Graphene as Infrared Light Sensor Material

The infrared (IR) photoresponse of graphene synthesized by an atmospheric chemical vapor deposition (CVD) system using a mixture of hydrogen and methane gases was studied. The IR sensor devices were fabricated using graphene films transferred onto a SiO2 substrate by a lift-off process. The quality of graphene was investigated with Raman spectroscopy and optical microscopy. The photoresponse was recorded under the illumination of IR light of wavelength 850 nm and intensity of around 0.216 mW/cm^2. The effects of temperature and hydrogenation on photoconductivity were also studied. It was found that the transient response and recovery times decreased with the temperature increase. The hydrogenation effect also caused a significant decrease in the photoresponse of the device. Although the net change in the photoresponse for IR light was lower at low illumination intensity levels, the transient responses were observed around 100 times faster than the recently reported CNT-based IR sensors.Comment: 8 pages, 8 pictures, and 1 table

Production of Hydrogen for Clean and Renewable Source of Energy for Fuel Cell Vehicles

This was a two-year project that had two major components: 1) the demonstration of a PV-electrolysis system that has separate PV system and electrolysis unit and the hydrogen generated is to be used to power a fuel cell based vehicle; 2) the development of technologies for generation of hydrogen through photoelectrochemical process and bio-mass derived resources. Development under this project could lead to the achievement of DOE technical target related to PEC hydrogen production at low cost. The PEC part of the project is focused on the development of photoelectrochemical hydrogen generation devices and systems using thin-film silicon based solar cells. Two approaches are taken for the development of efficient and durable photoelectrochemical cells; 1) An immersion-type photoelectrochemical cells (Task 3) where the photoelectrode is immersed in electrolyte, and 2) A substrate-type photoelectrochemical cell (Task 2) where the photoelectrode is not in direct contact with electrolyte. Four tasks are being carried out: Task 1: Design and analysis of DC voltage regulation system for direct PV-to-electrolyzer power feed Task 2: Development of advanced materials for substrate-type PEC cells Task 3: Development of advanced materials for immersion-type PEC cells Task 4: Hydrogen production through conversion of biomass-derived waste

Modeling of Displacement Micropump With Passive Check Valves

ABSTRACT Finite element analysis (FEA) of piezoelectrically actuated micropump was carried. The actuator was designed using a PZT (Lead zirconate titanate) layer coated on a flexural PVDF (Polyvinylede fluoride) membrane. The flow of liquid was controlled by the cantilever valves at both the inlet and outlet. The flow rate of the pump was estimated using the stroke volume due to the deflection of diaphragm. The optimum flow characteristics were estimated using the stroke volume as a function of frequency of power supply. The performance of the pump with and without the effect of valve on flow rate was also studied. The operation of the PZT actuator at higher frequencies would lead to self-heating of the material. This limitation on temperature was studied and the ways to reduce the self-heating were verified

Perovskites-Based Solar Cells: A Review of Recent Progress, Materials and Processing Methods

With the rapid increase of efficiency up to 22.1% during the past few years, hybrid organic-inorganic metal halide perovskite solar cells (PSCs) have become a research “hot spot” for many solar cell researchers. The perovskite materials show various advantages such as long carrier diffusion lengths, widely-tunable band gap with great light absorption potential. The low-cost fabrication techniques together with the high efficiency makes PSCs comparable with Si-based solar cells. But the drawbacks such as device instability, J-V hysteresis and lead toxicity reduce the further improvement and the future commercialization of PSCs. This review begins with the discussion of crystal and electronic structures of perovskite based on recent research findings. An evolution of PSCs is also analyzed with a greater detail of each component, device structures, major device fabrication methods and the performance of PSCs acquired by each method. The following part of this review is the discussion of major barriers on the pathway for the commercialization of PSCs. The effects of crystal structure, fabrication temperature, moisture, oxygen and UV towards the stability of PSCs are discussed. The stability of other components in the PSCs are also discussed. The lead toxicity and updated research progress on lead replacement are reviewed to understand the sustainability issues of PSCs. The origin of J-V hysteresis is also briefly discussed. Finally, this review provides a roadmap on the current needs and future research directions to address the main issues of PSCs

One-pot hydrothermal synthesis and fabrication of kesterite Cu2ZnSn(S,Se)4 thin films

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) powder was synthesized by a hydrothermal process. The thin films were fabricated by physical vapor deposition of CZTSSe powder followed by a thermal annealing process. The kesterite microstructure was identified by the X-ray diffraction and Raman spectroscopy. The morphology and elemental composition of CZTSSe thin films were also investigated. The dependence of resistance on the temperature of CZTSSe film was measured and the thermal activation energy of conductivity was estimated to be 0.33 eV based on Arrhenius plot of resistance versus temperature. A high absorption coefficient (> 104 cmâ1) of CZTSSe was found in the visible and NIR regions of the spectrum. A direct band gap structure with band gap energy of 1.46 eV was also estimated for CZTSSe films. The photoconductivity was measured under both AM 1.5G and NIR illumination and a stable and fully recoverable photoconductivity was observed for both as-deposited and annealed CZTSSe films. The annealed films show a higher photoconductivity than the as-deposited films under both AM 1.5G and NIR lights. Keywords: CZTSSe, Hydrothermal, Physical vapor deposition, Coating, Nanocrystals, Photovoltaic

The Impact of Graphene on the Fabrication of Thin Film Solar Cells: Current Status and Future Prospects

Commercial solar cells have a power conversion efficiency (PCE) in the range of 10–22% with different light absorbers. Graphene, with demonstrated unique structural, physical, and electrical properties, is expected to bring the positive effects on the development of thin film solar cells. Investigations have been carried out to understand whether graphene can be used as a front and back contacts and active interfacial layer in solar cell fabrication. In this review, the current progress of this research is analyzed, starting from the graphene and graphene-based Schottky diode. Also, the discussion was focused on the progress of graphene-incorporated thin film solar cells that were fabricated with different light absorbers, in particular, the synthesis, fabrication, and characterization of devices. The effect of doping and layer thickness of graphene on PCE was also included. Currently, the PCE of graphene-incorporated bulk-heterojunction devices have enhanced in the range of 0.5–3%. However, device durability and cost-effectiveness are also the challenging factors for commercial production of graphene-incorporated solar cells. In addition to the application of graphene, graphene oxides have been also used in perovskite solar cells. The current needs and likely future investigations for graphene-incorporated solar cells are also discussed

Analysis of current and future technologies of capsule endoscopy: A mini review

Many existing methods of endoscopy can be very uncomfortable and potentially even painful for a patient. Using a conventional endoscope is also limited in its usable range, unable to access a majority of the small bowel. Recent advancements in LEDs, optical design, and MEMS (microelectromechanical systems) technologies have provided the ability to create a wireless endoscope. Since its inception, the capsule endoscope has seen advancements in existing technology as well as the introduction of new components. As the capsule endoscope continues to advance, more application possibilities will grow as well.</p

Tribological Properties of 2D Materials and Composites—A Review of Recent Advances

This paper aims to provide a theoretical and experimental understanding of the importance of novel 2D materials in solid-film lubrication, along with modulating strategies adopted so far to improve their performance for spacecraft and industrial applications. The mechanisms and the underlying physics of 2D materials are reviewed with experimental results. This paper covers some of the widely investigated solid lubricants such as MoS2, graphene, and boron compounds, namely h-BN and boric acid. Solid lubricants such as black phosphorus that have gained research prominence are also discussed regarding their application as additives in polymeric materials. The effects of process conditions, film deposition parameters, and dopants concentration on friction and wear rate are discussed with a qualitative and quantitative emphasis that are supported with adequate examples and application areas and summarized in the form of graphs and tables for easy readability. The use of advanced manufacturing methods such as powder metallurgy and sintering to produce solid lubricants of superior tribological performance and the subsequent economic gain from their development as a substitute for liquid lubricant are also evaluated

Graphene/PVDF Nanocomposite-Based Accelerometer for Detection of Low Vibrations

A flexible piezoresistive sensor was developed as an accelerometer based on Graphene/PVDF nanocomposite to detect low-frequency and low amplitude vibration of industrial machines, which may be caused due to misalignment, looseness of fasteners, or eccentric rotation. The sensor was structured as a cantilever beam with the proof mass at the free end. The vibration caused the proof mass to accelerate up and down, which was converted into an electrical signal. The output was recorded as the change in resistance (response percentage) with respect to the acceleration. It was found that this accelerometer has a capability of detecting acceleration up to 8 gpk-pk in the frequency range of 20 Hz to 80 Hz. The developed accelerometer has the potential to represent an alternative to the existing accelerometers due to its compactness, simplicity, and higher sensitivity for low frequency and low amplitude applications