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Rockville, MD, United States

Josell D.,U.S. National Institute of Standards and Technology | Debnath R.,U.S. National Institute of Standards and Technology | Debnath R.,N5 Sensors, Inc. | Ha J.Y.,U.S. National Institute of Standards and Technology | And 6 more authors.
ACS Applied Materials and Interfaces | Year: 2014

This study presents windowless CdSe/CdTe thin film photovoltaic devices with in-plane patterning at a submicrometer length scale. The photovoltaic cells are fabricated upon two interdigitated comb electrodes prepatterned at micrometer length scale on an insulating substrate. CdSe is electrodeposited on one electrode, and CdTe is deposited by pulsed laser deposition over the entire surface of the resulting structure. Previous studies of symmetric devices are extended in this study. Specifically, device performance is explored with asymmetric devices having fixed CdTe contact width and a range of CdSe contact widths, and the devices are fabricated with improved dimensional tolerance. Scanning photocurrent microscopy (also known as laser beam induced current mapping) is used to examine local current collection efficiency, providing information on the spatial variation of performance that complements current-voltage and external quantum efficiency measurements of overall device performance. Modeling of carrier transport and recombination indicates consistency of experimental results for local and blanket illumination. Performance under simulated air mass 1.5 illumination exceeds 5% for all dimensions examined, and the best-performing device achieved 5.9% efficiency. © 2014 American Chemical Society.


Hangarter C.M.,U.S. National Institute of Standards and Technology | Debnath R.,U.S. National Institute of Standards and Technology | Debnath R.,University of Maryland University College | Debnath R.,N5 Sensors, Inc. | And 6 more authors.
ACS Applied Materials and Interfaces | Year: 2013

This paper details the use of scanning photocurrent microscopy to examine localized current collection efficiency of thin-film photovoltaic devices with in-plane patterning at a submicrometer length scale. The devices are based upon two interdigitated comb electrodes at the micrometer length scale prepatterned on a substrate, with CdSe electrodeposited on one electrode and CdTe deposited over the entire surface of the resulting structure by pulsed laser deposition. Photocurrent maps provide information on what limits the performance of the windowless CdSe/CdTe thin-film photovoltaic devices, revealing "dead zones" particularly above the electrodes contacting the CdTe which is interpreted as recombination over the back contact. Additionally, the impact of ammonium sulfide passivation is examined, which enables device efficiency to reach 4.3% under simulated air mass 1.5 illumination. © 2013 American Chemical Society.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: SMALL BUSINESS PHASE I | Award Amount: 166.24K | Year: 2014

The broader impact/commercial potential of this project is in various applications requiring real-time detection of toxic, explosive, and other harmful chemicals in a variety of environments. This innovative chemical sensor technology promises single-chip multianalyte sensors with significant cost savings resulting from enhanced performance, reliability, and lifetime. Developing ultra-small chemical detectors capable of detecting various toxic and hazardous chemicals in air reliably is essential in safeguarding individuals and communities. Such ultra-small multianalyte detectors could save lives of industrial workers and fire-fighters by making them more aware of their dangerous surrounding. Also next-generation of cloud-based, crowd-sourced, large-area sensor networks for urban monitoring can protect our communities from terrorist attacks. The diversity of potential industrial, environmental, and safety monitoring applications ensures sustainable growth paths in various domestic and international gas detection markets. The scientific component of this project will enhance the understanding of the complex processes occurring at the surfaces of these novel multicomponent nanoclusters, which could have profound impact in various other fields including photovoltaic, energy storage, and catalytic pollution-remediation.

This Small Business Innovation Research (SBIR) Phase I project will demonstrate single-chip ammonia (NH3) and carbon monoxide (CO) sensors using patent-pending innovation in multicomponent photocatalytic nanocluster-based hybrid sensor technology. Both NH3 and CO are toxic industrial chemicals with very serious health hazards, and often present in various industrial, farming, agricultural, and transportation related activities. High-performance mobile devices used in various operational situations represent a powerful infrastructure which could be leveraged for chemical monitoring. Due to their size and power requirement, traditional sensors are not suitable for mobile-platform deployment. Single-chip, ultra low-power selective detection of NH3 and CO will be a significant accomplishment towards the goal of development of mobile devices based multithreat monitors that can be used by industrial workers, civilians, first-responders, and soldiers for both personal safety and infrastructural security.


Grant
Agency: National Aeronautics and Space Administration | Branch: | Program: STTR | Phase: Phase I | Award Amount: 120.39K | Year: 2015

Extravehicular Mobility Units (EVU) are the necessary to perform elaborate, dynamic tasks in the biologically harsh conditions of space from International Space Station (ISS) external repairs to human exploration of planetary bodies. The EVUs have stringent requirements on physical and chemical nature of the equipment/components/processes, to ensure safety and health of the individual require proper functioning of its life-support systems. Monitoring the Portable Life Support System (PLSS) of the EVU in real time is to ensure the safety of the astronaut and success of the mission.N5 Sensors will demonstrate an ultra-small form factor, highly reliable, rugged, low-power sensor architecture that is ideally suited for monitoring trace chemicals in spacecraft environment. This will be accomplished by our patent-pending innovation in photo-enabled sensing utilizing a hybrid chemiresistor architecture, which combines the selective adsorption properties of multicomponent (metal-oxide and metal) photocatalytic nanoclusters together with the sensitive transduction capability of sub-micron semiconductor gallium nitride (GaN) photoconductors. For the phase I project we will demonstrate oxygen, carbon dioxide, and ammonia sensor elements on a single chip. Innovative GaN photoconductor design will enable high-sensitivity, low power consumption, and self-calibration for the sensor current drift. The multicomponent nanocluster layer design enables room-temperature sensing with high selectivity, resulting in significant power saving and enhanced reliability. The fabrication of the sensors will be done using traditional photolithography and plasma etching. The nanocluster functionalization layer will be deposited using sputtering methods. The sensor testing will be carried out to determine sensing range, sensitivity, selective, and response/recovery times.


Grant
Agency: Environmental Protection Agency | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.19K | Year: 2014

Measuring individual exposure in real-time can revolutionize air quality monitoring in communities everywhere. Such information would allow citizens to take preventive measures to reduce their exposures to air toxics, which would impact their health and quality of life tremendously. Mobile devices such as smart-phones and tablets represent a powerful infrastructure that could be leveraged to develop personal air monitors. However, traditional sensor technologies (e.g., electrochemical and photo-ionization detectors) commonly used for industrial safety monitoring, are big, power-hungry, and have limited sensitivity and lifetime.N5 Sensors, Inc. will demonstrate highly-selective sensor architecture, utilizing nanoengineered gallium nitride (GaN) photoconductors functionalized with multicomponent nanoclusters of metal-oxides and metals. Innovation in photoenabled sensing enables these sensors to operate at room-temperature, resulting in a significant reduction in operating power. The strength of N5 Sensors’ technology is that it uses all standard microfabrication techniques, which promises economical, multianalyte, single-chip sensor solution. Due to the use of inert wide-bandgap semiconductor, metal-oxides and noble metals, the environmental impact of the sensors during their life cycles is minimal. By combining the “designer'” adsorption properties of multicomponent nanoclusters together with sensitive transduction capability of nanostructured GaN backbones, N5 Sensors will demonstrate sensors for benzene, toluene, ethylbenzene, xylene—commonly referred to as BTEX. Feasibility of this approach will be demonstrated by designing sensors and testing their sensitivity to such chemicals with detection range from 500 ppt to 1 percent, with minimal cross-sensitivity to various components of environmental matrix, namely particulate matter, reactive gases and non-target gases. Sub-micron structures will be formed on GaN epitaxial thin-films on sapphire using lithography and plasma etching. Such structures will be functionalized with multicomponent nanoclusters of metal­oxides and metals using reactive-sputter deposition. The Phase 1 effort will demonstrate BTEX sensors, consuming<1 mW of power and through detailed testing establish their operation reliability, measurement accuracy and calibration needs. Innovative sensor designs and measurement protocols will be evaluated for increased reliability and accuracy. Completion of Phase 2 will result in an array of nanoengineered sensors on a single chip, each tailored to sense specific air toxics: BTEX, Ox, SOx, CO2, and O3.Future prospects of such low-power, small form-factor sensors include embedded-chip or plug-in module with multi­analyte sensor arrays for the smart phones for citizens and soldiers for acquiring real-time environmental information. An opportunity for commercialization is in low-cost, mobile devices-based trace air toxic monitors for rapid alert in indoor and outdoor environments.

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