Christopher F. Huebner

Toward Efficient Binders for Li-Ion Battery Si-Based Anodes: Polyacrylic Acid

Si-based Li-ion battery anodes offer specific capacity an order of magnitude beyond that of conventional graphite. However, the formation of stable Si anodes is a challenge because of significant volume changes occurring during their electrochemical alloying and dealloying with Li. Binder selection and optimization may allow significant improvements in the stability of Si-based anodes. Most studies of Si anodes have involved the use of carboxymethylcellulose (CMC) and poly(vinylidene fluoride) (PVDF) binders. Herein, we show for the first time that pure poly(acrylic acid) (PAA), possessing certain mechanical properties comparable to those of CMC but containing a higher concentration of carboxylic functional groups, may offer superior performance as a binder for Si anodes. We further show the positive impact of carbon coating on the stability of the anode. The carbon-coated Si nanopowder anodes, tested between 0.01 and 1 V vs Li/Li+ and containing as little as 15 wt % of PAA, showed excellent stability during the first hundred cycles. The results obtained open new avenues to explore a novel series of binders from the polyvinyl acids (PVA) family.

Electroluminescent colloidal inks for flexographic roll-to-roll printing

The academic and commercial interest in organic light-emitting devices is motivated in part by the potential of building devices utilizing simple and inexpensive fabrication routes, for example, commercial printing techniques. The focus on synthetically challenging small molecules and π-conjugated polymers for these devices is countered by the alternative of developing emissive materials that utilize an electroluminescent dye embedded in a hole and electron transporting host. In this effort, we exploit readily obtainable materials and simple fabrication routes to produce light-emitting colloidal particles, which in turn allows us to invoke the concept of a “particle device”. Specifically, we present colloidally based organic light emitting devices that can be designed to produce a range of colors by mixing together various ratios of red-, green-, and blue-emitting particles. These aqueous-based colloids are adaptable to form printing inks and may be utilized in fabricating devices through high-throughput commercial printing technologies.

Spectral Tuning of Conjugated Polymer Colloid Light-Emitting Diodes

In recent years, the importance of the polymer light-emitting diode (PLED) has grown immensely, proving very desirable in numerous applications because of very high efficiencies, low power consumption, and ease of fabrication. Typically, these devices have been constructed in a layered, thin-film fashion consisting of either electron- and hole-transport materials doped with a luminescent dye (Hebner, T. R.; Sturm, J. C. Appl. Phys. Lett. 1998, 73, 1775. Jiang, X.; Register, R. A.; Killeen, K. A.; Thompson, M. E.; Pschenitzka, F.; Hebner, T. R.; Sturm, J. C. J. Appl. Phys. 2002, 91, 6717. Yeh, K. M.; Chen, Y. Org. Electron. 2008, 9, 45-50. Oh, G. C.; Yun, J. J.; Park, S. M.; Son, S. H.; Han, E. M.; Gu, H. B.; Jin, S. H.; Yoon, Y. S. Mol. Cryst. Liq. Cryst. 2003, 405, 43-51. Lee, J. I.; Chu, H. Y.; Kim, S. H.; Do, L. M.; Zyung, T.; Hwang, D. H. Opt. Mater. 2003, 21, 205-210. Hwang, D.-H.; Park, M.-J.; Lee, C. Synth. Met. 2005, 152, 205-208) or a conjugated polymer that can be engineered to tune the emission of the PLED to particular wavelengths. Stable PLED aqueous colloidal dispersions were prepared containing poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], (MEH-PPV), poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO), and a binary poly(9,9-di-n-octylfluorenyl-2,7-diyl)/poly(2,5-dioctyl-1,4-phenylenevinylene) (PFO/POPPV) particle dispersion. Red-, green-, and blue-light-emitting colloidal dispersions could then be combined to achieve color-tailored emissions spanning the visible spectrum.

Polyaniline coated poly(butyl methacrylate) core-shell particles

Polyaniline coated poly(butyl methacrylate) core–shell particles were synthesized and formulated into electrically conductive colloidal inks appropriate for use in roll-to-roll printing. Since the first demonstration of an organic field-effect transistor, a specific interest in fabricating low-cost, large area organic electronics through the exploitation of conventional ink-jet, screen, or roll-to-roll printing technologies has developed. Using a commercial roll-to-roll printing press, interdigitated test figures were printed with the core–shell colloidal ink down to a line thickness of ca. 40 µm. The printed zones exhibited a conductivity of ca. 0.5 Ω−1 cm−1, though this conductivity could be modified by altering the composition of the ink to include more uncoated poly(butyl methacrylate) particles. Heating the printed zone above 35 °C allowed the core to flow, resulting in enhanced mechanical properties of the printed zone.

Copolymers of 2-(9H-Carbazol-9-yl)ethyl 2-Methylacrylate and 4-[5-(4-tert-Butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl 2-Methylacrylate: Correlating Hole Drift Mobility and Electronic Structure Calculations with Electroluminescence

Methacrylate monomers functionalized with pendant carbazole and oxadiazole moieties were copolymerized into random copolymers with varying carbazole/oxadiazole ratios. Specifically, the monomers of 2-(9H-carbazol-9-yl)ethyl 2-methylacrylate (CE) and 4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl 2-methylacrylate (tBPOP) were copolymerized in various ratios, and the inherent hole drift mobilities were assessed through time-of-flight techniques. At a field strength of 345 kV/cm, the homopolymer PCE exhibited a hole mobility of 5.9 x 10(-7) cm(2)/V.s, which was approximately twice the value of the technologically important poly(9-vinylcarbazole), which exhibited a value of 2.8 x 10(-7) cm(2)/V.s. The range of hole mobilities in the copolymers varied from 2.4 x 10(-8) cm(2)/V.s for copolymers containing 50 mol % of the carbazole-containing monomer residue to 3.0 x 10(-7) cm(2)/V.s for copolymers that incorporated 88 mol % of the residue. Density functional theory (B3LYP/6-21G*) and optical absorption derived highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of CE were -5.39 and -1.94 eV, respectively, while the corresponding oxadiazole monomer (tBPOP) had a HOMO energy of -5.99 eV and a LUMO energy of -2.23 eV. The mean luminous efficiency of coumarin 6 doped single-layer devices constructed from the poly(CE-co-tBPOP) copolymers indicated a relatively flat efficiency of ca. 0.25 cd/A over a wide carbazole mole fraction content of 0.30-0.70.

Biologically-based pressure activated thin-film battery

There is an industrial interest in utilizing large volume manufacturing processes such as printing (e.g. stencil, roll-to-roll) to produce thin-film functional components. These components will require power sources, for example thin-film batteries, and it would be advantageous to be able to produce these powering items in-line with the components. Traditional primary thin-film batteries have limited storage capacities due to mass limitations and unavoidable losses. The current effort demonstrates a zinc/manganese oxide reserve battery that has been produced through combination of stencil and roll-to-roll printing on a polyethylene terephthalate (PET) substrate utilizing fish roe for the ion conducting electrolyte storage and separator. The creation of a reserve battery which can be activated when power is required by the deformation of the battery is an approach to extend battery storage times.

Click functionalization of thin films fabricated by roll-to-roll printing of thermoplastic/thermoset core-shell colloids

AbstractA general methodology for producing ca. 140-nm thermoplastic/thermoset, core-shell colloids that are used as an ink in roll-to-roll printing is demonstrated. The printed films are subsequently modified in-line through a dip-click approach using the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The thermoplastic nature of the shell polymers in the particles allows the shell to delaminate when annealed above its glass transition temperature. This results in a printed film that is more robust and functional as it combines the durability of the thermoset core colloids and the flexibility of the thermoplastic shell polymers. The technique is demonstrated using core-shell particles with a crosslinked polystyrene core and co-/terpolymer shell that contains terminal alkynes for click functionalization. The core-shell particles were roll-to-roll printed and then annealed at 100 ∘C to yield coalesced films. The printed films were dipped in a solution containing an azide-modified fluorescein dye which resulted in the covalent attachment of the dye to the thin films via CuAAC. When the click reaction was allowed to proceed for 24 h, it was found that ca. 67% of the total functionalization occurred in the first hour. Due to the efficiency of this technique, the potential for large-scale production of printed films where an in-line chemical modification via CuAAC could be realized. Graphical AbstractA general methodology for producing ca. 140 nm thermoplastic/thermoset, core-shell colloids that can be used as an ink in roll-to-roll printing is demonstrated. The printed films are subsequently modified inline through a dip-click approach using the copper(I)- catalyzed azide-alkyne cycloaddition (CuAAC). The thermoplastic nature of the shell polymers in the particles allows the shell to delaminate when annealed above its glass transition temperature. This results in a printed film that is more robust and functional as it combines the durability of a thermoset core colloid with the flexibility of an alkyne-functionalized thermoplastic shell.

Asymmetric electrically conducting element printed from aqueously dispersed pentacene nanoparticles

Pentacene is an organic semiconductor with promising electronic properties, but it has been severely limited in application due to difficult and expensive processing. (Microelectron Eng, 88, 9, 2959–2963, 2011), (J Appl Phys, 109, 8, 083710, 2011) Generally, pentacene-based devices typically require high-vacuum processing, and/or synthetic modifications to the molecule must be incorporated. (Thin Solid Films, 427, 1-2, 367–370, 2003), (J Am Chem Soc, 129, 34, 10,308–10,309, 2007), (J Mater Chem C, 1, 11, 2193–2201, 2013), (ACS Nano, 7, 9, 7983–7991, 2013) We developed a technique to transform small molecule pentacene into an aqueously dispersed particulate material. Pentacene was introduced into a miniemulsion reaction and formed into nano-scale platelet-like particles. After the miniemulsion, the emulsified pentacene showed indefinite stability in the aqueous phase, which is key in a material used for printable electronics. Devices fabricated from the aqueously dispersed particles demonstrated behavior similar to a Zener diode with a breakdown voltage of ≈ 2 VDC.

Controlling emission color through Förster resonance energy transfer in hybrid colloidal particles

Hybrid particles from insoluble luminescent π-conjugated polymers were formed through a miniemulsion approach. The color characteristics of the PL for the particles could be tuned by exploiting the Förster resonance energy transfer between the polymers within a particle, while suppressing energy transfer between particles, and exhibited 1931 CIE x,y-color coordinates that ranged from 0.153, 0.071 to 0.267, 0.559 with corresponding dominant wavelengths of 466 nm to 536 nm with an excitation energy at a wavelength of 389 nm.