Liangbing Hu, University of Maryland
Guihua Yu, University of Texas at Austin
Leif Nyholm, Uppsala University
Horacio D. Espinosa, Northwestern University
Rusen Yang, University of Minnesota
R2: Energy Harvesting II
Tuesday PM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14
2:30 AM - *R2.01
Stretchable Transparent Nanogenerators Based on 1D/2D Piezoelectric and Triboelectric Nanostructures
Sang-Woo Kim 1
1Sungkyunkwan University (SKKU) Suwon Republic of KoreaShow Abstract
Energy harvesting systems based on piezoelectric and triboelectric nanomaterials are in great demand, as they can provide routes for the development of self-powered devices which are highly flexible, stretchable, mechanically durable, and can be used in a wide range of applications. Our recent research interest mainly focuses on the fabrication of nanogenerators (NGs) based on 1D/2D nanomaterials such as zinc oxide nanowire/nanosheets and graphene. Furthermore, the efforts towards developing triboelectric NGs using those materials are in progress.
3:00 AM - R2.02
Sponge-Like Piezoelectric Polymer Film for Scalable and Integratable Nanogenerators and Self-Powered Electronic Systems
Yanchao Mao 1 2 Ping Zhao 3 Geoffrey McConohy 4 Hao Yang 2 Yexiang Tong 2 Xudong Wang 1
1University of Wisconsin-Madison Madison USA2Sun Yat-sen University Guangzhou China3University of Minnesota-Duluth Duluth USA4University of Wisconsin-Madison Madison USAShow Abstract
Nanogenerator (NG) is a promising new concept for harvesting mechanical energy from ambient sources and developing self-powered electronic systems. Here, we report a development of flexible NGs from sponge-like nanoporous piezoelectric polyvinylidene fluoride (PVDF) thin films that were fabricated by a casting-etching method in wafer-scale. The nanoporous PVDF NGs can be directly attached to the surface of an electronic device (e.g. a cell phone), and effectively convert mechanical energy from ambient surface oscillations to electricity using the device&’s own weight to enhance the amplitude. An output voltage of 11.0 V and current of 9.8 mu;A was demonstrated using a 2 cm2 sized PVDF NG. Multiple PVDF NGs were integrated in series and operate synchronically to raise the output power for the operation of electronic devices. In conclusion, a novel integratable NG design based on sponge-like nanoporous piezoelectric PVDF thin films was successfully demonstrated. This type of NG can generate significantly electrical energy by harvesting mechanical energy from surface oscillations. This technique is considerably scalable and integratable, providing a promising solution for developing practical self-powered electronic devices.
3:15 AM - *R2.03
Piezo-Nano-Devices on Flexible Substrates: Challenges and Opportunities
Christian Falconi 1
1University of Tor Vergata Rome ItalyShow Abstract
Piezoelectric nanodevices can offer crucial advantages for energy harvesting, mechanical sensing/actuation, biomedical devices, optoelectronics, and more. In fact, in comparison with conventional piezoelectric materials, nanostructures can be highly deformed by tiny forces, exhibit outstanding mechanical properties, and can have substantially higher piezoelectric coefficients.
However, many issues must be addressed, both at the theoretical and at the technological level, in order to design and fabricate optimal piezo-nano-devices on flexible substrates.
In the first part of this presentation, I show how shape, electrical boundary conditions, position of contacts, type of mechanical input, and charge transport properties can all crucially affect the piezopotential, the mechanical-to-electrical conversion efficiency, and the on-off ratios of piezoelectric nanodevices. As an example, for a given mechanical input, laterally deflected cylindrical nanowires with total bottom contacts result in lower piezopotential and mechanical-to-electrical conversion efficiency than vertically compressed nanowires; as another example, the mechanical-to-electrical static conversion efficiency of vertically compressed nanowires is almost independent of strain at small strains and increases at higher strains, thus confirming that the ability of nanostructures to withstand extreme deformations without fracture may be a key for increasing the efficiency of nanogenerators. As another example, conical nanowires may prove advantageous for nanogenerators, piezotronics, and piezophototronics.
In the second part I will highlight the challenges to overcome for taking full advantage of piezoelectric nanodevices on flexible substrates, with special reference to both modeling (e.g. parasitic impedances, transient phenomena, and scaling of the electro-mechanical properties, including the Young modulus and piezoelectric coefficients) and fabrication (e.g. low-temperature processing and complexity of in-liquids real-time monitoring).
Finally, I will illustrate some piezoelectric nanodevices on flexible substrates.
3:45 AM - R2.04
Semiconductor Nanowire Laser: Fabrication, Tuning and Applications
Xiaowei Liu 1 Yuanpeng Wu 1 Pengfei Xu 1 Weisong Yang 1 Qing Yang 1 Shan Jiang 1
1Zhejiang University Hangzhou ChinaShow Abstract
High flexibility and easy tunability have been important advantages for one-dimensional nanowires (NWs) in wide applications of nanoscale integrated circuits and high sensitive sensor etc. We present our work on NW lasers from fabrication, tuning to applications. First of all, we fabricated various NW lasers: semiconductor NW-microfiber hybrid lasers , semiconductor NW-microdisk cavity hybrid lasers , and semiconductor NW-microfiber ultraviolet-green-red three color lasers . The hybrid structure laser combine the high gain of semiconductor and high quality factor of micro cavity, offering low threshold and easily manipulation properties. Secondly, we focus on achieving tuning/modulating/enhancing the afore-mentioned NW lasers. We demonstrate an efficient way to achieve wide wavelength tunable lasers on single non-doped CdSe NWs . The laser wavelengths are tuned from 746 nm to 706 nm by changing the length of a single NW (402-nm-diameter), spanning a range as large as 40 nm. The length dependent wavelength tuning is attributed to absorption-emission-absorption (AEA) of the propagating light in the NWs. We also utilize the bending effects to modulate the polarization of NW lasers . Furthermore, we work on the modulation of polarization and modes of NW lasers by electrical tuning. Finally, we use the tunable laser to achieve super-resolution microscope and investigate the behind new physical mechanism. Our work pioneered in the NW lasers may provide a way of fabricating ultra-compact nanophotonic devices and may find its applications in single molecule detection, integrated optical circuits, and optical communications etc.
Q. Yang, X. Jiang, X. Guo, Y. Chen, L. Tong, “Hybrid structure laser based on semiconductor nanowires and a silica microfiber knot cavity”, Appl. Phys. Lett. 94 (2009) 101108.
G. Wang, X. Jiang, M. Zhao, Y. Ma, H. Fan, Q. Yang, L. Tong, M. Xiao, “Microlaser based on a hybrid structure of a semiconductor nanowire and a silica microdisk cavity”, Opt. Express 20 (2012) 29472-29478.
Y. Ding, Q.Yang, X.Guo, S. Wang, F. Gu, J. Fu, Q. Wan, J. Cheng, and L. Tong, “Nanowires/microfiber hybrid structure multicolor laser”, Opt. Express 17 (2009) 21813.
J. Li , C. Meng , Y. Liu , X. Wu , Y. Lu , Y. Ye , L. Dai , L. Tong, X. Liu, Q. Yang “Wavelength Tunable CdSe Nanowire Lasers Based on the Absorption-Emission-Absorption Process” Adv. Mater. DOI: 10.1002/adma.201203692 (2012)
W. Yang, Y. Ma, Y. Wang, C. Meng, X.Wu, Y. Ye, L. Dai, L. Tong, X. Liu, Q. Yang, “Bending effects on lasing action of semiconductor nanowires”, Opt. Express 21 (2013) 2025-2031
4:30 AM - *R2.05
Stretchable Inorganic Photovoltaics and Mechanical Energy Harvesters
John Rogers 1
1University of Illinois Urbana USAShow Abstract
Large interconnected collections of small, ultrathin inorganic solar cells and piezoelectric elements provide routes to high performance energy production systems in flexible, and even stretchable, designs. This talk describes materials, techniques for assembly and concepts in mechanics for this type of technology. Device examples built using silicon, compound semiconductors and piezoelectric materials derived from wafer-scale sources of material illustrate an ability to achieve, simultaneously, high efficiency operation in energy conversion and extreme levels of flexibility and stretchability.
5:00 AM - R2.06
M13 Phage-Based Piezoelectric Energy Generation
Kwang Heo 1 2 Seung-Wuk Lee 1 2
1Univ. California, Berkeley Berkeley USA2Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
Piezoelectric materials can convert mechanical energy into electrical energy, and piezoelectric devices made of various inorganic materials and organic polymers have been demonstrated. However, synthesizing such materials often requires toxic materials, harsh conditions and/or complex procedures. Recently, it was shown that hierarchically organized natural materials, such as bones, collagen fibrils and peptide nanotubes, can display piezoelectric properties. In this paper, we will demonstrate our innovative approach to produce biomaterial-based piezoelectric energy generation. Recently, we establish that the piezoelectric and liquid crystalline properties of M13 bacteriophage (phage) can be used to generate electrical energy. Using piezoresponse force microscopy, we characterized the structure-dependent piezoelectric properties of phage at the molecular level. We then showed that self-assembled thin films of phage could exhibit piezoelectric strengths of up to 7.8 pm/V. It is also possible to modulate the dipole strength of phage, and hence tune their piezoelectric response by genetically engineering the phage&’s major coat proteins. Finally, we developed a phage-based piezoelectric generator that produces up to 100 nA of current and 900 mV of potential, and use it to operate a liquid crystal display. Because biotechnology techniques enable large-scale production of genetically modified phages, phage-based piezoelectric materials potentially offer a simple and environment-friendly approach to piezoelectricity generation.
5:15 AM - R2.07
Flexible Giant Magnetostrictive GaFe Films on Cylindrical, Nanoporous and Planar Substrates for Energy Harvesting Devices
Matt Hein 1 Eliot Estrine 1 Jung Jin Park 2 Sai Madhukar Reddy 1 Alison Flatau 3 Bethanie Stadler 1 2
1University of Minnesota Twin Cities Minneapolis USA2University of Minnesota Twin Cities Minneapolis USA3University of Maryland College Park USAShow Abstract
A number of unique and interesting energy harvesting devices utilizing materials with extremely large magnetostrictive constants (lambda;) such as TbFe (Terfenol) have been demonstrated in literature. When compared to piezoelectric devices though the number paper dealing with these materials is only a small fraction. The reason for this may be due to a lack of materials with suitable properties. Magnetostrictive materials can change the direction of their magnetization with the application of a stress which is referred to as the Villari effect. This action is analogous to rotating a magnet. By using Maxwells equations it can be seen that this rotation of magnetic moment can be used to harvest energy. GaFe (Galfenol) overcomes many limitations of typical magnetostrictive materials in that it has a large lambda;, is rare-earth-free, and ductile. In addition to that, our group has pioneered electrodeposition of the material which allows us to deposit thin films directly onto various substrates and structures. To date we have demonstrated deposition on planar substrates of glass, metals, Si, GaAs and into high aspect ratio nanoporous films using a rotating disc electrode (RDE). Recently, a technique for depositing directly onto a cylindrical substrate using a rotating cylinder electrode (RCE) has been developed with allows for direct integration of energy harvesting materials onto a shaft or tubular structure. EDS results of our cylindrical films show that we can control the composition of our alloy (10%-40% at.% Ga ) by adjusting the deposition potential 1.4 to 1.8V, the rotation rate 100 to 1000rpm, and by adjusting the ratio of Ga:Fe in solution. As deposited films have been measured using a capacitance bridge to have a lambda; between 50 and 120ppm, while our nanowires have been measured via atomic force microscopy to have a lambda; of 40ppm. With this unique ability to electrodeposit magnetostrictive material onto a wide range of substrates, new opportunity exist for developing integrated energy harvesting micro and nano-structured devices.
5:30 AM - R2.08
Output Power Enhancement of Flexible ZnO Nanogenerator By a CuO-ZnO P-N Junction Formation
Sung-Ho Shin 1 Min-Hyung Lee 3 Joo-Yun Jung 2 Junghyo Nah 1
1Chungnam National University Daejeon Republic of Korea2Korea Institute of Machinery and Materials Daejeon Republic of Korea3Kyung Hee University Yongin Republic of KoreaShow Abstract
Among several piezoelectric materials, ZnO has been considered as one of the most promising candidates for the realization of nanogenerator due to their nontoxicity and cost effectiveness by comparison to other materials. However, the performance of ZnO piezoelectric nanogenerator (NG) has been limited largely due to excessive electrons existing in ZnO, which screens piezoelectric potential generated by mechanical deformation of the crystal structure. Nominally undoped intrinsic ZnO exhibits n-type behavior due to defect levels induced by interstitials and oxygen vacancies, leading to Fermi level close to the conduction band edge. Thus, large excessive electrons can be easily found even at room temperature. To alleviate this issue, several attempts have been made up to date. In our report, as an alternate solution, we investigated CuO, p-type metal oxide semiconductor with a bandgap of 1.35 eV, to form a metal oxide only CuO-ZnO p-n junction, where CuO naturally demonstrates p-type behavior due to cation-deficiency, acting as a hole conductor. In this approach, we demonstrated greatly enhanced piezoelectric energy conversion performance of ZnO flexible piezoelectric NG, exhibiting 7-fold higher output voltages and one order of magnitude higher output currents by comparison to the devices without CuO layer.
5:45 AM - R2.09
Multilayer Stacked Flexible BatiO3 Nano-Composite Based Piezoelectric Nanogenerator for Enhanced Output Power Generation
Sung-Ho Shin 1 Min-Hyung Lee 2 Joo-Yun Jung 3 Junghyo Nah 1
1Chungnam National University Daejeon Republic of Korea2Korea Institute of Machinery and Materials Daejeon Republic of Korea3Kyung Hee University Yongin Republic of KoreaShow Abstract
ZnO nanogenerators(NGs) have gained great attentions as a material system to fabricate NGs due to nontoxicity and cost effectiveness of ZnO by comparison to other materials. However, relatively low piezoelectric dipole moment coupled with potential screening effect by excess electrons in ZnO (wurtzite crystal structure) necessitates additional process steps to realize high performance NGs. In this respect, several attempts have been made to fabricate NGs with perovskite ceramic materials such as PZT and BaTiO3. Inherent piezoelectric properties of these materials are superior to ZnO, providing a more advantageous platform to realize high performance NGs. Several reports have been made based on these material systems. In our work, we investigated NGs based on BaTiO3 nanoparticle composite, which is more environmental friendly material compared with PZT. The NGs were fabricated by forming a multilayer structure with BaTiO3-PVDF composite. Compared with previously demonstrated BaTiO3 composite based NG, our approach provides relatively simple fabrication process, allowing multiple layer stacking, which results in enhanced output power per unit area. After polling process at high electric field, the NGs consistently exhibits over 8 V peak-to-peak output voltage with a current density fo ~1.3 uA/cm^2 at normal bending conditions on a bending stage. Upon the applied pressure with a finger tip normal to the device surface, the devices show the output voltage and current density of ~50 V and ~10 uA/cm^2, respectively. Our simple approach allows to realize large scale high performance NGs with high flexibility and reliability.
R1: Energy Harvesting I
Horacio D. Espinosa
Tuesday AM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14
9:00 AM - R1.01
High Power Triboelectric Nanogenerator and Its Hybridization with Li-Ion Battery as Sustainable Flexible-Power-Unit
Sihong Wang 1 Zhong Lin Wang 1
1Georgia Institute of Technology Atlanta USAShow Abstract
The emergence of electronic devices/systems with unprecedented functionalities mandatorily requires portable, flexible and sustainable power sources. Energy harvesting technology that can efficiently generate electricity from ambient environmental energy is the prerequisite for the realization of such new power sources. But due to their intrinsic limitation of unstable and uncontrollable electrical output, it is desirable to hybridize them with energy storage devices into single units, which could be capable of sustainably providing a stable output through utilizing the energy in the environment.
For the electricity generation, mechanical energy is one of the best choices as energy source owing to its universally-existence in our living environment and human bodies. A new type of devices—triboelectric nanogenerators (TENGs)—based on contact electrification has been recently invented as an effective and adaptive technology to generate electricity from motions. However, because the device structure and material properties have not been optimized, the output is still insufficient for sustainably driving electronic devices/systems. Here, we demonstrated a rationally designed arch-shaped TENG as a flexible mechanical energy harvester with extremely-high power output. Through purposely introducing thermal stress on the surface, a flexible substrate was made into a naturally-bent shape, so that a steady gap formed between two triboelectric layers at strain-free conditions. This design facilitates the separation of the opposite tribo-charges, thus maximizes the electrical driving force. This unique structure, together with the surface modification of tribo-layers, helps to largely enhance the output voltage, and power density to 230 V and 128 kW/m3, respectively, with an efficiency as high as 10~39%. For the first time, it realized the instantaneous driving of tens of regular electronic devices (LEDs), and also the fully charging of a Li-ion battery. 
For the development of sustainable power sources, we further hybridized the arch-shaped TENG with a flexible Li-ion-battery into as a single device—a flexible self-charging power unit (SCPU), which allows a battery to be charged directly by ambient mechanical motion. This physical hybridization enables a new operation mode: the “sustainable mode”, in which the environmental mechanical energy is scavenged to charge the battery while the battery keeps driving an external load. In this mode, the demonstrated SCPU can provide a continuous and sustainable DC current of 2 µA at a stable voltage of 1.55 V for as long as there is mechanical motion/agitation. It can be used to continuously drive a UV sensor for extended period of time. Thus, the SCPU can serve as an independent and sustainable power unit, which will meet the general requirement of almost any electronic device. 
 Wang, S. H.; Wang, Z. L. et al. Nano Lett. 2013, 13, 2226-2233.
 Wang, S. H.; Wang, Z. L. et al. ACS Nano Under review.
R3: Poster Session I: Energy Conversion and Storage
Tuesday PM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 8-9
9:00 AM - R3.02
Preparation and Orange-Red Emission of Hierarchical PbTiO3/ZnO Nanostructures
Shan Jiang 1 Hui Zhao Ren 1 Gang Xu 1 Rong Gao Han 1
1Zhejiang University Hangzhou ChinaShow Abstract
One-dimensional (1D) piezoelectric and ferroelectric nanomaterials, such as PZT, ZnO nanowires, have attracted great attention due to their fascinating properties and potential applications ranging from high-density ferroelectric random access memory (FeRAM) and high performance nanogenerators [1,2]. In particular, hierarchical complex structure on the basis of ZnO nanowires has been designed and prepared to realize novel nanodevices in the recent work [3,4]. In this study, we apply a two-step hydrothermal process to fabricate hierarchical PbTiO3/ZnO (PTOZ) nanostructures. Unique brush-like three-dimensional (3D) nanostructures of the samples was achieved, where secondary ZnO nanorods grew on the surface of the single-crystal nanowires of ferroelectric tetragonal PbTiO3. The number density and the length/diameter ratio of the secondary ZnO can be easily tailored by changing the reaction time. Photoluminescence (PL) properties of the as-prepared and post-annealing treated samples were studied at room temperature. Compared with pure ZnO nanorods, such hybrid nanostructures show a stronger broad visible emission centered at 632nm. Moreover, after annealing treatment in air, the visible emission intensity of the samples was significantly enhancemed, accompanied with a red shift in the peak center.
The orange-red emission is commonly attributed to the presence of excess oxygen in the ZnO . For the PTOZ nanostructures, we proposed that the polarization surface of PbTiO3 nanowires could make additional contribution to the orange-red emission in the hierarchical PTOZ nanostructures by changing absorption of oxygen on their surfaces. These hybrid 3D nanostructures could be ideal candidates for optoelectronic and piezoelectronics nanodevice applications.
1. Xiao, Z.; Ren, Z. H.; Liu, Z. Y.; Wei, X.; Xu, G.; Liu, Y.; Li, X.; Shen, G. and Han, G. R. J.Mater.Chem.,2011, 21, 3562.
2. Wang, Z. L.; Zhu, G.; Yang, Y.; Wang, S. H. and Pan, C. F. Materials Today 2012, 15, 532-543.
3. Cheng, C. W.; Liu, B.; Yang, H. Y.; Zhou, W. W.; Sun, L.; Chen, R.; Yu, S. F.; Zhang, J. X.; Gong, H.; Sun, H. D. and Fan, J. H. ACS Nano. 2009, 10, 3069.
4. Qin, Y.; Wang, X. D. and Wang, Z. L. Nature. 2008, 451, 809.
5. Djuriscaron;icacute;, A. B.; Leung, Y. H.; Tam, K. H.; Hsu, Y. F.; Ding, L.; Ge, W. K.; Zhong, Y. C.; Wong, K. S.; Chan, W. K.; Tam, H. L.; Cheah, K. W.; Kwok, W. M. and Phillips, D. L. Nanotechnology 2007, 18, 095702.
9:00 AM - R3.04
Elucidating the Decomposition of PCBM During Evaporation: A Model Approach for the Evaluation of Small Molecule Semiconductor Films Processed by Physical Vapor Deposition.
Torben Adermann 1 Julia Maibach 2 Tobias Glaser 4 Ralph Eckstein 3 Eric Mankel 2 Norman Mechau 3 5 Annemarie Pucci 4 Manuel Hamburger 1 5 Thomas Mayer 2 Wolfram Jaegermann 2
1Heidelberg University Heidelberg Germany2TU Darmstadt Darmstadt Germany3Karlsruhe Institute of Technology Karlsruhe Germany4Heidelberg University Heidelberg Germany5InnovationLab GmbH Heidelberg GermanyShow Abstract
In the field of organic electronics a major research focus lies on the solution processabilty of organic semiconductor materials. Although some materials are designed for solution processing, i.e. Phenyl-C61-butyric acid methyl ester (PCBM), it is repeatedly reported in literature that deposition of PCBM via thermal evaporation in vacuum is performed to achieve either ultrathin or very clean films suitable for e.g. photoelectron spectroscopy characterization.
We have investigated the effects of thermal evaporation on PCBM in a very interdisciplinary approach, applying physical characterization techniques such as photoelectron (PES) and infrared (IR) spectroscopy in combination with device engineering and chemical analysis using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), ultra performance liquid chromatography-coupled mass spectrometry (UPLC-MS), and nuclear magnetic resonance spectroscopy (NMR). The methods were applied to thin films prepared by both solution based deposition techniques and thermal evaporation. It is found, that evaporation proves to be an inefficient deposition route for thin layers of chemically pure PCBM. Changes in the IR spectrum of the PCBM films already indicate a change in the molecular structure of PCBM. The UPLC chromatogram of the redissolved organic film proves the formation of several molecular species, including bare C60. Especially the crucible residue after evaporation contains a large fraction of disintegration products. 1H-NMR of the crucible residues shows the formation various new functional groups in the side-chain of PCBM. The effect of degradation on the electronic properties was however found to be limited, as an almost unchanged ionization potential of 6.1 eV was determined with UPS for both the solution processed as well as the evaporated films. By simulating the evaporation conditions by TGA, PCBM sample purity was reduced to roughly 90 %. Bulk-heterojunction solar cells were fabricated with pure and thermally treated PCBM samples to investigate their impact on device performance.
9:00 AM - R3.05
Wireless Power Harvesting via Flexible Magnetostrictive Nanoribbons
Huai-An Chin 1 Tian Liang 3 Shiyou Xu 4 Gerald Poirier 4 Nan Yao 4 Sigurd Wagner 1 Michael McAlpine 2
1Princeton University Princeton USA2Princeton University Princeton USA3Princeton University Princeton USA4Princeton University Princeton USAShow Abstract
The development of a method for wirelessly “radiating” power generated by biomechanical motion could enable new fundamental insights and applications in soft robotics, sensor networks and remote medical monitors. Biomechanical power harvesting is gaining interest due to decreasing power requirements in portable electronic devices. Various approaches have been investigated to harvest this biomechanical power, including piezoelectricity and triboelectricity. Significantly less explored is the use of magnetic materials for wireless harvesting of biomechanical power. For example, if a flexible magnetostrictive sample is interfaced with a biomechanical source, the persistent biomechanical motion will continuously deform the sample, which will radiate electromagnetic power.
Here we demonstrate the feasibility of wirelessly harvesting power from biomechanical motion using flexible magnetostrictive Terfenol-D nanoribbons, which were deposited, fabricated and transfer printed onto biocompatible silicone. A Terfenol-D film was sputterer-deposited onto an oxidized Si wafer substrate containing photolithographically patterned resist lines. Terfenol-D nanoribbons were obtained following lift-off. The transfer involved complete removal of the Si substrate, rendering the sample flexible. The flexible nanoribbons exhibited excellent magnetic characteristics; indeed, the observed saturation magnetization value of ~1.3 Tesla is, to our knowledge, the highest value reported to date for any sputtered Terfenol-D film. As a proof of principle for demonstrating the potential of the magnetostrictive nanoribbons to wirelessly harvest biomechanical power, flexible nanoribbon generators were attached to a wind-up toy capable of generating a flapping motion. The power wirelessly radiated from this system was then measured. The result indicates that magnetostrictive nanoribbons which are deformed periodically can transmit power to a receiver without any physical contact, enabling new advances in wirelessly harvesting power from a biomechanical source.
9:00 AM - R3.06
Polymer-Oxide Interface Delamination and Reliability in Protective Barriers
Scott G. Isaacson 1 Reinhold H. Dauskardt 1
1Stanford University Stanford USAShow Abstract
Interfaces between polymers and inorganic materials can be found at all levels of flexible organic electronics and photovoltaics, including in the active electronic or photovoltaic layers, at electrical contacts or interconnection lines, and within the protective encapsulation and transparent barrier layers. In the case of flexible protective barriers, the integrity of such polymer-inorganic interfaces are of critical importance to the lifetime of devices and their modules, since interfacial damage in the form of loss of adhesion or delamination can degrade device performance and create fast diffusion pathways for potentially harmful environmental species such as moisture and oxygen.
We present research methodologies for quantifying the effect of interfacial chemistry together with the role of environment, temperature and mechanical stress on the adhesion of model polymer-oxide interfaces. Measurements of adhesive strength are reported as a function of pre-exposure to accelerated aging conditions, including elevated temperature, ambient humidity, and irradiation with ultraviolet light. We demonstrate that adhesive strength is degraded after exposure to ultraviolet light, and use XPS measurements to correlate this degradation to photo-induced chemical changes at the interface. Importantly, we also show that the wavelength of the UV irradiation (UVA vs. UVB) affects many properties of the polymer-oxide system, including delamination behavior, adhesive strength, and the polymer yellowing rate. The importance of understanding such mechanisms of environmentally-assisted degradation of polymer-inorganic interfaces is underscored by the need for improved accelerated life testing procedures, which form the basis for more accurate lifetime predictions.
9:00 AM - R3.07
Enhanced Transparent Barrier Film Through Nanoscale Interface Structuring
Can Cai 1 Reinhold H Dauskardt 1
1Stanford University Stanford USAShow Abstract
The development of a cheap, flexible, and reliable barrier film technology is critical for the integration and commercialization of flexible photovoltaics and organic electronics devices. A promising emerging barrier technology utilizes multiple thin films of alternating organic/inorganic layers that is amenable to roll-to-roll processing while maintaining the desired ultra-low diffusion barrier properties. In operation, the barrier films are subject to weathering effects such as diurnal temperature cycling, moisture and chemical erosion, and UV degradation. The organic/inorganic interfaces are highly susceptible to damage from these degradation sources and limit the operational lifetime of the barrier film. We demonstrate a novel method to increase the organic/inorganic interfacial adhesion strength in a model system of poly (methyl methacrylate) (PMMA) and silicon oxide through interfacial patterning. An array of nanoscale patterns is etched into the PMMA through the use of nanosphere lithography. A thin layer of silicon oxide is conformally deposited onto the patterned PMMA through plasma enhanced chemical vapor deposition. The patterned interface exhibit an order of magnitude increase in adhesion strength over that of a non-patterned interface. X-ray photoelectron spectroscopy (XPS) of the delamination surface shows that the fracture pathway changes from the oxide/PMMA interface in the unpatterned system to within the PMMA in the patterned system. Absorption spectroscopy was used to determine the effect of the nanostructured interface on the optical transmission of the samples. Applied to barrier films, interfacial patterning can be used to increase adhesion between the organic/inorganic layers and resistance of delamination under environment degradation.
9:00 AM - R3.08
Preparation and Properties Study of Mo Thin Film Electrode Materials on Flexible Polyimide Substrates
Chao Li 1 2 Daqin Yun 2 Ran Zhang 2 Fengyan Zhang 2
1Auburn University Auburn USA2Xiamen University Xiamen ChinaShow Abstract
Molybdenum (Mo) thin films were prepared on flexible polyimide (PI) substrates by direct current (DC) magnetron sputtering method. Mo thin films prepared at different sputtering gas pressures and powers have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), four-probe resistivity meter and adhesion test, respectively. The influence of different deposition factors on the crystal structures, surface morphology, electrical and adhesion properties of Mo thin films have been discussed. The experiment results indicate that increasing sputtering gas pressures lead to worse crystal structures, worse electrical properties and better adhesion; the design of a bilayer Mo thin films can achieve better electrical and adhesion properties; increasing sputtering powers result in better electrical and adhesion properties, but it will lead to worse crystal structures and electrical and adhesion properties after beyond a certain power value. Therefore, a bilayer Mo thin film deposited at a higher sputtering power is more suitable for the back contact electrode of CIGS thin film solar cells.
9:00 AM - R3.09
Recharging Electric Vehicles During Motion to Extend the Range
Hal Gokturk 1
1Ecoken San Francisco USAShow Abstract
Range anxiety is considered as one of the major hurdles in the acceptance of a pure electric vehicle (EV) by the mass market. In order to alleviate this concern, auto makers are researching batteries which can store more energy per unit weight. However it might take decades of development to reach the energy density of gasoline even with the advanced formulations under consideration. The objective of this research is to consider an alternative approach which refreshes the batteries of an EV by delivering energy to the vehicle while in motion. Methods of directing intense energy beams to a moving target have been developed by Directed Energy Weapons Systems Program of the military and some of those can be adopted to EVs .
A typical EV has a large cross-sectional area (~10 m2) and a roof area which is about a third of the total cross-section (~3 m2). Three recharging schemes which take advantage of these aspects of the vehicle are proposed:
(a) By AC magnetic induction while the EV is moving at very slow speed, for example through a toll gate or temporarily stationary, for example waiting at a red light. AC current is provided to coils placed on the ground to create a time varying magnetic field perpendicular to the road surface. This magnetic field induces current in receiver coils wrapped around the EV. Frequency of the AC input needs to be set high (600 Hz or more) in order to provide a significant amount power during the brief presence of the vehicle over the coils.
(b) By permanent magnets placed on the road surface along highways. A static magnetic field perpendicular to the road surface is generated by sheets of magnets placed on the road surface. High speed motion of the vehicle over the magnetic field induces a current at receiver coils wrapped around the EV. Since this is a passive method which does not provide power, magnetic sheets are placed at downhill locations along the highway where the EV can maintain its motion with minimal battery usage.
(c) By a pulsed laser directed at photovoltaic (PV) panels placed on the roof of the EV. Diode lasers which are small and relatively inexpensive are installed on overhead structures such as traffic signs. The laser sends high power (kW) pulses to the roof of the EV as it approaches and passes below the laser unit. A conversion efficiency of 50% can be attained with a PV panel matched to the nearly monochromatic light of the laser.
Technical requirements necessary to refresh 1-3% of the energy stored in a typical EV battery will be provided during the presentation.
 R.J. Katt, "Selected Directed Energy Research and Development for U.S. Air Force Aircraft Applications," National Academies Press, Publication 18497, Washington, DC 2013
9:00 AM - R3.10
Reduced Graphene Oxide Thin Films as Ultrabarriers for Organic Electronics
Hisato Yamaguchi 1 2 Jimmy Granstrom 3 Wanyi Nie 1 Hossein Sojoudi 3 Takeshi Fujita 4 Damien Voiry 2 Mingwei Chen 4 Gautam Gupta 1 Aditya D Mohite 1 Manish Chhowalla 2
1Los Alamos National Laboratory Los Alamos USA2Rutgers University Piscataway USA3Georgia Institute of Technology Atlanta USA4Tohoku University Sendai JapanShow Abstract
Encapsulation of electronic devices based on organic materials that are prone to degradation even under normal atmospheric conditions with hermetic barriers is crucial for increasing their lifetime. A challenge is to develop “ultrabarriers” that are impermeable, flexible, and preferably transparent. Another important requirement is that they must be compatible with organic electronics fabrication schemes (i.e. must be solution processable, deposited at room temperature and be chemically inert). Here, we report lifetime increase of 1,300 hours for poly(3-hexylthiophene) (P3HT) films encapsulated by uniform and continuous thin (~10 nm) films of reduced graphene oxide (rGO). This level of protection against oxygen diffusion is substantially better than conventional polymeric barriers such as CytopTM, which degrades after only 350 hours despite being 400 nm thick. Analysis using atomic force microscopy, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy suggest that the superior oxygen gas barrier property of rGO is due to the close interlayer distance packing and absence of pinholes within the impermeable sheets. These material properties can be correlated to the enhanced lag time of 500 hours. Our results provide new insight for the design of high performance and solution processable transparent “ultrabarriers” for a wide range of encapsulation applications.
H.Yamaguchi et al. "Reduced Graphene Oxide Thin Films as Ultrabarriers for Organic Electronics" Adv. Energy Mater. (2013), Article first published online: 10 OCT 2013, doi: 10.1002/aenm.201300986
9:00 AM - R3.11
Origin of "Temporal Tail" in Decay Dynamics of MEH-PPV Films
Rajarshi Chakraborty 1 Lewis J Rothberg 2
1University of Rochester Rochester USA2University of Rochester Rochester USAShow Abstract
Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) has been considered as one of the potential and useful conducting polymers for various optoelectronic applications because of its solubility, flexibility, low cost and conductivity. It is accepted that quantum yield of films are less than their solution counterparts and has a “temporal tail” in the decay dynamics. We try to understand if a correlation exists between the “temporal tail” and quantum yield in films. We investigate the origin of a “temporal tail” by a temperature dependent study of the spectra. We also study the electric-field effect on the “tail” and describe the results on the basis of a model that implies that the long-lived `tail&’ luminescence in film is a result of energy transfer from “ H-like aggregates” present in the film.
9:00 AM - R3.12
Effective Piezo-Phototronic Enhancement of Solar Cell Performance by Tuning Material Properties
Xiaonan Wen 1 Wenzhuo Wu 1 Zhong Lin Wang 1 2
1Georgia Institute of Technology Atlanta USA2National Institute for Materials Science Tsukuba JapanShow Abstract
Piezo-phototronic effect is demonstrated in the ZnO/P3HT solar cell system and detailed study is conducted regarding the influence of crystallization and doping level of ZnO on the strength of piezo-phototronic effect as well as the overall solar cell performance. By testing and comparing five groups of samples prepared under different conditions, optimized parameters are determined for the most efficient piezo-phototronic enhancement of solar cell performance. The general principles and regularities provided in this study are universal and applicable to all solar cell systems involving piezoelectric semiconductor materials and could provide substantial guidance on further increasing performances of commercial solar cells based on CdTe, GaAs etc. and also spur the development of flexible solar cells for smart applications in various situations.
9:00 AM - R3.13
Photoemission Studies on the Effects of Micro/Nano Fillers in HEMT GaN Encapsulants
Viswas Purohit 1 2 Laurence Chevalier 2 Kaouther Daoud 2
1Alliance College of Engineering and Design Bangalore India2Universitamp;#233; de Rouen , Facultamp;#233; des Sciences et Techniques - Technopamp;#244;le du Madrillet Saint Etienne du Rouvray cedex FranceShow Abstract
Failures in electronic devices can be classified as i) catastrophic failures which destroy the device or ii) degradation failures which causes a reduction in device performance. Device bias, resultant channel temperature, passivation, and material interactions may all cause or contribute to failure. For the analysis of such types of defects, it is very important to access the ‘heart&’ of the device and to observe the front side of the die. This is done by removing the epoxy resin which plays an important part in insulation between the electrical parts of the device as well as to provide protection against atmospheric corrosion. The most widely used solution is to use the laser decapsulation process along with chemical depackaging technique to obtain a good surface of the die for further analysis. The use of silica for reinforcement of polymeric insulation like epoxy resin in microelectronic packaging industry is essential for its dielectric and thermal properties since, addition of silica improves the thermal dissipation . However, decapsulation of chips, tend to leave behind minute traces of this epoxy which remain bound to crevices of the semiconductor device.
In this paper, decapsulation studies were carried out on Gallium Nitride High Electron Mobility Transistor (GaN HEMT) devices and the physics of degradation attributed to epoxy was analyzed. Although the sealant materials are supposedly electrically inactive, a contribution to the device performance is observed. These electrically active traces are believed to contribute to the degradation in the performance of the device as evident by the IV measurements for different gate voltages. The use of photoemission microscopy for the analysis of this particular type of packaging related failure has been put forward in this work. The main aim of this paper is to study the effects of the remnant material on the performance of the component and to analyze its contribution towards electrical degradation by using photoemission microscopy.
9:00 AM - R3.14
Flexible Carbon Nanotube Based Power Fabrics for Harvesting Thermoelectricity to Operate an Electrochromic Sensor
Suk Lae Kim 1 Choongho Yu 1
1Texas Aamp;M University College Station USAShow Abstract
Single wall carbon nanotubes (CNT) were functionalized to p- or n-type materials, and a thermoelectric power generating device made of CNT films was designed and fabricated to operate a glucose sensor. The electronic transport properties were optimized by adjusting the amount of surfactants on CNTs for p-type films as well as reducing CNTs with multiple dopants for n-type. The thermopower and electrical conductivity of optimized n-type nanotubes were measured to be -86 µV/K and 5,200 S/m, respectively. The p-type nanotube samples have a thermopower and electrical conductivity value of +100 µV/K and 11,000 S/m, respectively. Electronic band structures with the Fermi level and carrier mobilities of the CNTs were experimentally investigated, which have elucidated the carrier type and relatively large thermopower values.
The thermoelectric device was made of 72 p-type and 72 n-type CNT films electrically connected in series and thermally in parallel so as to maximally utilize temperature gradients. This device produced 465 mV at a temperature gradient of ΔT = 49 K, which is much larger than those of typical polymer based composites. The thermoelectric device was integrated with a glucose sensor and the self-powered sensor system was operated by using 1.8 µW from the thermoelectric device at ΔT = 32 K. We demonstrated that flexible organic thermoelectric devices are promising for portable and self-powered sensors.
9:00 AM - R3.15
Multiferroic Behaviour in Double Perovskites Y2XMnO6 (X = Co, Ni)
Gyaneshwar Sharma 1 J. Saha 1 S. Patnaik 1
1Jawaharlal Nehru University New Delhi IndiaShow Abstract
At present considerable research interest exists for magnetic structure driven ferroelectricity in double perovskite oxides. We report an investigation of such properties in Y2XMnO6 (X = Co, Ni). On the basis of magnetic and crystal environment, we expect multiferroicity in these compounds that crystallize in P21/n space group. Under this symmetry, Co2+/Ni2+ are arranged alternately with respect to Mn4+ (along c-axis) in an one dimensional Ising chain. This leads to the development of up-up-down-down spin ordering below the magnetic ordering temperature. We have also synthesized phase pure Y2(Cu/Zn)MnO6 that do not possess P21/n symmetry and therefore no features related to magneto-electric coupling are expected.
In Y2CoMnO6, both DC and AC susceptibility as a function of temperature shows anti ferromagnetic transition at ~ 80K. By measuring pyroelectric current as a function of temperature, we confirm emergence of spontaneous ferroelectric polarization below the magnetic ordering temperature. We note that such high temperature improper ferroelectricity due to spin ordering is extremely rare. We identify that the up-up-down-down magnetic symmetry with the alternate magnetic ions along c-axis could give rise to such phenomena due to magneto-striction. The behaviour of induced polarization with varying poling field and temperature cycling confirm the development of genuine ferroelectricity at such high temperatures. This development of ferroelectricity with up-up-down-down ordering along c-axis is also confirmed by neutron diffraction measurement at T = 2.7 K. The saturation polarization is estimated to be ~ 65µC/m2 and saturation magnetization at 5T corresponds to 6.2 µB/ f.u. Preliminary results on Y2NiMnO6 confirm anti- ferromagnetic transition at TN ~ 86 K but the associated ferroelectricity is yet to be unambiguously established due to leaky characteristics.
R1: Energy Harvesting I
Horacio D. Espinosa
Tuesday AM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14
9:15 AM - R1.02
Length Effect on the Energy Conversion of a Zinc Oxide Nanowire
Ren Zhu 1 Rusen Yang 1
1University of Minnesota Minneapolis USAShow Abstract
Energy harvesting with piezoelectric material provides a compact and reliable method to convert the irregular mechanical energy in the environment into electric energy. Compared with traditional polycrystalline ceramics, single crystal piezoelectric nanostructures are more flexible and robust and they can accommodate larger strain input, which leads to a higher power density. Because of the non-toxicity and various existed synthesis methods, piezoelectric zinc oxide (ZnO) nanowire is widely studied for this application. ZnO is also a semiconductor and the internal free electron can partially screen the generated potential, while a Schottky contact helps block the charge from flowing through the nanowire. The effect of the free charge and the Schottky contact adds on the length dependence of the output from a nanowire, while such study is still lacking. Here by depositing a series of electrodes on a single ZnO nanowire sited on a flexible substrate, we characterized the energy conversion from a single nanowire with different length and different types of contact. This study shows the influence of the dimension and the semiconducting property of a nanowire on its mechanical-electric energy conversion, and it provides a critical design guideline for a high output ZnO nanogenerator.
9:30 AM - R1.03
A Piezotronic Component with a Flexible Ridge on Its Top Mimicking Finger Prints
Wu You 1 Liao Zhipeng 1 Li Xin 1 Liu Weihua 1 Zhang Yan 2 3
1Xi'an Jiaotong University Xi'an China2Lanzhou University Lanzhou China3Beijing Institute of Nanoenergy and Nanosystems,Chinese Academy of Sciences Beijing ChinaShow Abstract
Piezotronics based on piezoelectric fine wires have show diverse of potential applications [1-3]. A piezotronic device is normally characterized by its capable of output pulsed piezoelectrical signals upon a load of strain. Strain sensor or tactile sensor could be a promising application for piezotronic devices [1, 2]. This field is pioneered by Zhong Lin Wang&’s group. Zhong Lin Wang&’s group has just demonstrated a tactile imaging device based on an array of piezotronic transistors . This work opened a broad range of potential applications such as human-electronic interfacing, smart skin and micro- and nanoelectromechanical systems. The unique thing of this type of tactile sensor is that its function mechanism is similar with that of tactile sensing of human beings, which is essentially a bio-piezo effect.
In this report, we demonstrate a horizontally aligned piezotronic component based on a ZnO piezoelectric fine wire bridging between two copper electrodes. We integrate a fiber across the ZnO piezoelectric fine wire and so it forms a ridge across the piezotronic component after PDMS packaging. The ridge over the piezotronic component serves as a strain introducing component mimic human being finger prints. The devices are used to touch (press and slide on) a series of objects with period textures on the surface. The output piezoelectric pulses are recorded and correlated to the period textures of the objects been touched.
This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 61172041, 91123018, 61172040), and the Fundamental Research Funds for the Central Universities. The authors also thank Prof. Yong Qin for his valuable comments on the device fabrications.
 Wenzhuo Wu, Xiaonan Wen, Zhong Lin Wang, Taxel-Addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging, Science 340, 952 (2013).
 Rusen Yang, Yong Qin, Liming Dai and Zhong Lin Wang, Power generation with laterally packaged piezoelectric fine wires, Nature Nanotechnology, 4, 34-39 (2009).
 Jun Zhou, Yudong Gu, Peng Fei, Wenjie Mai, et al., Flexible Piezotronic Strain Sensor, Nano Lett. 8, 3035-3040 (2008).
9:45 AM - *R1.04
ZnO Nanorod Structures for Energy Harvesting
Steve Dunn 1 Nimra Jalali 1 Joe Briscoe 1 Mark Stewart 2 Markys Cain 2 Peter Wooliams 2 Leonard Loh 3 1
1QMUL London United Kingdom2NPL London United Kingdom3NYP Singapore SingaporeShow Abstract
I will present methods to fabricate, test and characterize ZnO nanorod-based energy harvesters and the impact of surface passivation of the ZnO on power output for a vibrational harvesting system and a photovoltaic. Previous studies have focused on improving the performance of these devices. In this regard, suppression of semiconductor carrier screening and improvement in device architecture had been reported. However, the impact of ZnO nanorod passivation on p-n junction devices has not been studied.
The first section of the presentation will discuss the passivation of ZnO nanorods using CuSCN in ZnO/PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)) p-n junction-type piezoelectric energy harvesting devices. The maximum power density across its optimal load is determined by testing the device across variable resistors showing higher output from passivated devices. The increase in voltage and voltage-driven current is discussed with relation to changes in the carrier lifetime.
A comparison between passivated and non-passivated ZnO devices shows that the passivated device generated an open-circuit voltage of 212 mV and short circuit current of 1 mA/cm2 which was around twice the value of non-passivated device (90 mV and 0.66 mA/cm2). When tested across a range of load resistances, the maximum power density was also found to have almost doubled from 36.00 µW/cm2 across a 1.38 k#8486; load for the non-passivated device to 64.40 µW/cm2 (1.67 k#8486;) for the passivated device. We deduce that the voltage and voltage-driven current density of the passivated ZnO device improved due to three-fold increase in carrier life time.
The second part of the presentation will focus on the photovoltaic (PV) effect of perovskite materials and methods of passivating the surface of ZnO to enable thin film growth. I will report on the design, fabrication and testing of a solid-state perovskite enhanced ZnO solar cell. The p-type perovskite material used was bismuth ferrite (BFO), so far not implemented in a ZnO solar cells.
The cell uses FTO and Au electrodes sandwiching semiconductor layers and a CuSCN hole conductor, the ZnO was sensitized with N719. XRD confirmed the presence of BFO with the presence of a single  BFO peak. The results show a significant increase in the performance with efficiencies increased by almost 3 times with the BFO coating with an efficiency of 0.272%. The BFO acts as a buffer from electron recombination. However, the relative increase in performance of the solar cell when BFO was added shows promise of BFO as a PV material.
In summary I will show that there are a range of energy harvesting devices that can be produced using a surface passivation layer on a ZnO nanorod architecture and that by careful control of the process parameters enhanced energy harvesting is possible.
10:15 AM - R1.05
A New Thin-Film-Based Flexible Technology for Energy Generation and Contact Sensing
Guang Zhu 1 Weiqing Yang 1 Zhong Lin Wang 1
1Georgia Institute of Technology Atlanta USAShow Abstract
In this work, we developed a new thin-film-based flexible technology for both energy generation and contact sensing. The device is rationally structured through stacking layers of flexible substrates, transparent electrodes, and electrification layers. By a unique operating principle that couples contact electrification and electrostatic induction, the device is able to produce electricity between electrodes as a result of contact with other objects. On one hand, it can be effectively used for power generation. Triggered by human foot steps, a device with dimensions of 15 cm by 15 cm could deliver a open-circuit voltage of 800 V and a maximum short-circuit current of 3 mA, corresponding to a maximum power density of 4.2 W/m2 that was delivered to an external load. As a direct power supply, it successfully lighted up over 1,000 LED bulbs simultaneously. On the other hand, it can also be applied for sensing applications as a self-powered sensor that does not require external power supplies. For a contact object that has an area of 6.5 cm2, the device exhibits an ultra-high sensitivity of 0.9 V/Pa. The produced electric signal from a device that was embedded under a carpet has been demonstrated to trigger a wireless alarm system when people walked by. Such a demonstration was also applicable for direct contact from a human finger and hand grabbing, indicating immediate applications of the technology in security, surveillance, tactile imaging, and touch pad technology, among others.
10:30 AM - *R1.06
Vibration and Flow Energy Harvesting Using Piezoelectric Cantilevers
Xiaotong Gao 1 Wan Y. Shih 2 Wei-Heng Shih 1
1Drexel University Philadelphia USA2Drexel University Philadelphia USAShow Abstract
It would be of great interest to develop energy harvesters that can convert ambient mechanical energies such as vibrations or air flows to power wireless devices such as sensors, controllers, transmitters and receivers. Over the past decade, piezoelectric cantilever (PC) energy harvesters have been increasingly investigated for this application. Traditional PCs consist of equal length of piezoelectric and nonpiezoelectric layers. Here we investigated the energy harvesting performance of PCs with unequal piezoelectric and nonpiezoelectric lengths (two-section PCs) both theoretically and experimentally. Under the application of step-wise tip forces it was shown that a longer nonpiezoelectric layer is preferred for generating a higher induced voltage while a longer piezoelectric layer reduces the induced voltage due to charge cancellation.^1 On the other hand under harmonic base vibrations, there exists an optimal nonpiezoelectric-to-piezoelectric length ratio at which output voltage, current, and power can be maximized.^2 Theoretically, a two-section PC was considered within the framework of a beam theory for step-wise tip forces and within the framework of Euler-Bernoulli beam theory with electromechanical coupling for harmonic base vibrations. The results of the theoretical analysis were in good agreement with the experiments.
To utilize air flow, we present a piezoelectric flow energy harvester (PFEH) by adding a cylindrical extension to a piezoelectric cantilever. The flow induced vibration of the cylindrical extension causes the piezoelectric cantilever to vibrate at the natural frequency of the PFEH. The PFEH provides a low-cost, compact and scalable power source for small electronics by harvesting energy from ambient flows such as wind and water streams.^3 Prototypes were tested in both laminar and turbulent air flows demonstrating the feasibility of the design. Turbulence excitation was found to be the dominant driving mechanism of the PFEH with additional vortex shedding excitation contribution in the lock-in region. The voltage and power output of the PFEH increased with increasing size of the extension. We also showed that a rectangular extension helped generate a higher voltage and power than a circular one of the same dimensions. Finally, the PFEH was successfully used to power a green LED intermittently with an instant power output of more than 12 mW by using a charge storage capacitor and a low-power temperature sensor continually with an average power output of 18 mu;W at 4.7 m/s wind velocity.
1. X. Gao, W. Y. Shih, and W.-H. Shih, Smart Mater. Struct., 18, 125018 (2009)
2. X. Gao, W.-H. Shih, and W. Y. Shih, Appl. Phys. Lett. 97, 233503 (2010)
3. X. Gao, W.-H. Shih and W. Y. Shih, IEEE Transactions on Industrial Electronics, 60, 1116-1118 (2013)
11:30 AM - *R1.07
Triboelectric Nanogenerators as New Energy Technology for Self-Powered Systems and as Active Mechanical and Chemical Sensors
Zhong Lin Wang 1
1Georgia Institute of Technolog Atlanta USAShow Abstract
Triboelectrification is an effect that is known to each and every one probably ever since the ancient Greek time, but it is usually taken as a negative effect and is avoided in many technologies. We have recently invented a triboelectric nanogenerator (TENG) that is used to convert mechanical energy into electricity by a conjunction of triboelectrification and electrostatic induction. As for this power generation unit, in the inner circuit, a potential is created by the triboelectric effect due to the charge transfer between two thin organic/inorganic films that exhibit opposite tribo-polarity; in the outer circuit, electrons are driven to flow between two electrodes attached on the back sides of the films in order to balance the potential. Ever since the first report of the TENG in January 2012, the output power density of TENG has been improved for five orders of magnitude within 12 months. The area power density reaches 313 W/m2, volume density reaches 490 kW/m3, and a conversion efficiency of ~50% has been demonstrated. The TENG can be applied to harvest all kind mechanical energy that is available but wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tire, wind, flowing water and more. Alternatively, TENG can also be used as a self-powered sensor for actively detecting the static and dynamic processes arising from mechanical agitation using the voltage and current output signals of the TENG, respectively, with potential applications for touch pad and smart skin technologies. The TENG is possible not only for self-powered portable electronics, but also as a new energy technology with a potential of contributing to the world energy in the near future.
 Z.L. Wang “Triboelectric Nanogenerators as New Energy Technology for Self-Powered Systems and as Active Mechanical and Chemical Sensors”, ACS Nano, DOI 10.1021/nn404614z.
12:00 PM - *R1.08
Vertically Aligned Barium Titanate Nanowires Arrays for Energy Harvesting
Henry A Sodano 1
1University of Florida Gainesville USAShow Abstract
Nano electromechanical systems (NEMS) developed using piezoelectric nanowires have gained an immense interest in energy harvesting applications as they are able to convert several different forms of mechanical energy sources into electric power and thereby function as reliable power sources for ultra-low power wireless electronics. In this work, a piezoelectric nanowire vibrational energy harvester is fabricated through the development of a synthesis process for vertically aligned barium titanate (BaTiO3) nanowire arrays directly on a conductive substrate. These poled ferroelectric NW arrays are characterized through direct vibration excitation and demonstrated to provide efficient harvesting of mechanical vibrational energy producing an average power density of ~6.27 mu;W/cc from 1g acceleration. In order to substantiate the superior energy harvesting performance of the newly developed BaTiO3 NW arrays, a direct comparison is made with conventional ZnO NW arrays. It will be shown that the ferroelectric BaTiO3 NW energy harvester has ~16 times greater power density than the ZnO NW NEMS energy harvester from the same acceleration input. In addition to energy harvesting applications nanowire arrays can also find use in dynamics sensors, however, to date, no results have demonstrated the capability to use aligned piezoelectric nanowire arrays as a highly accurate nano-electromechanical system-based dynamic sensor with a wide operating bandwidth and high coherence. It will also be shown that the ferroelectric nanowires can provide excellent sensitivity to dynamic excitation and function as an accurate accelerometer. A high sensitivity of up to 50mVg-1 is observed from the sensor composed of vertically aligned barium titanate nanowire arrays, thus providing performance comparable to many commercial accelerometer systems.
12:30 PM - R1.09
Flexible Thermoelectric Devices Based on Indium Phosphide Nanowire Networks on Copper
Kate J Norris 1 2 Brian Tuan 3 Junce Zhang 1 2 David M. Fryauf 1 2 Juan J. Diaz Leon 1 2 Elane Coleman 4 Gary S. Tompa 4 Nobuhiko P Kobayashi 1 2
1University of California Santa Cruz Santa Cruz USA2Advanced Studies Laboratories, Univ. of California Santa Cruz - NASA Ames Research Center moffett Field USA3The Harker School San Jose USA4Structured Materials Industries, Inc., Piscataway USAShow Abstract
More than 50% of total input energy is wasted as heat in various industrial processes. If we could harness a small fraction of the waste heat while satisfying the economic demands of cost versus performance, then thermoelectric (TE) power generation could bring substantial positive impacts. To meet these demands single-crystal semiconductor nanowire networks have been investigated as a method to achieve advanced TE devices because of their predicted large reduction in thermal conductivity and increase in power factor.
To further our goal of developing practical and economical TE devices, we designed and developed a material platform that combines a semiconductor nanowire network and a semiconductor thin film integrated directly on a mechanically flexible metallic substrate. We assessed the potential of this platform by using indium phosphide (InP) nanowire networks and a doped poly-silicon (poly-Si) thin film combined on copper sheets. InP nanowires were grown by metal organic chemical vapor deposition (MOCVD). In the nanowire network, InP nanowires were grown in three-dimensional networks in which electrical charges and heat travel under the influence of their characteristic scattering mechanisms over a distance much longer than the mean length of the constituent nanowires. Subsequently, plasma-assisted CVD was utilized to form a poly-Si thin film to prevent electrical shorting when an ohmic copper top contact was made. An additional facet to this design is the utilization of multiple materials to address the various temperature ranges at which each material is most efficient at heat to energy conversion. The utilization of multiple materials could enable the enhancement of total power generation for a given temperature gradient. We will investigate the use of poly-Si thin films combined with InP nanowires to enhance TE properties. TE parameters, power production, and challenges of a large area nanowire device on a flexible metallic substrate will be presented. We will discuss our design and testing of a new large area, scalable, mechanically flexible TE devices.
12:45 PM - R1.10
Hybrid Energy Generator Using Triboelectric and Piezoelectric Effects
WooSuk Jung 1 Seok-Jin Yoon 1 Chong-Yun Kang 1
1Korea Institute of Science and Technology(KIST) Seoul Republic of KoreaShow Abstract
A way to response the energy consumption and to produce sustainable nonpolluting power source is energy harvesting from our environment, as a renewable energy source. This energy source are always available everywhere, such as a vibration, wind, fluid, etc. Recently, there have been attempts to fabricate energy generators using piezoelectric, pyroelectric, triboelectric materials, and so on. Here, we concurrently use piezoelectric and triboelectic effects to produce a high output power. Contact electrification between the PVDF film and a PTFE sheet generate electrical signals by triboelectric and electrostatic effects, and the PVDF film also produce piezoelectricity when applied a mechanical force. An arch-shape PI film was attached to the PVDF film, which plays role in driving force for bending and releasing. An Al and two Au electrodes were deposited on the PTFE sheet and the both sides of the PVDF film, respectively. In the experimental results, the PVDF film produced higher output current than the triboelectricity, in contrary the output voltage from triboelectric effect was much higher than the PVDF film when being pressed the generator. Finally, the two effects were connected parallelly, resulting in the output voltage of ~ 100 V and the output current of ~220 uA in dimension of 7 X 4 cm2. The generating power was successfully tested with 60 LEDs lighting. Thus, we expect that this hybrid harvesting technique using triboelectric and piezoelectric effects can be used in various applications as a power source and apply to electronics directly.
Liangbing Hu, University of Maryland
Guihua Yu, University of Texas at Austin
Leif Nyholm, Uppsala University
Horacio D. Espinosa, Northwestern University
Rusen Yang, University of Minnesota
R5: Energy Conversion and Storage II
Wednesday PM, April 23, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14
2:30 AM - *R5.01
High-Performance Transparent and Semi-Transparent Polymer Solar Cells
Yang Yang 1 Chun-Chao Chen 1 Letian Dou 1 Wei-Hsuan Chang 1 Min Cai 1 Gang Li 1
1UCLA Los Angeles USAShow Abstract
Polymer solar cell (PSC) technology is an efficient and cost-effective solution for harvesting of solar energy. Transparent PSCs, in particular, have great potential for building-integrated photovoltaics, where the photovoltaic elements can simultaneously serve as building materials and power generators while maintaining an attractive building exterior.
In this talk, I will talk about high-performance, visibly transparent or semi-transparent polymer solar cells fabricated via solution processing. The photoactive layer of the single-junction PSCs harvest solar energy largely from the near-infrared region while being less sensitive to visible photons. In a conventional single junction device consisting of a highly transparent silver nanowire metal oxide composite top electrode, a 4% power-conversion efficiency (PCE) was achieved with a maximum transparency of 66% at 550 nm. To further enhance the performance and tune the external appearance, tandem device architectures were employed. New low bandgap polymers based on benzodithiophene and diketopyrrolopyrrole units were designed and synthesized. A novel interconnecting layer between the two sub-cells was also designed to make efficient tandem devices. As a result tandem devices recorded a high PCE of 7% with a maximum transparency of 30% at 550 nm while a PCE of 6% was achieved with a maximum transparency of 40% at 550 nm (device area = 0.1 cm2). Finally, we demonstrate non-transparent flexible devices with PCEs over 4% and large area (device area = 10 cm2) devices with PCEs over 3.5%. By incorporating transparent silver nanowire electrode, we believe semi-transparent, large area devices with PCE over 2% is in reach shortly.
3:00 AM - *R5.02
Optimizing the Properties of Graphene and Graphene Quantum Dots for Energy Applications
Byung Hee Hong 1 Joonhee Moon 1 Youngsoo Kim 2 Uk Sim 3 Jung Kyu Kim 4 Ki Tae Nam 3 Jong Hyeok Park 4
1Seoul National University Seoul Republic of Korea2Seoul National University Seoul Republic of Korea3Seoul National University Seoul Republic of Korea4Sungkyunkwan University Suwon Republic of KoreaShow Abstract
Graphene is a promising electrode material for various flexible energy applications, but its conductivity and work-function need to be optimized to enhance the performance of graphene-based energy devices. This can be performed by various doping methods including atomic substitution, molecular adsorption, covalent functionalization, substrate induced doping, and the use of metallic thin films or nanoparticles. The substitution of carbon atoms with B or N as well as the covalent functionalization are advantageous in terms of long-term stability, which is, however, unfavorable due to significant decrease in carrier mobility and conductivity. Thus, we report a simple method to tune the electrical properties of CVD graphene by molecular vapors, where the dopants in vapor phase are mildly adsorbed on graphene surface without direct contact with solution. The vapor-phase doping provides not only very high carrier concentration but also good long-term stability in air, which is particularly important for practical energy and display applications.
On the other hand, graphene quantum dots (GQDs) exhibit great potential for various optoelectronic applications due to their size-dependent and edge-sensitive photoluminescence properties. Previously, GQDs were mainly synthesized from graphene oxides by chemical exfoliation under strongly acidic environment or by multi-step lithographic methods including masking, patterning and lift-off, which hindered the efficient preparation of high-quality GQDs for practical applications. In addition, nitrogen-functionalization or doping is known to be very helpful to tailor the intrinsic properties of GQDs, but it needs further complicated wet-chemical reactions. Here we present a very simple solvent-free method to prepare nitrogen-doped GQDs (N-GQDs) by directly applying nitrogen plasma to as-grown graphene on Cu. The resulting N-GQDs can be transferred as a film-like layer or easily dispersed in an organic solvent. We confirm that the N-GQDs whose sizes are narrowly distributed around ~5 nm show strong photoluminescence when excited at 365 nm, which would be useful for a wide range of optoelectronic, electrochemical, and energy storage applications.
3:30 AM - R5.03
Toward Intrinsically Stretchable Organic Semiconductors: Mechanical Properties of High-Performance Conjugated Polymers
Darren Lipomi 1 Suchol Savagatrup 1 Timothy O'Connor 1 Adam Printz 1 Aliaksandr Zaretski 1
1University of California, San Diego La Jolla USAShow Abstract
The fragility of many modern organic semiconductors might limit their applicability in applications demanding mechanical compliance. For example, many pure polymers, polymer-fullerene blends, and the transparent conductor indium tin oxide all fracture at tensile strains of two percent or less on compliant substrates. The design of organic semiconductors that can be deformed significantly would facilitate roll-to-roll production, mechanical robustness for potable applications, conformal bonding to curved surfaces other than cylinders, and would enable large-scale solar farms based on ultra thin organic modules that can survive forces of the outdoor environment. This paper describes our efforts to understand and control the structural parameters that influence the mechanical properties of modern conjugated polymers. Our conclusions include the effect of the side chain in determining the elasticity, ductility, and adhesion of polymers and their blends with fullerenes, and how this effect can be predicted by theory. Ultra-compliant materials are used for the first time in solar cell that can be stretched and conformed to hemispherical surfaces without damage. We also describe the synthesis of all-conjugated block copolymers whose goal is to maximize both electronic properties and mechanical compliance. A new polymerization based on cross-coupling of conjugated “macromonomers” enables block-copolymer-like materials from step-growth polymerizations. Mechanical and photovoltaic properties of these segmented copolymers are also reported. Our results should inform the engineering of new semiconducting polymers for flexible and stretchable applications.
3:45 AM - R5.04
Carbon Nanotube Active-Matrix Backplanes for Mechanically Flexible Visible Light and X-Ray Imagers
Zhibin Yu 1 Toshitake Takahashi 1 Ali Javey 1
1UC Berkeley Berkeley USAShow Abstract
Recent advancements in the processing of electronically monodisperse carbon nanotubes have enabled the exploration of a wide range of functional devices based on random networks of nanotubes. In particular, thin film transistors (TFTs) using solution-processed semiconductor-enriched nanotubes have been demonstrated to exhibit excellent electrical properties with high uniformity on both rigid and flexible substrates. High hole mobilites of up to 50 cm2/Vs with high Ion/Ioff of up to 106 have been reported for nanotube TFTs. Here, we monolithically integrate organic photodetectors (OPDs) made of regioregular poly(3-hexylthiophene) (P3HT) and [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) on top of a nanotube backplane consisting of an 18×18 pixel array (physical size of 2 cm by 1.5 cm). The absorption spectrum of P3HT:PCBM bulk-heterojunction photodetectors is optimal for visible light imaging applications. Furthermore, by integrating a Gd2O2S:Tb (GOS) scintillator film on top of the imager, a mechanically flexible X-ray imager is demonstrated.
4:30 AM - *R5.05
Materials Challenges and Integration Strategies for Flexible Energy Devices and Systems
Zhenan Bao 1
1Stanford University Stanford USAShow Abstract
In this talk, I will discuss new polymers we have been developing for high performance solar cells. We also developed a variety of functional polymers for Si-based lithium ion battery electrodes.
5:00 AM - R5.06
Photonic Flash Sintering of Metal Based Conductive Inks for Printed Solar Cells on Flexible Foils
Robert Abbel 1 Michael Grouchko 2 Yulia Galagan 1 Erica W. C. Coenen 1 Tim van Lammeren 1 Eric Rubingh 1 Shlomo Magdassi 2 Pim Groen 1 3
1Holst Centre - TNO Eindhoven Netherlands2The Hebrew University of Jerusalem Jerusalem Israel3Delft University of Technology Delft NetherlandsShow Abstract
The broad application of solar energy harvesting in everyday products, e. g. by integration in clothing, requires mechanically flexible photovoltaic (PV) cells to be available in large volumes and at low costs. PV devices with indium tin oxide (ITO) free transparent electrodes printed on plastic foils are promising candidates for this approach, because they can be produced on large scale in an industrial roll-to-roll fabrication process. In order to compensate for the rather high resistive losses in ITO-free transparent conductive materials, current collecting grids comprising high electrical conductivities need to be included to reduce the sheet resistances. Printing and subsequent sintering of conductive inks or pastes based on metal nanoparticle dispersions is a convenient deposition method for these structures. The traditional approach of sintering by prolonged heating has the decisive disadvantage of being rather slow, thereby requiring long processing times and being difficult for application in R2R manufacturing. This is especially true if inexpensive commodity polymers are used as the substrate materials, which cannot withstand high temperatures. In addition, inks containing nanoparticles based on non-noble metals are prone to oxidation during thermal sintering, which demands working under protective atmosphere. Sintering methods which are fast enough to allow R2R processing at reasonable speeds and avoid oxidation even when operating in air are therefore in high demand.
In this contribution, photonic flash sintering is presented as a fast and highly efficient processing technology for improving the conductivities of printed metal nanoparticle structures on plastic foils. Due to the selective heating of the metal deposits by the absorption of visible light flashes, for which the substrate itself is transparent, high temperatures can be achieved locally for very short times. Using this approach, resistivity drops of more than six orders of magnitude are achieved within fractions of a second. For silver based inks, both integration in printed organic solar cells with improved power conversion efficiencies and R2R application have been demonstrated. Because the photonic sintering process occurs much faster than the oxidation of copper nanoparticles, the technology can also be applied to copper inks without the need of a protective atmosphere.
5:15 AM - R5.07
Effects of Oxygen Plasma Treatment and E-Beam Evaporation on Stretchability and Contact Properties of AgNWs/PDMS-Based Stretchable Electrodes
Haopeng Wang 1 2 Jing Bai 1 Jianguo Cao 2 Debao Zhou 1
1University of Minnesota Duluth Duluth USA2University of Science and Technology Beijing Beijing ChinaShow Abstract
In this work, we presented the fabrication and testing of four types of stretchable electrodes design for piezoresistive sensor base on silver-nanowires (AgNWs) and polydimethylsiloxane (PDMS). The effect of oxygen plasma treatment and electron beam evaporation (e-beam evaporation) on the stretchability and contact resistance between the electrodes and piezoresistive material were investigated with the assistance of SEM images and EDS spectra. The oxygen plasma treatment could degrade the stretchability and contact quality, but improved the metal layer evaporated on the AgNWs/PDMS conductor. The e-beam evaporation could optimize the contact quality and insulate the AgNWs network from effect of oxygen plasma treatment. However, the untreated PDMS usually had a poor adhesion with the metal layer. So for the performance improvement of AgNWs/PDMS electrode, efforts should be made on design of the fabricating process or introduction of new technology that could keep the density of the AgNWs network, meanwhile enhance the adhesion strength of metal layer to the AgNWs/PDMS conductor. The results could be used to guide the fabrication of qualified electrodes that comprise high stretchability and low contact resistance for skin-like piezoresistive sensor.
5:30 AM - R5.08
Complementary Absorbing Star-Shaped Small Molecules for Organic Ternary Solar Cells
Hyojung Cha 1 Chan Eon Park 1
1POSTECH Pohang Republic of KoreaShow Abstract
Two anthracene-based star-shaped conjugated small molecules, 5',5''-(9,10-bis((4-hexylphenyl)ethynyl)anthracene-2,6-diyl)bis(5-hexyl-2,2'-bithiophene), HBantHBT, and 5',5''-(9,10-bis(phenylethynyl)anthracene-2,6-diyl)bis(5-hexyl-2,2'-bithiophene), BantHBT, were used as electron-cascade donor materials by incorporating them into organic photovoltaic cells prepared using a poly((5,5-E-alpha-((2-thienyl)methylene)-2-thiopheneacetonitrile)-alt-2,6-[(1,5-didecyloxy)naphthalene])) (PBTADN):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) blend. The small molecules penetrated the PBTADN:PC71BM blend layer to yield complementary absorption spectra through appropriate energy level alignment and optimal domain sizes for charge carrier transfer. A high short-circuit current (JSC) and fill factor (FF) were obtained using solar cells prepared with the ternary blend. The highest photovoltaic performance of the PBTADN:BantHBT:PC71BM blend solar cells was characterized by a JSC of 11.0 mAcm-2, an open circuit voltage (VOC) of 0.91 V, a FF of 56.4%, and a power conversion efficiency (PCE) of 5.6% under AM1.5G illumination (with a high intensity of 100 mW-2). The effects of the small molecules on the ternary blend were investigated by comparison with the traditional poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) system.
5:45 AM - R5.09
Graphene Coated Electrically Conductive Cotton Apparel
Yarjan Abdul Samad 1 Yuanqing Li 1 Saeed Alhassan 2 Kin Liao 1
1Khalifa University of Science technology and research Abu Dhabi United Arab Emirates2The Petroleum Institute Abu Dhabi United Arab EmiratesShow Abstract
There is an inevitable need to increase our dependence on renewable and sustainable energy resources. In addition to harvesting energy from the solar, wind, and biomass resources, there is a decent amount of work being done on harvesting energy from smaller resources such as the human body for smaller mobile energy needs such as charging or powering gadgets. Cotton, composed of cellulose and hemicellulose and used for apparels, is well known for both its thermal and electrical insulating properties. However, it needs to be electrically conductive to enable transfer of small amounts of electrical charges. In this study we present a facile technique of coating graphene layers on cotton fibers, making them electrically conductive without compromising its mechanical properties. The electrically conductive cotton as apparel can be potentially used to monitor and analyze one&’s heart rate and breathing and cool down one&’s body on a hot summer's day. Scanning electron microscopy (SEM) was used to carry out morphological studies of the surface and interface of graphene layers and cotton fibers. An insulation resistance meter and a digital voltmeter were used to measure the electrical conductivity of pristine and the graphene coated cotton fibers respectively.
R4: Energy Conversion and Storage I
Wednesday AM, April 23, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14
9:00 AM - *R4.01
Nanochemistry Involved in Microbattery Fabrication for Remote Sensing and In-Situ Diagnosis
Jun Liu 1 Jie Xiao 1 Samuel Cartmell 1 Honghao Chen 1 Qiang Wang 1 Terence Lozano 1 Thomas Carlson 1 Daniel Deng 1 Jianzhi Hu 1
1Pacific Northwest National Laboratory Richland USAShow Abstract
PNNL is developing a new generation of micro-batteries based on lithium/ carbon monofluoride (Li/CFx with x = 1) chemistry. This talk will review the fundamental chemistry, engineering design and the applications of such micro-batteries. The project was motivated by the Juvenile Salmon Acoustic Telemetry System (JSATS) project supported by the U.S. Army Corps of Engineers, Portland District, to develop the smallest micro-acoustic transmitter commercially available to date. To study smaller fish and permit implantation by injection using a needle, the JSATS micro-acoustic transmitter was reduced in weight and volume. The micro-battery achieves a steady high-rate pulse current with required lifetime while significantly reduces the weight and volume. The newly designed micro-batteries have intrinsically lower impedance than the batteries currently used in JSATS transmitters, leading to significantly improved electrochemical performances within a wide operating temperature range from -5°C to 25°C. The high power, long life micro-batteries can have potential for many other applications and have been used as in-situ probe to understand the chemical transformations in advanced lithium batteries.
R6: Poster Session II: Energy Conversion and Storage
Wednesday PM, April 23, 2014
Marriott Marquis, Yerba Buena Level, Salons 8-9
9:00 AM - R6.01
Improvements in Organic Microstructures that Convert Light into Mechanical Motion
Lingyan Zhu 1 Rabih O. Al-Kaysi 2 Taehyung Kim 1 Christopher J. Bardeen 1
1University of California Riverside Riverside USA2King Saud bin Abdulaziz University for Health Sciences Riyadh Saudi ArabiaShow Abstract
Photovoltaic materials convert photon energy into stored electrical energy that can be used to generate mechanical work. Less attention has been paid to the direct conversion of light into mechanical work. Such photomechanical materials can be useful not only for solar energy conversion, but also as power sources for nanomachines. In order to harness photomechanical materials as power sources for nanomachines design, their photomechanical response needs to be (i) reversible, (ii) stable and (iii) fast. We have used molecular crystalline nanometer and micron-scale structures that absorb near ultraviolet and visible light and then execute well-defined motions such as twisting, bending and coiling. Examples include microribbons composed of 9-anthracenecarboxylic acid (9AC) that twist and untwist repeatedly under uniform illumination condition; and nanowires of dimethyl 2-(3-(anthracen-9-yl)allylidene)-malonate (DMAAM) that curl into tightly coiled bundles upon irradiation.
We recently began investigating fluorinated anthracene derivatives, which show significantly improved photomechanical response. Microneedles composed of 1-fluoro-9-anthracenecarboxylic acid (1F-9AC) respond 3~4 times faster than those composed of unsubstituted 9-anthracenecarboxylic acid (9AC) and have better photostability. The photo-induced motion can be repeated more than 100 times. These needles can do useful work, for example by moving heavy cubic NaCl crystals in viscous solution. Preliminary attempts to incorporate 1F-9AC crystalline microribbons into lipid bilayers in order to control their placement on surfaces will also be described. This work will aid in advancing the design of flexible energy conversion devices.
9:00 AM - R6.02
Graphene and Nanowire Optothermal Field Effect Transistors with Piezoelectric Substrates
Yang-Fang Chen 1 Chun-Yi Hsieh 1 Meng-Lin Lu 1 Ju-Ying Chen 1 Yung-Ting Chen 1 Wei-Jyun Tan 1 Wan Y. Shih 2 Wei-Heng Shih 3
1National Taiwan University Taipei Taiwan2Drexel University Philadelphia USA3Drexel University Philadelphia USAShow Abstract
We have developed two types of optothermal field effect transistors (FET) based on the pyroelectric effect of the piezoelectric substrates. The first example is a graphene-lead zirconate titanate (PZT) system.1 Under the incidence of an infrared (IR) laser beam, the drain current can be increased or decreased depending on the direction of the polarization of the PZT substrate. The drain current sensitivity of the optothermal FET can reach up to 360 nA/mW at a drain field of 6.7 kV/m more than 5 orders of magnitude higher than that of the photogating transistors based on carbon nanotube on SiO2/Si substrate. Graphene is an excellent component for pyroelectric FET due to its high optical transparency and conductance.
The second example is a composite consisting of single zinc oxide nanowire and lead zirconate titanate (ZnO NW-PZT).2 Under IR laser illumination, the transconductance of the ZnO NW can be modulated by optothermal gating. The drain current can be increased or decreased by IR illumination depending on the polarization orientation of the PbZr0:3Ti0:7O3 (PZT) substrate. Furthermore, by combining the photocurrent behavior in the UV range and the optothermal gating effect in the IR range, the wide spectrum of response of current to light offers a variety of opportunities for nanoscale optoelectronic devices.
1. C.-Y. Hsieh, Y.-T. Chen, W.-J. Tan, Y.-F. Chen, W. Y. Shih, and W.-H. Shih, “Graphene-PZT Optothermal Field Effect Transistors,” Appl. Phys. Lett., 100, 113507 (2012)
2. C.-Y. Hsieh, M.-L. Lu, J.-Y. Chen, Y.-T. Chen, Y.-F. Chen, W. Shih, and W.-H. Shih, "Single ZnO nanowire-PZT Optothermal Field Effect Transistors," Nanotechnology, 23, 355201 (2012)
9:00 AM - R6.03
Stretchable GaAs Solar Cells Using Transfer Printing Technique
Wonjung Choi 1 Sungjin Jo 1
1Kyungpook National University Daegu Republic of KoreaShow Abstract
We have fabricated stretchable GaAs solar cells using transfer printing technique. First, GaAs solar cell layers were grown on a GaAs wafer by metal organic vapor deposition(MOCVD) with AlAs sacrificial layer. For the separation of solar cell layers from GaAs wafer, AlAs sacrificial layer was selectively etched by diluted hydrogen fluoride solution. Because of high etching selectivity between GaAs solar cell layer and AlAs sacrificial layer, GaAs solar cells were separated from GaAs wafer without any damage. The GaAs solar cell layers separated by this epitaxial lift off technique were transfer printed onto the pre-strained substrate for the formation of noncoplanar interconnects. The microcell array with deformable interconnects can isolate the solar cell layers from strains that could cause fracture because the interconnects accommodate nearly all of the deformation. We observed photovoltaic characteristics of GaAs solar cells before and after transfer printing. Also, the mechanical properties of the stretchable solar cells were investigated using systematic stretching tests.
9:00 AM - R6.04
Controlled Growth of NiCo2O4 1D, 2D and Hybrid Nanostructures on Various Substrates as Binder-Free Electrodes for High Performance Supercapacitors
Genqiang Zhang 1
1TUM-CREATE Centre for Electromobility Singapore SingaporeShow Abstract
Supercapacitors have been considered as one of the most promising energy storage devices because of their many advantages including high power density, faster charge/discharge process and longer lifespan Unfortunately, the practical applications of supercapacitors are largely hindered due to the lack of high-performance electrode materials at a reasonable cost. The development of nanostructured materials, especially metal oxides, will undoubtedly provide a promising solution to enhance the capacitive performance because of their high surface area, short electron and ion transport pathways. At the same time, it is also noted that the poor intrinsic conductivity of these oxide materials, extra contact resistance and increased “dead surface” due to the introduction of conductive agent and polymer binder during the conventional thin film electrode preparation still seriously limit their performance. Recently, an emerging new concept is to grow electroactive nanostructures on conductive substrates to be directly used as integrated electrodes for supercapacitors, which could solve the above mentioned problems.In this work, different NiCo2O4 nanostructures including nanowires, hybrid nanowires and mesoporous nanosheets can be successfully grown on various conductive substrates including Ni foam, Ti foil, stainless steel foil and flexible graphic papers, with simple low temperature and environmentally friendly solution methods. The supercapacitive performance of these structures is investigated in details.
From the comparison of their supercapacitive performance, it is notable that the NiCo2O4 mesoporous nanosheets-Ni foam architecture exhibits the best, wich both higher areal capacitance and better cycling stability. The possible reasons could be related to the structural features of the architecture: First, the mesoporous feature of the NiCo2O4 nanosheets largely increases the amount of electroactive sites. In addition, the highly porous film structure formed by the interconnected nanosheets greatly facilitates transport of the electrolyte. Furthermore, the direct growth of interconnected two-dimensional nanosheets on conductive substrate could ensure good mechanical adhesion, and more importantly good electrical contact with the conductive substrate that also serves as the current collector in such highly integrated electrodes. The FESEM images of the NiCo2O4 mesoporous nanosheets after charging/discharging for 3000 cycles at a high current density of 25 mA/cm2 indicate that the morphology and structure of the nanosheets are well retained except for the increased roughness on the nanosheet surface, caused by the high rate redox reactions during the repeated charge/discharge processes.
9:00 AM - R6.05
Super-Flexible Ionic Polymer Gel Based Nanocomposite Generator
Sung Yun Chung 1 Jieun Ko 1 Jeeyoung Yoo 1 Zhenxing Yin 1 Youn Sang Kim 1 2
1Seoul National University Seoul Republic of Korea2Advanced Institutes of Convergence Technology Suwon Republic of KoreaShow Abstract
Energy harvesting nanotechniques have been remarkably developed for last five years for micro/nano-power devices and self-powered sensor systems. The miniaturized micro/nano devices can generate electrical power in various mechanism based on piezoelectric, pyroelectric, electromagnetic and triboelectric effects. On the other hand, the energy storage system for the created electricity from the nanounits is significant issue for continuous and practical energy generation devices. Accordingly, energy units, which simultaneous convert and storage electrical power will be significant prospects for the future energy harvesters. Alternately, ionic liquids associated electrochemical systems for energy scavenging and storage are ideal for this purpose.
Ionic liquids are defined as liquids composed entirely of ions in fluid form. The ionic liquids are utilized in wide range of applications such as lithium batteries, fuel cells, supercapacitors and electromechanical actuators as electron-conducting materials. Among those applications, the electromechanical actuators show a strain deformation in the device under stimulus of an applied voltage. However, the reverse effect of the electrical unit under the mechanical strain then may leads to energy creation using the ion liquid based electrochemical transducers.
Flexibility and stretchability of energy harvesters are also important features for body-movement-driven-devices such as artificial muscles, wearable human patches and electronic cloth. Recently, several researches on flexible nanocomposite based generators have been demonstrated for energy generation with high flexibility.
In this work, the ionic polymer gel was adopted as an electron-conducting polymer to fabricate a nanocomposite generator which convert mechanical energy into electrochemical energy. The nanocomposite consists of the ionic liquid 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, [EMI]-[TFSI], in polymer matrix for flexibility and transformability to any distortionally bent changes. As-fabricated nanocomposite based energy harvesting cell acts as a transducer which can convert and store electrical power based on electrochemical potential difference and electrostatical energy strorage system. This approach suggests new operation mechanism in energy harvesting technique with a strong advantage to the energy charging system.
This highly flexible nanocomposite generator is versatile to acquire irregular or random mechanical energy sources from variable environmental conditions for self-powering biomechanical applications such as artificial muscles and wearable human patches and electronic cloth.
9:00 AM - R6.06
Superhydrophobic Sponge-Structured Triboelectric Nanogenerator for Sustainable Energy Harvesting
Jinsung Chun 1 Keun Young Lee 2 Joonmo Park 1 Sang-Woo Kim 2 Jeong Min Baik 1
1Ulsan National Institute of Science and Technology Ulsan Republic of Korea2Sungkyunkwan University Suwon Republic of KoreaShow Abstract
Harvesting energy from the ambient mechanical energy sources are highly desirable for powering portable electronics, biomedical, and healthcare applications. Recently, a new type of power generating device based on triboelectric effects coupled with electrostatic effects have been demonstrated to be a powerful means of harvesting the mechanical energy. However, most of such triboelectric generators required sophisticated design and a high degree of integration. Nanoparticles and nanowires-based generators is also likely to deform and degrade under large applied force. Here, we present a new type of triboelectric generator structure based on an inverse opal structured film, named as a sponge film. The sponge film becomes more flexible than the flat film, increasing the contact area and the capacitance by the increase in effective ε/d value under the same force. Not only triboelectric charges on both the contacting surfaces but also additional charges on inner pore surfaces by the electrostatic induction may help to enhance the electrical output performance. Thus, the sponge-structured generators show large output power of approximately 4.8 mW /cm2, giving over 10-fold enhancement compared with the flat film. In addition, by coating more hydrophobic Teflon layer on the surface of the sponge-structured film as well as the surface of inner pores, we will show that the generator is less sensitive to the humidity.
9:00 AM - R6.07
The Novel Low Band Gap Conjugated Polymer Based on Alkoxysubstituted-MBI Units for Organic Photovoltaic Cells
Joo Young Shim 1 Tae-hyo Kim 2 Juae Kim 1 Jinwoo Kim 1 Jin Young Kim 2 Hongsuk Suh 1
1Pusan National University Busan Republic of Korea2Ulsan National Institute of Science and Technology Ulsan Republic of KoreaShow Abstract
The research for the achievement of efficient organic photovoltaics (OPVs) has become one of the most popular topics in recent years caused by their potential to be analternative source of green energy. Polymer solar cells have many desirable features including large-scale fabrication utilizing low cost solution processability. The development of novel materials is necessary to enhance the coverage of the solar spectrum and the absorption coefficients, which can improve the lower power conversion efficiency and smaller photo current as compared to the case of inorganic solar cells. The HOMO energy level of the donor, such as low band gap conjugated polymer, and the LUMO energy level of the acceptor, PCBM, needs to be optimized to maximize the attainable open circuit voltage (Voc)
Main chain donorminus;acceptor (Dminus;A) alternating design is a very efficient way to tune the absorption and energy level of conjugated polymers through the intramolecular charge transfer from donor to acceptor unit. In this work Dioctyloxy substituted dimethyl-2H-benzimidazole (DOMBI) was prepared and copolymerized with thiophene (or bithiophene) and carbazole using both Stille and Suzuki polymerization. In DOMBI, the sulfur at 2-position of BT unit was replaced with dialkyl substituted carbon and dioctyloxy groups were introduced at 5,6-position of MBI unit. In addition to this, dioctyloxy groups on 5,6-position will improve the absorption at the longer wavelength region. The devices with PTDOMBI with PC71BM showed VOC value of 0.58 V, JSC value of 4.03 mA/cm2, and FF of 0.32 giving power conversion efficiency of 0.76%.
9:00 AM - R6.08
The Influence of Electrode and Separator Thickness on the Cell Resistance of Cellulose/Polypyrrole Composite-Based Energy Storage Devices
Nils Petter Valtteri Tammela 1 Henrik Olsson 1 Zhao-hui Wang 2 Martin Sjodin 1 Maria Stramp;#248;mme 1 Leif Nyholm 2
1Engineering Sciences Uppsala Sweden2Department of Chemistry - The amp;#197;ngstramp;#246;m Laboratory Uppsala SwedenShow Abstract
There is currently a strong need for development of inexpensive, flexible, light-weight and environmentally friendly energy storage devices . As a result of this, research is carried out to develop versatile and flexible electrode materials as a complement to the materials used in contemporary batteries and supercapacitors. This has resulted in an increased interest in electronically conducting polymers as it is well-known [2, 3] that these materials can be used to manufacture all-polymer-based batteries and supercapacitors. The latter devices, however, generally suffer from problems due to low capacities, low charging rates, poor cycling stability and rapid self-discharge . Possible approaches to circumvent, at least some of these problems, involve the use of composites comprising conducting polymers and carbon nanotubes  or nanocellulose .
We have shown  that flexible cellulose and polypyrrole composites, obtained by chemical polymerization of pyrrole on a cellulose substrate derived from the Cladophora sp. algae, can be used as paper-based electrode materials for environmental friendly charge storage devices. As these types of devices exhibit good cycling stability even at high charge and discharge rates, this type of devices provide exciting possibilities for the development of green and foldable devices as well as for a range of new applications which are incompatible with conventional batteries and supercapacitors.
This presentation will focus on the results of our recent research concerning the cell resistance of polypyrrole and cellulose composite based charge storage devices. It will be shown that this cell resistance is influenced by both the thickness of the polypyrrole/cellulose composite and that of the separator. The influence of the porosity of the separator, and the contact resistances between the current collectors and the composite, on the cell resistance, as well as the possibilities of designing inexpensive all-organic energy storage devices with promising performance regarding cycling stability and rate capability will also be discussed.
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9:00 AM - R6.09
Benzodithiophene-Based Low-Band Gap Small Molecule for Organic Solar Cell
Juae Kim 1 Joo Young Shim 1 Jinwoo Kim 1 Hongsuk Suh 1
1Pusan National University Busan Republic of KoreaShow Abstract
Organic photovoltaic (OPV) devices provide a offer great opportunities as renewable energy sources. The design and synthesis of low-bandgap polymers for use as electron donor materials for bulk heterojunction (BHJ) have attracted remarkable attention. A series of new donor-acceptor π-conjugated small molecules incorporating benzodithiophene(BDT) as an electron donating unit have designed and synthesized in solar cells with phenanthrothiadiazole(PT) and dimethyl-2H-benzimidazole(MBI) as the electron accepting unit. The DBDTPT and DBDTMBI, were synthesized by stille reaction and evaluated in OPVs. The DBDTPT shows absorption band with maximum peak at about 361 nm in solution. The HOMO and LUMO levels of DBDTPT were exhibited at -5.46 and -3.65 eV, respectively. The small molecule has good thermal stability. The HOMO-LUMO energy bandgaps of this material shows 1.81 eV for DBDTPT.
9:00 AM - R6.10
Enhanced Light Out-Coupling of Organic Light Emitting Diodes on Conductive Transparent Silver Nanowires Electrodes
Bola Lee 1 Sungjun Kim 1 Illhwan Lee 1 Jong-Lam Lee 1
1pohang university Pohang Republic of KoreaShow Abstract
Indium tin oxide (ITO) and Al-doped zinc oxide are generally used for transparent conductive electrodes, but they have a number of weakness. Sputtering to produce such metal oxide thin films is not only too expensive in cost, but also fragility of the film cracking when the substrate is bent, leading to device malfunction. Silver nanowires (Ag NWs) have emerged as one of the most promising alternative for a traditional metal-oxide transparent electrode such as ITO, because they suggest optical transmittance and surface resistivity identical to their contenders. However, previous work does not fully exploit the superior properties to that of control devices on ITO substrates.
In this work, we present a novel way of preparing highly transparent and conductive Ag NWs electrodes using mayer rod method, which shows enhanced device performance compared to device using ITO electrodes. The sheet resistance of Ag NW film on a substrate is 20-50 Omega;/sq. Within the spectrum range from 400 to 800 nm, the optical transmittance is over 86% for lambda; >480 nm. The device can be fabricated by the direct deposition of small molecular weight organic materials and a metal cathode on the Ag NWs anodes. The devices using Ag NWs results in an enhancement of the luminance value at least 10% compared to that from a conventional OLED on ITO substrates.
9:00 AM - R6.12
Stretching and Conformal Bonding of Organic Solar Cells to Hemispherical Surfaces
Timothy F. O'Connor 1 Aliaksandr V. Zaretski 1 Bijan A. Shiravi 1 Suchol Savagatrup 1 Adam D. Printz 1 Mare Ivana Diaz 1 Darren J. Lipomi 1
1University of Californai, San Diego San Diego USAShow Abstract
Herein we describe the stretching and conformal bonding (i.e., decal-transfer printing) of organic solar cells in both the “conventional” and “inverted” configurations to hemispherical glass surfaces with radii of 8 mm. This action produces equivalent biaxial tensile strains of 24%, which many materials used in organic electronic devices cannot accommodate without fracture. Consideration of the mechanical properties of conjugated polymers reveals a surprising effect of a single structural parameter—the length of the alkyl side chain—on the elasticity and ductility of regioregular polythiophene. This analysis enables selection of materials that can accommodate sufficient tensile strain for non-planar applications. For polymer-fullerene solar cells, devices based on the elastic and ductile poly(3-octylthiophene) (P3OT) exhibit typical photovoltaic properties when bonded to hemispherical glass substrates, while those based on the relatively brittle poly(3-hexylthiophene) (P3HT) exhibit extensive cracking, which degrades the photovoltaic effect significantly. The results suggest that mechanical properties should be taken into account when designing and selecting organic semiconductors for applications that demand significant deformation.
9:00 AM - R6.13
Flexoelectric Response in Ferroelectric and Relaxor Polymers
Shashi Poddar 1 2 Stephen Ducharme 1 2
1University of Nebraska Lincoln USA2University of Nebraska Lincoln USAShow Abstract
Unlike piezoelectric polarization change, which is caused by the stress, the flexoelectric polarization change is caused by the strain gradient. The crystal non-centrosymmetry requirement essential for piezoelectric response is replaced by the non-centrosymmetry of the sample geometry as long as the sizes involved are small enough to make the flexoelectric response appreciable. Tagantsev estimated the flexoelectric coefficient µ, the ratio of the induced polarization to the strain gradient in ionic crystals, to be of order ke/a, where k is the dielectric constant, and e/a asymp; 0.4 nC/m, the ratio of the ionic charge to the lattice constant.
In our studies, we investigated the flexoelectric response in ferroelectric copolymers of vinylidene fluoride with trifluoroethylene (VDF-TrFE) and relaxor terpolymers of VDF-TrFE with chlorotrifluoroethylene. By using a simple cantilever measurement technique, while monitoring remanent polarization through the pyroelectric response, we are able to measure the flexoelectric response in thin films and isolate and correct for piezoelectric contributions, which would otherwise dominate the flexoelectric measurements. The upper limit for the flexoelectric coefficient of the copolymer P(VDF-TrFE) was mu; le; 191 ± 17 nC/m in the ferroelectric phase and µ = 18 ± 1 nC/m in the paraelectric phase. The relaxor terpolymer P(CVDF-TrFE-CTFE) had µ = 30 ± 1.5 nC/m at room temperature. Temperature-dependent studies were also carried out to better understand the origin of the flexoelectric response. In the case of the relaxor terpolymer, the flexoelectric signal as a function of temperature scaled very closely with the dielectric constant, as has been proposed in the case of oxide ferroelectrics. To further reduce the piezoelectric response in the copolymer, we cooled samples at zero field to reduce the remnant polarization to less than 2% of its maximum value. Even with this there is still a residual piezoelectric contribution to the overall signal. These studies are aimed to harvest the flexoelectric energy as an alternative to piezoelectric analogues.
9:00 AM - R6.14
Design of a Printed and Flexible Solar Energy Harvesting Device with Integrated Power Conversion and Storage
Aminy E. Ostfeld 1 Abhinav Gaikwad 1 Ana Claudia Arias 1
1University of California, Berkeley Berkeley USAShow Abstract
Most applications of non-grid-connected solar modules require battery storage and power electronics for maximum power point tracking and battery charge control. Although flexible solar modules, flexible batteries, and flexible electronic circuits have each been extensively studied and optimized, they are typically fabricated separately, and power conversion circuits used for solar energy harvesting usually consist of conventional electronic components mounted on a rigid printed circuit board. Compared to subtractive processes such as printed circuit board etching and photolithography, additive printing processes for electronic device fabrication can reduce materials waste and process complexity. Additive processes also allow a diversity of devices to be fabricated on the same substrate in a single production line. Furthermore, since multiple components of a solar energy harvesting system require similar materials functionalities, such as metal contacts and interconnects, each printing pass could be used to deposit layers of multiple components at the same time. Thus, printing offers great potential for high-throughput and low-cost production of integrated solar energy harvesting and storage systems. We have fabricated flexible photovoltaics, batteries, capacitors, resistors and inductors using a variety of scalable printing techniques compatible with roll-to-roll or sheet-by-sheet fabrication processes. We present a strategy for production of multiple types of passive components simultaneously on the same substrate, and a design for a solar sheet in which a printed solar module, battery and power electronics are integrated together into a single flexible piece.
9:00 AM - R6.15
High Transparency Display Privacy Filter Using Image Distortion
Jin-Ha Kim 1 2 Hun K. Im 1 Seung S. Lee 1 Kwang-Cheol Lee 2
1Korea Advanced Institute f Science and Technology Daejeon Republic of Korea2Korea Research Institute of Standards and Science Daejeon Republic of KoreaShow Abstract
In this paper, we propose a novel privacy filter to prevent disclosure of personal information, while maintaining the high transmittance. Transparent vertical array structure was introduced given that it distorts the image by refraction and total reflection . In contrast to the conventional display privacy filter which significantly decreases normal transmittance , the proposed privacy filter rarely affects the normal transmittance as it does not include the opaque material. To confirm the feasibility of our model, transparent cubic structure with refractive index of 1.5 was analyzed using lay tracing method . It was found that the refraction and reflection of obliquely incident light in the transparent cubic structure result in the copy, displacement, and loss of the image, yielding distortion of image. Further, this simulation results were confirmed with the actual test results conducted with PDMS (1.4 cm x 1.4 cm x 1.8 cm) vertical array structure.
Finally, the privacy filter film which is the array of transparent PDMS vertical structure (100 mu;m x 100 mu;m x 200 mu;m) was fabricated by MEMS technology . The privacy filter film on the smart phone rarely influenced the display in the normal direction whereas clear recognition of the texts was unachievable when looking from the side. Thus, the suggested privacy filter is well-suited for the mobile display device given that it provides high transmittance and it requires simple fabrication process which can lead to mass production.
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9:00 AM - R6.16
Use of Layer-by-Layer Assembled MWNT/Mn3O4 Nanocomposite Electrodes in High Performance All-Solid-State Flexible Micro-Supercapacitor
Geumbee Lee 1 Daeil Kim 2 Junyeong Yun 2 Jeong Sook Ha 1 2
1Korea University Seoul Republic of Korea2Korea University Seoul Republic of KoreaShow Abstract
Supercapacitors as electrical energy storage devices have exhibited a high power density but a low energy density compared to batteries. In order to improve rather poor energy density of supercapacitors, various pseudocapacitve metal oxides have been actively investigated. Among those metal oxides, manganese oxide has attracted extensive interest owing to its advantages such as cost-efficiency, high energy capacity, natural abundance, and environmentally friendly property. However, the low electrical conductivity of manganese oxide limited its use as electrode materials to be combined with highly conductive carbon-based materials including carbon nanotubes
In this study, we report on the fabrication of planar-type flexible micro-supercapacitors (MSCs) using Au electrodes coated with MWNT film and the top-most layer of MWNT/Mn3O4 nanoparticle (NP) composite. MWNT thin film was formed via layer-by-layer (LBL) assembly of MWNTs functionalized with amine group and MWNTs with carboxyl group in water, and the hydrothermally synthesized composite of MWNT/Mn3O4 NP was coated on top of the MWNT film. In the planar-type MSC, the ion-channel length was 150 mu;m. By using PVA-H3PO4 gel electrolyte, the fabricated MSCs worked in the potential between 0 and 0.8 V. The addition of the top layer MWNT/Mn3O4 NP composite enhanced the performance of the MSCs dramatically to give a volumetric capacitance of 38.8 F/cm3 at scan rate of 10 mV/s and the Coulomb efficiency of ~100%: the volumetric capacitance of 2.8 F/cm3 was obtained in case of using just MWNT film. Even after the repetitive operation by 10^4 times, the capacitance remained ~88.3% of the original value.
MSC arrays fabricated on a PET film showed stable electrochemical properties upon 1,000 times bending with both compressive and tensile stress. Furthermore, we could increase the output voltage and the capacitance by deliberately designing the circuit of MSC arrays, which could operate various active nano-devices.
9:00 AM - R6.17
Flexible Energy-Storage Materials for The Integration of Flexible Electronics
Kyung M. Choi 1
1University of California Irvine USAShow Abstract
A novel sol-gel condition that produces a highly compressed organic/inorganic hybrid glass has been discovered. The compressed sol-gel glass was based on alkylene-bridged polysilsesquioxane doped with chromium. The sol-gel thin film prepared under a novel acidic condition has shown a low thermal conductivity and a high compressibility. Interestingly, the highly compressed hybrid glass also showed a strong ‘acoustic response&’ as strong as liquid. Usually, when the laser beam goes through a solid medium, the density wave is linear; because, in solid media, heat doesn&’t decay through the solid medium effectively. The acoustic response generated from the novel glass was as compressive as liquid. In laser experiments, we calculated ‘coefficient of phonon diffraction (D),&’ which was proportional to the coefficient of thermal conductivity. The number (D) of the novel glass was FIVE times smaller than that of a normal glass; the thermal conductivity of the novel glass was FIVE times less than that of a normal glass. Due to its low thermal conductivity, the sol-gel film serves like a ‘HEAT GENERATOR (ENERGY-STORAGE MATERIAL)&’; the heat gets transferred into expansion or compression wave effectively. This is a new concept that could bring novel energy storage materials with a good optical clarity. It can also be fabricated on a variety of substrates and thus can be used for flexible electronics, including flexible energy-storage, energy conversion, and optically transparent energy devices.
9:00 AM - R6.18
Direct Synthesis of TiO2 Nanorod Arrays on Ti Foil for Flexible Supercapacitor Application
Zhi Zheng 1 Jiajun Chen 1 Weilie Zhou 1
1University of New Orleans New Orleans USAShow Abstract
Flexible energy storage devices have received tremendous interest recently due to the increasing demand for sustainable and renewable energy in modern electronic industry. In this study, TiO2 nanorod arrays grown directly on Ti foil were prepared by a facile one-step wet chemical synthesis process. The morphology and microstructures of the as-prepared samples were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. By using a three-electrode system, the electrochemical properties of the TiO2 nanorod arrays are systematically investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy tests. The TiO2 nanorod arrays showed a good specific capacitance and exhibited excellent cycle life by retaining more than 98% of the initial specific capacitance after 1000 cycles. The growth mechanism of these TiO2 nanorod arrays will be discussed in the presentation.
9:00 AM - R6.19
Ferroelectric Effect on Energy Level Offset in P3HT/ZnO Photovoltaic Devices with Self-Assembled P(VDF-TrFE)
Kyung-Sik Shin 1 Tae Yun Kim 2 Gyu Cheol Yoon 1 Manoj Kumar Gupta 1 Sung Kyun Kim 2 Sang-Woo Kim 1 2
1Sungkyunkwan University Suwon Republic of Korea2Sungkyunkwan University Suwon Republic of KoreaShow Abstract
The interfacial properties of semiconducting materials are important to establish the working mechanisms of optoelectronic devices as well as to improve their performance. The electronic structure at an interface could strongly depend on how the materials make contact with each other, which in turn is governed by many factors such as interfacial dipole moments induced by the molecular orientation and electronic coupling of the materials. Accordingly, it is necessary to investigate that how the properties of p/n interfaces influence device performance under conditions that more closely resemble those of an actual device. Well-defined bilayer structures could be more suitable for the fundamental investigation of p/n (or donor/acceptor) interfaces in organic optoelectronics. However, the bilayer devices composed of organic donor/acceptor materials often induce diffusion and intermixing of the donor and acceptor molecules at the interface by application of heat and pressure during transfer the films. Therefore, to investigate the relation between their structure and device performance, novel architectures with well-defined interfaces are needed.
Here we fabricated the novel architecture of self-assembled P(VDF-TrFE):P3HT-composited photoactive layer that consists of P3HT domain in P(VDF-TrFE) matrix for hybrid photovoltaic devices (HPDs) and demonstrated the ferroelectric effect on photovoltaic behavior and energy band tuning at donor-acceptor interface. The P(VDF-TrFE):P3HT/ZnO-device exhibits the enhanced diode behavior and photovoltaic characteristics as compared to the P3HT:ZnO HPD. Further, VOC has been tuned by control application of forward and reversed external electric fields in HPD. These dramatic changes in photovoltaic behavior depending on the poling process indicate that photovoltaic performance can be enhanced by the artificial control of dipole moments in ferroelectric materials, leading to additional driving force for charge extraction and the change in the energy band at donor-acceptor interface of HPDs.
R4: Energy Conversion and Storage I
Wednesday AM, April 23, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14