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Lee Y, Aplan MP, Seibers ZD, Xie R, Culp TE, Wang C, Hexemer A, Kilbey SM, Wang Q, Gomez ED. Random Copolymers Allow Control of Crystallization and Microphase Separation in Fully Conjugated Block Copolymers. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b01859] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Huang S, Makarem M, Kiemle SN, Zheng Y, He X, Ye D, Gomez EW, Gomez ED, Cosgrove DJ, Kim SH. Dehydration-induced physical strains of cellulose microfibrils in plant cell walls. Carbohydr Polym 2018; 197:337-348. [DOI: 10.1016/j.carbpol.2018.05.091] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 05/05/2018] [Accepted: 05/30/2018] [Indexed: 01/08/2023]
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53
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Culp TE, Ye D, Paul M, Roy A, Behr MJ, Jons S, Rosenberg S, Wang C, Gomez EW, Kumar M, Gomez ED. Probing the Internal Microstructure of Polyamide Thin-Film Composite Membranes Using Resonant Soft X-ray Scattering. ACS Macro Lett 2018; 7:927-932. [PMID: 35650967 DOI: 10.1021/acsmacrolett.8b00301] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Characterization of the internal morphology of thin film composite membranes used in reverse osmosis (RO) is a prerequisite for understanding the connection between microstructure and water transport properties and is necessary for the design of membranes with improved performance. Here, we examine a series of fully aromatic polyamide active layers of RO membranes that vary in crosslinking using a combination of resonant soft X-ray scattering (RSoXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Analysis of RSoXS profiles reveals a correlation between membrane structure and crosslinking density. Through a combination of scattering contrast calculations, TEM, and AFM micrographs, we assign the dominant contribution to RSoXS data as either surface roughness or chemical heterogeneity, depending on the X-ray energy used. Altogether, our results demonstrate the utility of soft X-ray scattering to examine the microstructure of water filtration membranes.
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Ye D, Kiemle SN, Rongpipi S, Wang X, Wang C, Cosgrove DJ, Gomez EW, Gomez ED. Resonant soft X-ray scattering reveals cellulose microfibril spacing in plant primary cell walls. Sci Rep 2018; 8:12449. [PMID: 30127533 PMCID: PMC6102304 DOI: 10.1038/s41598-018-31024-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 08/10/2018] [Indexed: 12/22/2022] Open
Abstract
Cellulose microfibrils are crucial for many of the remarkable mechanical properties of primary cell walls. Nevertheless, many structural features of cellulose microfibril organization in cell walls are not yet fully described. Microscopy techniques provide direct visualization of cell wall organization, and quantification of some aspects of wall microstructure is possible through image processing. Complementary to microscopy techniques, scattering yields structural information in reciprocal space over large sample areas. Using the onion epidermal wall as a model system, we introduce resonant soft X-ray scattering (RSoXS) to directly quantify the average interfibril spacing. Tuning the X-ray energy to the calcium L-edge enhances the contrast between cellulose and pectin due to the localization of calcium ions to homogalacturonan in the pectin matrix. As a consequence, RSoXS profiles reveal an average center-to-center distance between cellulose microfibrils or microfibril bundles of about 20 nm.
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Zhang W, Milner ST, Gomez ED. Nematic Order Imposes Molecular Weight Effect on Charge Transport in Conjugated Polymers. ACS CENTRAL SCIENCE 2018; 4:413-421. [PMID: 29632888 PMCID: PMC5879482 DOI: 10.1021/acscentsci.8b00011] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Indexed: 05/05/2023]
Abstract
Nematic order, in the bulk or at interfaces, is ubiquitous for semiflexible conjugated polymers. Nevertheless, the effect of liquid crystalline order on charge transport remains unclear. Using an analytical model, we demonstrate that nematic order leads to an enhancement in charge mobilities when compared to isotropic chains. Furthermore, we predict a quadratic dependence of the charge mobility on molecular weight of the chains. Analysis of the probability of forming hairpin defects also shows how the persistence length affects charge transport in conjugated polymers. We speculate that the prevalence of nematic order in conjugated polymers explains the reported increase in charge mobilities with molecular weight.
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Seibers ZD, Le TP, Lee Y, Gomez ED, Kilbey SM. Impact of Low Molecular Weight Poly(3-hexylthiophene)s as Additives in Organic Photovoltaic Devices. ACS APPLIED MATERIALS & INTERFACES 2018; 10:2752-2761. [PMID: 29309125 DOI: 10.1021/acsami.7b13078] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Despite tremendous progress in using additives to enhance the power conversion efficiency of organic photovoltaic devices, significant challenges remain in controlling the microstructure of the active layer, such as at internal donor-acceptor interfaces. Here, we demonstrate that the addition of low molecular weight poly(3-hexylthiophene)s (low-MW P3HT) to the P3HT/fullerene active layer increases device performance up to 36% over an unmodified control device. Low MW P3HT chains ranging in size from 1.6 to 8.0 kg/mol are blended with 77.5 kg/mol P3HT chains and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) fullerenes while keeping P3HT/PCBM ratio constant. Optimal photovoltaic device performance increases are obtained for each additive when incorporated into the bulk heterojunction blend at loading levels that are dependent upon additive MW. Small-angle X-ray scattering and energy-filtered transmission electron microscopy imaging reveal that domain sizes are approximately invariant at low loading levels of the low-MW P3HT additive, and wide-angle X-ray scattering suggests that P3HT crystallinity is unaffected by these additives. These results suggest that oligomeric P3HTs compatibilize donor-acceptor interfaces at low loading levels but coarsen domain structures at higher loading levels and they are consistent with recent simulations results. Although results are specific to the P3HT/PCBM system, the notion that low molecular weight additives can enhance photovoltaic device performance generally provides a new opportunity for improving device performance and operating lifetimes.
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Shin YK, Sengul MY, Jonayat ASM, Lee W, Gomez ED, Randall CA, Duin ACTV. Development of a ReaxFF reactive force field for lithium ion conducting solid electrolyte Li1+xAlxTi2−x(PO4)3 (LATP). Phys Chem Chem Phys 2018; 20:22134-22147. [DOI: 10.1039/c8cp03586e] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Using a ReaxFF reactive force field, we investigated the composition-dependent ionic conductivity and the Li migration behaviors in Li1+xAlxTi2−x(PO4)3 solid electrolyte.
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Smith BH, Zhang Q, Kelly MA, Litofsky JH, Kumar D, Hexemer A, You W, Gomez ED. Fluorination of Donor-Acceptor Copolymer Active Layers Enhances Charge Mobilities in Thin-Film Transistors. ACS Macro Lett 2017; 6:1162-1167. [PMID: 35650936 DOI: 10.1021/acsmacrolett.7b00716] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Several recent reports have demonstrated that fluorinated analogues of donor/acceptor copolymers surpass nonfluorinated counterparts in terms of performance in electronic devices. Using a copolymer series consisting of fluorinated, partially fluorinated, and nonfluorinated benzotriazole, we confirm that the addition of fluorine substituents beneficially impacts charge transport in polymer semiconductors. Transistor measurements demonstrated a factor of 5 increase in carrier mobilities with the degree of fluorination of the backbone. Furthermore, grazing-incidence X-ray diffraction data indicates progressively closer packing between the conjugated cores and an overall greater amount of π-stacking in the fluorinated materials. It is likely that attractive interactions between the electron-rich donor and fluorinated electron-deficient acceptor units induce very tightly stacking crystallites, which reduce the energetic barrier for charge hopping. In addition, a change in crystallite orientation was observed from primarily edge-on without fluorine substituents to mostly face-on with fluorinated benzotriazole.
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Zhao D, Gimenez-Pinto V, Jimenez AM, Zhao L, Jestin J, Kumar SK, Kuei B, Gomez ED, Prasad AS, Schadler LS, Khani MM, Benicewicz BC. Tunable Multiscale Nanoparticle Ordering by Polymer Crystallization. ACS CENTRAL SCIENCE 2017; 3:751-758. [PMID: 28776017 PMCID: PMC5532707 DOI: 10.1021/acscentsci.7b00157] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Indexed: 05/17/2023]
Abstract
While ∼75% of commercially utilized polymers are semicrystalline, the generally low mechanical modulus of these materials, especially for those possessing a glass transition temperature below room temperature, restricts their use for structural applications. Our focus in this paper is to address this deficiency through the controlled, multiscale assembly of nanoparticles (NPs), in particular by leveraging the kinetics of polymer crystallization. This process yields a multiscale NP structure that is templated by the lamellar semicrystalline polymer morphology and spans NPs engulfed by the growing crystals, NPs ordered into layers in the interlamellar zone [spacing of [Formula: see text] (10-100 nm)], and NPs assembled into fractal objects at the interfibrillar scale, [Formula: see text] (1-10 μm). The relative fraction of NPs in this hierarchy is readily manipulated by the crystallization speed. Adding NPs usually increases the Young's modulus of the polymer, but the effects of multiscale ordering are nearly an order of magnitude larger than those for a state where the NPs are not ordered, i.e., randomly dispersed in the matrix. Since the material's fracture toughness remains practically unaffected in this process, this assembly strategy allows us to create high modulus materials that retain the attractive high toughness and low density of polymers.
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Zhang W, Gomez ED, Milner ST. Predicting Flory-Huggins χ from Simulations. PHYSICAL REVIEW LETTERS 2017; 119:017801. [PMID: 28731776 DOI: 10.1103/physrevlett.119.017801] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Indexed: 06/07/2023]
Abstract
We introduce a method, based on a novel thermodynamic integration scheme, to extract the Flory-Huggins χ parameter as small as 10^{-3}kT for polymer blends from molecular dynamics (MD) simulations. We obtain χ for the archetypical coarse-grained model of nonpolar polymer blends: flexible bead-spring chains with different Lennard-Jones interactions between A and B monomers. Using these χ values and a lattice version of self-consistent field theory (SCFT), we predict the shape of planar interfaces for phase-separated binary blends. Our SCFT results agree with MD simulations, validating both the predicted χ values and our thermodynamic integration method. Combined with atomistic simulations, our method can be applied to predict χ for new polymers from their chemical structures.
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Aplan MP, Gomez ED. Recent Developments in Chain-Growth Polymerizations of Conjugated Polymers. Ind Eng Chem Res 2017. [DOI: 10.1021/acs.iecr.7b01030] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Xie R, Lee Y, Aplan MP, Caggiano NJ, Müller C, Colby RH, Gomez ED. Glass Transition Temperature of Conjugated Polymers by Oscillatory Shear Rheometry. Macromolecules 2017. [DOI: 10.1021/acs.macromol.7b00712] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Cooksey TJ, Singh A, Le KM, Wang S, Kelley EG, He L, Vajjala Kesava S, Gomez ED, Kidd BE, Madsen LA, Robertson ML. Tuning Biocompatible Block Copolymer Micelles by Varying Solvent Composition: Core/Corona Structure and Solvent Uptake. Macromolecules 2017. [DOI: 10.1021/acs.macromol.6b02580] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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64
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Kuei B, Gomez ED. Chain conformations and phase behavior of conjugated polymers. SOFT MATTER 2016; 13:49-67. [PMID: 27506183 DOI: 10.1039/c6sm00979d] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Conjugated polymers may play an important role in various emerging optoelectronic applications because they combine the chemical versatility of organic molecules and the flexibility, stretchability and toughness of polymers with semiconducting properties. Nevertheless, in order to achieve the full potential of conjugated polymers, a clear description of how their structure, morphology, and macroscopic properties are interrelated is needed. We propose that the starting point for understanding conjugated polymers includes understanding chain conformations and phase behavior. Efforts to predict and measure the persistence length have significantly refined our intuition of the chain stiffness, and have led to predictions of nematic-to-isotropic transitions. Exploring mixing between conjugated polymers and small molecules or other polymers has demonstrated tremendous advancements in attaining the needed properties for various optoelectronic devices. Current efforts continue to refine our knowledge of chain conformations and phase behavior and the factors that influence these properties, thereby providing opportunities for the development of novel optoelectronic materials based on conjugated polymers.
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Adhikari JM, Gadinski MR, Li Q, Sun KG, Reyes-Martinez MA, Iagodkine E, Briseno AL, Jackson TN, Wang Q, Gomez ED. Controlling Chain Conformations of High-k Fluoropolymer Dielectrics to Enhance Charge Mobilities in Rubrene Single-Crystal Field-Effect Transistors. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:10095-10102. [PMID: 27717022 DOI: 10.1002/adma.201602873] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 08/04/2016] [Indexed: 06/06/2023]
Abstract
A novel photopatternable high-k fluoropolymer, poly(vinylidene fluoride-bromotrifluoroethylene) P(VDF-BTFE), with a dielectric constant (k) between 8 and 11 is demonstrated in thin-film transistors. Crosslinking P(VDF-BTFE) reduces energetic disorder at the dielectric-semiconductor interface by controlling the chain conformations of P(VDF-BTFE), thereby leading to approximately a threefold enhancement in the charge mobility of rubrene single-crystal field-effect transistors.
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Vakhshouri K, Smith BH, Chan EP, Wang C, Salleo A, Wang C, Hexemer A, Gomez ED. Signatures of Intracrystallite and Intercrystallite Limitations of Charge Transport in Polythiophenes. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01086] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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67
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Zhang W, Gomez ED, Milner ST. Using surface-induced ordering to probe the isotropic-to-nematic transition for semiflexible polymers. SOFT MATTER 2016; 12:6141-7. [PMID: 27345760 DOI: 10.1039/c6sm01258b] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Semiflexible polymers undergo a weakly first order isotropic-to-nematic (IN) phase transition when the volume fraction ϕ is high enough that random alignment of the backbone segments is no longer viable. For semiflexible chains, the critical volume fraction ϕc is governed by the backbone stiffness Np. To locate the IN phase transition, we perform molecular dynamics (MD) simulations of bead-spring chains confined between two impenetrable parallel surfaces. We use the impenetrable surfaces to induce nematic-isotropic interfaces for semiflexible chains in the isotropic phase. By progressively increasing the backbone stiffness Np, we observe the propagation of surface-induced nematic order above a critical stiffness N for a given ϕ. Using the simulation results N(ϕ), we construct the IN phase boundry in the ϕ-Np plane, from which the scaling relation between ϕc and Np is obtained. For semiflexible chains with Np ≤ 5.78, our results suggest ϕc ∼ Np(-1), consistent with prediction by Khokhlov and Semenov. For chains with Np ≥ 5.78, we observe a new scaling regime in which ϕc ∼ Np(-2/3).
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Lee C, Li Y, Lee W, Lee Y, Choi J, Kim T, Wang C, Gomez ED, Woo HY, Kim BJ. Correlation between Phase-Separated Domain Sizes of Active Layer and Photovoltaic Performances in All-Polymer Solar Cells. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01069] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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69
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Snyder CR, Gomez ED. Phase Behavior of Poly(3-hexylthiophene-2,5-diyl). JOURNAL OF POLYMER SCIENCE. PART B, POLYMER PHYSICS 2016; 54:1202-1206. [PMID: 29187773 PMCID: PMC5702943 DOI: 10.1002/polb.24027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The phase behavior of many conjugated polymers is rich with both crystalline and liquid crystalline phases. Recent computational efforts have identified the isotropic-to-nematic transition temperature for polymers such as poly(3-hexylthiophene-2,5-diyl) (P3HT). Herein, model predictions are combined with experimentally determined values of the equilibrium melting temperature as a function of chain length to provide the complete phase behavior for P3HT. Additionally, because a full description of the phase behavior requires proper accounting for the regioregularity of the chain, a thermodynamic relationship is derived to predict this behavior as a function of both chain length and regioregularity and the impact of regioregularity on the expected phase diagram is discussed.
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Wang S, Xie R, Vajjala Kesava S, Gomez ED, Cochran EW, Robertson ML. Close-Packed Spherical Morphology in an ABA Triblock Copolymer Aligned with Large-Amplitude Oscillatory Shear. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b00505] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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71
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Guo C, Lee Y, Lin YH, Strzalka J, Wang C, Hexemer A, Jaye C, Fischer DA, Verduzco R, Wang Q, Gomez ED. Photovoltaic Performance of Block Copolymer Devices Is Independent of the Crystalline Texture in the Active Layer. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b00370] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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72
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73
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Lee Y, Gomez ED. Challenges and Opportunities in the Development of Conjugated Block Copolymers for Photovoltaics. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b00112] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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74
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Le TP, Shang Z, Wang L, Li N, Vajjala Kesava S, O’Connor JW, Chang Y, Bae C, Zhu C, Hexemer A, Gomez EW, Salleo A, Hickner MA, Gomez ED. Miscibility and Acid Strength Govern Contact Doping of Organic Photovoltaics with Strong Polyelectrolytes. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b00724] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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75
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Kuang H, Janik MJ, Gomez ED. Quantifying the role of interfacial width on intermolecular charge recombination in block copolymer photovoltaics. ACTA ACUST UNITED AC 2015. [DOI: 10.1002/polb.23757] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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