We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices.

The production of renewable solar fuel through CO2 photoreduction, namely artificial photosynthesis, has gained tremendous attention in recent times due to the limited availability of fossil-fuel resources and global climate change caused by rising anthropogenic CO2 in the atmosphere. In this study, graphene oxide (GO) decorated with copper nanoparticles (Cu-NPs), hereafter referred to as Cu/GO, has been used to enhance photocatalytic CO2 reduction under visible-light. A rapid one-pot microwave process was used to prepare the Cu/GO hybrids with various Cu contents. The attributes of metallic copper nanoparticles (∼4-5 nm in size) in the GO hybrid are shown to significantly enhance the photocatalytic activity of GO, primarily through the suppression of electron-hole pair recombination, further reduction of GO's bandgap, and modification of its work function. X-ray photoemission spectroscopy studies indicate a charge transfer from GO to Cu. A strong interaction is observed between the metal content of the Cu/GO hybrids and the rates of formation and selectivity of the products. A factor of greater than 60 times enhancement in CO2 to fuel catalytic efficiency has been demonstrated using Cu/GO-2 (10 wt % Cu) compared with that using pristine GO.

We demonstrate a polymer-free method that can routinely transfer relatively large-area graphene to any substrate with advanced electrical properties and superior atomic and chemical structures as compared to the graphene sheets transferred with conventional polymer-assisted methods. The graphene films that are transferred with polymer-free method show high electrical conductance and excellent optical transmittance. Raman spectroscopy and X-ray/ultraviolet photoelectron spectroscopy also confirm the presence of high quality graphene sheets with little contamination after transfer. Atom-resolved images can be obtained using scanning tunneling microscope on as-transferred graphene sheets without additional cleaning process. The mobility of the polymer-free graphene monolayer is as high as 63,000 cm(2) V(-1) s(-1), which is 50% higher than the similar sample transferred with the conventional method. More importantly, this method allows us to place graphene directly on top of devices made of soft materials, such as organic and polymeric thin films, which widens the applications of graphene in soft electronics.

No abstract

Photodegradation of organic pollutants in aqueous solution is a promising method for environmental purification. Photocatalysts capable of promoting this reaction are often composed of noble metal nanoparticles deposited on a semiconductor. Unfortunately, the separation of these semiconductor-metal nanopowders from the treated water is very difficult and energy consumptive, so their usefulness in practical applications is limited. Here, a precisely controlled synthesis of a large-scale and highly efficient photocatalyst composed of monolayered Au nanoparticles (AuNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNA) through a bifunctional surface molecular linker is demonstrated. Thioctic acid with sufficient steric stabilization is used as a molecular linker. High density unaggregated AuNPs bonding on entire surfaces of ZNA are successfully prepared on a conductive film/substrate, allowing easy recovery and reuse of the photocatalysts. Surprisingly, the ZNA-AuNPs heterostructures exhibit a photodegradation rate 8.1 times higher than that recorded for the bare ZNA under UV irradiation. High density AuNPs, dispersed perfectly on the ZNA surfaces, significantly improve the separation of the photogenerated electron-hole pairs, enlarge the reaction space, and consequently enhance the photocatalytic property for degradation of chemical pollutants. Photoelectron, photoluminescence and photoconductive measurements confirm the discussion on the charge carrier separation and photocatalytic experimental data. The demonstrated higher photodegradation rates demonstrated indicate that the ZNA-AuNPs heterostructures are candidates for the next-generation photocatalysts, replacing the conventional slurry photocatalysts.

Natural systems display sophisticated control of light-matter interactions at multiple length scales for light harvesting, manipulation, and management, through elaborate photonic architectures and responsive material formats. Here, we combine programmable photonic function with elastomeric material composites to generate optomechanical actuators that display controllable and tunable actuation as well as complex deformation in response to simple light illumination. The ability to topographically control photonic bandgaps allows programmable actuation of the elastomeric substrate in response to illumination. Complex three-dimensional configurations, programmable motion patterns, and phototropic movement where the material moves in response to the motion of a light source are presented. A “photonic sunflower” demonstrator device consisting of a light-tracking solar cell is also illustrated to demonstrate the utility of the material composite. The strategy presented here provides new opportunities for the future development of intelligent optomechanical systems that move with light on demand.

Mechanically guided assembly techniques yield complex 3D microvascular networks with multifunctional characteristics.

To expand the applications of graphene in optoelectronics and microelectronics, simple and effective doping processes need to be developed. In this paper, we demonstrate an aqueous process that can simultaneously transfer chemical vapor deposition grown graphene from Cu to other substrates and produce stacked graphene/dopant intercalation films with tunable work functions, which differs significantly from conventional doping methods using vacuum evaporation or spin-coating processes. The work function of graphene layers can be tuned from 3.25 to 5.10 eV, which practically covers the wide range of the anode and cathode applications. Doped graphene films in intercalation structures also exhibit excellent transparency and low resistance. The polymer-based solar cells with either low work function graphene as cathodes or high work function graphene as anodes are demonstrated.