Co-reporter:Brian Schmatz, Zhibo Yuan, Augustus W. Lang, Jeff L. Hernandez, Elsa Reichmanis, and John R. Reynolds
ACS Central Science September 27, 2017 Volume 3(Issue 9) pp:961-961
Publication Date(Web):August 16, 2017
DOI:10.1021/acscentsci.7b00232
The ability to process conjugated polymers via aqueous solution is highly advantageous for reducing the costs and environmental hazards of large scale roll-to-roll processing of organic electronics. However, maintaining competitive electronic properties while achieving aqueous solubility is difficult for several reasons: (1) Materials with polar functional groups that provide aqueous solubility can be difficult to purify and characterize, (2) many traditional coupling and polymerization reactions cannot be performed in aqueous solution, and (3) ionic groups, though useful for obtaining aqueous solubility, can lead to a loss of solid-state order, as well as a screening of any applied bias. As an alternative, we report a multistage cleavable side chain method that combines desirable aqueous processing attributes without sacrificing semiconducting capabilities. Through the attachment of cleavable side chains, conjugated polymers have for the first time been synthesized, characterized, and purified in organic solvents, converted to a water-soluble form for aqueous processing, and brought through a final treatment to cleave the polymer side chains and leave behind the desired electronic material as a solvent-resistant film. Specifically, we demonstrate an organic soluble polythiophene that is converted to an aqueous soluble polyelectrolyte via hydrolysis. After blade coating from an aqueous solution, UV irradiation is used to cleave the polymer’s side chains, resulting in a solvent-resistant, electroactive polymer thin film. In application, this process results in aqueous printed materials with utility for solid-state charge transport in organic field effect transistors (OFETs), along with red to colorless electrochromism in ionic media for color changing displays, demonstrating its potential as a universal method for aqueous printing in organic electronics.
Co-reporter:Caroline Grand, Wojciech Zajaczkowski, Nabankur Deb, Chi Kin Lo, Jeff L. Hernandez, David G. Bucknall, Klaus Müllen, Wojciech Pisula, and John R. Reynolds
ACS Applied Materials & Interfaces April 19, 2017 Volume 9(Issue 15) pp:13357-13357
Publication Date(Web):April 5, 2017
DOI:10.1021/acsami.6b16502
The performance of devices relying on organic electronic materials, such as organic field-effect transistors (OFET) and organic photovoltaics (OPV), is strongly correlated to the morphology of the conjugated material in thin films. For instance, several factors such as polymer solubility, weak intermolecular forces between polymers and fullerene derivatives, and film drying time impact phase separation in the active layer of a bulk heterojunction OPV device. In an effort to probe the influence of polymer assembly on morphology of polymer thin films and phase separation with fullerene derivatives, five terthiophene-alt-isoindigo copolymers were synthesized with alkyl side-chains of varying lengths and branching on the terthiophene unit. These P[T3(R)-iI] polymers were designed to have similar optoelectronic properties but different solubilities in o-dichlorobenzene and were predicted to have different tendencies for crystallization. All polymers with linear alkyl chains exhibit similar thin film morphologies as investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM). The main differences in electronic and morphological properties arise when P[T3(R)-iI] is substituted with branched 2-ethylhexyl (2EH) side-chains. The bulky 2EH substituents lead to a blue-shifted absorption, a lower ionization potential, and reduced ordering in polymer thin films. The five P[T3-iI] derivatives span hole mobilities from 1.5 × 10–3 to 2.8 × 10–2 cm2 V–1 s–1 in OFET devices. In OPV devices, the 2EH-substituted polymers yield open-circuit voltages of 0.88 V in BHJ devices yet low short-circuit currents of 0.8 mA cm–2, which is explained by the large phase separation observed by AFM in blends of P[T3(2EH)-iI] with PC71BM. In these P[T3(R)-iI] systems, the propensity for the polymers to self-assemble prior to aggregation of PC71BM molecules was key to achieving fine phase separation and increased short-circuit currents, eventually resulting in power conversion efficiencies of 5% in devices processed using a single solvent.Keywords: bulk heterojunction solar cells; donor−acceptor polymers; isoindigo; organic field-effect transistors; organic photovoltaics; polymer fullerene blends; thin film morphology;
Co-reporter:Rylan M. W. WolfeJohn R. Reynolds
Organic Letters 2017 Volume 19(Issue 5) pp:
Publication Date(Web):February 20, 2017
DOI:10.1021/acs.orglett.6b03830
The synthesis of thienopyrroledione (TPD) has been updated to reduce the number of synthetic steps, remove hazardous and toxic reagents, reduce the amount of byproduct waste, and reduce the use of solvents when unnecessary. Diverse functionalization is possible, introducing 16 examples in yields from 34% to 95%. This reaction scheme was shown to be general for thiophene imides, and a more thorough exploration into side chain engineering is presented with TPD acceptors often used in organic electronic applications.
Co-reporter:Natasha B. TeranJohn R. Reynolds
Chemistry of Materials 2017 Volume 29(Issue 3) pp:
Publication Date(Web):January 20, 2017
DOI:10.1021/acs.chemmater.6b04725
Donor–acceptor systems are ubiquitous redox-active materials in electrochromic devices, making the study of their neutral and charged state characteristics expedient for the design of materials with improved properties. In this paper, we explore the absorption properties of the neutral and oxidized states of two dioxythiophene- and benzothiadiazole-containing penta- and hepta-heterocycles (EPBPE, EPPBPPE) having a monodisperse, well-defined π-conjugated structure, using electrochemistry, optical absorption and electron paramagnetic resonance (EPR) spectroscopy, spectroelectrochemistry, and microscopy. The molecules and their precursors were obtained via a direct (hetero)arylation coupling strategy that exploits stoichiometric control to obtain well-defined ter- and penta-heterocycles from bifunctional heteroarenes. Both molecules show intense and narrow dual-band absorptions in the visible region, reflecting the discrete nature of their π-systems, leading to strongly colored neutral states. The electron-rich dioxythiophene units enable access to their radical cation and dication states at potentials below 5 mV and 260 mV (vs ferrocene/ferrocenium), respectively, and give rise to stability toward repeated oxidative switching (voltammetric cycling). EPR and absorption spectroscopy of their chemically and electrochemically derived oxidized states showed them to be dominated by polaronic, π-dimeric, and, in the case of EPPBPPE, bipolaronic charge carriers. These species exhibited transitions with maxima in the near-IR region, leading to highly transmissive oxidized states and promising structures for high contrast electrochromics. A polymer (Poly-EPBPE) that maintains a discrete conjugated segment along the backbone was also designed using EPBPE as the multi-ring heterocycle linked together with an aliphatic n-decyl chain, to obtain a mechanically robust yet solution processable material. Poly-EPBPE showed narrow optical transitions and well-resolved oxidation waves in solution that correlated strongly with the properties of EPBPE. However, strong intermolecular interactions were observed in the absorption spectroscopy and electrochemistry of its film state. The oxidized state absorption properties of Poly-EPBPE reflected these interactions, with absorption properties dominated by π-dimers and higher order aggregates, leading to irreversibility in its film spectroelectrochemistry. The coupled structural, optical, electrochemical, magnetic, and microscopic studies enabled us to propose potential resonance structures of the charge carriers in these discrete conjugated systems and inform the design of high contrast electrochromic materials.
Co-reporter:Augustus W. Lang;James F. Ponder, Jr.;Anna M. Österholm;Nicole J. Kennard;Rayford H. Bulloch
Journal of Materials Chemistry A 2017 vol. 5(Issue 45) pp:23887-23897
Publication Date(Web):2017/11/21
DOI:10.1039/C7TA07932J
Water-processed, aqueous electrolyte supercapacitors are demonstrated incorporating an alternating copolymer of a functionalized 3,4-propylenedioxythiophene unit with a 2,2′-bis(3,4-ethylenedioxythiophene) unit (PE2) into carbon nanotube textiles. The side chains functionalizing PE2 allow the solubility to be tuned from the organic soluble precursor polymer, to a water-soluble polyelectrolyte, and finally to a solvent resistant form by a dilute acid wash (SR-PE2). Thin SR-PE2 films (60 μg cm−2) are electroactive over a wide potential window with a mass capacitance of 54 F g−1 at a discharge rate of 1.6 s (38 A g−1). These films exhibit a 65% capacitance retention at an 80 millisecond discharge time (560 A g−1). Flexible, free-standing electrodes were fabricated by depositing SR-PE2 onto a nonwoven carbon nanotube textile (CNT-T) and were assembled into symmetrical, flexible supercapacitors where the addition of polymer resulted in a boost in volumetric capacitance by 400 percent compared to the bare CNT-T electrode. Independent of whether the SR-PE2 films are cast from an organic solvent or water, device electrodes exhibit 11.4 F cm−3 (45 mF cm−2, 15.9 F g−1) which leads to an energy density of 0.10 mW h cm−3 at 7.5 mW cm−3 considering the total device volume. The CNT-T imparts a high degree of flexibility allowing the supercapacitors to retain 88% of their charge storage capacity when bent to a 0.8 mm radius as well as complete capacitance retention after 2000 bending cycles to a 3.5 mm radius. The devices assembled in air with a benign KCl electrolyte maintained 83% capacitance retention after 10 000 charge/discharge cycles highlighting the stability of these materials and utility for this processing approach for high throughput energy storage devices.
Co-reporter:Geert Pirotte;Shruti Agarkar;Bing Xu;Junxiang Zhang;Laurence Lutsen;Dirk Vanderzande;He Yan;Pamela Pollet;Wouter Maes;Seth R. Marder
Journal of Materials Chemistry A 2017 vol. 5(Issue 34) pp:18166-18175
Publication Date(Web):2017/08/29
DOI:10.1039/C7TA05627C
Continuous flow chemistry has been shown to be a suitable method for the large-scale preparation of conjugated polymers with uniform structural and macromolecular characteristics, which is especially relevant when applying these materials in optoelectronic devices. The molecular weight and dispersity of conjugated polymers have a major effect on final device performance through a combination of processing and morphological considerations. In this work, the low bandgap polymer PffBT4T-2OD (‘PCE-11’), which provides highly efficient bulk heterojunction solar cells, is synthesized by continuous flow chemistry using an easily mountable home-made apparatus. The influence of various reaction parameters on the material characteristics is investigated. Particular attention is devoted to tuning of the molecular weight, as this has a major impact on solubility and processability of the resultant polymer and, ultimately, solar cell performance. We find that temperature, monomer concentration, and injection volume of the polymerization mixture are significant parameters that can be used to optimize the control over molecular weight. The same protocol is then also applied to a structurally similar polymer with longer alkyl side chains, PffBT4T-2DT, affording important advantages in terms of processing due to its higher solubility. An average power conversion efficiency of 9.4% for bulk heterojunction solar cells using PC71BM as the acceptor phase is achieved based on this flow-synthesized polymer.
Co-reporter:Jeff L. Hernandez;Nabankur Deb;Rylan M. W. Wolfe;Chi Kin Lo;Sebastian Engmann;Lee J. Richter
Journal of Materials Chemistry A 2017 vol. 5(Issue 39) pp:20687-20695
Publication Date(Web):2017/10/10
DOI:10.1039/C7TA05214F
To develop an understanding of the effect spin coating or blade coating have on the morphology of polymer:fullerene thin films for organic solar cells, we have investigated the morphology of poly[5-(2-hexyldecyl)-1,3-thieno[3,4-c]pyrrole-4,6-dione-alt-5,5-(2,5-bis(3-dodecylthiophene-2-yl)-thiophene)] (P(T3-TPD)) blended with phenyl-C71-butyric acid methyl ester (PC71BM) using the solvent additive 1,8-diiodooctane (DIO). When P(T3-TPD) : PC71BM mixtures are cast with DIO, we observed a fivefold increase in power conversion efficiency (PCE) from 1% to >5% for both spin and blade coated devices. We found the morphology and OPV performance are remarkably similar for spin and blade coated films without having to re-optimize the processing solution or coating temperature. We attribute the robust coating behavior to processing an aggregated solution of P(T3-TPD) : PC71BM. Further, in order to gain insight into how the common solvent additive DIO enhances thin film morphology, in situ UV-vis absorbance and reflection spectroscopies, coupled with thin film morphology characterization, was performed to develop a mechanistic understanding of the solidification process. In situ and static measurements revealed that DIO increases the nucleation density, reducing domain size and additionally increases the polymer crystallinity and phase purity.
Co-reporter:Natasha B. Teran; Guang S. He; Alexander Baev; Yanrong Shi; Mark T. Swihart; Paras N. Prasad; Tobin J. Marks
Journal of the American Chemical Society 2016 Volume 138(Issue 22) pp:6975-6984
Publication Date(Web):May 27, 2016
DOI:10.1021/jacs.5b12457
Exploiting synergistic cooperation between multiple sources of optical nonlinearity, we report the design, synthesis, and nonlinear optical properties of a series of electron-rich thiophene-containing donor–acceptor chromophores with condensed π-systems and sterically regulated inter-aryl twist angles. These structures couple two key mechanisms underlying optical nonlinearity, namely, (i) intramolecular charge transfer, greatly enhanced by increased electron density and reduced aromaticity at chromophore thiophene rings and (ii) a twisted chromophore geometry, producing a manifold of close-lying excited states and dipole moment changes between ground and excited states that are nearly twice that of untwisted systems. Spectroscopic, electrochemical, and nonlinear Z-scan measurements, combined with quantum chemical calculations, illuminate relationships between molecular structure and mechanisms of enhancement of the nonlinear refractive index. Experiment and calculations together reveal ground-state structures that are strongly responsive to the solvent polarity, leading to substantial negative solvatochromism (Δλ ≈ 102 nm) and prevailing zwitterionic/aromatic structures in the solid state and in polar solvents. Ground-to-excited-state energy gaps below 2.0 eV are obtained in condensed π-systems, with lower energy gaps for twisted versus untwisted systems. The real part of the second hyperpolarizability in the twisted structures is much greater than the imaginary part, with the highest twist angle chromophore giving |Re(γ)/Im(γ)| ≈ 100, making such chromophores very promising for all-optical-switching applications.
Co-reporter:Romain Stalder, Sreenivasa Reddy Puniredd, Michael Ryan Hansen, Unsal Koldemir, Caroline Grand, Wojciech Zajaczkowski, Klaus Müllen, Wojciech Pisula, and John R. Reynolds
Chemistry of Materials 2016 Volume 28(Issue 5) pp:1286
Publication Date(Web):February 17, 2016
DOI:10.1021/acs.chemmater.5b03968
A series of donor–acceptor isoindigo (iI)-based copolymers synthesized with increasing numbers of thiophene rings in the repeat unit (from zero to three thiophene rings, including silole and germole-bridged fused bithiophene units) is applied toward solution-processed OFET devices. Differential pulse voltammetry on thin films of the polymers recorded LUMO energy levels confined within a 0.1 eV range around 3.9 eV, while their bandgaps are estimated at 1.5 to 1.7 eV. The interchain π-stacking distance of each sample was evaluated from the 2D-WAXS diffraction patterns of annealed extruded filaments and the GIWAXS patterns of thin films, and were found to be all in the same range, between 3.65 and 3.75 Å for the thin films. Both p-type and n-type charge transport in thin film bottom gate, bottom contact transistor devices were recorded. In particular, the copolymer P(T-iI) containing one thiophene ring afforded well-balanced ambipolar p-type and n-type mobilities of 0.04 cm2/(V s) and 0.1 cm2/(V s), respectively. Under our processing conditions, the charge transport properties evolved from exclusively n-type to solely p-type as the number of thiophene rings within the repeat unit is increased to three rings in the case of P(T3-iI). This was observed despite all polymers displaying similar LUMO energy levels, interchain π-stacking distances, and microscopic thin film morphology (all face-on arrangement on the dielectric surface). This prompted a molecular-scale morphological analysis of P(T-iI) and P(T3-iI) in particular, using solid-state NMR spectroscopy in order to further investigate the stark difference in n-type mobilities between these two polymers. Using the complete assignment of solution 2D-NMR spectra of a thiophene-iI-thiophene model compound as guideline, the analysis of proton–carbon correlations in the solid-state 2D 13C{1H} FSLG-HETCOR NMR spectra of P(T-iI) and P(T3-iI) revealed differences in the molecular environment surrounding each iI unit. The latter suggests a stronger correlation of neighboring iI units in P(T-iI), whereas a stronger intermixing of iI and thiophenes prevails in P(T3-iI). We conclude that, in this study, the choice of the donor unit length within the primary structure of the D–A polymer can be responsible for hindering its n-type character.
Co-reporter:R. H. Bulloch and J. R. Reynolds
Journal of Materials Chemistry A 2016 vol. 4(Issue 3) pp:603-610
Publication Date(Web):23 Dec 2015
DOI:10.1039/C5TC03536H
Many proposed applications for electrochromic polymers (ECPs), which are designed to modulate the intensity or spectral power density of light, center around the interaction between the ECPs and the incident light. The long-term effects of the interaction of light and ECPs are rarely discussed in the literature, yet is a crucial parameter in materials evaluation in many applications. With the goal of examining the photo-stability of select ECPs, two polymers were selected for study, which are representative of both 3,4-dioxythiophene (DOT) and 3,4-dioxypyrrole (DOP) based materials. Samples of each material were sealed in glass cells under varying atmospheric conditions using a polyisobutylene-based barrier sealant and irradiated under a solar simulator for time periods ranging from 24 hours to one month. Following irradiation, electrochromic performance was assessed via both electrochemical and spectroelectrochemical methods. Additionally, X-ray photoelectron spectroscopy (XPS) was used to study chemical changes following irradiation. We report here that, following irradiation, no change in electrochromic performance (as measured by Δ%T at λmax) nor spectra recorded via XPS was observed in films encapsulated under an inert atmosphere, suggesting that conditions of irradiation alone are insufficient to degrade the performance of either ECP structure.
Co-reporter:Anna M. Österholm, James F. Ponder Jr., Justin A. Kerszulis, and John R. Reynolds
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 21) pp:13492-13498
Publication Date(Web):May 19, 2016
DOI:10.1021/acsami.6b02434
We have designed fully soluble ProDOTx-EDOTy copolymers that are electrochemically equivalent to electropolymerized PEDOT without using any surfactants or dispersants. We show that these copolymers can be incorporated as active layers in solution processed thin film supercapacitors to demonstrate capacitance, stability, and voltage similar to the values of those that use electrodeposited PEDOT as the active material with the added advantage of the possibility for large scale, high-throughput processing. These Type I supercapacitors provide exceptional cell voltages (up to 1.6 V), highly symmetrical charge/discharge behavior, promising long-term stability exceeding 50 000 charge/discharge cycles, as well as energy (4–18 Wh/kg) and power densities (0.8–3.3 kW/kg) that are comparable to those of electrochemically synthesized analogues.
Co-reporter:Toan V. Pho, Matthew V. Sheridan, Zachary A. Morseth, Benjamin D. Sherman, Thomas J. Meyer, John M. Papanikolas, Kirk S. Schanze, and John R. Reynolds
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 14) pp:9125
Publication Date(Web):March 31, 2016
DOI:10.1021/acsami.6b00932
The ligand 5-PO3H2-2,2′:5′,2″-terthiophene-5-trpy, T3 (trpy = 2,2′:6′,2″-terpyridine), was prepared and studied in aqueous solutions along with its metal complex assembly [Ru(T3)(bpy)(OH2)]2+ (T3-Ru-OH2, bpy = 2,2′-bipyridine). T3 contains a phosphonic acid group for anchoring to a TiO2 photoanode under aqueous conditions, a terthiophene fragment for light absorption and electron injection into TiO2, and a terminal trpy ligand for the construction of assemblies comprising a molecular oxidation catalyst. At a TiO2 photoanode, T3 displays efficient injection at pH 4.35 as evidenced by the high photocurrents (∼350 uA/cm2) arising from hydroquinone oxidation. Addition of [Ru(bpy)(OTf)][OTf]2 (bpy = 2,2′-bipyridine, OTf– = triflate) to T3 at the free trpy ligand forms the molecular assembly, T3-Ru-OH2, with the oxidative catalyst fragment: [Ru(trpy)(bpy)(OH2)]2+. The new assembly, T3-Ru-OH2, was used to perform efficient light-driven oxidation of phenol (230 μA/cm2) and benzyl alcohol (25 μA/cm2) in a dye-sensitized photoelectrosynthesis cell.Keywords: C−H activation; dye-sensitized photoelectrosynthesis cell; dye-sensitized solar cell; organic alcohol oxidation; solar fuels;
Co-reporter:James F. Ponder Jr., Sandra L. Pittelli, and John R. Reynolds
ACS Macro Letters 2016 Volume 5(Issue 6) pp:714
Publication Date(Web):May 24, 2016
DOI:10.1021/acsmacrolett.6b00250
The first example of a solution processable dioxythiophene-alt-dioxyselenophene polymer, ProDOT-EDOS, prepared via direct (hetero)arylation polymerization is reported and its optical and electrochemical properties are compared to the all thiophene analog, ProDOT-EDOT, and other relevant dioxythiophene polymers. By substituting the sulfur atom for a selenium atom on one of the monomers in the repeat unit a significant red-shift of both the neutral (41 nm, 132 meV) and polaronic (106 nm, 126 meV) absorbances results, as well as a 160 mV reduction in the onset of oxidation compared to ProDOT-EDOT. Spray-cast films of the polymer electrochemically switch from a vibrant blue charge neutral state to a color neutral and highly transmissive oxidized state.
Co-reporter:James F. Ponder Jr., Anna M. Österholm, and John R. Reynolds
Macromolecules 2016 Volume 49(Issue 6) pp:2106-2111
Publication Date(Web):March 4, 2016
DOI:10.1021/acs.macromol.5b02638
Copolymerization of alkoxy-functionalized 3,4-propylenedioxythiophenes (ProDOTs) with unfunctionalized 3,4-ethylenedioxythiophenes (EDOTs) in varying ratios using direct arylation yields a series of solution processable polymers with highly tunable optical and electronic properties. Within this series, we have identified ProDOT–EDOT2, a copolymer containing 67% EDOT compositionally, that combines the low oxidation potential, the redox behavior, and the deep-blue neutral color that are characteristic of PEDOT with the high solubility, exceptional electrochromic contrast, and color neutrality in the oxidized state characteristic of alkoxy-functionalized PProDOTs.
Co-reporter:Caroline Grand, Sujin Baek, Tzung-Han Lai, Nabankur Deb, Wojciech Zajaczkowski, Romain Stalder, Klaus Müllen, Wojciech Pisula, David G. Bucknall, Franky So, and John R. Reynolds
Macromolecules 2016 Volume 49(Issue 11) pp:4008-4022
Publication Date(Web):May 20, 2016
DOI:10.1021/acs.macromol.6b00540
Since being introduced to the open literature in 2010, the isoindigo heterocycle has been extensively studied as a novel electron-deficient building block for organic electronic materials in conjugated polymers, discrete length oligomers, and molecular systems, particularly targeting high charge mobility values and ambipolar transport in organic field effect transistors, along with high power conversion efficiencies in organic photovoltaic devices. This article introduces results obtained on copolymers of isoindigo with thiophene and alkylated terthiophenes to highlight fundamental characteristics in isoindigo-based polymers and the resulting organic field-effect transistors and photovoltaic devices. By comparing and contrasting the optoelectronic properties, thin film morphology, organic field-effect transistor (OFET) mobilities, and organic photovoltaic (OPV) performance to previously reported polymers, structure–processing–property relationships were uncovered. In particular, isoindigo-containing polymers with more rigid backbones and higher coherence lengths in thin films lead to increased charge mobility in OFET devices. In OPV devices, efficiencies over 6% can be obtained by balancing high ionization potentials typically dictating the open-circuit voltage and the charge transfer energy, and blend morphology impacting short-circuit currents. Furthermore, the impact of polymer structure on solubility and on phase separation in blends with PC71M is discussed, with isoindigo-based polymers exhibiting lower solubility possibly leading to more fiber-like morphologies stemming either from polymer dissolution in the casting solvent or from polymer self-assembly during film formation. This fiber-like polymer morphology remains unaffected by the presence of processing additives, such as 1,8-diiodooctane. These structure–property relationships developed for isoindigo-based polymers can also be discussed in the broader context of diketopyrrolopyrrole (DPP) and thienoisoindigo (TiI) as electron-deficient moieties that can also be doubly substituted on their amide functionality.
Co-reporter:Justin A. Kerszulis, Rayford H. Bulloch, Natasha B. Teran, Rylan M. W. Wolfe, and John R. Reynolds
Macromolecules 2016 Volume 49(Issue 17) pp:6350-6359
Publication Date(Web):August 19, 2016
DOI:10.1021/acs.macromol.6b01114
A family of five electrochromic polymers (ECPs) based on 3,4-dioxythiophenes (XDOTs) (where X = ethylene (E) and propylene (Pro)) or a 3,4-diacyclic-substituted dioxythiophene (AcDOT, Ac) as main chain donors coupled in a random fashion with the sterically relaxed (i.e., low torsional energy barriers to planarity) donor–acceptor–donor unit EDOT–BTD–EDOT (EBE, BTD = 2,1,3-benzothiadiazole) were synthesized using direct heteroarylation polymerization conditions. Designed as broadly light absorbing materials to improve overall contrast, ECPs were solution spray-cast into thin films, and their electrochromic properties were measured and compared against the previously reported ECP-Black (random copolymer composed of ProDOT and BTD). These new polymers exhibit enhanced integrated contrasts across the visible region (380–780 nm, Δ%Tint) larger than 45%, the highest achieved being ∼52%, a substantial improvement over ECP-Black (Δ%Tint = ∼32%). Increasing torsional strain of the main chain donor units moves the short wavelength peak to higher energy, allowing hue control. Increasing the composition of the EBE monomer in random copolymers yields more level and uniform absorption across the visible, reducing hue saturation and giving more muted colors relative to the normally vibrantly colored ECPs with no observable loss in contrast. Pro-Ac0.65/EBE0.35 gave the highest integrated electrochromic contrast with color values (L*a*b* where L* indicates lightness, a* defines green and red, and b* defines blue and yellow hues, for negative and positive values, respectively), indicating improved color neutrality (45, 5, 3) when compared to ECP-Black (47, 3, −14). Two-component solution blends of Pro-Ac0.65/EBE0.35 with the previously reported all donor polymer ProDOT2-EDOT in differing weight ratios were prepared and cast into films giving more aesthetically pleasing black-to-transmissive electrochromes, while maintaining a high integrated contrast at ∼51%. The use of EBE demonstrates the synthetic capability to improve the contrast of broadly absorbing ECPs for black or dark-to-transmissive applications in electrochromic window and display-type devices.
Co-reporter:Kangli Cao, D. Eric Shen, Anna M. Österholm, Justin A. Kerszulis, and John R. Reynolds
Macromolecules 2016 Volume 49(Issue 22) pp:8498-8507
Publication Date(Web):November 11, 2016
DOI:10.1021/acs.macromol.6b01763
The design of high bandgap electrochromic polymers (ECPs) that switch from a high energy absorbing colored state to a near-IR absorbing colorless state requires a challenging balance to be struck between achieving large changes in the absorption profile while maintaining sufficiently low oxidation potentials for use in full-color electrochromic devices. Previous studies on high bandgap ECPs have investigated structure–property relationships in dioxythiophenes copolymerized with various arylenes. Here, we expand this understanding by looking more closely at the effect of the dioxythiophene moiety as well as by varying the substituents on the arylene moiety. Three ECPs have been synthesized to perform this study with repeat units composed of electron-rich dimethoxyphenylene in alternation with dimers of 3,4-dialkoxy- and 3,4-propylenedioxythiophenes, yielding high gap polymers that are vibrant yellow or orange in the charge neutral state. Comparing these newly synthesized polymers to a structurally similar set previously reported, we elucidate the subtle steric and electronic effects that govern bandgap and redox properties in dioxythiophene copolymers.
Co-reporter:Chi Kin Lo, John R. Reynolds
Polymer 2016 Volume 99() pp:741-747
Publication Date(Web):2 September 2016
DOI:10.1016/j.polymer.2016.07.066
•A DPP monomer, with n-decyl alkyl chains attached to the thiophenes directly adjacent to the DPP core, was synthesized.•P(T-DPP) and P(TT-DPP), with the n-decyl DPP, and thiophene based electron rich moieties, were synthesized.•Greater polymer:fullerene intermixing improves charge transport and extraction, and thus Jsc and PCE in P(TT-DPP).Two donor polymers containing thiophene (T) and thienothiophene (TT) as the electron rich, and diketopyrrolopyrrole (DPP) as the electron poor, moieties were synthesized and utilized in organic photovoltaic (OPV) devices. We appended n-decyl side chains onto the thiophenes directly adjacent to the di-hexyldecyl substituted DPP center core to ensure solubility of the resulting polymers. We observed the impact of active layer morphologies, as determined by grazing-incidence wide angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM), on solar cell characteristics. Compared to devices fabricated with the thiophene-containing polymer P(T-DPP), devices with poly(thienothiophene-alt-diketopyrrolopyrrole), P(TT-DPP), exhibited higher average power conversion efficiency (PCE) of 3.0% and short circuit current (Jsc) of 10.4 mA/cm2. This higher performance is attributed to an improved charge transport and extraction as a result of a greater degree of intermixing in P(TT-DPP) and fullerene thin film.
Co-reporter:J. A. Kerszulis, K. E. Johnson, M. Kuepfert, D. Khoshabo, A. L. Dyer and J. R. Reynolds
Journal of Materials Chemistry A 2015 vol. 3(Issue 13) pp:3211-3218
Publication Date(Web):19 Feb 2015
DOI:10.1039/C4TC02685C
A series of vibrantly coloured π-conjugated electrochromic polymers (ECPs) were designed and synthesized with the goal of extracting structure–property relationships from subtle changes in steric strain or relaxation. These are soluble all donor, electron rich, alternating polymers based on repeat units of 3,4-ethylenedioxythiophene (EDOT), 3,4-propylenedioxythiophene (ProDOT), and an acyclic dioxythiophene (AcDOT) in varying combinations to tune steric interactions and the subsequent optical absorption for fine colour control. Two families of polymers were formed where ProDOT2–EDOT, ProDOT–EDOT, and ProDOT2–EDOT2 constitute new shades of blues while AcDOT2–ProDOT, AcDOT–ProDOT, and AcDOT–EDOT yield new hues of magentas with the homopolymers of ProDOT and AcDOT and the copolymer AcDOT2–EDOT2 serving as comparisons. The polymers were synthesized using direct (hetero)arylation polymerization. Examinations of the optoelectronic properties via cyclic voltammetry, spectroelectrochemistry, and colorimetry show that by subtly varying the level of steric relaxation or strain in the form of EDOT or AcDOT content, lower or higher energy absorption transitions are produced respectively. This increase in relaxation or strain allows more short or long wavelength light to transmit, giving new shades of blues or magentas respectively. Since these are all donating polymers, they exhibit changes in contrast no less than 70% at the λmax with the exception of AcDOT–EDOT. The most desirable electrochromic properties were achieved with ProDOT2–EDOT2 and AcDOT2–ProDOT, with band gaps (Eg) and neutral state L*a*b* colour values (−a* and +a* correspond to green and red and −b* and +b* correspond to blue and yellow respectively and L* represents the lightness) of 1.74 eV, 37, 12, −63 and 2.01 eV, 56, 59, −16 respectively. The highly transmissive oxidized state colour values for ProDOT2–EDOT2 and AcDOT2–ProDOT are 92, −3, −3 and 91, −2, −1 respectively. These structure–property relationships grant a greater ability to tune light absorption across the visible, with colour properties similar to ECPs made through other methods without using donor–acceptor effects. This all donor steric tuning method leads to considerably higher levels of transparency when the polymers are fully oxidized.
Co-reporter:D. Eric Shen, Anna M. Österholm and John R. Reynolds
Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:9715-9725
Publication Date(Web):03 Sep 2015
DOI:10.1039/C5TC01964H
Throughout the literature, a variety of counter electrode materials have been used in conjugated polymer-based electrochromic devices (ECDs) without a comparative understanding of their effects on the electrochromic properties of the device. In this study, we show that poor ECD performance, often attributed to electrochromic polymer (ECP) stability, is in fact largely due to an inappropriate choice of counter electrode. We have compared a set of counter electrode materials used in the ECD literature in magenta-to-clear and black-to-clear devices and evaluated how they affect the device parameters including contrast, switching time, stability, and voltage requirements. We demonstrate that through the appropriate choice of counter electrode material (i) the operating voltage can be lowered, (ii) no additional equilibration/break-in time is required, and (iii) the contrast and switching times of the ECP is maintained when incorporated into a device. Furthermore, we show that even unencapsulated ECDs with ECP-Magenta as the vibrantly colored material assembled and operated under ambient conditions can withstand over 10000 switches without compromising contrast or switching time.
Co-reporter:Rayford H. Bulloch, Justin A. Kerszulis, Aubrey L. Dyer, and John R. Reynolds
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 3) pp:1406
Publication Date(Web):January 12, 2015
DOI:10.1021/am507514z
Electrochromic polymers (ECPs) have been shown to be synthetically tunable, producing a full palette of vibrantly colored to highly transmissive polymers. The development of these colored-to-transmissive ECPs employed synthetic design strategies for broad color targeting; however, due to the subtleties of color perception and the intricacies of polymer structure and color relationships, fine color control is difficult. In contrast, color mixing is a well-established practice in the printing industry. We have identified three colored-to-transmissive switching electrochromic polymers, referred to as ECP-Cyan (ECP-C), ECP-Magenta (ECP-M), and ECP-Yellow (ECP-Y), which, via the co-processing of multicomponent ECP mixtures, follow the CMY color mixing model. The presented work qualitatively assesses the thin film characteristics of solution co-processed ECP mixtures. To quantitatively determine the predictability of the color properties of ECP mixtures, we estimated mass extinction coefficients (εmass) from solution spectra of the CMY ECPs and compared the estimated and experimentally observed color values of blends via a calculated color difference (ΔEab). The values of ΔEab range from 8 to 26 across all mixture compositions, with an average value of 15, representing a reasonable degree of agreement between predicted and observed color values. We demonstrate here the ability to co-process ECP mixtures into vibrantly colored, visually continuous films and the ability to estimate the color properties produced in these mixed ECP films.Keywords: color mixing; colorimetry; conjugated electroactive polymers; electrochromism; organic electronics
Co-reporter:Anna M. Österholm, D. Eric Shen, Justin A. Kerszulis, Rayford H. Bulloch, Michael Kuepfert, Aubrey L. Dyer, and John R. Reynolds
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 3) pp:1413
Publication Date(Web):January 9, 2015
DOI:10.1021/am507063d
We report a straightforward strategy of accessing a wide variety of colors through simple predictive color mixing of electrochromic polymers (ECPs). We have created a set of brown ECP blends that can be incorporated as the active material in user-controlled electrochromic eyewear. Color mixing of ECPs proceeds in a subtractive fashion, and we acquire various hues of brown through the mixing of cyan and yellow primaries in combination with orange and periwinkle-blue secondary colors. Upon oxidation, all of the created blends exhibit a change in transmittance from ca. 10 to 70% in a few seconds. We demonstrate the attractiveness of these ECP blends as active materials in electrochromic eyewear by assembling user-controlled, high-contrast, fast-switching, and fully solution-processable electrochromic lenses with colorless transmissive states and colored states that correspond to commercially available sunglasses. The lenses were fabricated using a combination of inkjet printing and blade-coating to illustrate the feasibility of using soluble ECPs for high-throughput and large-scale processing.Keywords: color mixing; dioxythiophenes; electrochromic devices; electrochromic eyewear; electrochromic polymers; organic electronics
Co-reporter:R. Stalder, A. Mavrinskiy, C. Grand, W. Imaram, A. Angerhofer, W. Pisula, K. Müllen and J. R. Reynolds
Polymer Chemistry 2015 vol. 6(Issue 8) pp:1230-1235
Publication Date(Web):08 Jan 2015
DOI:10.1039/C4PY01551G
The triphosgene carbonate synthesis is adapted as a convenient route towards an alternating main-chain rod/coil polycarbonate based on a telechelic sexithiophene oligomer, yielding an electroactive polymer that is a vibrantly electrochromic material despite the conjugation break. This polymer displays morphological behaviour typical of a liquid-crystalline polymer, with stacking distances between chromophores suitable for potential charge transport applications.
Co-reporter:Jeff L. Hernandez, Elsa Reichmanis, John R. Reynolds
Organic Electronics 2015 Volume 25() pp:57-65
Publication Date(Web):October 2015
DOI:10.1016/j.orgel.2015.05.025
Semiconducting conjugated polymers have drawn a great deal of attention over the past decade due to their solution processability and potential use in roll to roll fabrication of organic solar cells. Here, we report the effect of solvent vapor pressure on poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) blade coated inverted solar cells using ZnO as the electron transporting layer and MoO3 as the hole transporting layer. The resultant morphology and device performance are investigated for devices processed from solvents with varied vapor pressure and a mixed solvent. We report that the use of a mixed solvent system is advantageous for controlling the initial vapor pressure of the processing solution, thereby controlling the phase separated morphology between P3HT and PCBM which impacts ultimate solar cell performance.Blade coating of P3HT:PCBM organic solar cells has been carried out using active layer solutions of varied initial vapor pressure. It is demonstrated that a “sweet spot” in the solution properties leads to the optimum bulk heterojunction morphology and power conversion efficiency.
Co-reporter:Unsal Koldemir, Sreenivasa Reddy Puniredd, Manfred Wagner, Sefaattin Tongay, Tracy D. McCarley, George Dimitrov Kamenov, Klaus Müllen, Wojciech Pisula, and John R. Reynolds
Macromolecules 2015 Volume 48(Issue 18) pp:6369-6377
Publication Date(Web):September 3, 2015
DOI:10.1021/acs.macromol.5b01252
Optimized microstructure through control of both intra- and intermolecular interactions in organic semiconductors is critical for enhancing and optimizing charge transport for the realization of next-generation low-cost, mechanically flexible, and easy to process high performance, organic field effect transistors (OFETs). Herein, we report donor–acceptor alternating copolymers of dithienogermole (DTG) with 2,1,3-benzothiadiazole (BTD) and probe the importance of end groups on the control of molecular order and microstructure as it relates to the enhancement of charge carrier transport. Partial end-capping reactions, confirmed by 1H NMR and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analyses, on the DTG–BTD copolymer provided significant improvement in grazing incidence wide angle X-Ray scattering (GIWAXS) determined polymer ordering in thin films. Consequently, OFETs exhibited charge-carrier mobilities up to 0.60 cm2/(Vs) for the end-capped copolymer, which are an order of magnitude higher in comparison to the non-end-capped analogue, which displayed a mobility of 0.077 cm2/(Vs). We emphasize that a simple synthetic approach, the introduction of end-capping groups which remove reactive functionalities, can be effective in the development of next-generation OFET and solar materials by promising better control of the polymer organization.
Co-reporter:Aubrey L. Dyer;Rayford H. Bulloch;Yinhua Zhou;Bernard Kippelen;Fengling Zhang
Advanced Materials 2014 Volume 26( Issue 28) pp:4895-4900
Publication Date(Web):
DOI:10.1002/adma.201401400
Co-reporter:Romain Stalder, Jianguo Mei, Kenneth R. Graham, Leandro A. Estrada, and John R. Reynolds
Chemistry of Materials 2014 Volume 26(Issue 1) pp:664
Publication Date(Web):October 5, 2013
DOI:10.1021/cm402219v
Isoindigo (iI) has proven successful as an electron-accepting building block for the preparation of electroactive materials for organic electronics. Its high yielding and scalable synthesis has enabled the rapid development of a large number of molecular and polymeric iI-based materials with remarkable physical properties. This perspective provides an overview of the fundamental properties of isoindigo and summarizes the progress in the development of new materials for varied electronic applications during the last 3 years, focusing in particular on organic photovoltaics (OPVs) and organic field effect transistors (OFETs). The fundamental electronic properties of isoindigo are discussed in the context of the substitution pattern effect (5,5′ vs 6,6′) on the frontier orbitals energies and optical properties. The development of molecular systems in the 6,6′-iI configuration for OPVs is examined with an emphasis on molecular design for improved electronic properties thanks to fine-tuning of the active layer morphology via crystallization control. Numerous copolymers of iI have been reported, with both electron-rich and electron-poor comonomers. The homopolymer of isoindigo displays electron-accepting and electrochromic properties and serves as a polymeric surrogate for fullerenes in all-polymer solar cells. The copolymers’ absorption profiles span the entire visible spectrum into the near-infrared, up to 900 nm. Bulk-heterojunction solar cells based on iI copolymers have reached up to 6.3% efficiency. While the effect of processing additives and cell architecture are important, the unique electronic properties of iI polymers also provide useful insight on energetic losses within blends with fullerenes. Selected copolymers also perform highly in air-stable field effect transistors, with p-type mobilities exceeding 3 cm2/(V s). New concepts concerning the effect of backbone curvature and side-chain branching or polarity have been investigated using iI copolymers. Additionally, some all-acceptor copolymers display n-type mobility. As the design of iI materials evolves, structural modifications of the iI core emerge, targeting ambipolar charge transport and enhanced backbone planarity. Overall, isoindigo provides the field of organic electronics with impressive performance as well as a valuable platform for structure–property relationship investigation.Keywords: electron-acceptor; isoindigo; organic photovoltaics; organic transistors; π-conjugated materials;
Co-reporter:D. Eric Shen, Leandro A. Estrada, Anna M. Österholm, Danielle H. Salazar, Aubrey L. Dyer and John R. Reynolds
Journal of Materials Chemistry A 2014 vol. 2(Issue 20) pp:7509-7516
Publication Date(Web):10 Apr 2014
DOI:10.1039/C4TA01375A
A number of variables contribute to the electropolymerization, and the electrochemical properties, of electroactive polymers. However, few studies have attempted to acquire a unified understanding of the effects of all these variables, specifically as it relates to the capacitance of the material, as the number of experiments and resources required is large. Here, the effects of seven variables on the areal capacitance of the electropolymerized dimethyl derivative of poly(3,4-propylenedioxythiophene) (PProDOT-Me2) films are analyzed utilizing a fractional factorial design of experiments to reduce the number of experiments an order of magnitude. From this analysis, PProDOT-Me2 films were electropolymerized from an optimal set of variables to reproducibly afford films displaying the highest capacitances observed within this study. Devices were assembled from the optimized conditions, and the capacitance, energy, and power densities are reported in a framework that allows for meaningful comparison and understanding relative to commercially available supercapacitors. The supercapacitors fabricated in this study show promise towards being integrated as power sources for low-power, lightweight and flexible organic electronic devices.
Co-reporter:Coralie A. Richard, Zhenxing Pan, Anand Parthasarathy, Frank A. Arroyave, Leandro A. Estrada, Kirk S. Schanze and John R. Reynolds
Journal of Materials Chemistry A 2014 vol. 2(Issue 25) pp:9866-9874
Publication Date(Web):23 May 2014
DOI:10.1039/C4TA01199F
A series of four quadrupolar (Donor)2Acceptor-acid (D2A) sensitizers, based on two acceptor cores (dibenzophenazine (DBP) or dithienophenazine (DTP)), were synthesized and their optoelectronic and photovoltaic properties were investigated. 4-Hexyl-thien-2-yl groups were employed as donor units, to produce regioisomers depending on their connecting position to the core. This architectural design leads to the investigation of the structure–property relationships of the dyes, both in solution and upon integration in dye-sensitized solar cells (DSSCs). Within sets of regioisomers, frontier orbital levels and absorption properties differed, but the photovoltaic performances of the DSSCs were similar. When examining the effect of the core, the electronic properties (absorbance, LUMO level) predicted a more favourable electron injection for the DTP systems. However, the open circuit voltages are ∼100 mV greater for the DBP systems.
Co-reporter:Romain Stalder, Dongping Xie, Ashraful Islam, Liyuan Han, John R. Reynolds, and Kirk S. Schanze
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 11) pp:8715
Publication Date(Web):May 7, 2014
DOI:10.1021/am501515s
We report on a sexithienyl and two donor–acceptor−donor oligothiophenes, employing benzothiadiazole and isoindigo as electron-acceptors, each functionalized with a phosphonic acid group for anchoring onto TiO2 substrates as light-harvesting molecules for dye sensitized solar cells (DSSCs). These dyes absorb light to wavelengths as long as 700 nm, as their optical HOMO/LUMO energy gaps are reduced from 2.40 to 1.77 eV with increasing acceptor strength. The oligomers were adsorbed onto mesoporous TiO2 films on fluorine doped tin oxide (FTO)/glass substrates and incorporated into DSSCs, which show AM1.5 power conversion efficiencies (PCEs) ranging between 2.6% and 6.4%. This work demonstrates that the donor–acceptor–donor (D-A-D) molecular structures coupled to phosphonic acid anchoring groups, which have not been used in DSSCs, can lead to high PCEs.Keywords: benzothiadiazole; conjugated oligomer; donor-acceptor chromophore; dye sensitized solar solar cell; isoindigo; phosphonate anchoring group;
Co-reporter:Rayford H. Bulloch, Justin A. Kerszulis, Aubrey L. Dyer, and John R. Reynolds
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 9) pp:6623
Publication Date(Web):April 21, 2014
DOI:10.1021/am500290d
Although synthetic efforts have been fruitful in coarse color control, variations to an electrochromic polymer (ECP) backbone are less likely to allow for the fine control necessary to access the variations and shades of color needed in display applications. Through the use of thin films of cyan, magenta, and yellow ECPs, non-emissive subtractive color mixing allows the color of an electrochromic device (ECD) to be selected and tailored, increasing access to various subtle shades and allowing for a non-emissive display to exhibit a wide range of colors. Using a dual-active ECD, subtractive color mixing utilizing the cyan–magenta–yellow (CMY) primary system was examined. The bounds of the gamut, or the subset of accessible colors, using these three 3,4-propylenedioxythiophene (PProDOT)-derived materials in combination with the recently recognized 3,4-propylenedioxypyrrole-based minimally color changing polymer (MCCP) were mapped, highlighting the benefit of applying subtractive color mixing toward the development of full-color non-emissive displays. Here, we demonstrate that ECPs are suitable for the generation of a wide gamut of colors through secondary mixing when layered as two distinct films, exhibiting both vibrantly colored and highly transmissive states.Keywords: color mixing; colorimetry; conjugated electroactive polymers; electrochromic devices; electrochromism; organic electronics;
Co-reporter:Coralie A. Richard, Zhenxing Pan, Hsien-Yi Hsu, Seda Cekli, Kirk S. Schanze, and John R. Reynolds
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 7) pp:5221
Publication Date(Web):March 25, 2014
DOI:10.1021/am500535k
We report on quadrupolar (donor)2–acceptor sensitizers for dye-sensitized solar cells (DSSCs). The acceptor units are based on dithieno[2,3-a:3′,2′-c]phenazine and dithieno[3,2-a:2′,3′-c]phenazine coupled to thiophene donors. The optoelectronic and photophysical properties of two sets of isomers reveal a rigid structure for linear isomers and an efficient nonradiative decay for branched isomers. These sensitizers were integrated into DSSCs, and the quadrupolar structure is an operational design, as the IPCE reached up to 38% from 400 nm to 600 nm. The lengthening of the donor chain increases the efficiency, demonstrating the appeal of these oligomeric dyes for DSSCs.Keywords: donor−acceptor interactions; dye-sensitized solar cells; photovoltaic; thiophene oligomeric dyes;
Co-reporter:Justin A. Kerszulis, Chad M. Amb, Aubrey L. Dyer, and John R. Reynolds
Macromolecules 2014 Volume 47(Issue 16) pp:5462-5469
Publication Date(Web):August 6, 2014
DOI:10.1021/ma501080u
A series of conjugated polymers were designed and synthesized to extract structure–property relationships with the goal of yielding yellow-to-transmissive switching electrochromes. The polymers are based on repeat units of propylenedioxythiophene (ProDOT) in alternation with a variety of arylenes including 1,4-phenylene (ProDOT-Ph), 2,7-fluorene (ProDOT-Fl), 2,7-carbazole (ProDOT-Cbz), 2,5-dimethoxy-1,4-phenylene (ProDOT-Ph(MeO)2), and 2,7-pyrene (ProDOT-Py). Additionally, a random copolymer containing ProDOT and two different arylene units was produced: ProDOT-phenylene-ProDOT-dimethoxyphenylene (R-ProDOT-Ph/Ph(MeO)2) and two polymers with a ProDOT dimer in alternation with pyrene and phenylene composed ProDOT2-pyrene (ProDOT2-Py) and ProDOT2-phenylene (ProDOT2-Ph), respectively. The polymers were synthesized using Suzuki polycondensation. Examinations of the optoelectronic properties via UV–vis–NIR spectroscopy, differential pulse voltammetry, and spectroelectrochemistry show that varying the electron richness of the polymer by utilizing more electron rich arylenes, dimers of ProDOT, or less electron rich arylenes, the oxidation potential could be decreased or increased, respectively, ranging from 270 to 650 mV. Through subtle C–H ortho interactions from the arylene unit, yellow neutral state colors were maintained with transmissive or near-transmissive oxidized states. Colorimetry utilizing L*a*b*, where a*b* values correlate to the chroma or saturation of a color (note: −a* and +a* correspond to green and red and −b* and +b* correspond to blue and yellow, respectively) and L* represents the lightness, was used to show the maintenance of yellow colors in the neutral states. Herein, the yellow polymers had L* values above 84.0, a* values ranging from −11.6 to 24.8, and b* values greater than 47.6. In the oxidized states, the most transmissive forms had L* values above 70.0, a* values ranging from −2.1 to 2.0, and b* values ranging from −6.8 to −0.1. These structure–property relationships grant access to conjugated polymers with high energy absorbance in the visible, while allowing variability in redox potentials, providing a deeper understanding in yielding yellow-to-transmissive electrochromic polymers.
Co-reporter:Andrew M. Spring, Leandro A. Estrada, Svetlana V. Vasilyeva, Andrew G. Rinzler, and John R. Reynolds
Macromolecules 2014 Volume 47(Issue 8) pp:2556-2560
Publication Date(Web):April 2, 2014
DOI:10.1021/ma500009s
In this paper, we report the synthesis and characterization of a well-controlled and acid degradable poly(acetal) which can adsorb strongly to the surface of carbon nanotubes (CNTs). These polymers, generated via acyclic diene metathesis (ADMET), incorporate pendant pyrene groups that are well-known to associate strongly to CNTs by noncovalent interactions. Films and solutions of the polymer were degraded through the controlled addition of aqueous hydrochloric acid in ethanol. The polymer’s ability to adsorb to and be removed from a CNT film was also evaluated.
Co-reporter:Cephas E. Small;Sai-Wing Tsang;Song Chen;Sujin Baek;Chad M. Amb;Jegadesan Subbiah;Franky So
Advanced Energy Materials 2013 Volume 3( Issue 7) pp:909-916
Publication Date(Web):
DOI:10.1002/aenm.201201114
Abstract
Polymer bulk heterojunction solar cells based on low bandgap polymer:fullerene blends are promising for next generation low-cost photovoltaics. While these solution-processed solar cells are compatible with large-scale roll-to-roll processing, active layers used for typical laboratory-scale devices are too thin to ensure high manufacturing yields. Furthermore, due to the limited light absorption and optical interference within the thin active layer, the external quantum efficiencies (EQEs) of bulk heterojunction polymer solar cells are severely limited. In order to produce polymer solar cells with high yields, efficient solar cells with a thick active layer must be demonstrated. In this work, the performance of thick-film solar cells employing the low-bandgap polymer poly(dithienogermole-thienopyrrolodione) (PDTG-TPD) was demonstrated. Power conversion efficiencies over 8.0% were obtained for devices with an active layer thickness of 200 nm, illustrating the potential of this polymer for large-scale manufacturing. Although an average EQE > 65% was obtained for devices with active layer thicknesses > 200 nm, the cell performance could not be maintained due to a reduction in fill factor. By comparing our results for PDTG-TPD solar cells with similar P3HT-based devices, we investigated the loss mechanisms associated with the limited device performance observed for thick-film low-bandgap polymer solar cells.
Co-reporter:Jesse R. Mers;Sai-Wing Tsang;Michael J. Hartel;Tzung-Han Lai;Song Chen;Chad M. Amb;Franky So
Advanced Functional Materials 2013 Volume 23( Issue 23) pp:2993-3001
Publication Date(Web):
DOI:10.1002/adfm.201202269
Abstract
The detailed characterization of solution-derived nickel (II) oxide (NiO) hole-transporting layer (HTL) films and their application in high efficiency organic photovoltaic (OPV) cells is reported. The NiO precursor solution is examined in situ to determine the chemical species present. Coordination complexes of monoethanolamine (MEA) with Ni in ethanol thermally decompose to form non-stoichiometric NiO. Specifically, the [Ni(MEA)2(OAc)]+ ion is found to be the most prevalent species in the precursor solution. The defect-induced Ni3+ ion, which is present in non-stoichiometric NiO and signifies the p-type conduction of NiO, as well as the dipolar nickel oxyhydroxide (NiOOH) species are confirmed using X-ray photoelectron spectroscopy. Bulk heterojunction (BHJ) solar cells with a polymer/fullerene photoactive layer blend composed of poly-dithienogermole-thienopyrrolodione (pDTG-TPD) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are fabricated using these solution-processed NiO films. The resulting devices show an average power conversion efficiency (PCE) of 7.8%, which is a 15% improvement over devices utilizing a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. The enhancement is due to the optical resonance in the solar cell and the hydrophobicity of NiO, which promotes a more homogeneous donor/acceptor morphology in the active layer at the NiO/BHJ interface. Finally, devices incorporating NiO as a HTL are more stable in air than devices using PEDOT:PSS.
Co-reporter:Kenneth R. Graham, Romain Stalder, Patrick M. Wieruszewski, Dinesh G. Patel, Danielle H. Salazar, and John R. Reynolds
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 1) pp:63
Publication Date(Web):December 3, 2012
DOI:10.1021/am301944g
Tailor-made additives, which are molecules that share the same molecular structure as a parent molecule with only slight structural variations, have previously been demonstrated as a useful means to control crystallization dynamics in solution. For example, tailor-made additives can be added to solutions of a crystallizing parent molecule to alter the crystal growth rate, size, and shape. We apply this strategy as a means to predictably control morphology in molecular bulk-heterojunction (BHJ) photovoltaic cells. Through the use of an asymmetric oligomer substituted with a bulky triisobutylsilyl end group, the morphology of BHJ blends can be controlled resulting in a near doubling (from 1.3 to 2.2%) in power conversion efficiency. The use of tailor-made additives provides promising opportunities for controlling crystallization dynamics, and thereby film morphologies, for many organic electronic devices such as photovoltaics and field-effect transistors.Keywords: bulk-heterojunction; morphology control; organic photovoltaic; tailor-made additive;
Co-reporter:Kyukwan Zong, James J. Deininger, and John R. Reynolds
Organic Letters 2013 Volume 15(Issue 5) pp:1032-1035
Publication Date(Web):February 19, 2013
DOI:10.1021/ol303529w
4,4′-Bis-(4-pentenyl)-dithieno[3,2-b:2′,3′-d]germole was synthesized as a functional building block for the efficient preparation of dithienogermole (DTG) derivatives with varying alkyl chain lengths and pendant functionalities in excellent yields. These derivatives were efficiently isolated via olefin cross-metathesis followed by hydrogenation.
Co-reporter:Leandro A. Estrada, James J. Deininger, George D. Kamenov, and John R. Reynolds
ACS Macro Letters 2013 Volume 2(Issue 10) pp:869
Publication Date(Web):September 17, 2013
DOI:10.1021/mz4003886
We report the use of direct (hetero)arylation polymerizations (DHAP) as a means of obtaining 3,4-propylenedioxythiophene-based conjugated polymers for use in electrochromics. This method offers a rapid route to achieving polymers in high yields with simplified purification procedures and low residual metal content, as determined by inductive coupled plasma-mass spectrometry (ICP-MS). The studied polymers possess comparable electrochromic properties to those previously reported by our group, implying that their switching ability from a colored to a transmissive state is independent of the residual metallic impurities.
Co-reporter:Li Wang, Egle Puodziukynaite, Erik M. Grumstrup, Aaron C. Brown, Shahar Keinan, Kirk S. Schanze, John R. Reynolds, and John M. Papanikolas
The Journal of Physical Chemistry Letters 2013 Volume 4(Issue 14) pp:2269-2273
Publication Date(Web):June 26, 2013
DOI:10.1021/jz401089v
A light-harvesting macromolecular assembly (PT-Ru) consisting of a poly(3-hexylthiophene) (P3HT) scaffold and pendant Ru(II) polypyridyl complexes that exhibits rapid and efficient formation of a long-lived charge-separated state is described here. Photoinduced electron transfer from the polymer backbone to Ru(II) was investigated by femtosecond transient absorption spectroscopy. Photoexcitation at 388 nm results in the excitation of both the polymer backbone and Ru(II) complexes, with relative excitation probabilities of 60 and 40%, respectively. The dominant pathway (∼85%) for decay of the polymer excited state is direct electron transfer from the polymer scaffold to Ru(II), forming a positive polaron and a reduced complex [RuII(L)2(L–)]+, denoted Ru(I). The charge-separated state PT+•-Ru(I) is long-lived, persisting for 20–60 μs, and is attributed to the high mobility of holes on the polymer backbone, which facilitates spatial separation of the electron and hole, delaying recombination. The remaining 15% of the polymer excited states undergo an alternate deactivation mechanism, possibly energy transfer to Ru(II), forming Ru(II)*. Ru(II)* formed by either direct excitation or energy transfer undergoes back energy transfer to the scaffold, forming the low-lying polymer triplet state on the nanosecond time scale.Keywords: electron transfer; energy transfer; femtosecond; P3HT; pump−probe;
Co-reporter:Song Chen;Cephas E. Small;Chad M. Amb;Jegadesan Subbiah;Tzung-han Lai;Sai-Wing Tsang;Jesse R. Mers;Franky So
Advanced Energy Materials 2012 Volume 2( Issue 11) pp:
Publication Date(Web):
DOI:10.1002/aenm.201290053
Co-reporter:Song Chen;Cephas E. Small;Chad M. Amb;Jegadesan Subbiah;Tzung-han Lai;Sai-Wing Tsang;Jesse R. Mers;Franky So
Advanced Energy Materials 2012 Volume 2( Issue 11) pp:1333-1337
Publication Date(Web):
DOI:10.1002/aenm.201200184
Co-reporter:Pierre M. Beaujuge ; Hoi Nok Tsao ; Michael Ryan Hansen ; Chad M. Amb ; Chad Risko ; Jegadesan Subbiah ; Kaushik Roy Choudhury ; Alexei Mavrinskiy ; Wojciech Pisula ; Jean-Luc Brédas ; Franky So ; Klaus Müllen
Journal of the American Chemical Society 2012 Volume 134(Issue 21) pp:8944-8957
Publication Date(Web):May 18, 2012
DOI:10.1021/ja301898h
Given the fundamental differences in carrier generation and device operation in organic thin-film transistors (OTFTs) and organic photovoltaic (OPV) devices, the material design principles to apply may be expected to differ. In this respect, designing organic semiconductors that perform effectively in multiple device configurations remains a challenge. Following “donor–acceptor” principles, we designed and synthesized an analogous series of solution-processable π-conjugated polymers that combine the electron-rich dithienosilole (DTS) moiety, unsubstituted thiophene spacers, and the electron-deficient core 2,1,3-benzothiadiazole (BTD). Insights into backbone geometry and wave function delocalization as a function of molecular structure are provided by density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level. Using a combination of X-ray techniques (2D-WAXS and XRD) supported by solid-state NMR (SS-NMR) and atomic force microscopy (AFM), we demonstrate fundamental correlations between the polymer repeat-unit structure, molecular weight distribution, nature of the solubilizing side-chains appended to the backbones, and extent of structural order attainable in p-channel OTFTs. In particular, it is shown that the degree of microstructural order achievable in the self-assembled organic semiconductors increases largely with (i) increasing molecular weight and (ii) appropriate solubilizing-group substitution. The corresponding field-effect hole mobilities are enhanced by several orders of magnitude, reaching up to 0.1 cm2 V–1 s–1 with the highest molecular weight fraction of the branched alkyl-substituted polymer derivative in this series. This trend is reflected in conventional bulk-heterojunction OPV devices using PC71BM, whereby the active layers exhibit space-charge-limited (SCL) hole mobilities approaching 10–3 cm2 V–1 s–1, and yield improved power conversion efficiencies on the order of 4.6% under AM1.5G solar illumination. Beyond structure–performance correlations, we observe a large dependence of the ionization potentials of the polymers estimated by electrochemical methods on polymer packing, and expect that these empirical results may have important consequences on future material study and device applications.
Co-reporter:Dinesh G. (Dan) Patel ; Fude Feng ; Yu-ya Ohnishi ; Khalil A. Abboud ; So Hirata ; Kirk S. Schanze
Journal of the American Chemical Society 2012 Volume 134(Issue 5) pp:2599-2612
Publication Date(Web):January 31, 2012
DOI:10.1021/ja207978v
We report on the comparison of the electronic and photophysical properties of a series of related donor–acceptor–donor oligomers incorporating the previously known 2H-benzo[d][1,2,3]triazole (BTz) moiety as the acceptor and the recently reported BTzTD acceptor, a hybrid of BTz and 2,1,3-benzothiadiazole (BTD). Although often implied in the polymer literature that BTz has good acceptor character, we show that this moiety is best described as a weak acceptor. We present electrochemical, computational, and photophysical evidence supporting our assertion that BTzTD is a strong electron acceptor while maintaining the alkylation ability of the BTz moiety. Our results show that the identity of the central atom (N or S) in the benzo-fused heterocyclic ring plays an important role in both the electron-accepting and the electron-donating ability of acceptor moieties with sulfur imparting a greater electron-accepting ability and nitrogen affording greater electron-donating character. We report on the X-ray crystal structure of a BTzTD trimer, which exhibits greater local aromatic character in the region of the triazole ring and contains an electron-deficient sulfur that imparts strong electron-accepting ability. Additionally, we examine the transient absorption spectra of BTzTD and BTz oligomers and report that the BTz core promotes efficient intersystem crossing to the triplet state, while the presence of the thiadiazole moiety in BTzTD leads to a negligible triplet yield. Additionally, while BTz does not function as a good acceptor, oligomers containing this moiety do function as excellent sensitizers for the generation of singlet oxygen.
Co-reporter:Kenneth R. Graham;Patrick M. Wieruszewski;Romain Stalder;Michael J. Hartel;Jianguo Mei;Franky So
Advanced Functional Materials 2012 Volume 22( Issue 22) pp:4801-4813
Publication Date(Web):
DOI:10.1002/adfm.201102456
Abstract
Solvent additives provide an effective means to alter the morphology and thereby improve the performance of organic bulk-heterojunction photovoltaics, although guidelines for selecting an appropriate solvent additive remain relatively unclear. Here, a family of solvent additives spanning a wide range of Hansen solubility parameters is applied to a molecular bulk-heterojunction system consisting of an isoindigo and thiophene containing oligomer as the electron donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the electron acceptor. Hansen solubility parameters are calculated using the group contribution method and compared with the measured solubilities for use as a screening method in solvent additive selection. The additives are shown to alter the morphologies in a semipredictable manner, with the poorer solvents generally resulting in decreased domain sizes, increased hole mobilities, and improved photovoltaic performance. The additives with larger hydrogen bonding parameters, namely triethylene glycol (TEG) and N-methyl-2-pyrrolidone (NMP), are demonstrated to increase the open circuit voltage by ~0.2 V. Combining a solvent additive observed to increase short circuit current, poly(dimethylsiloxane), with TEG results in an increase in power conversion efficiency from 1.4 to 3.3%.
Co-reporter:Romain Stalder, Dongping Xie, Renjia Zhou, Jiangeng Xue, John R. Reynolds, and Kirk S. Schanze
Chemistry of Materials 2012 Volume 24(Issue 16) pp:3143
Publication Date(Web):August 17, 2012
DOI:10.1021/cm301351j
Three linear asymmetrically functionalized conjugated molecules composed of five or six aromatic rings were synthesized, bearing a terminal phosphonic acid group, with the objective of enabling their grafting onto inorganic CdSe nanocrystals. These chromophores—oligo(phenylene ethynylenes), oligothiophenes, or donor–acceptor–donor oligothiophenes with a benzothiadiazole acceptor—were designed with decreasing HOMO–LUMO energy gaps such that increasing amounts of light could be absorbed toward the longer wavelengths up to 600 nm. Electrochemical measurements show that the energy offsets between the HOMO and LUMO energies of the organic molecules and the energy bands of the CdSe nanocrystals are well-suited for charge transfer between the organic and inorganic components. The characteristics of each component’s excited state are studied by fluorescence spectroscopy and the interaction between the conjugated molecules and the CdSe nanocrystals in dilute solutions is monitored by photoluminescence quenching. In the latter experiments, where ester and acid derivatives are compared, the pronounced difference in luminescence quenching supports the ability of the phosphonic acid groups to strongly anchor onto the surface of the nanocrystals. Moreover, these results suggest that charge transfer likely occurs between the organic and the inorganic compounds, and appropriate ratios for the corresponding organic/inorganic hybrids preparation are identified. The preparation by direct ligand exchange and the photophysical properties of the hybrids are described, and spectroscopic analysis estimates that the nanocrystals are covered, on average, with 100–200 electroactive organic molecules. The incident photon-to-electron conversion efficiency reflects the solution absorption of the hybrids because it shows the response from both organic and inorganic components.Keywords: conjugated oligomers; donor−acceptor; hybrid materials; nanocrystals; phosphonic acid;
Co-reporter:Merve Ertas, Ryan M. Walczak, Rajib K. Das, Andrew G. Rinzler, and John R. Reynolds
Chemistry of Materials 2012 Volume 24(Issue 3) pp:433
Publication Date(Web):February 2, 2012
DOI:10.1021/cm201110t
This paper reports a novel supercapacitor electrode design based on poly(3,4-propylenedioxypyrrole) (PProDOP) electropolymerized onto thin films of single walled carbon nanotubes (SWNTs) on glass substrates. This permits the electropolymerization of thicker PProDOP films than can be deposited onto flat gold-coated Kapton electrodes and a correspondingly greater capacitance per unit area. A pyrene functionalized polyfluorene, designated Sticky-PF, was designed and used as an effective monolayer interfacial adhesion modifier between the SWNT films and PProDOP via noncovalent self-assembly onto the SWNT film surfaces before polymer electrodeposition. The thickness of the electrodeposited PProDOP was found to be self-limiting at thicknesses characteristic of each substrate electrode. Optimized areal capacitance values for PProDOP on flat gold and Sticky-PF coated SWNT films were measured to be 8.1 mF/cm2 and 16.4 mF/cm2, respectively, with the twofold enhancement due to the thicker films possible on the SWNT electrode. The specific capacitance of PProDOP on gold and Sticky-PF|SWNT film substrates were found to be similar at 141 F/g and 122 F/g, respectively, indicating the capacitance to be due to the electroactive polymer. The areal capacitance values of the corresponding supercapacitor devices constructed with Au/Kapton substrates was 3.2 mF/cm2, whereas a significantly greater value of 8.8 mF/cm2 was measured for the Sticky-PF|SWNT film substrates. The supercapacitors prepared using the Au/Kapton substrates were highly stable, retaining 80% of their electroactivity after 32 700 nonstop charge/discharge cycles (100% depth of discharge). Supercapacitors made using the Sticky-PF|SWNT substrates showed a steady loss of capacitance to about 57% of the original value (to 5.0 mF/cm2) after 32 700 charge/discharge cycles, which was still 38% larger than the initial capacitance of the gold electrode devices.Keywords: capacitance; carbon nanotubes; conducting polymers; electrochemical capacitors; poly(3,4-propylenedioxypyrrole); pyrene functionalized polyfluorene; supercapacitor electrodes;
Co-reporter:Eric P. Knott, Michael R. Craig, David Y. Liu, Joseph E. Babiarz, Aubrey L. Dyer and John R. Reynolds
Journal of Materials Chemistry A 2012 vol. 22(Issue 11) pp:4953-4962
Publication Date(Web):31 Jan 2012
DOI:10.1039/C2JM15057C
As the colour palette of solution processable electrochromic conjugated polymers has extended from hues of purple and blue to vibrant colours such as yellow, orange, red, green, and cyan, the need for a counter electrode material that provides charge balance in electrochromic devices, but lends minimal colour, has become increasingly necessary. Nowhere is this more true than in absorptive/transmissive window-type devices where a high level of transparency and near colourlessness is needed in the device bleached state. This argument can also be extended to absorptive/reflective display-type devices where an “on” (coloured) and “off” (bleached or white) state is desired. Here, we report the development of a highly electroactive, low colouration efficiency propylenedioxypyrrole-based polymer that exhibits a low redox potential and minimal colour saturation in both fully neutralised and fully oxidised states. Thin films of the polymer, spray-cast onto transparent electrodes exhibited relatively low composite colouration efficiencies at 555 nm of 35 cm2C−1, contrasted with the the high colouration efficiency ECP-Magenta that exhibits 633 cm2C−1. We further demonstrate the utilisation of this polymer as an effective charge balancing counter electrode material in an absorptive/transmissive window-type device wherein the vibrantly coloured state and highly transmissive, near colourless bleached state of ECP-Magenta is maintained giving an overall device contrast of 61% at 540 nm.
Co-reporter:Pengjie Shi, Chad M. Amb, Aubrey L. Dyer, and John R. Reynolds
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 12) pp:6512
Publication Date(Web):December 7, 2012
DOI:10.1021/am3015394
This paper describes the synthesis of two new blue to transmissive donor–acceptor electrochromic polymers: a polymer synthesized using an alternating copolymerization route (ECP-Blue-A) and a polymer synthesized using a random copolymerization (ECP-Blue-R) by Stille polymerization. These polymers utilize side chains with four ester groups per donor moiety, allowing organic solubility in the ester form, and water solubility upon saponification to their carboxylate salt form. We demonstrate that the saponified polymer salts of ECP-Blue-A and ECP-Blue-R (WS-ECP-Blue-A and WS-ECP-Blue-R) can be processed from aqueous solutions into thin films by spray-casting. Upon the subsequent neutralization of the thin films, the resulting polymer acid films are solvent resistant and can be electrochemically switched between their colored state and a transmissive state in a KNO3/water electrolyte solution. The polymer acids, WS-ECP-Blue-A-acid and WS-ECP-Blue-R-acid, show electrochromic contrast Δ%T of 38% at 655 nm and 39% at 555 nm for a 0.5 s switch, demonstrating the advantage of an aqueous compatible electrochrome switchable in high ionic conductivity aqueous electrolytes. The results of the electrochromic properties study indicate that these polymers are promising candidates for aqueous processable and aqueous switching electrochromic materials and devices as desired for applications where environmental impact is of importance.Keywords: electrochromism; Stille polymerization; water-soluble electroactive polymers;
Co-reporter:Chad M. Amb, Michael R. Craig, Unsal Koldemir, Jegadesan Subbiah, Kaushik Roy Choudhury, Suren A. Gevorgyan, Mikkel Jørgensen, Frederik C. Krebs, Franky So, and John R. Reynolds
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 3) pp:1847
Publication Date(Web):February 21, 2012
DOI:10.1021/am300156p
The practical application of organic photovoltaic (OPV) cells requires high throughput printing techniques in order to attain cells with an area large enough to provide useful amounts of power. However, in the laboratory screening of new materials for OPVs, spin-coating is used almost exclusively as a thin-film deposition technique due its convenience. We report on the significant differences between the spin-coating of laboratory solar cells and slot-die coating of a blue-green colored, low bandgap polymer (PGREEN). This is one of the first demonstrations of slot-die-coated polymer solar cells OPVs not utilizing poly(3-hexylthiophene):(6,6)-phenyl-C61-butyric acid methyl ester (PCBM) blends as a light absorbing layer. Through synthetic optimization, we show that strict protocols are necessary to yield polymers which achieve consistent photovoltaic behavior. We fabricated spin-coated laboratory scale OPV devices with PGREEN: PCBM blends as active light absorbing layers, and compare performance to slot die-coated individual solar cells, and slot-die-coated solar modules consisting of many cells connected in series. We find that the optimum ratio of polymer to PCBM varies significantly when changing from spin-coating of thinner active layer films to slot-die coating, which requires somewhat thicker films. We also demonstrate the detrimental impacts on power conversion efficiency of high series resistance imparted by large electrodes, illustrating the need for higher conductivity contacts, transparent electrodes, and high mobility active layer materials for large-area solar cell modules.Keywords: low band gap polymers; polymer solar cells; roll-to-roll printing/coating; slot-die coating;
Co-reporter:Frank A. Arroyave, Coralie A. Richard, and John R. Reynolds
Organic Letters 2012 Volume 14(Issue 24) pp:6138-6141
Publication Date(Web):December 5, 2012
DOI:10.1021/ol302704v
A straightforward synthesis of the fused-aromatic dione benzo[1,2-b:6,5-b′]dithiophene-4,5-dione (BDTD) has been developed. This fused-aromatic dione was subjected to various chemical transformations to generate diverse molecules with potential use in π-conjugated materials for organic electronics.
Co-reporter:Leandro A. Estrada, David Y. Liu, Danielle H. Salazar, Aubrey L. Dyer, and John R. Reynolds
Macromolecules 2012 Volume 45(Issue 20) pp:8211-8220
Publication Date(Web):October 4, 2012
DOI:10.1021/ma3016129
Poly[6,6′-bis(ethylene-3,4-dioxythien-2-yl)]-N,N′-dialkylisoindigo (PBEDOT-iI) was synthesized and incorporated as an electroactive material into electrochemical supercapacitors (ESCs) in type I and type III configurations. In type I ESCs, PBEDOT-iI provides a specific power of ∼360 W/kg and specific energy of ∼0.5 Wh/kg, while retaining about 80% of its electroactivity over 10 000 cycles. In addition, we report on the use of PBEDOT-iI in type III supercapacitors where operating voltages as high as 2.5 V were achieved with specific energies of ca. 15 Wh/kg, albeit with limited stability.
Co-reporter:Li Wang, Egle Puodziukynaite, Ryan P. Vary, Erik M. Grumstrup, Ryan M. Walczak, Olga Y. Zolotarskaya, Kirk S. Schanze, John R. Reynolds, and John M. Papanikolas
The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 17) pp:2453-2457
Publication Date(Web):August 15, 2012
DOI:10.1021/jz300979j
This Letter describes the synthesis and photophysical characterization of a Ru(II) assembly consisting of metal polypyridyl complexes linked together by a polyfluorene scaffold. Unlike many scaffolds incorporating saturated linkages, the conjugated polymer in this system acts as a functional light-harvesting component. Conformational disorder breaks the conjugation in the polymer backbone, resulting in a chain composed of many chromophore units, whose relative energies depend on the segment lengths. Photoexcitation of the polyfluorene by a femtosecond laser pulse results in the excitation of polyfluorene, which then undergoes direct energy transfer to the pendant Ru(II) complexes, producing Ru(II)* excited states within 500 fs after photoexcitation. Femtosecond transient absorption data show the presence of electron transfer from PF* to Ru(II) to form charge-separated (CS) products within 1–2 ps. The decay of the oxidized and reduced products, PF+• and Ru(I), through back electron transfer are followed using picosecond transient absorption methods.Keywords: metal polypyridyl complexes; organic chromophore; photoinduced energy transfer; polymer assembly; redox separation; spectroscopy;
Co-reporter:Hayden T. Black, Ian Pelse, Rylan M. W. Wolfe and John R. Reynolds
Chemical Communications 2016 - vol. 52(Issue 87) pp:NaN12880-12880
Publication Date(Web):2016/10/14
DOI:10.1039/C6CC06443D
A new halochromic compound is reported with pronounced UV/Vis spectral responses that depend on the extent of protonation and on the counter-ion structure. The absorption can be controlled over the entire visible spectrum and into the near-IR via a protonation-induced assembly mechanism. Thin-films were used for colorimetric detection of acid vapors.
Co-reporter:Frank A. Arroyave
Macromolecules () pp:
Publication Date(Web):July 24, 2012
DOI:10.1021/ma300684t
A convenient and efficient deiodination polycondensation method for the synthesis of dioxypyrrole-based (XDOP) polymers is reported. N-Halosuccinimides, iodine, and bromine were evaluated as halogenating agents to produce 2,5-halodioxypyrroles in situ via halodecarboxylation of 3,4-dioxypyrrole-2,5-dicarboxylic acids, which were then polymerized at 60 °C using dichloromethane or chloroform as solvent. When iodine and N-iodosuccinimide were employed as electrophilic halogen sources, the methodology produced macromolecules (Mn = 6.2–22.9 kDa) in satisfactory yields (55–71%) for two N-alkyl-3,4-dialkyloxypyrrole-based monomers that were tested. This method can be employed to produce a variety of XDOP-based homopolymers and regioregular copolymers starting from discrete oligomers under relatively mild reaction conditions.
Co-reporter:D. Eric Shen, Leandro A. Estrada, Anna M. Österholm, Danielle H. Salazar, Aubrey L. Dyer and John R. Reynolds
Journal of Materials Chemistry A 2014 - vol. 2(Issue 20) pp:NaN7516-7516
Publication Date(Web):2014/04/10
DOI:10.1039/C4TA01375A
A number of variables contribute to the electropolymerization, and the electrochemical properties, of electroactive polymers. However, few studies have attempted to acquire a unified understanding of the effects of all these variables, specifically as it relates to the capacitance of the material, as the number of experiments and resources required is large. Here, the effects of seven variables on the areal capacitance of the electropolymerized dimethyl derivative of poly(3,4-propylenedioxythiophene) (PProDOT-Me2) films are analyzed utilizing a fractional factorial design of experiments to reduce the number of experiments an order of magnitude. From this analysis, PProDOT-Me2 films were electropolymerized from an optimal set of variables to reproducibly afford films displaying the highest capacitances observed within this study. Devices were assembled from the optimized conditions, and the capacitance, energy, and power densities are reported in a framework that allows for meaningful comparison and understanding relative to commercially available supercapacitors. The supercapacitors fabricated in this study show promise towards being integrated as power sources for low-power, lightweight and flexible organic electronic devices.
Co-reporter:Coralie A. Richard, Zhenxing Pan, Anand Parthasarathy, Frank A. Arroyave, Leandro A. Estrada, Kirk S. Schanze and John R. Reynolds
Journal of Materials Chemistry A 2014 - vol. 2(Issue 25) pp:NaN9874-9874
Publication Date(Web):2014/05/23
DOI:10.1039/C4TA01199F
A series of four quadrupolar (Donor)2Acceptor-acid (D2A) sensitizers, based on two acceptor cores (dibenzophenazine (DBP) or dithienophenazine (DTP)), were synthesized and their optoelectronic and photovoltaic properties were investigated. 4-Hexyl-thien-2-yl groups were employed as donor units, to produce regioisomers depending on their connecting position to the core. This architectural design leads to the investigation of the structure–property relationships of the dyes, both in solution and upon integration in dye-sensitized solar cells (DSSCs). Within sets of regioisomers, frontier orbital levels and absorption properties differed, but the photovoltaic performances of the DSSCs were similar. When examining the effect of the core, the electronic properties (absorbance, LUMO level) predicted a more favourable electron injection for the DTP systems. However, the open circuit voltages are ∼100 mV greater for the DBP systems.
Co-reporter:R. H. Bulloch and J. R. Reynolds
Journal of Materials Chemistry A 2016 - vol. 4(Issue 3) pp:NaN610-610
Publication Date(Web):2015/12/23
DOI:10.1039/C5TC03536H
Many proposed applications for electrochromic polymers (ECPs), which are designed to modulate the intensity or spectral power density of light, center around the interaction between the ECPs and the incident light. The long-term effects of the interaction of light and ECPs are rarely discussed in the literature, yet is a crucial parameter in materials evaluation in many applications. With the goal of examining the photo-stability of select ECPs, two polymers were selected for study, which are representative of both 3,4-dioxythiophene (DOT) and 3,4-dioxypyrrole (DOP) based materials. Samples of each material were sealed in glass cells under varying atmospheric conditions using a polyisobutylene-based barrier sealant and irradiated under a solar simulator for time periods ranging from 24 hours to one month. Following irradiation, electrochromic performance was assessed via both electrochemical and spectroelectrochemical methods. Additionally, X-ray photoelectron spectroscopy (XPS) was used to study chemical changes following irradiation. We report here that, following irradiation, no change in electrochromic performance (as measured by Δ%T at λmax) nor spectra recorded via XPS was observed in films encapsulated under an inert atmosphere, suggesting that conditions of irradiation alone are insufficient to degrade the performance of either ECP structure.
Co-reporter:J. A. Kerszulis, K. E. Johnson, M. Kuepfert, D. Khoshabo, A. L. Dyer and J. R. Reynolds
Journal of Materials Chemistry A 2015 - vol. 3(Issue 13) pp:NaN3218-3218
Publication Date(Web):2015/02/19
DOI:10.1039/C4TC02685C
A series of vibrantly coloured π-conjugated electrochromic polymers (ECPs) were designed and synthesized with the goal of extracting structure–property relationships from subtle changes in steric strain or relaxation. These are soluble all donor, electron rich, alternating polymers based on repeat units of 3,4-ethylenedioxythiophene (EDOT), 3,4-propylenedioxythiophene (ProDOT), and an acyclic dioxythiophene (AcDOT) in varying combinations to tune steric interactions and the subsequent optical absorption for fine colour control. Two families of polymers were formed where ProDOT2–EDOT, ProDOT–EDOT, and ProDOT2–EDOT2 constitute new shades of blues while AcDOT2–ProDOT, AcDOT–ProDOT, and AcDOT–EDOT yield new hues of magentas with the homopolymers of ProDOT and AcDOT and the copolymer AcDOT2–EDOT2 serving as comparisons. The polymers were synthesized using direct (hetero)arylation polymerization. Examinations of the optoelectronic properties via cyclic voltammetry, spectroelectrochemistry, and colorimetry show that by subtly varying the level of steric relaxation or strain in the form of EDOT or AcDOT content, lower or higher energy absorption transitions are produced respectively. This increase in relaxation or strain allows more short or long wavelength light to transmit, giving new shades of blues or magentas respectively. Since these are all donating polymers, they exhibit changes in contrast no less than 70% at the λmax with the exception of AcDOT–EDOT. The most desirable electrochromic properties were achieved with ProDOT2–EDOT2 and AcDOT2–ProDOT, with band gaps (Eg) and neutral state L*a*b* colour values (−a* and +a* correspond to green and red and −b* and +b* correspond to blue and yellow respectively and L* represents the lightness) of 1.74 eV, 37, 12, −63 and 2.01 eV, 56, 59, −16 respectively. The highly transmissive oxidized state colour values for ProDOT2–EDOT2 and AcDOT2–ProDOT are 92, −3, −3 and 91, −2, −1 respectively. These structure–property relationships grant a greater ability to tune light absorption across the visible, with colour properties similar to ECPs made through other methods without using donor–acceptor effects. This all donor steric tuning method leads to considerably higher levels of transparency when the polymers are fully oxidized.
Co-reporter:D. Eric Shen, Anna M. Österholm and John R. Reynolds
Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN9725-9725
Publication Date(Web):2015/09/03
DOI:10.1039/C5TC01964H
Throughout the literature, a variety of counter electrode materials have been used in conjugated polymer-based electrochromic devices (ECDs) without a comparative understanding of their effects on the electrochromic properties of the device. In this study, we show that poor ECD performance, often attributed to electrochromic polymer (ECP) stability, is in fact largely due to an inappropriate choice of counter electrode. We have compared a set of counter electrode materials used in the ECD literature in magenta-to-clear and black-to-clear devices and evaluated how they affect the device parameters including contrast, switching time, stability, and voltage requirements. We demonstrate that through the appropriate choice of counter electrode material (i) the operating voltage can be lowered, (ii) no additional equilibration/break-in time is required, and (iii) the contrast and switching times of the ECP is maintained when incorporated into a device. Furthermore, we show that even unencapsulated ECDs with ECP-Magenta as the vibrantly colored material assembled and operated under ambient conditions can withstand over 10000 switches without compromising contrast or switching time.
Co-reporter:Eric P. Knott, Michael R. Craig, David Y. Liu, Joseph E. Babiarz, Aubrey L. Dyer and John R. Reynolds
Journal of Materials Chemistry A 2012 - vol. 22(Issue 11) pp:NaN4962-4962
Publication Date(Web):2012/01/31
DOI:10.1039/C2JM15057C
As the colour palette of solution processable electrochromic conjugated polymers has extended from hues of purple and blue to vibrant colours such as yellow, orange, red, green, and cyan, the need for a counter electrode material that provides charge balance in electrochromic devices, but lends minimal colour, has become increasingly necessary. Nowhere is this more true than in absorptive/transmissive window-type devices where a high level of transparency and near colourlessness is needed in the device bleached state. This argument can also be extended to absorptive/reflective display-type devices where an “on” (coloured) and “off” (bleached or white) state is desired. Here, we report the development of a highly electroactive, low colouration efficiency propylenedioxypyrrole-based polymer that exhibits a low redox potential and minimal colour saturation in both fully neutralised and fully oxidised states. Thin films of the polymer, spray-cast onto transparent electrodes exhibited relatively low composite colouration efficiencies at 555 nm of 35 cm2C−1, contrasted with the the high colouration efficiency ECP-Magenta that exhibits 633 cm2C−1. We further demonstrate the utilisation of this polymer as an effective charge balancing counter electrode material in an absorptive/transmissive window-type device wherein the vibrantly coloured state and highly transmissive, near colourless bleached state of ECP-Magenta is maintained giving an overall device contrast of 61% at 540 nm.
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![3,3-BIS(BROMOMETHYL)-2,4-DIHYDROTHIENO[3,4-B][1,4]DIOXEPINE](http://img.cochemist.com/ccimg/701300/701209-98-5.png)
![3,3-BIS(BROMOMETHYL)-2,4-DIHYDROTHIENO[3,4-B][1,4]DIOXEPINE](http://img.cochemist.com/ccimg/701300/701209-98-5_b.png)
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![2,2',3,3'-Tetrahydro-5,5'-bithieno[3,4-b][1,4]dioxine](http://img.cochemist.com/ccimg/195700/195602-17-6_b.png)
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![POLY[3,3-BIS[[(2-ETHYLHEXYL)OXY]METHYL]-3,4-DIHYDRO-2H-THIENO[3,4-B][1,4]DIOXEPIN-6,8-DIYL]](http://img.cochemist.com/ccimg/783400/783322-81-6_b.png)
![3,3-Bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine](http://img.cochemist.com/ccimg/634600/634591-75-6.png)
![3,3-Bis(((2-ethylhexyl)oxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine](http://img.cochemist.com/ccimg/634600/634591-75-6_b.png)
