Archives—February 2011


Hybrid Nanomaterials and New Designs for Energy Conversion and Storage Applications

Friday, February 25, 2011 3:30 pm – 4:30 pm
Room G05, Rekhi Hall

Leela Mohana Reddy Arava
Postdoctoral Research Fellow, Department of Mechanical Engineering and Materials Science
Rice University

Abstract

In response to the needs of modern society and emerging ecological concerns, it is nowessential to provide efficient, low-cost, and environmentally friendly electrochemicalenergy conversion and storage devices. These electrochemical devices are expected tohave pronounced technological impact on the society – especially for powering anincreasingly diverse range of portable electronic and vehicular applications.Rechargeable Lithium-ion batteries and Fuel cells are amongst the most promisingcandidates in terms of their wide spread applicability, owing to their high energy andpower densities. The performance of these devices depends intimately on the propertiesof materials used to build them. This talk will focus on the new designs and performanceof the next generation of energy and power delivery devices by the use of tailorednanostructured materials and by nanoscale engineering. Some of the current challengespertaining to the energy storage technology and the effective utilization of new electrodematerials such as graphene and carbon nanotubes will be discussed. Furthermore, thetalk will also evaluate approaches for optimization of the Li-ion battery performance withnovel designs, leading to prototype nanoscale 3D battery architectures offeringimprovements in energy and power density with respect to the geometrical foot print ofdevices.


Bottom-Up Novel Hybrid Nanostructures for Solar Energy Harvesting

Monday, February 21, 2011 3:30 pm – 4:30 pm
Room G05, Rekhi Hall

Shenqiang Ren
Department of Materials Science and Engineering
Massachusetts Institute of Technology

Abstract

Nanostructured materials – including atomic clusters, quantum dots, nanowires or nanotubes –have dimensions in the range of 1 to 100 nm, the length scale that offers unique and sizetunable properties. They provide solutions to some of the current challenges in science andengineering, and would potentially lead to discoveries of new phenomena and novelapplications that are impossible to realize with their bulk counterparts. A challenging task in thisarea is to manipulate nanostructured materials and assemble them into desired structural forms– one, two or three-dimensional structures – so that their unique physical properties can beharvested. Among the bottom-up strategies, self-assembly of nanostructured materials andorganic conjugated polymers provides a promising route to the build-up of complex systems withimmense flexibility in terms of nanoscale building blocks and resulting novel physical properties.Current research is focused mainly on nanostructured hybrid solar cells that combine thebenefits of inorganic materials (thermal and chemical stability, high charge transport, solutionprocessing) and organic materials (strongly absorbing, mechanical flexibility, low-cost).

In this talk, I will discuss my research on rational design of self-assembling nanostructuredphotovoltaic systems on scales from molecular through macroscopic, to the development of“synthetic” strategies. Specifically, I will focus on three main topics: (a) bridging quantum dotsand conjugated polymer nanowires for efficient (>4%) hybrid solar cells; the data provides aunique new insight into the operation of hybrid bulk heterojunction devices and providesdirections to further improvements; (b) drying mediated self-assembly of inorganic nanowirehybrid solar cell; prospects for further enhancement will be discussed; (c) self-assembly of allconjugated block copolymers combined with metal oxide. The key aim of this study is to developa better understanding of the parameters that control such interfacial charge transfer processes.Another critical aim of this work is to develop quantitative structure-function relationships thatcan be used to guide the design and development of efficient nanostructured organic-inorganichybrid solar cells


Infrared Photodetectors for Conformal Substrates

Friday, February 18, 2011 3:30 pm – 4:30 pm
Room G05, Rekhi Hall

Jeramy D. Zimmerman
Department of Electrical Engineering and Computer Science
University of Michigan

Abstract

Simple lens systems generally suffer from Petzval field curvature aberrations and focus on a curvedsurface; therefore, complicated lens systems are needed to create the flat focal surface required byconventional semiconductor fabrication techniques. To simplify the optics systems, we are designingimagers with curved imaging surfaces, which reduces other optical aberrations as well as system weight.The adoption of curved focal planes requires the development of new processing techniques and newmaterials for conformal surfaces. This talk will focus on two infrared-sensitive organic semiconductorphotodetector systems developed at the University of Michigan for use on conformal substrates.

Organic photodetectors are efficient (20-80% quantum efficient) in the visible region of the spectrum, butvery few organic materials exist with useful photoresponse beyond λ ≈ 1000 nm. Carbon nanotubes(CNTs) have band gaps that absorb in the λ ≈ 1000 to 2000 nm region, motivating our development of aprocedure to use single-wall CNTs wrapped with conjugated polymers as a photoactive component inphotodetectors. We have demonstrated that excitons on CNTs can be dissociated at CNTC60 interfaces, and have created the first photovoltaic detectors fabricated from bulk CNT films. Detectorspecific detectivities above D*=1010 cm-Hz½/W were demonstrated from λ ≈ 400 to 1400 nm, with peakexternal quantum efficiencies of approximately EQE=2% at λ ≈ 1155 and 1300 nm.[1]

More recently, we demonstrated a new porphyrin tape-based organic semiconductor materials systemwith the highest quantum efficiencies demonstrated to date at peak wavelengths greater than λ ≈ 1000nm. The porphyrin tapes consist of two porphyrin units triply linked to form a rigid tape with variousfunctional groups at the terminus of the tape, notably a pyrene group bonded in either one or twolocations. We have demonstrated quantum efficiencies of up to EQE=4% (D*=9×1011 cm-Hz½/W) at λ ≈1080 nm for a singlybonded pyrene end group and EQE=13% (D*=8×1010 cm-Hz½/W) at λ ≈ 1400 nm fora doubly-bonded pyrene end group.[2]

The presentation will discuss fabrication and analysis of devices and materials and conclude with afuture outlook and other applications for these materials.

  1. M. S. Arnold, J. D. Zimmerman, C. K. Renshaw, X. Xu, R. R. Lunt, C. M. Austin and S. R. Forrest, Nano Lett.9 (9), 3354-3358 (2009).
  2. J. D. Zimmerman, V. V. Diev, K. Hanson, R. R. Lunt, E. K. Yu, M. E. Thompson and S. R. Forrest, Adv. Mater.22 (25), 2780-2783 (2010).

Microstructural Engineering for Solar Photovoltaic Devices

Monday, February 14, 2011 2:00 pm – 3:00 pm
Room G06, Rekhi Hall

Dr. Joshua M. Pearce
Department of Mechanical and Materials Engineering
Queen’s University, Canada

Abstract

Although, solar photovoltaic (PV) electrical production is technologically feasible, growing rapidlyand a environmentally-benign solution to society’s energy requirements, its costs must declinefor deployment at the necessary TW scale. This presentation will review two fundamentalapproaches to reach this goal using microstructural engineering of PV devices. The firstapproach uses relatively inefficient, but proven hydrogenated amorphous silicon (a-Si:H)-basedsolar cells. Thin film cells from a-Si:H are currently the least expensive PV and possess anexcellent ecological balance sheet.  Utilizing AFM, TEM, and real time spectroscopicellipsometry to track the phase of Si:H, the evolutionary nature (protocrystallinity) and substratedependence of its growth were established. This enabled the contributions of the carrierrecombination from the p/i interface regions and the bulk to the dark and light current-voltage (IV) characteristics of a-Si:H p-i-n and n-i-p solar cells to be separated and identified. By applyingthis knowledge of both microstructure and recombination a-Si:H solar cell performance can beimproved to improve efficiency and the cost of electricity provided. The second approach usespotentially ultra-high efficiency indium gallium nitride (InGaN) PV. InGaN shows such incrediblepromise as a PV material due to the ability to modify its band gap by adjusting the ratio ofindium and gallium in the film. A multi-layered cell of InGaN can be made with band gapsranging from 0.7eV (InN) to 3.4eV (GaN), which nearly covers the entire range of the solarspectrum. InGaN has been grown by plasma enhanced evaporation in nanocolumn crystals,which provide optical enhancement and reduce strain during growth and defects. Thus, a welldesigned InGaN solar cell could absorb and convert a much higher fraction of solar energy intoelectricity. The presentation reports on the first stage of research on the characterization andmicrostructural engineering of InGaN nanocolumns. Conclusions are drawn from theexperimental evidence and a path is outlined for future research using both of these approachesto assist society move towards a sustainable energy system using solar photovoltaic devices.


Effect of Electric Field on Hydrogen Storage over Carbonaceous Sorbents at Ambient Temperature

Friday, February 4, 2011 3:00 pm – 4:00 pm
Room 610, M&M Building

Zheng Zhang
Graduate Student
Materials Science and Engineering
Michigan Technological University

Abstract

Storage and transportation of hydrogen in large quantities at small volume iscurrently a big obstacle on the way of hydrogen application. The primaryissue for hydrogen adsorption is weak interactions between hydrogen andthe surface of solid materials, which results in negligible sorption capacity atroom temperature. To solve this problem, electric field was introduced to theprocess of hydrogen adsorption at ambient temperature. For a certaincommercial activated carbon (NAC) with surface area of 1836m2/g, 12.5%and 18.5% enhancements were obtained at 80 bar under 1500V and 2000V.The enhancements were considered to be brought by strong orbitalinteractions between electrically charged sorbent and hydrogen. Moreover,dielectric phase, TiO2, was added to activated carbon to hold electricalcharges around carbon particles without distributing onto the body surface.Employing 2000V electric potential to the samples showed up to 100%enhancement.


In the News

View the news article

Associate Professor Jarek Drelich (MSE), Associate Professor Tim Scarlett (SS) and graduate student Patrick Bowen (MSE) were featured by the Polish Agency Press in a news publication, “Science and Scholarship in Poland.” The story was about their work on a new way of dating ceramic artifacts that could one day shave thousands of dollars off the cost of doing archaeological research.