Tobacco Mosaic Virus Implemented as an Interfacial Layer in Organic Photovoltaic Cells

Organic photovoltaics (OPVs) are flexible, light weight, and economical to produce due to low processing temperatures, solution processing, and print fabrication. This makes them optimal for a wide range of applications. However, the efficiencies of OPVs are currently not high enough for them to be viable in the market or to be able to compete with inorganic photovoltaics. Therefore the integration of new materials and methods into OPVs in order to increase their efficiency is a vital field. One way to increase the efficiency of OPVs is to increase the surface area in-between layers to allow for enhanced electron transport. The Tobacco Mosaic Virus (TMV) is a common virus with a long, cylindrical structure which can easily incorporate metal coating onto its shell. TMV has already been added perpendicularly onto cathode surfaces in microbatteries and has resulted in increased capacitance and decreased resistance. This same effect in OPVs would greatly increase the surface area and efficiency. Since TMV has not been implemented into OPVs previously, we have been working on how to add the TMV to our desired layer most effectively. Currently we are testing it as a replacement or possible dopant for the PEDOT:PSS interfacial layer. So far we have found TMV to work as an interfacial layer, but not as well as PEDOT:PSS. Using different solutions and application methods we hope to increase the effectiveness and make it a viable interfacial layer to increase OPV efficiencies

Polymer-based Thermoelectric Devices

Currently, over 50% of all energy generated in the US is lost as waste heat, and thermoelectric generators offer a promising means to recoup some of this energy, if their efficiency is improved. While organic thermoelectric materials lack the efficiency of their inorganic counterparts, they are composed of highly abundant resources and have low temperature processing conditions. Recently, a new class of redox-active polymers, radical polymers, has exhibited high electrical conductivity in an entirely amorphous medium. In addition, these radical polymers have a simple synthetic scheme and can be highly tunable to provide desired electrical properties. In this study, the thermoelectric properties of a nitroxide radical-based polymer, poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA), is evaluated in a doped state. 4-ethylbenzenesulfonic acid (EBSA) is used to dope PTMA solutions. The Seebeck coefficient and conductivity measurements were collected to calculate the thermoelectric power factor of the material at an average temperature of 40 ˚C. We expect to find that doped PTMA has a peak power factor of ~10-2 μW m-1 K-2. While these power factor values would not exceed a state-of-the-art organic semiconductor, they would show that radical polymers are a viable alternative to pi-conjugated semiconducting polymers. These redox-active polymers are still a new type of semiconducting polymer; therefore, this study could suggest that further research is necessary to determine their full capabilities and the radical solutions they may have to offer

Synthesis and Characterization of Bismuth Telluride Nanoparticles for Use in Flexible Polymer-Nanoparticle Hybrid Thermoelectric Devices

Polymer-based thermoelectric materials, which can have readily-tuned properties through simple control of their chemistry, offer the promise of providing flexible, lightweight, and low-cost modules for the environmentally-friendly conversion of waste heat to electricity without the need for moving parts. As such, they have started to be explored in applications ranging from improved building efficiency to increased mileage in automobiles. However, widespread implementation of these materials is limited due to their low performance relative to their mechanically-rigid, heavy inorganic material-based counterparts. Therefore, a critical need exists to design polymer-nanoparticle composite materials to increase the energy conversion of thin film thermoelectric devices. Specifically, bismuth telluride (Bi2Te3) nanoparticles embedded in a conducting polymer matrix of poly(ethylene dioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) have provided promising initial results. Here, we aim to improve upon this system through a combination of designer chemistry and interfacial engineering. Specifically, Bi2Te3 nanoparticles were synthesized in an aqueous solution at a low temperature in the presence of PEDOT:PSS. This allowed the conducting polymer to coat the surface of the nanoparticle, which should improve the device performance. The purified polymer-coated nanoparticles were cast into thin films, and the thermoelectric properties of the composite materials were evaluated. Importantly, the performance of the polymer-nanoparticle composite thin films increased by a factor of 2 with increased Bi2Te3 loading while still retaining the mechanical integrity associated with polymer-based materials. We anticipate that, with systematic device optimization, this class of materials will provide a solid launching point for the implementation of polymer-based thermoelectric modules

Detecting Trace Explosives with Organic Electronic Devices

Trinitrotoluene (TNT) is a commonly used explosive and poses a significant risk to security arenas across the globe. The use of organic electronics for the detection of explosive residues allows for large scale, solution-processible, and environmentally stable devices with a high selectivity for TNT detection. Currently, fluorescence-based sensors are used in TNT detection, but the synthesis of the fluorescent molecules can be complicated and costly. Hence, we introduce a new design paradigm to overcome this limitation. Specifically, organic field-effect transistors (OFETs) were created using 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene as the active material to collect a baseline mobility and the on current to off current ratio (ON/OFF). Then, blends of TIPS-pentacene and varying concentrations of TNT were used in OFETs, and the change in the ON/OFF and charge carrier mobility were evaluated. With the introduction of TNT, the ON/OFF increases in value and it was observed that the concentration of the TNT in the film blend has an effect on how much the ON/OFF and hole mobility increases. The measured change in the ON/OFF were used to create a calibration curve that shows the dependence of the TNT concentration. A device that incorporates the TIPS-pentacene FET could eventually be used to sweep an area or surface for the presence of dangerous explosives through a change in an electrical signal in the device and interpretation of the calibration curves

Radical Polymers as Anodic Charge Extraction Layers in Small Molecule Organic Photovoltaic Devices

Organic photovoltaic (OPV) devices based on the copper (II) phthalocyanine(CuPc)/ fullerene(C60) system are an innovative photovoltaic technology optimal for situations requiring low-cost, transparent, and flexible devices. Furthermore, the high degree of reproducibility of this system allows for the ready study of new OPV technologies. Here, we have used this system to elucidate systematic structure-property-performance relationships for a new OPV anode modifier. The addition of interfacial modifier materials between the organic CuPc/C60 layers and the metallic anode drastically can improve efficiency. Radical polymers are a class of polymers with aliphatic backbones and pendent stabilized radical groups. Here, we utilize poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA) to examine the feasibility of radical polymers as anode modifiers. OPV devices utilizing a PTMA thin film deposited onto an ITO substrate (anode) with subsequent CuPc and C60 active layers followed by a BCP cathode modifier and an aluminum layer (cathode) were fabricated using thermal evaporation. Device performance was evaluated by measuring current density as a function of voltage during simulated solar radiation. Addition of a thin layer of PTMA between the ITO and CuPc layers increased device power conversion efficiency to approximately 0.95% from a control of 0.57%, likely due to enhancement of the crystal structure of the CuPc layer. The addition of interfacial modifiers significantly increases the overall efficiency, and consequently, viability of CuPc/C60 OPV devices, and this logic should be extendable to a myriad of other polymer based solar cell designs

Design of Triblock Polymers for Water Filtration as Nanoporous Membranes

Clean, usable water is quickly becoming a less abundant natural resource for residential, commercial, and industrial applications. Developing advanced and efficient membranes as filtration components for water-treatment processes will help supply a growing society the clean water it needs. Triblock polymers have recently become of interest for their potential to create membranes that have higher selectivity while also having higher flux values than current commercially available ultrafiltration membranes. The synthesis of a triblock polymer consisting of polyisoprene (PI), polystyrene (PS), and either poly(N,N-dimethylacrylamide) (PDMA) or poly(tert-butyl acrylate) (PtBA) is reported. Each block of the polymer is synthesized via a sequential reverse addition-fragmentation chain transfer (RAFT) polymerization mechanism to achieve controlled, high molecular weights and narrow molecular weight distributions. The triblock polymer is synthesized such that the volume fractions of the PI, PS, and PDMA/PtBA blocks are about 25%, 45%, and 30%, respectively, to achieve optimal mechanical properties and pore functionality within the membrane. Subsequently, the membrane is prepared following the non-solvent induced phase separation (SNIPS) method

Oil Recovery in Low Temperature and Salinity Reservoir Rock Using Anionic and Anionic/Cationic Surfactant Formulations

As oil reserves are being depleted in the United States, there is an increasing need to recover the trapped oil in the reservoir rock which accounts for up to 60% of the total oil available. This oil may be recovered using chemical enhanced oil recovery (EOR) techniques. In our case study, we investigated viable EOR surfactant/polymer formulations for conditions conducive to high efficiency oil recovery in ultra-low salinity, low temperature, and high hardness reservoirs. Formulations were screened for Winsor Phase I (microemulsions) or Winsor Phase III (bicontinuous emulsions),: both of which are conducive to high efficiency oil recovery. Strong emulsion phase behavior at low salinities was observed in binary surfactant mixtures of anionic alkyl-alkoxy sulfates (at \u3e 16,000 ppm). Using a novel anionic/cationic formulation, emulsion phase behavior was observed at the ultra-low reservoir salinity of 10,000 ppm. These formulations demonstrate industrially viable surfactant/polymer formulations that can used for high efficiency EOR in low temperature-salinity and high hardness reservoirs within the continental United States and abroad

Synthesis, Characterization, and Thermoelectric Properties of Radical Siloxanes

More than half of the annual energy consumption in the United States is lost as waste heat. Polymer-based thermoelectric devices have the potential to utilize this waste heat both sustainably and cost-effectively. Although conjugated polymers currently dominate research in organic thermoelectrics, the potential of using polymers with radical pendant groups have yet to be realized. These polymers have been found to be as conductive as pristine (i.e., not doped) poly(3-hexylthiophene) (P3HT), a commonly-used charge-transporting conjugated polymer. This could yield promising avenues for thermoelectric material design as radical polymers are more synthetically tunable and are hypothesized to have a high Seebeck coefficient. In this report, the compound 4,4,5,5-tetramethyl-2-(3-vinylphenyl)imidazolidine-1,3-diol was synthesized and then used to produce a polymer with a radical pendant group. A polysiloxane backbone was synthetically targeted to produce a material with a low glass transition temperature. The polymer is then characterized for its material and thermoelectric properties

Optimal Surfactant Selection for Chemical Enhanced Oil Recovery in Low Temperature, Low Salinity, High Hardness Reservoirs

Based on the environmental properties of a crude oil reservoir, only 20-30 % of oil product can be recovered using primary and secondary extraction methods. The remaining stranded oil can only be recovered via various enhanced oil recovery methods. Chemical enhanced oil recovery (EOR) uses specialty chemicals to extract trapped oil in rock layers by generating in-situ microemulsion in the presence of reservoir brine and oil. In this case study, phase behavior tests are conducted for microemulsion formation between the surfactant solution and the oil. The phase behavior tests model reservoirs with low temperature and low salinity. In order to narrow the selection of surfactants for testing, phase behavior tests and interfacial tension experiments were used to determine the equivalent alkane carbon number (EACN) of the oil in this reservoir. Along with phase testing, extensive interfacial tension measurements were carried out with the model oil and the reservoir fluid at various salinities. The reservoir sample oil was determined to have an EACN of around 12, which effectively models the hydrocarbon part of the multicomponent crude oil similar to a dodecane system. These results facilitate in method development for EACN determination and in the selection of the surfactants that will create optimum emulsion for high efficiency oil recovery in low temperature and low salinity reservoirs typical to the Illinois basin in the United States

Investigation of ITX Derivative Photoinitiators for Depletion Lithography

Direct laser writing (DLW) with two-photon polymerization (TPP) allows for fabricating 3-dimensional nano-scale polymer structures by focusing an ultrafast laser inside a photoresist system consisting of a monomer and photoinitiator. The photoinitiator is excited by the laser and triggers the polymerization process of the monomer. Stimulated emission depletion (STED), which was designed for resolution enhancement for microscopy, could be applied to this process and inhibit the polymerization with an additional laser for depletion. This STED process can be used to increase the resolution of the 3D printing. However, the photoresist for STED-DLW should contain a photoinitiator that is sensitive to both the writing laser and the depleting laser, and very few initiators currently exist which meet these strict requirements. Previous studies on 7-diethylamino-3-thenoylcoumarin (DETC) and isopropyl thioxanthone (ITX) have revealed their initiation and depletion capabilities. However, some derivatives of ITX also have the potential to be used as STED inspired photoinitiators. The behaviors of these derivatives are tested by varying the power of both the writing and depleting lasers and the writing speed. Comparisons are made between the different photoresist systems by investigating the writing and depletion thresholds as well as printed structure quality. Results show that ITX derivatives have good writing performance at low writing power, but they have poor response to the depletion laser