors, phototransistors, and photo-switchable superlattices. An exploration of distinct traits in 2D-TMDs and organic semiconductors delves into the applications of TMDO hybrid heterostructures. This review provides insights into the synthesis of 2D-TMDs and organic layers, covering fabrication techniques and challenges. Band bending and charge transfer via band energy alignment are explored from both structural and molecular orbital perspectives. The progress in emission modulation, including charge transfer, energy transfer, doping, defect healing, and phase engineering, is presented. The recent advancements in 2D-TMDO-based optoelectronic synaptic devices, including various 2D-TMDs and organic materials for neuromorphic applications are discussed. The section assesses their compatibility for synaptic devices, revisits the operating principles, and highlights the recent device demonstrations. Existing challenges and potential solutions are discussed. Finally, the review concludes by outlining the current challenges that span from synthesis intricacies to device applications, and by offering an outlook on the evolving field of emerging TMDO heterostructures.

Adaptive Neural Activation and Neuromorphic Processing via Drain-Injection Threshold-Switching Float Gate Transistor Memory

Hetero-modulated neural activation is vital for adaptive information processing and learning that occurs in brain. To implement brain-inspired adaptive processing, previously various neurotransistors oriented for synaptic functions are extensively explored, however, the emulation of nonlinear neural activation and hetero-modulated behaviors are not possible due to the lack of threshold switching behavior in a conventional transistor structure. Here, a 2D van der Waals float gate transistor (FGT) that exhibits steep threshold switching behavior, and the emulation of hetero-modulated neuron functions (integrate-and-fire, sigmoid type activation) for adaptive sensory processing, are reported. Unlike conventional FGTs, the threshold switching behavior stems from impact ionization in channel and the coupled charge injection to float gate. When a threshold is met, a sub-30 mV dec-1 increase of transistor conductance by more than four orders is triggered with a typical switch time of approximately milliseconds. Essentially, by feeding light sensing signal as the modulation input, it is demonstrated that two typical tasks that rely on adaptive neural activation, including collision avoidance and adaptive visual perception, can be realized. These results may shed light on the emulation of rich hetero-modulating behaviors in biological neurons and the realization of biomimetic neuromorphic processing at low hardware cost.

Nonadiabatic Dynamics Simulations for Photoinduced Processes in Molecules and Semiconductors: Methodologies and Applications

Nonadiabatic dynamics (NAMD) simulations have become powerful tools for elucidating complicated photoinduced processes in various systems from molecules to semiconductor materials. In this review, we present an overview of our recent research on photophysics of molecular systems and periodic semiconductor materials with the aid of ab initio NAMD simulation methods implemented in the generalized trajectory surface-hopping (GTSH) package. Both theoretical backgrounds and applications of the developed NAMD methods are presented in detail. For molecular systems, the linear-response time-dependent density functional theory (LR-TDDFT) method is primarily used to model electronic structures in NAMD simulations owing to its balanced efficiency and accuracy. Moreover, the efficient algorithms for calculating nonadiabatic coupling terms (NACTs) and spin-orbit couplings (SOCs) have been coded into the package to increase the simulation efficiency. In combination with various analysis techniques, we can explore the mechanistic details of the photoinduced dynamics of a range of molecular systems, including charge separation and energy transfer processes in organic donor-acceptor structures, ultrafast intersystem crossing (ISC) processes in transition metal complexes (TMCs), and exciton dynamics in molecular aggregates. For semiconductor materials, we developed the NAMD methods for simulating the photoinduced carrier dynamics within the framework of the Kohn-Sham density functional theory (KS-DFT), in which SOC effects are explicitly accounted for using the two-component, noncollinear DFT method. Using this method, we have investigated the photoinduced carrier dynamics at the interface of a variety of van der Waals (vdW) heterojunctions, such as two-dimensional transition metal dichalcogenides (TMDs), carbon nanotubes (CNTs), and perovskites-related systems. Recently, we extended the LR-TDDFT-based NAMD method for semiconductor materials, allowing us to study the excitonic effects in the photoinduced energy transfer process. These results demonstrate that the NAMD simulations are powerful tools for exploring the photodynamics of molecular systems and semiconductor materials. In future studies, the NAMD simulation methods can be employed to elucidate experimental phenomena and reveal microscopic details as well as rationally design novel photofunctional materials with desired properties.

Optical Enhancement of Indirect Bandgap 2D Transition Metal Dichalcogenides for Multi-Functional Optoelectronic Sensors

The unique electrical and optical properties of transition metal dichalcogenides (TMDs) make them attractive nanomaterials for optoelectronic applications, especially optical sensors. However, the optical characteristics of these materials are dependent on the number of layers. Monolayer TMDs have a direct bandgap that provides higher photoresponsivity compared to multilayer TMDs with an indirect bandgap. Nevertheless, multilayer TMDs are more appropriate for various photodetection applications due to their high carrier density, broad spectral response from UV to near-infrared, and ease of large-scale synthesis. Therefore, this review focuses on the modification of the optical properties of devices based on indirect bandgap TMDs and their emerging applications. Several successful developments in optical devices are examined, including band structure engineering, device structure optimization, and heterostructures. Furthermore, it introduces cutting-edge techniques and future directions for optoelectronic devices based on multilayer TMDs.

Ultrahigh UV Responsivity Quasi-Two-Dimensional BixSn1-xO2 Films Achieved through Surface Reaction

In this study, quasi-two-dimensional BixSn1-xO2 (BTO) thin films were fabricated using a liquid metal transfer method. The ultraviolet (UV) photodetector based on BTO thin films was constructed, and the ultrahigh responsivity of 589 A/W was observed at 300 nm UV light illumination. Interestingly, by dropping ethanol during light-off period, the recovery time induced by the persistent photoconductivity (PPC) effect is reduced from 1.65 × 103 s to 5.71 s. Furthermore, the recovery time can also be reduced by dropping methanol, propylene glycol, NaNO2, and Na2SO3 after light termination. The working mechanisms are attributed to the rapid consumption of holes stored in BTO thin films by reaction with those solutions. This work demonstrates that the BTO thin films have potential applications in high-performance UV detectors and present an innovation route to weaken the PPC effects in semiconductors by introducing chemical liquids on their surface.

Coherent Phonon Manipulation via Electron-Phonon Interaction for Facilitated Relaxation of Metastable Centers in ZnO

Methods that allow versatile manipulation of metastable centers in semiconductors are highly important owing to their potential for quantum information processing and computations. In this study, we demonstrate that the electron-phonon interaction enables phonon participation to promote relaxation of metastable centers in ZnO, which is known for its persistent photoconductivity (PPC) effect. Experimentally, we show that continuous infrared (IR) radiation (1064 nm, ∼30 mW/cm2) promotes longitudinal optical phonons via the Fröhlich interaction and increases the PPC relaxation rate by ∼4 folds. More importantly, we discover that coherent phonons activated by an ultrashort pulse IR laser of the same power increased the relaxation rate by ∼1200-fold, as confirmed by ultrafast transient spectroscopy to be correlated to the excitation of coherent acoustic phonons via the inverse piezoelectric effect. We expect this study to provide valuable guidance for the development of novel quantum and photoactive devices.

Unraveling the Effect of Stacking Configurations on Charge Transfer in WS2 and Organic Semiconductor Heterojunctions

Photoinduced interfacial charge transfer plays a critical role in energy conversion involving van der Waals (vdW) heterostructures constructed of inorganic nanostructures and organic materials. However, the effect of molecular stacking configurations on charge transfer dynamics is less understood. In this study, we demonstrated the tunability of interfacial charge separation in a type-II heterojunction between monolayer (ML) WS2 and an organic semiconducting molecule [2-(3″',4'-dimethyl-[2,2':5',2':5″,2″'-quaterthiophen]-5-yl)ethan-1-ammonium halide (4Tm)] by rational design of relative stacking configurations. The assembly between ML-WS2 and the 4Tm molecule forms a face-to-face stacking when 4Tm molecules are in a self-aggregation state. In contrast, a face-to-edge stacking is observed when 4Tm molecule is incorporated into a 2D organic-inorganic hybrid perovskite lattice. The face-to-face stacking was proved to be more favorable for hole transfer from WS2 to 4Tm and led to interlayer excitons (IEs) emission. Transient absorption measurements show that the hole transfer occurs on a time scale of 150 fs. On the other hand, the face-to-edge stacking resulted in much slower hole transfer without formation of IEs. This inefficient hole transfer occurs on a similar time scale as A exciton recombination in WS2, leading to the formation of negative trions. These investigations offer important fundamental insights into the charge transfer processes at organic-inorganic interfaces.

Self-Powered Sb2Te3/MoS2 Heterojunction Broadband Photodetector on Flexible Substrate from Visible to Near Infrared

Van der Waals (vdWs) heterostructures, assembled by stacking of two-dimensional (2D) crystal layers, have emerged as a promising new material system for high-performance optoelectronic applications, such as thin film transistors, photodetectors, and light-emitters. In this study, we showcase an innovative device that leverages strain-tuning capabilities, utilizing a MoS₂/Sb₂Te₃ vdWs p-n heterojunction architecture designed explicitly for photodetection across the visible to near-infrared spectrum. These heterojunction devices provide ultra-low dark currents as small as 4.3 pA, a robust photoresponsivity of 0.12 A W^-1, and reasonable response times characterized by rising and falling durations of 0.197 s and 0.138 s, respectively. These novel devices exhibit remarkable tunability under the application of compressive strain up to 0.3%. The introduction of strain at the heterojunction interface influences the bandgap of the materials, resulting in a significant alteration of the heterojunction's band structure. This subsequently shifts the detector's optical absorption properties. The proposed strategy of strain-induced engineering of the stacked 2D crystal materials allows the tuning of the electronic and optical properties of the device. Such a technique enables fine-tuning of the optoelectronic performance of vdWs devices, paving the way for tunable high-performance, low-power consumption applications. This development also holds significant potential for applications in wearable sensor technology and flexible electro-optic circuits.

Fast-Response Micro-Phototransistor Based on MoS2/Organic Molecule Heterojunction

Over the past years, molybdenum disulfide (MoS₂) has been the most extensively studied two-dimensional (2D) semiconductormaterial. With unique electrical and optical properties, 2DMoS₂ is considered to be a promising candidate for future nanoscale electronic and optoelectronic devices. However, charge trapping leads to a persistent photoconductance (PPC), hindering its use for optoelectronic applications. To overcome these drawbacks and improve the optoelectronic performance, organic semiconductors (OSCs) are selected to passivate surface defects, tune the optical characteristics, and modify the doping polarity of 2D MoS₂. Here, we demonstrate a fast photoresponse in multilayer (ML) MoS₂ by addressing a heterojunction interface with vanadylphthalocyanine (VOPc) molecules. The MoS₂/VOPc van der Waals interaction that has been established encourages the PPC effect in MoS₂ by rapidly segregating photo-generated holes, which move away from the traps of MoS₂ toward the VOPc molecules. The MoS₂/VOPc phototransistor exhibits a fast photo response of less than 15 ms for decay and rise, which is enhanced by 3ordersof magnitude in comparison to that of a pristine MoS₂-based phototransistor (seconds to tens of seconds). This work offers a means to realize high-performance transition metal dichalcogenide (TMD)-based photodetection with a fast response speed.

Ultrafast Charge Transfer 2D MoS2 /Organic Heterojunction for Sensitive Photodetector

The 2D MoS₂ with superior optoelectronic properties such as high charge mobility and broadband photoresponse has attracted broad research interests in photodetectors (PD). However, due to the atomic thin layer of 2D MoS₂ , its pure photodetectors usually suffer from inevitable drawbacks such as large dark current, and intrinsically slow response time. Herein, a new organic material BTP-4F with high mobility is successfully stacked with 2D MoS₂ film to form an integrated 2D MoS₂ /organic P-N heterojunction, facilitating efficient charge transfer as well as significantly suppressed dark current. As a result, the as-obtained 2D MoS₂ /organic (PD) has exhibited excellent response and fast response time of 332/274 µs. The analysis validated photogenerated electron transition from this monolayer MoS₂ to subsequent BTP-4F film, whereas the transited electron is originated from the A^- exciton of 2D MoS₂ by temperature-dependent photoluminescent analysis. The ultrafast charge transfer time of ≈0.24 ps measured by time-resolved transient absorption spectrum is beneficial for efficient electron-hole pair separation, greatly contributing to the obtained fast photoresponse time of 332/274 µs. This work can open a promising window to acquire low-cost and high-speed (PD).

Emerging MoS2 Wafer-Scale Technique for Integrated Circuits

As an outstanding representative of layered materials, molybdenum disulfide (MoS2) has excellent physical properties, such as high carrier mobility, stability, and abundance on earth. Moreover, its reasonable band gap and microelectronic compatible fabrication characteristics makes it the most promising candidate in future advanced integrated circuits such as logical electronics, flexible electronics, and focal-plane photodetector. However, to realize the all-aspects application of MoS2, the research on obtaining high-quality and large-area films need to be continuously explored to promote its industrialization. Although the MoS2 grain size has already improved from several micrometers to sub-millimeters, the high-quality growth of wafer-scale MoS2 is still of great challenge. Herein, this review mainly focuses on the evolution of MoS2 by including chemical vapor deposition, metal-organic chemical vapor deposition, physical vapor deposition, and thermal conversion technology methods. The state-of-the-art research on the growth and optimization mechanism, including nucleation, orientation, grain, and defect engineering, is systematically summarized. Then, this review summarizes the wafer-scale application of MoS2 in a transistor, inverter, electronics, and photodetectors. Finally, the current challenges and future perspectives are outlined for the wafer-scale growth and application of MoS2.

Interfacial Coupling and Modulation of van der Waals Heterostructures for Nanodevices

In recent years, van der Waals heterostructures (vdWHs) of two-dimensional (2D) materials have attracted extensive research interest. By stacking various 2D materials together to form vdWHs, it is interesting to see that new and fascinating properties are formed beyond single 2D materials; thus, 2D heterostructures-based nanodevices, especially for potential optoelectronic applications, were successfully constructed in the past few decades. With the dramatically increased demand for well-controlled heterostructures for nanodevices with desired performance in recent years, various interfacial modulation methods have been carried out to regulate the interfacial coupling of such heterostructures. Here, the research progress in the study of interfacial coupling of vdWHs (investigated by Photoluminescence, Raman, and Pump-probe spectroscopies as well as other techniques), the modulation of interfacial coupling by applying various external fields (including electrical, optical, mechanical fields), as well as the related applications for future electrics and optoelectronics, have been briefly reviewed. By summarizing the recent progress, discussing the recent advances, and looking forward to future trends and existing challenges, this review is aimed at providing an overall picture of the importance of interfacial modulation in vdWHs for possible strategies to optimize the device's performance.

Natural p-n Junctions at the MoS2 Flake Edges

Two-dimensional (2D) semiconductors are holding promises as channel materials for field-effect transistors. Compared to traditional three-dimensional (3D) semiconductors whose electronic and optical properties are hindered by dangling bonds and trap states at the surfaces, 2D materials with saturated chemical bonds on the surface maintain the excellent properties even when device thickness scales down to monolayer. However, dangling bonds are unavoidable at their edges, which are often overlooked and should have important effects on the devices. Here, we show that the edges of as-exfoliated and etched MoS₂ are naturally p-type doped and can form p-n junctions with the bulk of the flake. The width of these edge regions is around 20 nm. While their existence could present challenges for the shrinkage of devices, they can be exploited to form rectifying or optoelectronic devices based on a single flake of MoS₂ without the need of an elaborate extrinsic doping process.

A non-linear two-dimensional float gate transistor as a lateral inhibitory synapse for retinal early visual processing

Synaptic transistors that accommodate concurrent signal transmission and learning in a neural network are attracting enormous interest for neuromorphic sensory processing. To remove redundant sensory information while keeping important features, artificial synaptic transistors with non-linear conductance are desired to apply filter processing to sensory inputs. Here, we report the realization of non-linear synapses using a two-dimensional van der Waals (vdW) heterostructure (MoS₂/h-BN/graphene) based float gate memory device, in which the semiconductor channel is tailored via a surface acceptor (ZnPc) for subthreshold operation. In addition to usual synaptic plasticity, the memory device exhibits highly non-linear conductance (rectification ratio >10⁶), allowing bidirectional yet only negative/inhibitory current to pass through. We demonstrate that in a lateral coupling network, such a float gate memory device resembles the key lateral inhibition function of horizontal cells for the formation of an ON-center/OFF-surround receptive field. When combined with synaptic plasticity, the lateral inhibition weights are further tunable to enable adjustable edge enhancement for early visual processing. Our results here hopefully open a new scheme toward early sensory perception via lateral inhibitory synaptic transistors.

Back-Gated van der Waals Heterojunction Manipulates Local Charges toward Fine-Tuning Hydrogen Evolution

Charge redistribution plays a prominent role in interpreting the intrinsic electrocatalytic mechanism. Establishing a quantitative relationship between the local charges and electrochemical performance can fundamentally update the design philosophies beyond conventional methods. We describe exertion of an external electric field in the cobalt phthalocyanine (CoPc)/MoS₂ heterojunction to finely manipulate intermolecular charge transfer. The injected charges (e^- ) from CoPc to MoS₂ migrate to natural S vacancies and enhance Mo-H bonding. Moreover, the band gap of MoS₂ and CoPc can be readily tuned by the electric field, verifying band engineering at the heterointerface. In situ photoluminescence spectra and gate-dependent electrochemical measurement reveal a linear correlation between the charge accumulation and hydrogen evolution reaction (HER) activity. This approach provides a new strategy for the design of catalysts, enabling precise regulation of the electronic configuration to improve catalytic activity.

Recent progress in 2D hybrid heterostructures from transition metal dichalcogenides and organic layers: properties and applications in energy and optoelectronics fields

Atomically thin transition metal dichalcogenides (TMDs) present extraordinary optoelectronic, electrochemical, and mechanical properties that have not been accessible in bulk semiconducting materials. Recently, a new research field, 2D hybrid heteromaterials, has emerged upon integrating TMDs with molecular systems, including organic molecules, polymers, metal-organic frameworks, and carbonaceous materials, that can tailor the TMD properties and exploit synergetic effects. TMD-based hybrid heterostructures can meet the demands of future optoelectronics, including supporting flexible, transparent, and ultrathin devices, and energy-based applications, offering high energy and power densities with long cycle lives. To realize such applications, it is necessary to understand the interactions between the hybrid components and to develop strategies for exploiting the distinct benefits of each component. Here, we provide an overview of the current understanding of the new phenomena and mechanisms involved in TMD/organic hybrids and potential applications harnessing such valuable materials in an insightful way. We highlight recent discoveries relating to multicomponent hybrid materials. Finally, we conclude this review by discussing challenges related to hybrid heteromaterials and presenting future directions and opportunities in this research field.

Properties at the interface of the pristine CdSe and core-shell CdSe-ZnS quantum dots with ultrathin monolayers of two-dimensional MX2 (M: Mo, W; X: S, Se, Te) heterostructures from density functional theory

In this work, eight van der Waals heterojunctions based on CdSe or CdSe-ZnS quantum dots (QDs) and four commonly used two-dimensional transition metal dichalcogenides (2D-TMDs) are theoretically designed. On the basis of the constructed structures, density functional theory (DFT) method is employed to investigate the structural and optoelectronic related properties of these heterojunctions in detail. Specifically, their electronic properties including charge density differences, density of states, and band offsets are calculated, based on which band alignment types as well as their potentials as novel photovoltaic materials are discussed. According to these calculations, we proposed that several van der Waals heterostructures including MoS₂/CdSe, MoTe₂/CdSe, WSe₂/CdSe, MoTe₂/CdSe-ZnS, and WSe₂/CdSe-ZnS might be used as potential photovoltaic materials due to their type II band alignment characteristics. Moreover, the WSe₂/CdSe-ZnS heterostructure is expected to have optimal photovoltaic performance attributed to their large bond offsets and band gaps, which could not only facilitate charge separation processes, but also slow down charge recombination. Our present theoretical work could be helpful for the future experimental design of novel CdSe QDs and 2D-TMD based van der Waals heterostructures with excellent photovoltaic performances.

Enhanced Electron Transfer and Spin Flip through Spin-Orbital Couplings in Organic/Inorganic Heterojunctions: A Nonadiabatic Surface Hopping Simulation

The circumstances of transferred electrons across organic/inorganic interfaces have attracted intensive interest because of the distinctive electronic structure properties of those two components. Leveraging ab initio nonadiabatic molecular dynamics methods in conjunction with spin dynamics induced by spin-orbital couplings (SOCs), this study reports two competitive channels during photoinduced dynamical processes in the prototypical ZnPc/monolayer MoS₂ heterojunction. Interestingly, the electron-transfer and relaxation processes occur simultaneously because of the enhancement of electron-phonon couplings and expansion of dynamical pathways by SOCs, suggesting that the electron-transfer rate and relaxation processes can be tuned by SOCs, hence yielding the performance promotion of photovoltaic and photocatalytic devices. Additionally, approximately half of the transferred electrons flip their spin within 1.6 ps because of strong SOCs in MoS₂, achieving great agreement with experimental measurements. This investigation provides instructive perspectives for designing novel devices and applications based on organic/inorganic heterojunctions, demonstrating the importance of spin dynamics simulations in exploring sophisticated photoinduced processes in materials.

Interlayer exciton emission in a MoS2/VOPc inorganic/organic van der Waals heterostructure

Heterostructures built from two-dimensional (2D) materials and organic semiconductors offer a unique platform for addressing many fundamental physics and construction of functional devices by taking advantage of both the 2D materials and organic semiconductors. We report interlayer exciton emission in the near infrared range around 1.54 eV (∼805 nm) from the heterostructure of pyramidal VOPc (p-type) and transition metal dichalcogenide monolayer MoS₂ (VOPc/MoS₂). This contrasts the observation of photoluminescence (PL) from the SnCl₂Pc/MoS₂ heterostructure despite both being type-II heterostructures. We attribute the exciton emission to the carrier transition from the generated interface mid-gap states of VOPc to the ground states of MoS₂ in the heterostructure system as predicted from density functional theory (DFT) calculations. Furthermore, the observed PL signal of the VOPc/MoS₂ heterostructure shows blue shift, while the PL peak of the SnCl₂Pc/MoS₂ heterostructure shows red shift. Our finding opens up a new avenue to tune the optoelectronic properties of the van der Waals heterojunctions consisting of 2D materials and organic semiconductors for optoelectronic applications.

All-Solution-Processed Van der Waals Heterostructures for Wafer-Scale Electronics

2D van der Waals (vdW) materials have been considered as potential building blocks for use in fundamental elements of electronic and optoelectronic devices, such as electrodes, channels, and dielectrics, because of their diverse and remarkable electrical properties. Furthermore, two or more building blocks of different electronic types can be stacked vertically to generate vdW heterostructures with desired electrical behaviors. However, such fundamental approaches cannot directly be applied practically because of issues such as precise alignment/positioning and large-quantity material production. Here, these limitations are overcome and wafer-scale vdW heterostructures are demonstrated by exploiting the lateral and vertical assembly of solution-processed 2D vdW materials. The high exfoliation yield of the molecular intercalation-assisted approach enables the production of micrometer-sized nanosheets in large quantities and its lateral assembly in a wafer-scale via vdW interactions. Subsequently, the laterally assembled vdW thin-films are vertically assembled to demonstrate various electronic device applications, such as transistors and photodetectors. Furthermore, multidimensional vdW heterostructures are demonstrated by integrating 1D carbon nanotubes as a p-type semiconductor to fabricate p-n diodes and complementary logic gates. Finally, electronic devices are fabricated via inkjet printing as a lithography-free manner based on the stable nanomaterial dispersions.

Surface Charge Transfer Doping of MoS2 Monolayer by Molecules with Aggregation-Induced Emission Effect

Surface charge transfer doping has attracted much attention in modulating the optical and electrical behavior of 2D transition metal dichalcogenides (TMDCs), where finding controllable and efficient dopants is crucial. Here, 1,1,2,2-tetraphenylethylene (TPE) derivative molecules with aggregation-induced emission (AIE) effect were selected as adjustable dopants. By designing nitro and methoxyl functional groups and surface coating, controlled p/n-type doping can be achieved on a chemical vapor deposition (CVD) grown monolayer, MoS2. We investigated the electron transfer behavior between these two dopants and MoS2 with fluorescence, Raman, X-ray photoelectron spectra and transient absorption spectra. 1,1,2,2-Tetrakis(4-nitrophenyl)ethane (TPE-4NO2) with a negative charge aggregation can be a donor to transfer electrons to MoS2, while 1,1,2,2-Tetrakis(4-methoxyphenyl)ethane (TPE-4OCH3) is the opposite and electron-accepting. Density functional theory calculations further explain and confirm these experimental results. This work shows a new way to select suitable dopants for TMDCs, which is beneficial for a wide range of applications in optoelectronic devices.

Photoelectric effect of hybrid ultraviolet-sensitized phototransistors from an n-type organic semiconductor and an all-inorganic perovskite quantum dot photosensitizer

Low-dimensional all-inorganic perovskite quantum dots (QDs) have been increasingly developed as photo-sensing materials in the field of photodetectors because of their strong light-absorption capability and broad bandgap tunability. Here, solution-processed hybrid phototransistors built by a dithienothiophenoquinoid (DTTQ) n-type organic semiconductor transport channel mixing with a colloidal CsPbBr₃ perovskite QD photosensitizer are demonstrated by manipulating the relative volume ratio from 10 : 0 to 9 : 1, 7 : 3, 5 : 5, 3 : 7, 1 : 9, and 0 : 10. This results in a significantly enhanced photodetection performance owing to the advantages of a high UV absorption cross-section based on the perovskite QDs, efficient carrier transport abilities from the DTTQ semiconductor, and the photogating effect between the bulk heterojunction photocarrier transfer interfaces. The optimized DTTQ : QD (3 : 7) hybrid phototransistor achieves a high photoresponsivity (R) of 7.1 × 10⁵ A W^-1, a photosensitivity (S) of 1.8 × 10⁴, and a photodetectivity (D) of 3.6 × 10¹³ Jones at 365 nm. Such a solution-based fabrication process using a hybrid approach directly integrated into a sensitized phototransistor potentially holds promising photoelectric applications towards advanced light-stimulated photodetection.

Molecular Approach to Engineer Two-Dimensional Devices for CMOS and beyond-CMOS Applications

Two-dimensional materials (2DMs) have attracted tremendous research interest over the last two decades. Their unique optical, electronic, thermal, and mechanical properties make 2DMs key building blocks for the fabrication of novel complementary metal-oxide-semiconductor (CMOS) and beyond-CMOS devices. Major advances in device functionality and performance have been made by the covalent or noncovalent functionalization of 2DMs with molecules: while the molecular coating of metal electrodes and dielectrics allows for more efficient charge injection and transport through the 2DMs, the combination of dynamic molecular systems, capable to respond to external stimuli, with 2DMs makes it possible to generate hybrid systems possessing new properties by realizing stimuli-responsive functional devices and thereby enabling functional diversification in More-than-Moore technologies. In this review, we first introduce emerging 2DMs, various classes of (macro)molecules, and molecular switches and discuss their relevant properties. We then turn to 2DM/molecule hybrid systems and the various physical and chemical strategies used to synthesize them. Next, we discuss the use of molecules and assemblies thereof to boost the performance of 2D transistors for CMOS applications and to impart diverse functionalities in beyond-CMOS devices. Finally, we present the challenges, opportunities, and long-term perspectives in this technologically promising field.

Mechanistic Investigation of Molybdenum Disulfide Defect Photoluminescence Quenching by Adsorbed Metallophthalocyanines

Lattice defects play an important role in determining the optical and electrical properties of monolayer semiconductors such as MoS₂. Although the structures of various defects in monolayer MoS₂ are well studied, little is known about the nature of the fluorescent defect species and their interaction with molecular adsorbates. In this study, the quenching of the low-temperature defect photoluminescence (PL) in MoS₂ is investigated following the deposition of metallophthalocyanines (MPcs). The quenching is found to significantly depend on the identity of the phthalocyanine metal, with the quenching efficiency decreasing in the order CoPc > CuPc > ZnPc, and almost no quenching by metal-free H₂Pc is observed. Time-correlated single photon counting (TCSPC) measurements corroborate the observed trend, indicating a decrease in the defect PL lifetime upon MPc adsorption, and the gate voltage-dependent PL reveals the suppression of the defect emission even at large Fermi level shifts. Density functional theory modeling argues that the MPc complexes stabilize dark negatively charged defects over luminescent neutral defects through an electrostatic local gating effect. These results demonstrate the control of defect-based excited-state decay pathways via molecular electronic structure tuning, which has broad implications for the design of mixed-dimensional optoelectronic devices.

Mechanism, Material, Design, and Implementation Principle of Two-Dimensional Material Photodetectors

Two-dimensional (2D) materials may play an important role in future photodetectors due to their natural atom-thin body thickness, unique quantum confinement, and excellent electronic and photoelectric properties. Semimetallic graphene, semiconductor black phosphorus, and transition metal dichalcogenides possess flexible and adjustable bandgaps, which correspond to a wide interaction spectrum ranging from ultraviolet to terahertz. Nevertheless, their absorbance is relatively low, and it is difficult for a single material to cover a wide spectrum. Therefore, the combination of phototransistors based on 2D hybrid structures with other material platforms, such as quantum dots, organic materials, or plasma nanostructures, exhibit ultra-sensitive and broadband optical detection capabilities that cannot be ascribed to the individual constituents of the assembly. This article provides a comprehensive and systematic review of the recent research progress of 2D material photodetectors. First, the fundamental detection mechanism and key metrics of the 2D material photodetectors are introduced. Then, the latest developments in 2D material photodetectors are reviewed based on the strategies of photocurrent enhancement. Finally, a design and implementation principle for high-performance 2D material photodetectors is provided, together with the current challenges and future outlooks.

The Schottky-Mott Rule Expanded for Two-Dimensional Semiconductors: Influence of Substrate Dielectric Screening

A comprehensive understanding of the energy level alignment mechanisms between two-dimensional (2D) semiconductors and electrodes is currently lacking, but it is a prerequisite for tailoring the interface electronic properties to the requirements of device applications. Here, we use angle-resolved direct and inverse photoelectron spectroscopy to unravel the key factors that determine the level alignment at interfaces between a monolayer of the prototypical 2D semiconductor MoS₂ and conductor, semiconductor, and insulator substrates. For substrate work function (Φ_sub) values below 4.5 eV we find that Fermi level pinning occurs, involving electron transfer to native MoS₂ gap states below the conduction band. For Φ_sub above 4.5 eV, vacuum level alignment prevails but the charge injection barriers do not strictly follow the changes of Φ_sub as expected from the Schottky-Mott rule. Notably, even the trends of the injection barriers for holes and electrons are different. This is caused by the band gap renormalization of monolayer MoS₂ by dielectric screening, which depends on the dielectric constant (ε_r) of the substrate. Based on these observations, we introduce an expanded Schottky-Mott rule that accounts for band gap renormalization by ε_r -dependent screening and show that it can accurately predict charge injection barriers for monolayer MoS₂. It is proposed that the formalism of the expanded Schottky-Mott rule should be universally applicable for 2D semiconductors, provided that material-specific experimental benchmark data are available.

Lattice Defect Engineering Enables Performance-Enhanced MoS2 Photodetection through a Paraelectric BaTiO3 Dielectric

Carrier mobility and density are intrinsically important in nanophoto/electronic devices. High-dielectric-constant coupled polarization-field gate ferroelectrics are frequently studied and partially capable in achieving large-scale tuning of photoresponse, but their light absorption and carrier density seem generally ineffective. This raises questions about whether a similarly high-dielectric-constant paraelectric gate dielectric could enable tuning and how the principles involved could be established. In this study, by deliberately introducing lattice defects in high-dielectric-constant paraelectric, cubic BaTiO₃ (c-BTO) was explored to fabricate MoS₂ photodetectors with ultrahigh detection ability and outstanding field-effect traits. An organic-metal-based spin-coating cum annealing method was used for the c-BTO synthesis, with an optimized thickness (300 nm), by introducing lattice defects properly but maintaining a large dielectric constant (55 at 1k Hz) and low dielectric loss (0.06 at 1k Hz), which renders the enhanced visible-light region absorption. As a result of the synergistically enhanced mobility and photoabsorption, the MoS₂/BTO FET exhibits promising merits, for example, on/off ratio, subthreshold swing, and mobilities for high-performance photodetectors with excellent responsivity (600 AW^-1) and detectivity (1.25 × 10¹² Jones). Thus, this work facilitates the establishment of a lattice defect induced sub-bandgap absorption landmap for synergistically enhanced photoresponse for high-performance photodetector exploration.

MoS2 and CdMoS4 nanostructure-based UV light photodetectors

We have developed MoS₂ nanosheets and CdMoS₄ hierarchical nanostructures based on a UV light photodetector. The surface morphologies of the as-prepared samples were investigated via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The performance parameters for the present photodetectors are investigated under the illumination of UV light having a wavelength of ∼385 nm. Upon the illumination of UV light, the CdMoS₄-based photodetector device showed a better response to UV light compared to the MoS₂ device in terms of photoresponsivity, response time (∼72 s) and recovery time (∼94 s). Our results reveal that CdMoS₄ hierarchical nanostructures are practical for enhancing the device performance.

Enhanced photoactivity of ZnPc@WS2 heterojunction by CuBi2O4 and its application for photoelectrochemical detection of 5-formyl-2'-deoxycytidine

The endogenous epigenetic marker 5-formylcytosine (5 fC) is introduced by 5-methylcytosine (5 mC) oxidation under action of enzyme oxidation, and plays an important role in many life activities. Since the content of 5 fC in mammalian tissues and cells is very low, it is necessary to exploit a sensitive and specific detection method to further understand the function of 5 fC. In this work, a sensitively and selectively photoelectrochemical (PEC) biosensor was developed for 5-formyl-2'-deoxycytidine (5fdC) detection. CuBi₂O₄/ZnPc@WS₂ was used as photoactive material, where the formed ternary heterojunction structure greatly enhanced the PEC response and increased the detection sensitivity. Positively charged polyethyleneimine (PEI) was employed as 5fdC recognition and capture unit, where the amine group on PEI specifically reacted with aldehyde group of 5fdC to form stable amide bond. 4-Carboxyphenylboronic acid (4-CPBA) was adopted as crosslinker for 5fdC and amino functionalized CuBi₂O₄ based on the covalent interaction between 1,3-diol bond on 5fdC and boric acid structure on 4-CPBA, and the covalent interaction between -COOH on 4-CPBA and -NH₂ on amino functionalized CuBi₂O₄. On the basis of the positive synergistic effect of ZnPc and CuBi₂O₄ on improving the photoelectric performance of WS₂, the separation of photo-generated electron-hole pairs in semiconductors were promoted, and the examination range was expanded from 0.1 to 500 nM, and the detection limit was 0.0483 nM (3σ). Based on the unique covalent reaction between -NH₂ and -CHO, the PEC biosensor has excellent detection sensitivity, and can even separate 5fdC from 5-methylcytosine deoxyribonucleoside and 5-hydroxymethylcytosine deoxyribonucleoside. The effect of antibiotics and heavy metals on the 5fdC content in wheat tissue genome has also been further investigated using this sensor.

Rational design of monolayer transition metal dichalcogenide@fullerene van der Waals photovoltaic heterojunctions with time-domain density functional theory simulations

van der Waals heterojunctions formed by transition metal dichalcogenides (TMDs) and fullerenes are promising candidates for novel photovoltaic devices due to the excellent optoelectronic properties of both TMDs and fullerenes. However, relevant experimental and theoretical investigations remain scarce to the best of our knowledge. Herein, we have first employed static density functional theory (DFT) calculations in combination with time-domain density functional theory (TDDFT) based nonadiabatic dynamics simulations to rationally evaluate the photovoltaic performances of four TMD@fullerene heterostructures, i.e. WSe₂@C₆₀, WSe₂@C₇₀, MoTe₂@C₆₀ and MoTe₂@C₇₀, respectively. Our simulation results indicate that the C₇₀-based heterostructures overall have better photoinduced electron transfer efficiencies than their C₆₀-based counterparts, among which the performance of the WSe₂@C₇₀ heterostructure is the best and the electron transfer from WSe₂ to C₇₀ almost accomplishes within 1 ps. In addition, the large build-in potential of about 0.75 eV of WSe₂@C₇₀ is beneficial for the charge separation processes. Our present work not only selects the van der Waals TMD@fullerene heterojunctions that might have excellent photovoltaic properties, but also paves the way for the rational design of novel heterojunctions with better optoelectronic performances with DFT and TDDFT simulations in the future.

Electronic Structure of Metallophthalocyanines, MPc (M = Fe, Co, Ni, Cu, Zn, Mg) and Fluorinated MPc

We compute the electronic structure and optical excitation energies of metal-free and transition-metal phthalocyanines (H₂Pc and MPc for M = Fe, Co, Ni, Cu, Zn, Mg) using density functional theory with optimally tuned range-separated hybrid functionals (OT-RSH). We show that the OT-RSH approach provides photoemission spectra in quantitative agreement with experiments as well as optical band gaps within 10% of their experimental values, capturing the interplay of localized d-states and delocalized π-π* states for these organometallic compounds. We examine the tunability of MPcs and H₂Pc through fluorination, resulting in quasi-rigid shifts of the molecular orbital energies by up to 0.7 eV. Our comprehensive data set provides a new computational benchmark for gas-phase phthalocyanines, significantly improving upon other density-functional-theory-based approaches.

Phthalocyanines: An Old Dog Can Still Have New (Photo)Tricks!

Phthalocyanines have enjoyed throughout the years the benefits of being exquisite compounds with many favorable properties arising from the straightforward and diverse possibilities of their structural modulation. Last decades appreciated a steady growth in applications for phthalocyanines, particularly those dependent on their great photophysical properties, now used in several cutting-edge technologies, particularly in photonic applications. Judging by the vivid reports currently provided by many researchers around the world, the spotlight remains assured. This review deals with the use of phthalocyanine molecules in innovative materials in photo-applications. Beyond a comprehensive view on the recent discoveries, a critical review of the most acclaimed/considered reports is the driving force, providing a brief and direct insight on the latest milestones in phthalocyanine photonic-based science.

Single WTe2 Sheet-Based Electrocatalytic Microdevice for Directly Detecting Enhanced Activity of Doped Electronegative Anions

The high electrical conductivity of 1T'-WTe₂ deserves particular attention and may show a high potential for hydrogen evolution reaction (HER) catalysis. However, the actual activity certainly does not match expectations, and the inferior HER activity is actually still ambiguous at the atomic level. Unraveling the underlying HER behaviors of 1T'-WTe₂ will give rise to a new family of HER catalysts. Our structural analysis reveals that the inferior activity could result from insufficient charge density around the Te site and blocked adsorption channel at the W site, which cause too weak hydrogen adsorption. Herein, we fabricated a single WTe₂ sheet-based electrocatalytic microdevice for directly extracting enhanced HER activity of doped electronegative F atoms. The overpotential at -10 mA cm^-2 reduced to 0.27 V after F doping compared to 0.45 V for the original state. In situ electrochemical measurement and electrical tests on a single sheet indicate that doped F can regulate surface charge and hydrogen adsorption behavior. Furthermore, the theory simulation uncovers that the smaller atomic radius of F contributes to an empty coordination environment; meanwhile, strong electronegativity induces hydrogen adsorption. Thus, the ΔG_H^* at W sites around the doped F is as low as 0.18 eV. Synergistically modulating the charge properties and opening steric hindrance provides a new pathway to rationally construct electrocatalysts and beyond.

Solution-Processed MoS2 Film with Functional Interfaces via Precursor-Assisted Chemical Welding

Molybdenum disulfide (MoS₂) presents fascinating properties for next-generation applications in diverse fields. However, fully exploiting the best properties of MoS₂ in largescale practical applications still remains a challenge due to lack of proper processing methods. Solution-based processing can be a promising route for scalable production of MoS₂ nanosheets, but the resulting assembled film possesses an enormous number of interfaces that significantly compromise the intrinsic electrical properties. Herein, we demonstrate the solution processing of MoS₂ and subsequent precursor-assisted chemical welding to form defective MoS_2-x at the nanosheet interfaces. The formation of defective MoS_2-x significantly reduces the electrical contact resistances, and thus the chemically welded MoS₂ film exhibits more than 2 orders of magnitude improved electrical conductivity. Furthermore, the chemical welding provides MoS_2-x interface induced additional defect originated functionalities for diverse applications such as broadband photodetection over the near-infrared range and improved electrocatalytic activity for hydrogen evolution reactions. Overall, this precursor-assisted chemical welding strategy can be a facile route to produce high-quality MoS₂ films with low-quality defective MoS_2-x at the interfaces having multifunctionalities in electronics, optoelectronics, and electrocatalysis.