Defect engineering is widely applied in transition metal dichalcogenides (TMDs) to achieve electrical, optical, magnetic, and catalytic regulation. Vacancies, regarded as a type of extremely delicate defect, are acknowledged to be effective and flexible in general catalytic modulation. However, the influence of vacancy states in addition to concentration on catalysis still remains vague. Thus, via high throughput calculations, the optimized sulfur vacancy (S-vacancy) state in terms of both concentration and distribution is initially figured out among a series of MoS2 models for the hydrogen evolution reaction (HER). In order to realize it, a facile and mild H2O2 chemical etching strategy is implemented to introduce homogeneously distributed single S-vacancies onto the MoS2 nanosheet surface. By systematic tuning of the etching duration, etching temperature, and etching solution concentration, comprehensive modulation of the S-vacancy state is achieved. The optimal HER performance reaches a Tafel slope of 48 mV dec–1 and an overpotential of 131 mV at a current density of 10 mA cm–2, indicating the superiority of single S-vacancies over agglomerate S-vacancies. This is ascribed to the more effective surface electronic structure engineering as well as the boosted electrical transport properties. By bridging the gap, to some extent, between precise design from theory and practical modulation in experiments, the proposed strategy extends defect engineering to a more sophisticated level to further unlock the potential of catalytic performance enhancement.

1wileyonlinelibrary.com schemes, the fl exible functional sensors are competitive and attractive candidates for promoting the advancement of sensing system. Recently, for the achievement of sensing devices, the printing technique has attracted widespread attention and been pursued to deposit various materials, like carbon materials, [ 13,23,24 ] polymers, [ 25,26 ] metals, [ 12,27 ] and semiconductors, [ 28,29 ] because the process is low energy consumption while maintaining the unique properties of the materials. By this way, the fl exible devices can be cheaper and easily produced.Graphite, one of carbon allotropes, has been increasing wide and keen interests of researchers, due to a wonder material of graphene. [ 9,[30][31][32] Pencil, a day-to-day material, is a nanocomposite of graphite and intercalated clay. [33][34][35] Being layered or pelleted, pencil lead can be exfoliated by using a gentle force. The drawing process can easily deposit graphite onto a rough paper, which contains massive amounts of cellulose fi bers and offer a naturally porous structure. [ 13,36 ] Pencil-trace drawn on printing papers is perhaps the simplest and easiest way of constructing graphite-based devices. The pen-on-paper (PoP) approach, a basic printing technique, offers a unique method to fabricate fl exible devices, such as strain sensors, [ 35 ] biosensors, [ 19,37 ] microfl uidic chips, [ 38 ] electronic devices, [ 34,39 ] photoconductive sensors, [ 29,40 ] and energy-storage devices. [ 33,41,42 ] Most of these devices have a response to force-induce changes in capacitance [ 33 ] and resistivity. [ 35 ] The microcontact-reversible sensing can effectively translate the microstructural deformations into electrical signals on active fl exible substrates. [ 6,9,43,44 ] As the potential to make fl exible, lightweight, portable, biocompatible, economical, and environment-friendly products, the PoP approach has an important role on the breakthroughs toward fl exible and wearable sensing devices.Herein, we demonstrate that the application of PoP approach can be expanded further to crucial fl exible sensing devices. We evaluated the repeatability of bending-unbending and the robustness of the strain sensors applied by loading. The strain sensors have a rapid respond to microdeformation changes and can be used to monitor various structural change and even human motion through facilitative and effective installing designs. Typically, the microdeformation of <0.13% strain can be detected. Compared with the recently reported fl exible sensing devices, the strain sensors behave signifi cant Flexible and Highly Sensitive Strain Sensors Fabricated by Pencil Drawn for Wearable MonitorXinqin Liao , Qingliang Liao , Xiaoqin Yan , Qijie Liang , Haonan Si , Minghua Li , Hualin Wu , Shiyao Cao , and Yue Zhang * Functional electrical devices have promising potentials in structural health monitoring system, human-friendly wearable interactive system, smart robotics, and even future multifunctional intelligent room. Here, a low-cost fabrication s...

Abstract2D transition metal dichalcogenide (2D‐TMD) materials and their van der Waals heterostructures (vdWHs) have inspired worldwide efforts in the fields of electronics and optoelectronics. However, photodetectors based on 2D/2D vdWHs suffer from performance limitations due to the weak optical absorption of their atomically thin nature. In this work, taking advantage of an excellent light absorption coefficient, low‐temperature solution‐processability, and long charge carrier diffusion length, all‐inorganic halides perovskite CsPbI3− xBrx quantum dots are integrated with monolayer MoS2 for high‐performance and low‐cost photodetectors. A favorable energy band alignment facilitating interfacial photocarrier separation and efficient carrier injection into the MoS2 layer inside the 0D–2D mixed‐dimensional vdWHs are confirmed by a series of optical characterizations. Owing to the synergistic effect of the photogating mechanism and the modulation of Schottky barriers, the corresponding phototransistor exhibits a high photoresponsivity of 7.7 × 104 A W−1, a specific detectivity of ≈5.6 × 1011 Jones, and an external quantum efficiency exceeding 107%. The demonstration of such 0D–2D mixed‐dimensional heterostructures proposed here would open up a wide realm of opportunities for designing low‐cost, flexible transparent, and high‐performance optoelectronics.

Fundamental understanding of charge behavior inside heterostructures is of vital importance for advancing high-performance optoelectronic applications. However, the charge behavior of 0D-2D mixed-dimensional van der Waals heterostructures (MvdWHs) in the photoexcited state remains elusive. In this work, an energy band alignment protocol is adopted to realize effective energy band structure engineering inside 0D-2D MvdWHs of perovskite quantum dots and MoS 2 monolayer with precisely designed typical type I and type II heterostructures, respectively. A profile and in-depth understanding of interfacial photoinduced charge behavior is determined from two opposite perspectives based on MvdWHs. Sufficient comparison of a series of optical characterization results, including Raman shift, quenched photoluminescence, visualized suppressed fluorescence intensity, and shortened fluorescence lifetime imaging, clearly verifies that interfacial charge behavior can be tailored by varying the band alignment in 0D-2D MvdWHs. Furthermore, the photoresponse performance and the relatively stronger and weaker photogating effects of such MvdWH-based phototransistors also demonstrate modulation of interfacial charge behavior in 0D-2D MvdWHs via energy band structure engineering, which is still feasible for optoelectronic performance optimization. These results are expected to shed light on designing novel functional devices and advancing the development process of 0D-2D MvdWHs in the foreseeable future.proposed stacked van der Waals heterostructures (vdWHs) have inspired worldwide efforts with rapid development of 2D materials. Such layer-by-layer assembled vdWHs could benefit from the high carrier mobilities, large surface-to-volume ratios, and especially flexible and semitransparent properties of atomically thin 2D materials. [4] However, the enhanced interlayer Coulombic interactions and Auger scattering processes in these 2D/2D vdWHs [5] as well as the inability to easily tune the energy band alignment for of the two given 2D layered materials has a great influence on the interfacial charge behavior, which is crucial to the performance of heterostructure-based functional devices. More recently, another type of vdWH was developed by integrating sizetunable semiconducting OD quantum dots (QDs) with 2D layered materials. This type of 0D-2D mixed-dimensional van der Waals heterostructure (MvdWH) has been demonstrated to possess various advantages, such as reduced Coulombic interactions, [6] easy preparation, and less constrained interfacial states. In addition, the interface in MvdWHs is more complex than that in conventional heterostructures, inducing interfacial disorder, synergistic effects, proximity effects, abrupt transitions of state density, and many other intriguing phenomena or properties. [4b,7] Hence, by combining the various remarkable optical properties of 0D-QDs with the unusual physical properties of 2D layered materials, 0D-2D MvdWHs may generate a fascinating interfacial charge behavior and exciting device performanc...

The matching of charge transport layer and photoactive layer is critical in solar energy conversion devices, especially for planar perovskite solar cells based on the SnO2 electron‐transfer layer (ETL) owing to its unmatched photogenerated electron and hole extraction rates. Graphdiyne (GDY) with multi‐roles has been incorporated to maximize the matching between SnO2 and perovskite regarding electron extraction rate optimization and interface engineering towards both perovskite crystallization process and subsequent photovoltaic service duration. The GDY doped SnO2 layer has fourfold improved electron mobility due to freshly formed C−O σ bond and more facilitated band alignment. The enhanced hydrophobicity inhibits heterogeneous perovskite nucleation, contributing to a high‐quality film with diminished grain boundaries and lower defect density. Also, the interfacial passivation of Pb−I anti‐site defects has been demonstrated via GDY introduction.

The NH4PbI3‐based phase transformation is realized by simply adding NH4I additive, in order to simultaneously control perovskite nucleation and crystal growth. Regarding the nucleation process, the NH4+ with small ionic radius preferentially diffuses into the [PbI6]4− octahedral layer to form NH4PbI3, which compensates the lack of CH3NH3I (MAI) precipitation. The generation of NH4PbI3 intermediate phase results in extra heterogeneous nucleation sites and reduces the defects derived from the absence of MA+. Regarding the crystal growth process, the cation exchange process between MA+ and NH4+, instead of the MAs directly entering, successfully retards the crystal growth. Such NH4PbI3 consumption process slows down the crystal growth, which effectively improves the perovskite quality with lowered defect density. The cooperation of these two effects eventually leads to the high‐quality perovskite with enlarged grain size, prolonged photoluminescence lifetime, lowered defect density, and increased carrier concentration, as well as the finally enhanced photovoltaic performance. Moreover, NH3 as a byproduct further facilitates the proposed transformation process and no external residue remains even without any post‐treatment. Such methodology of introducing a novel phase transformation to simultaneously control nucleation and crystal growth processes is of universal significance for further devotion in the foreseeable perovskite solar cells (PSCs) evolution.

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Although the library of 2D atomic crystals has greatly expanded over the past years, research into graphene is still one of the focuses for both academia and business communities. Due to its unique electronic structure, graphene offers a powerful platform for exploration of novel 2D physics, and has significantly impacted a wide range of fields including energy, electronics, and photonics. Moreover, the versatility of combining graphene with other functional components provides a powerful strategy to design artificial van der Waals (vdWs) heterostructures. Aside from the stacked 2D–2D vdWs heterostructure, in a broad sense graphene can hybridize with other non‐2D materials through vdWs interactions. Such mixed‐dimensional vdWs (MDWs) structures allow considerable freedom in material selection and help to harness the synergistic advantage of different dimensionalities, which may compensate for graphene's intrinsic shortcomings. A succinct overview of representative advances in graphene‐based MDWs heterostructures is presented, ranging from assembly strategies to applications in optoelectronics. The scientific merit and application advantages of these hybrid structures are particularly emphasized. Moreover, considering possible breakthroughs in new physics and application potential on an industrial scale, the challenges and future prospects in this active research field are highlighted.