Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G25: Focus Session: Organic Electronics and Photonics - Novel Devices and Fabrication |
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Sponsoring Units: DMP Chair: David Gundlach, National Institute of Standards and Technology Room: 503 |
Tuesday, March 4, 2014 11:15AM - 11:27AM |
G25.00001: Solution Processable Electrochemiluminescent Ion Gels for Flexible, Low Voltage, Emissive Displays on Plastic Hong Chul Moon, Timothy P. Lodge, C. Daniel Frisbie We have expanded the functionality of ion gels and successfully demonstrated low voltage, flexible electrochemiluminescent (ECL) devices using patterned ECL gels. An ECL device composed of only an emissive gel and two electrodes was fabricated on an ITO-coated substrate by solution casting the ECL gel and brush-painting the top silver electrode. The device turned on at an AC voltage as low as 2.6 V ($-$1.3 V $\sim$ $+$1.3 V) and showed a relatively rapid response (sub-ms). Also, we varied the mechanical properties of the ECL gel simply by substituting polystyrene-block-poly(methyl methacrylate)-block-polystyrene (SMS) with commercially available poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)), enabling the fabrication of flexible ECL devices on any target substrate by the ``cut-and-stick'' strategy. This simple, rubbery ECL gel should be attractive for flexible electronics applications such as displays on packaging. [Preview Abstract] |
Tuesday, March 4, 2014 11:27AM - 11:39AM |
G25.00002: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 11:39AM - 11:51AM |
G25.00003: Charge-extraction analysis of organic and inorganic dielectrics for organic field-effect transistors Josue Martinez Hardigree, Thomas Dawidczyk, Mathias Nyman, Ronald Osterbacka, Howard Katz Organic field-effect transistors (OFETs) offer the promise of low-power, inexpensively-processed electronic devices. However, high threshold voltages (Vt) required for operation and poor Vt stability due to gate bias stress in OFETs has limited their adoption in high duty-cycle applications such as display technology. Herein we employ the charge extraction in a linearly-increasing voltage (CELIV) method to investigate the Vt stability of polarized gate dielectrics consisting of pristine and polarized polystyrene (PS) and perfluorinated polystyrene (F-PS). CELIV measurements were carried out on representative gate stacks analogous to previously-investigated p-type OFETs (J. Appl. Phys. doi: 10.1063/1.1427136). We compare CELIV transients of pristine and polarized polystyrene (PS) and perfluorinated polystyrene (F-PS) dielectrics in representative pentacene OFET gate stacks, correlating transient differences and Vt stability to the observed surface potential measurements of lateral OFETs fabricated using a recently-developed method (Appl. Phys. Lett., doi: 10.1063/1.3684977). [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G25.00004: Enhanced performance of ferroelectric-based all organic transistors and capacitors through choice of solvent Grant Knotts, Anagh Bhaumik, Kartik Ghosh, Suchismita Guha We examine the role of solvents in the performance of pentacene devices using the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFe) as a gate insulating layer. High dipole moment solvents such as dimethyl sulfoxide used to dissolve the copolymer for spin casting increase the charge carrier mobility in field-effect transistors by nearly an order of magnitude as compared to lower dipole moment solvents. The polarization in Al/PVDF-TrFe/Au metal-ferroelectric-metal devices is also investigated. An increase in remnant polarization of $\sim$ 20{\%} is observed in the sample using dimethyl sulfoxide as the ferroelectric solvent. Interestingly, at low applied electric fields of $\sim$ 100 MV/m a remnant polarization is seen in the high dipole moment device that is nearly 3.5 times larger than the value observed in the lower dipole moment samples, suggesting that the degree of dipolar order is higher at low operating voltages for the high dipole moment device. Detailed analysis of the capacitance characteristics of metal-insulator-semiconductor structure is performed. The density of interface trap states is nearly an order of magnitude lower for the high dipole moment device. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G25.00005: Micro-processing of Hybrid Field-Effect Transistor Arrays using Picosecond Lasers Robert Ireland, Yu Liu, Josef Spalenka, Supriya Jaiswal, Shingo Oishi, Kenshi Fukumitsu, Mochizuki Ryosuke, Padma Gopalan, Paul Evans, Howard Katz We use a solid-state picosecond laser to pattern thin-film semiconductors that completely cover a substrate and utilize an array of top-contact electrodes, particularly for materials with high chemical sensitivity or resistance. Picosecond laser processing is fully data-driven, both thermally and mechanically non-invasive, and exploits highly localized non-linear optical effects. We investigate FETs comprised of p-channel tellurium and organic semiconductor molecules sequentially vapor-deposited onto Si/SiO$_{2}$ substrates. Secondly, zinc oxide and zinc-tin oxide are used for high mobility n-channel FETs, cast onto Si/SiO$_{2}$ by sol-gel method. Finally, zinc oxide FETs are prepared as photomodulatable devices using rhenium bipyridine as a light-sensitive electron-donating molecule. The laser effectively isolates FETs while charge carrier mobility is maintained, but leakage currents through the FET dielectric are drastically reduced, and other functions are enhanced. For instance, the ratio of measured gate current to photocurrent for photomodulatable FETs drops from a factor of five to zero after laser isolation, in both forward and reverse bias. We also observe a threshold voltage shift in organic semiconductors after laser isolation, possibly due to local charging effects. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G25.00006: Investigating Organic Field Effect Transistors with Reduced Graphene Oxide Electrodes of Different Reduction Efficiency Narae Kang, Saiful I. Khondaker Organic field-effect transistors (OFETs) have received much attention owing to their flexibility, transparency, and low-cost of fabrication. One of the major limiting factors in fabricating high-performance OFET is the large injection barrier at metal electrodes/organic semiconductor interface, which results in low charge injection from metal electrodes to organic semiconductor. Graphene has been suggested as an alternative electrode material due to its high work function, extraordinary electronic properties and strong $\pi $-$\pi $ interaction with organic molecule; all of which can reduce the injection barrier at the electrode/organic interface. In particular, due to its solubility, large scale production, and its chemical functionality, reduced graphene oxide (RGO) has been introduced as a promising electrode for OFETs. Its tunability of electrical and optical properties can make RGO a highly desired electrode material because the work function match is essential for better charge injection at electrode/organic interface. In this talk, we will discuss the fabrication of OFETs with RGO of different reduction efficiency as an electrode material. We will also present the electrical transport properties fabricated devices. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G25.00007: Effect of device geometry on organic electrochemical transistor switching speeds Jacob Friedlein, Robert McLeod, Sean Shaheen It has been demonstrated that redox switching of PEDOT:PSS can be used as the basis for the modulation of channel current in organic electrochemical transistors (OECTs). In this work, we examine the response time of OECTs with different geometries and electrolyte compositions. In particular, we demonstrate which OECT dimensions (thickness, channel length, channel width, and gate-channel distance) have the strongest influence on switching speed and how the switching speed scales with these dimensions. We fabricate our OECTs on glass with evaporated gold electrodes. The PEDOT:PSS is spin-cast to form an approximately 100 nm film. OECT channels are defined by subtractively patterning the PEDOT:PSS film using a microcutter, and the electrolyte is printed from solution using a microcontact printing platform (for solid-state electrolytes) or drop cast (for liquid electrolytes). We characterize these devices with drain voltages $\sim$ 100 mV and gate voltages of $\sim$ 2 V, and we typically obtain drain currents of $\sim$ 50 $\mu$A with ON/OFF ratios up to 100 and switching times of 10 -- 1000 s. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G25.00008: A Facile Approach for P3HT/ZnO hybrid Synthesis for Solar Cell Application Chi-An Dai, Yi-Huan Lee, Yu-Ping Lee, Yang-Hui Yang, Leeyih Wang The fabrication of organic/inorganic hybrid materials based on conducting polymers and semiconducting nanoparticles has gathered great attentions recently due to its potential applications in renewable energy such as solar cells. However, problems occur as the two pre-synthesized materials are mixed since the resulting hybrids typically undergo macrophase separation with increasing nanoparticle loadings, leading to reduced charge separation and transport. To this end, a number of methods have been pursued to achieve a favorable dispersion of nanoparticles in hybrid solar cells. In this study, we have developed an in-situ synthesis method followed by a heating treatment to grow highly elongated P3HT/ZnO nanofibrils. The optoelectronic property and the solar cell performance of the resulting hybrid will be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G25.00009: Assembly of Hybrid Solar Cells: Polythiophene Wrapped CdSe Nanorods Sirinya Chantarak, Todd Emrick, Thomas P. Russell We prepared cadmium selenide nanorods (CdSe NRs) covered with three types of polythiophenes: poly(3-hexylthiol thiophene), poly(3-hexylamine thiophene), and poly(3-hexylphosphonate thiophene) with thiol, amine, and phosphonate functional groups, respectively, to anchor to the nanorods. This led to a thin layer of p-type conducting polymer covering the n-type inorganic nanorods. A vertically-oriented assembly of polythiophene-functionalized CdSe NRs on a conducting substrate was obtained with the use of an applied electric field. Ternary nanocomposites of CdSe-polythiophene-graphene were obtained via $\pi $-$\pi $ stacking. These oriented CdSe NRs-polythiophenes nanocomposites y potential applications in hybrid photovoltaic devices. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G25.00010: Morphology control of phase separated ferroelectric-semiconductor polymer blends for organic memory Gregory Su, Andrew Jacobs, Edward Kramer, Michael Chabinyc The ability to store memory is essential for many electronic applications. All-organic memory devices based on a blend of a ferroelectric polymer and a semiconducting polymer have recently shown great promise for low-cost memory technology based on ferroelectricity. The thin film morphology of the phase separated ferroelectric-semiconductor polymer blend is critically important for working devices and improved operation. However, precise morphology control has so far been relatively unattainable. Here, we report on a new semiconducting polythiophene with a modified side chain structure (PEPT) that demonstrates a greatly improved phase separated morphology with the well-studied ferroelectric polymer poly[(vinylidenefluoride-co-trifluoroethylene] (PVDF-TrFE). Thin film surface and bulk characterization via microscopy, soft X-ray spectroscopy, and X-ray scattering experiments reveal that PEPT:PVDF-TrFE blends exhibit domain sizes that are easily tunable through simple parameters such as blend ratio. These results demonstrate progress toward achieving organic ferroelectric-semiconductor memory with optimized morphology and the techniques required for thorough thin film surface and bulk characterization. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G25.00011: Progress Toward Tunable White Light-Emitting Electrochemical Cells Tyko Shoji, Amanda Norell Bader, Janelle Leger The high photoluminescence efficiency, narrow emission peaks, and size-tunable band gaps of quantum dots (QDs) make them attractive for application to light emitting devices. However, charge injection barriers due to the insulating surface ligands of QDs often result in undesired emission from the polymer host material. Additionally, typical QD devices have also suffered from voltage-dependent emission color, most likely caused by shifts in the emission zone under different applied voltages. One promising approach to addressing these issues is through the incorporation of QDs in a single layer light-emitting electrochemical cell (LEC). In the generally accepted model of LEC operation, an analog of a self-assembled p{\-}i{\-}n junction forms under an applied bias. The homogenous blend of QDs throughout the polymer ensures a consistent concentration of QDs in the emission zone despite recombination zone shifts during operation. Light emission occurs within a thin intrinsic region, facilitating QD emission and limiting emission from the polymer host. Our group has demonstrated precise color-tunable emission in QD LECs by adjusting the mass ratios of two different quantum dots blended in a single LEC. We discuss our progress in extending these results to the development of white light-emitting QD LECs. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G25.00012: Normally-ON and Normally-OFF Carbon Nanotube-based Ionic-Liquid Supercapacitor-Gated Vertical Organic Field-Effect Transistors Jonathan Yuen, Alexander Cook, Julia Bykova, Vidisha Srivastav, Joseph Micheli, Anvar Zakhidov We report on novel implementations of the vertical organic field effect transistor (VOFET). Instead of a typical capacitor below the organic diode, a carbon nanotube (CNT) based ionic-liquid supercapacitor (or ionic gate) is on top. The present work has been motivated by the discovery that the conductivity and work function of carbon nanotubes can be strongly modified by electric double layer charging (EDLC) in an electrolyte as much as $+$/-0.7eV. The conductivity of EDLC CNT is enhanced by a factor of two. By coupling the ionic gate with an organic diode, charge injection into the diode can be controlled via modulation of the workfunction of the CNT electrode, resulting in transistor-like behavior. Additionally, the high capacitance of the supercapacitor will enable the VOFET to be operated at low voltages. The entire device is processed under ambient conditions with no vacuum equipment used. We have tested VOFETs with two different materials, p-type P3HT and n-type PC$_{70}$BM. The polarity of the charge transported in the material determines the charge injection rate and whether the device is a normally-ON or a normally-OFF transistor. Both devices have high current transport, excellent output characteristics, good on-off ratios and low operation voltages. We believe that these novel VOFETs will have exciting potential for various future electronic applications. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G25.00013: Studies on Structure Property Relations in Printed Polymer Semiconductors Nikhila Mahadevapuram, Saeed Ahmadi Vaselabadi, David Reza Shakarisaz, Joseph Strzalka, Paul Ruchhoeft, Gila Stein Printed polymer semiconductors can be used in systems which require precise control on domain placements and for sequential casting like in sensors, multi color light-emitting diodes or tandem solar cells. Morphology in polymer semiconductors places an important role on carrier mobility. Polymer crystals help in charge transport. In this work, we used helium ion beam lithography to irradiate polymer films and study crystallinity and carrier mobility. Thin films of poly (3-hexylthiphene) P3HT were irradiated with helium ion beam and light absorption properties were measured using UV-Vis spectroscopy. Crystal orientations in irradiated P3HT films were investigated using grazing incidence wide angle X-ray scattering (GIWAXS). Degree of crystallinity in irradiated polymer films were estimated by constructing pole figures. Charge mobility was estimated from device measurements. It was observed that the light absorption properties were retained in irradiated polymer films. Irradiation can influence both crystal orientations and charge mobility as a function of exposure dose. In summary, polymer crystallinity can be independently varied using this technique and a better understanding of the charge transport and device function can be established. [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G25.00014: Transfer Printing Controlled by Substrate Thickness Michael Bartlett, Alfred Crosby Transfer printing techniques have played an important role in electronics, biology and other fabrication processes. These techniques have been demonstrated to control interfacial adhesion through prescribed actuation mechanisms, surface patterns, or by changing the interfacial adhesion energy through chemical treatments or kinetic control. Here we present a simple transfer printing mechanism which is governed by the geometric confinement of soft, polymeric substrates. As the substrate thickness decreases the adhesive force capacity increases, allowing objects to be printed to thinner substrates without any specific actuation, chemical treatment, or surface topography. This functionality is experimentally demonstrated by printing millimeter and centimeter-scale silicon wafers to progressively thinner substrates. We further show the selective transfer of objects based on position and how these techniques can be used in roll-to-roll processes. We support these experiments with a theoretical model which demonstrates how interfacial confinement enables the precise control of adhesive force capacity, as well as a mechanism to increase interfacial strength. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G25.00015: Fast Printing and In-Situ Morphology Observation of Organic Photovoltaics using Slot-Die Coating Feng Liu, Sunzida Ferdous, Cheng Wang, Alexander Hexamer, Thomas Russell The solvent-processibility of polymer semiconductors is a key advantage for the fabrication of large area, organic bulk-heterojunction (BHJ) photovoltaic devices. Most reported power conversion efficiencies (PCE) are based on small active areas, fabricated by spin-coating technique. In general, this does not reflect device fabrication in an industrial setting. To realize commercial viability, devices need to be fabricated in a roll-to-roll fashion. The evolution of the morphology associated with different processing parameters, like solvent choice, concentration and temperature, needs to be understood and controlled. We developed a mini slot-die coater, to fabricate BHJ devices using various low band gap polymers mixed with phenyl-C71-butyric acid methyl ester (PCBM). Solvent choice, processing additives, coating rate and coating temperatures were used to control the final morphology. Efficiencies comparable to lab-setting spin-coated devices are obtained. The evolution of the morphology was monitored by in situ scattering measurements, detecting the onset of the polymer chain packing in solution that led to the formation of a fibrillar network in the film. [Preview Abstract] |
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