The important role of water in growth of monolayer transition metal dichalcogenides

2D transition metal dichalcogenides (TMDs) are commonly grown by chemical vapor deposition using transition metal oxides as solid precursors. Despite the widespread use of this technique, challenges in reproducibility, coverage, and material quality are pervasive, suggestive of unknown and uncontrolled process parameters. In this communication, we demonstrate the impact of water vapor on this growth process. Our results show a direct correlation between gas phase water content and the morphology of TMD films. In particular, we show that the presence of water enhances volatilization, and therefore the vapor transport of tungsten and molybdenum oxide. Surprisingly, we find that water not only plays an important role in volatilization but is also compatible with TMD growth. In fact, carefully controlled humidity can consistently produce high quality, luminescent materials

Multiple Roles of a Non-fullerene Acceptor Contribute Synergistically for High-Efficiency Ternary Organic Photovoltaics

Ternary structure is an important design strategy to obtain high-efficiency non-fullerene organic photovoltaics (OPVs). However, the role of the third component to the standard binary system is still unclear. Here, a wide-bandgap small-molecule acceptor, denoted IDT-T, is synthesized and used together with a wide-bandgap donor polymer, PBDB-T, and a low-bandgap acceptor, ITIC, for fullerene-free ternary solar cells. The ternary cell features an enhanced power conversion efficiency (PCE) up to 12.2%, together with improved photocurrent density, open-circuit voltage (VOC), and fill factor. Studies of the thin films indicate that IDT-T functions as an energy-level mediator, a fluorescence resonance energy-transfer donor, an electron acceptor, and a crystallization modulator in the blend, which contribute synergistically in the ternary blend to deliver a higher VOC, more efficient exciton generation, suppressed bimolecular charge recombination and enhanced charge transport, and an overall high photovoltaic performance. Very recently, non-fullerene acceptors (NFAs) based on low-bandgap small molecules have emerged as a new class of acceptors that rival the dominance of fullerene-based acceptors. Such discovery also stimulates promising device architectures such as ternary solar cells, with a handful that have achieved high power conversion efficiencies above 12%. The primary effort, however, has been focusing on low-bandgap NFAs that exploit complementary absorption and energy-level cascade. Herein we report a rare example of a wide-bandgap NFA that leads to high-performance ternary solar cells without relying on full absorption complementarity of all three components. Detailed studies revealed the multiple roles of this acceptor in blend films, which contribute synergistically to improved device characteristics. This work may inspire new design principles of potent wide-bandgap NFAs, which will open the door to high-efficiency organic photovoltaic devices through new opportunities such as multi-component solar cells. The marriage of non-fullerene acceptors (NFAs) and ternary solar cell architecture has brought about great advances in organic photovoltaics. The primary effort, however, has been focusing on low-bandgap NFAs that exploit complementary absorption and energy-level cascade. Here we report a wide-bandgap NFA IDT-T that functions as an energy-level mediator, a fluorescence resonance energy-transfer donor, an electron acceptor, and a crystallization modulator, which contribute synergistically in a ternary blend to yield high organic photovoltaic device performance

Multiple Roles of a Non-fullerene Acceptor Contribute Synergistically for High-Efficiency Ternary Organic Photovoltaics

Ternary structure is an important design strategy to obtain high-efficiency non-fullerene organic photovoltaics (OPVs). However, the role of the third component to the standard binary system is still unclear. Here, a wide-bandgap small-molecule acceptor, denoted IDT-T, is synthesized and used together with a wide-bandgap donor polymer, PBDB-T, and a low-bandgap acceptor, ITIC, for fullerene-free ternary solar cells. The ternary cell features an enhanced power conversion efficiency (PCE) up to 12.2%, together with improved photocurrent density, open-circuit voltage (VOC), and fill factor. Studies of the thin films indicate that IDT-T functions as an energy-level mediator, a fluorescence resonance energy-transfer donor, an electron acceptor, and a crystallization modulator in the blend, which contribute synergistically in the ternary blend to deliver a higher VOC, more efficient exciton generation, suppressed bimolecular charge recombination and enhanced charge transport, and an overall high photovoltaic performance. Very recently, non-fullerene acceptors (NFAs) based on low-bandgap small molecules have emerged as a new class of acceptors that rival the dominance of fullerene-based acceptors. Such discovery also stimulates promising device architectures such as ternary solar cells, with a handful that have achieved high power conversion efficiencies above 12%. The primary effort, however, has been focusing on low-bandgap NFAs that exploit complementary absorption and energy-level cascade. Herein we report a rare example of a wide-bandgap NFA that leads to high-performance ternary solar cells without relying on full absorption complementarity of all three components. Detailed studies revealed the multiple roles of this acceptor in blend films, which contribute synergistically to improved device characteristics. This work may inspire new design principles of potent wide-bandgap NFAs, which will open the door to high-efficiency organic photovoltaic devices through new opportunities such as multi-component solar cells. The marriage of non-fullerene acceptors (NFAs) and ternary solar cell architecture has brought about great advances in organic photovoltaics. The primary effort, however, has been focusing on low-bandgap NFAs that exploit complementary absorption and energy-level cascade. Here we report a wide-bandgap NFA IDT-T that functions as an energy-level mediator, a fluorescence resonance energy-transfer donor, an electron acceptor, and a crystallization modulator, which contribute synergistically in a ternary blend to yield high organic photovoltaic device performance

2D materials advances: From large scale synthesis and controlled heterostructures to improved characterization techniques, defects and applications

The rise of two-dimensional (2D) materials research took place following the isolation of graphene in 2004. These new 2D materials include transition metal dichalcogenides, mono-elemental 2D sheets, and several carbide- and nitride-based materials. The number of publications related to these emerging materials has been drastically increasing over the last five years. Thus, through this comprehensive review, we aim to discuss the most recent groundbreaking discoveries as well as emerging opportunities and remaining challenges. This review starts out by delving into the improved methods of producing these new 2D materials via controlled exfoliation, metal organic chemical vapor deposition, and wet chemical means. We look into recent studies of doping as well as the optical properties of 2D materials and their heterostructures. Recent advances towards applications of these materials in 2D electronics are also reviewed, and include the tunnel MOSFET and ways to reduce the contact resistance for fabricating high-quality devices. Finally, several unique and innovative applications recently explored are discussed as well as perspectives of this exciting and fast moving field

2D materials advances: From large scale synthesis and controlled heterostructures to improved characterization techniques, defects and applications

The rise of two-dimensional (2D) materials research took place following the isolation of graphene in 2004. These new 2D materials include transition metal dichalcogenides, mono-elemental 2D sheets, and several carbide- and nitride-based materials. The number of publications related to these emerging materials has been drastically increasing over the last five years. Thus, through this comprehensive review, we aim to discuss the most recent groundbreaking discoveries as well as emerging opportunities and remaining challenges. This review starts out by delving into the improved methods of producing these new 2D materials via controlled exfoliation, metal organic chemical vapor deposition, and wet chemical means. We look into recent studies of doping as well as the optical properties of 2D materials and their heterostructures. Recent advances towards applications of these materials in 2D electronics are also reviewed, and include the tunnel MOSFET and ways to reduce the contact resistance for fabricating high-quality devices. Finally, several unique and innovative applications recently explored are discussed as well as perspectives of this exciting and fast moving field

Low-Cost, Disposable, Flexible and Highly Reproducible Screen Printed SERS Substrates for the Detection of Various Chemicals

Ideal SERS substrates for sensing applications should exhibit strong signal enhancement, generate a reproducible and uniform response, and should be able to fabricate in large-scale and low-cost. Herein, we demonstrate low-cost, highly sensitive, disposable and reproducible SERS substrates by means of screen printing Ag nanoparticles (NPs) on a plastic PET (Polyethylene terephthalate) substrates. While there are many complex methods for the fabrication of SERS substrates, screen printing is suitable for large-area fabrication and overcomes the uneven radial distribution. Using as-printed Ag substrates as the SERS platform, detection of various commonly known chemicals have been done. The SERS detection limit of Rhodamine 6G (R6G) is higher than the concentration of 1 × 10(−10) M. The relative standard deviation (RSD) value for 784 points on the detection of R6G and Malachite green (MG) is less than 20% revealing a homogeneous SERS distribution and high reproducibility. Moreover, melamine (MA) is detected in fresh liquid-milk without additional pretreatment, which may accelerate the application of rapid on-line detection of MA in liquid milk. Our screen printing method highlights the use of large-scale printing strategies for the fabrication of well-defined functional nanostructures with applications well beyond the field of SERS sensing