Christine K. Luscombe

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Organization: University of Washington

Department: Department of Material Science and Engineering

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Polymer

Hyperbranched Polymers

Organic Chemistry

Organic Solar Cells

Chemicals
References

Fully Conjugated Graft Copolymers Comprising a P-Type Donor–Acceptor Backbone and Poly(3-hexylthiophene) Side Chains Synthesized Via a “Graft Through” Approach

Co-reporter:David F. Zeigler, Katherine A. Mazzio, and Christine K. Luscombe

Macromolecules 2014 Volume 47(Issue 15) pp:5019-5028

Publication Date(Web):July 29, 2014

DOI:10.1021/ma5009435

A series of fully conjugated graft copolymers containing poly(3-hexylthiophene) (P3HT) side chains and a p-type carbazole-diketopyrrolopyrrole (CbzDPP) donor–acceptor backbone were synthesized via a graft through Suzuki polymerization. The macromonomers were formed by externally initiating P3HT growth from a boronic ester-functionalized carbazole via Kumada catalyst transfer polycondensation. Subsequently, this macromonomer was copolymerized with a DPP monomer via a graft through Suzuki polymerization to yield the final graft copolymers. The graft copolymers exhibit optical and electronic properties of both P3HT and the CbzDPP polymers independently due to the break in conjugation between the carbazole unit and P3HT chain. Moreover, these properties reflect the relative proportion of P3HT and CbzDPP polymers; shorter P3HT chain lengths lead to graft copolymers that possess more CbzDPP character and vice versa. The macromonomers were characterized by gel permeation chromatography, mass spectrometry, and UV–visible spectroscopy. The graft copolymers were further investigated using gel permeation chromatography, UV–visible spectroscopy, cyclic voltammetry, differential scanning calorimetry, and atomic force microscopy. Finally, organic field effect transistors were fabricated using the graft copolymers and compared to an analogous linear CbzDPP copolymer. Ultimately, the graft copolymers with the longest P3HT chains (ca. 75 repeat units) exhibited almost exclusively P3HT characteristics, possessing a small CbzDPP internal charge transfer (ICT) peak and only p-type conductivity (μh ∼ 6 × 10–4 cm2 V–1 s–1). Conversely, the graft copolymers with the shortest P3HT chains (ca. 10 repeat units) showed significant CbzDPP character, including a strong ICT peak and ambipolar mobilities (μh ∼ 5 × 10–3 cm2 V–1 s–1; μe ∼ 7 × 10–4 cm2 V–1 s–1).

Thiophene based hyperbranched polymers with tunable branching using direct arylation methods

Co-reporter:Ken Okamoto, Jeremy B. Housekeeper, Forrest E. Michael and Christine K. Luscombe

Polymer Chemistry 2013 vol. 4(Issue 12) pp:3499-3506

Publication Date(Web):15 Apr 2013

DOI:10.1039/C3PY00412K

An efficient one-pot synthesis of branched poly(3-alkylthiophene)s (b-P3ATs) is achieved via a dehydrohalogenative polycondensation reaction. The structures of the b-P3ATs are assigned based on 1H NMR spectra by comparing them to a model dendritic polymer and oligo(3-hexylthiophene-2,4-diyl). The palladium-catalyzed dehydrohalogenative polycondensation of 2-bromo-3-alkylthiophenes was found to provide P3AT with tunable degree of branching (DB = 0–0.42) and high molecular weights. Viscosity measurements of the different b-P3ATs indicate that they display a more globular morphology compared to regiorandom P3AT and regioregular P3AT in solution, thereby confirming the branched structure.

Room-temperature carbonsulfur bond formation from Ni(II) -aryl complex via cleavage of the SS bond of disulfide moieties

Co-reporter:Ken Okamoto;Jeremy B. Housekeeper

Applied Organometallic Chemistry 2013 Volume 27( Issue 11) pp:639-643

Publication Date(Web):

DOI:10.1002/aoc.2975

Abstract

The formation of ArSY (Y: C(= S)NMe₂, Ph, P(= O)(OEt)₂) by reductive elimination from σ-aryl complexes (M(PPh₃)₂PhBr, M = Ni, Pd), associated with disulfides (YS−SY, Y: C(=S)NMe₂ (1), Ph (2), P(=O)(OEt)₂ (3)), at ambient temperature, has been investigated. Various mechanistic features of disulfide bond (S−S) cleavage have been elucidated using disulfide 1 by ³¹P NMR spectroscopy and matrix-assisted laser desorption/ionization–time of flight mass spectrometric investigations. Based upon the results of nucleophilic cleavage of the S−S bond by PPh₃, studies of the reductive elimination process show that when M(PPh₃)₂PhBr is mixed with disulfide 1, competitive reactions occur between the PPh₃ ligand, disulfide 1 and a trace amount of water, leading to low C−S coupling yields; an oxidation reaction of PPh₃ with disulfide and water occur prior to C−S cross-coupling, and phosphonium ion intermediates are likely involved. However, when the disulfide 1 is pretreated with PPh₃, the Ni(II) σ-aryl complex affords the C−S coupling product nearly quantitatively at room temperature. The pretreatment method is also effective for the coupling reaction of disulfide 2 and Ni(II) σ-aryl complex. The difference between Ni(II) and Pd(II) σ-aryl complexes on C−S bond formation by reductive elimination can be explained by the affinity of metal for the thiolate ligands derived from the cleaved disulfide. Copyright © 2013 John Wiley & Sons, Ltd.

C–H Arylation Reaction: Atom Efficient and Greener Syntheses of π-Conjugated Small Molecules and Macromolecules for Organic Electronic Materials

Co-reporter:Ken Okamoto, Junxiang Zhang, Jeremy B. Housekeeper, Seth R. Marder, and Christine K. Luscombe

Macromolecules 2013 Volume 46(Issue 20) pp:8059-8078

Publication Date(Web):August 20, 2013

DOI:10.1021/ma401190r

π-Conjugated small molecules, oligomers, and macromolecules are being used in the fabrication of a wide variety of organic electronic devices such as organic field-effect transistors (OFETs), organic photovoltaic (OPV) devices, and organic light-emitting diodes (OLEDs). Efficient syntheses involving fewer steps, fewer toxic reagents, and highly reactive compounds are needed to lower the cost of materials in a manner that is fundamentally more eco-friendly. Additionally, synthetic approaches for π-conjugated materials with more functional group tolerance are desirable to expand the range of properties that can be realized in such materials. Developing new synthetic routes to materials can both broaden the scope of science that can be explored and increase the probability that interesting materials can be developed in an economically viable manner for inclusion in consumer products. One such synthetic strategy that can impact all of these issues is carbon–hydrogen bond activation and subsequent carbon–carbon bond formation (C–H functionalization). While the C–H functionalizations represented by direct arylation-based methods are not as developed as the widely used Stille and Suzuki methods at this stage, they allow for the use of readily accessible halogenated aromatic substances and can negate the need for toxic organotin reagents. They also hold promise of allowing for the synthesis of previously inaccessible materials. In this Perspective, our goal is to provide an overview of the current status in this challenging field by highlighting (1) the history of preparing π-conjugated small molecules and macromolecules via cross-coupling reactions, (2) advances in preparation of versatile π-conjugated small molecules and macromolecules via transition-metal-catalyzed direct arylation, and (3) the scope, limitations, and challenges for materials science.

Synthesis and characterization of fused-thiophene containing naphthalene diimide n-type copolymers for organic thin film transistor and all-polymer solar cell applications

Co-reporter:Mingjian Yuan;Matthew M. Durban;Peter D. Kazarinoff;David F. Zeigler;Andrew H. Rice;Yukari Segawa

Journal of Polymer Science Part A: Polymer Chemistry 2013 Volume 51( Issue 19) pp:4061-4069

Publication Date(Web):

DOI:10.1002/pola.26812

ABSTRACT

Naphthalene diimide copolymers are attractive n-type materials due to their high electron affinities, high electron mobilities, and exceptional stability. Herein, we report a series of NDI-fused-thiophene based copolymers with each copolymer differing in the number of fused thiophenes in the donor monomer. Increasing the number of fused-thiophene moieties within an NDI-copolymer backbone is shown to not only enable tuning of the electronic structure but also improve charge mobilities within the active layer of organic field-effect transistors. Electron mobilities and on/off ratios as high as 0.012 cm² V⁻¹ s^-1 and I_on/I_off > 10⁵ were measured from n-channel thin-film transistors fabricated using NDI-xfTh copolymers. Bulk heterojunction solar cell devices were also fabricated from the NDI-xfTh copolymer series in blends with poly(3-hexylthiophene) (P3HT) with PNDI-4fTh-based devices yielding the largest J_sc (0.57 mA cm⁻²) and fill factor (55%) in addition to the highest measured PCE for this series (0.13%). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4061–4069

Constructing Regioregular Star Poly(3-hexylthiophene) via Externally Initiated Kumada Catalyst-Transfer Polycondensation

Co-reporter:Mingjian Yuan, Ken Okamoto, Hugo A. Bronstein, and Christine K. Luscombe

ACS Macro Letters 2012 Volume 1(Issue 3) pp:392

Publication Date(Web):February 27, 2012

DOI:10.1021/mz3000368

A synthetic route was developed for the preparation of di- and trifunctional Ni complex-based initiators. Each initiator affords well-defined 2-arm (V-shaped) and 3-arm (Y-shaped) regioregular poly(3-hexylthiophene) (rr-P3HT) with controlled molecular weight and narrow polydispersities by the externally initiated Kumada catalyst-transfer polycondensation. The core spacer length and end o-tolylhalide group of the functional initiators exhibited differences in reactivity and show that the biphenyl spacers are effective for the synthesis of V-shaped and Y-shaped rr-P3HTs.

Surface-Initiated Synthesis of Poly(3-methylthiophene) from Indium Tin Oxide and its Electrochemical Properties

Co-reporter:Natalia Doubina, Judith L. Jenkins, Sergio A. Paniagua, Katherine A. Mazzio, Gordon A. MacDonald, Alex K.-Y. Jen, Neal R. Armstrong, Seth R. Marder, and Christine K. Luscombe

Langmuir 2012 Volume 28(Issue 3) pp:1900-1908

Publication Date(Web):December 9, 2011

DOI:10.1021/la204117u

Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm. Electrochemical oxidative doping of these films was used to manipulate their near surface composition and effective work function. Doped states of the P3MT film are maintained even after the sample is removed from solution and potential control confirming the robustness of the films. Such materials with controllable thicknesses and electronic properties have the potential to be useful as interlayer materials for organic electronic applications.

Oligoselenophene Derivatives Functionalized with a Diketopyrrolopyrrole Core for Molecular Bulk Heterojunction Solar Cells

Co-reporter:Katherine A. Mazzio, Mingjian Yuan, Ken Okamoto, and Christine K. Luscombe

ACS Applied Materials & Interfaces 2011 Volume 3(Issue 2) pp:271

Publication Date(Web):January 10, 2011

DOI:10.1021/am100920s

Solution-processable oligoselenophenes functionalized with diketopyrrolopyrrole cores have been synthesized for use as the donor material in bulk heterojunction solar cells. The optical absorption of these materials extends to the edge of the visible spectrum. Power conversion efficiencies of 1.53 ± 0.04% for DPPS and 0.84 ± 0.04% for DPPDS were obtained under simulated 100 mW/cm2 AM 1.5G irradiation for devices when PC61BM was used as an acceptor. DPPS showed hole mobilities of 4 × 10−5 cm2/(V s) and a peak external quantum efficiency (EQE) of 25%, while DPPDS showed hole mobilities of 2 × 10−5 cm2/(V s) and a peak EQE of 19%. To the best of our knowledge, these are the first oligoselenophenes that have been reported in molecular bulk heterojunction solar cells and this study could serve as a springboard for the design and optimization of high-performance selenophene-containing photovoltaics.Keywords (keywords): bulk heterojunction solar cells; oligoselenophenes; organic electronics; organic field-effect transistors; organic photovoltaics; small molecule semiconductors

Controlled polymerizations for the synthesis of semiconducting conjugated polymers

Co-reporter:Ken Okamoto and Christine K. Luscombe

Polymer Chemistry 2011 vol. 2(Issue 11) pp:2424-2434

Publication Date(Web):14 Jun 2011

DOI:10.1039/C1PY00171J

Conjugated polymers have been under active development since the 1970s as the active material in organic field-effect transistors (OFETs), photovoltaic devices and the emissive layer in light-emitting diodes (LEDs). Extensive work has been performed to investigate the physics and chemistry of these materials, and a variety of semiconducting polymers have been synthesized using a range of polymerization techniques. One of the most important key technologies is to obtain a well-controlled polymerization, which provides polymers with narrow polydispersities and defined molecular weights. In this paper, we describe the recent progress on the synthesis of semiconducting polymers as classified as polyphenylenes, polyphenylenevinylenes, polythiophenes, polyfluorene and their block copolymers by the use of controlled polymerizations.

Synthesis and Characterization of Solution-Processable Ladderized n-Type Naphthalene Bisimide Copolymers for OFET Applications

Co-reporter:Matthew M. Durban, Peter D. Kazarinoff, Yukari Segawa, and Christine K. Luscombe

Macromolecules 2011 Volume 44(Issue 12) pp:4721-4728

Publication Date(Web):June 3, 2011

DOI:10.1021/ma2004822

Solution-processable n-type ladder-based polymers are highly desirable due to their potential capability to form strong π–π interactions. A series of 5 highly soluble naphthalene diimide (NDI) polymers are presented, differing in the degree to which they are able to form imine-bridged ladder polymer structures. Average electron mobilities as high as 0.0026 cm2 V–1 s–1, which show an electron-mobility improvement of 4 orders of magnitude following ladderization, and on/off current ratios on the order of 104 are reported for the novel material PNDI-2BocL, an alkyl-substituted poly(benzoquinolinophenanthrolinedione). The structure–property relationship of the aforementioned series of copolymers is presented and discussed as it pertains to organic field-effect transistor (OFET) performance.

Controlling Vertical Morphology within the Active Layer of Organic Photovoltaics Using Poly(3-hexylthiophene) Nanowires and Phenyl-C61-butyric Acid Methyl Ester

Co-reporter:Andrew H. Rice, Rajiv Giridharagopal, Sam X. Zheng, Fumio S. Ohuchi, David S. Ginger, and Christine K. Luscombe

ACS Nano 2011 Volume 5(Issue 4) pp:3132

Publication Date(Web):March 28, 2011

DOI:10.1021/nn2002695

In this study, we demonstrate how the vertical morphology of bulk heterojunction solar cells, with an active layer consisting of self-assembled poly(3-hexylthiophene) (P3HT) nanowires and phenyl-C61-butyric acid methyl ester (PCBM), can be beneficially influenced. Most device fabrication routes using similar materials employ an annealing step to influence active layer morphology, but this process can create an unfavorable phase migration where P3HT is driven toward the top of the active layer. In contrast, we demonstrate devices that exhibit an increase in relative fullerene concentration at the top of the active layer by introducing the donor phase as a solid nanowire in the active layer solution and altering the pre-spin drying time. X-ray photoelectron spectroscopy and conductive and photoconductive atomic force microscopy provide detailed images of how the surface of the active layer can be influenced; this is done by tracking the concentration and alignment of P3HT and PCBM domains. Using this new procedure, devices are made with power conversion efficiencies surpassing 2%. Additionally, we show that nanowires grown in the presence of the fullerene perform differently than those that are grown and mixed separately; exposure to the nanowire during self-assembly may allow the fullerene to coat nanowire surfaces and influence the photocurrent within the device.Keywords: bulk heterojunction solar cells; conductive AFM; P3HT nanowires; photoconductive AFM

Benzo[2,1-b;3,4-b]dithiophene-based low-bandgap polymers for photovoltaic applications

Co-reporter:Mingjian Yuan;Andrew H. Rice

Journal of Polymer Science Part A: Polymer Chemistry 2011 Volume 49( Issue 3) pp:701-711

Publication Date(Web):

DOI:10.1002/pola.24481

Abstract

The synthesis of four alternating copolymers using benzo[2,1-b;3,4-b′]dithiophene (BDP) as the common donor unit is presented. Before the synthesis, theoretical calculations that we performed predicted that the incorporation of BDP, which consists of fused dithiophene units with a benzene ring, into these polymers would produce a low-lying highest occupied molecular orbital (HOMO) energy level. Low-lying HOMO levels are desirable to produce high open circuit voltages (V_OC) in organic bulk heterojunction (BHJ) photovoltaic devices. The polymers' structural characterization, as well as the preliminary results of their performance in BHJ devices, using (6,6)-phenyl C₆₁-butyric acid methyl ester as the electron acceptor, is presented. The V_OC values follow the expected trend: increasing with decreasing HOMO level of the polymer. High V_OC values of 0.81 and 0.82 V have been obtained from two polymers: PBDPBT and PBDPDPP. The initial power conversion efficiency achieved in these unoptimized devices was 1.11% because of relatively low J_SC values. The variation observed in the J_SC values between the four polymers is discussed. Device performance is expected to increase with optimization of processing conditions for the devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Steric Effects of the Initiator Substituent Position on the Externally Initiated Polymerization of 2-Bromo-5-iodo-3-hexylthiophene

Co-reporter:Natalia Doubina, Sergio A. Paniagua, Alexandra V. Soldatova, Alex K. Y. Jen, Seth R. Marder, and Christine K. Luscombe

Macromolecules 2011 Volume 44(Issue 3) pp:512-520

Publication Date(Web):January 12, 2011

DOI:10.1021/ma1024494

Externally initiated polymerization of 2-bromo-3-hexyl-5-iodothiophene was attempted from four aryl and thiophene based small molecule initiators functionalized with a phosphonate moiety. Initiated poly(3-hexylthiophene) product was obtained in various yields depending on the nature of the initiating molecule. Reaction intermediates for the oxidative addition and the ligand exchange steps were analyzed utilizing both experimental and theoretical methods. It was observed that an ortho substituent plays a crucial role in the outcome of the polymerization mechanism and that aryl based initiators are generally more stable than thiophene based initiators. Density functional theory (DFT) calculations revealed the importance of the steric effects on the success of the externally initiated chain growth polymerization mechanism.

OTFT performance of air-stable ester-functionalized polythiophenes

Co-reporter:Peter D. Kazarinoff, Patrick J. Shamburger, Fumio S. Ohuchi and Christine K. Luscombe

Journal of Materials Chemistry A 2010 vol. 20(Issue 15) pp:3040-3045

Publication Date(Web):19 Feb 2010

DOI:10.1039/B927164C

A series of three air-stable ester-functionalized polythiophenes were tested for performance and stability in organic thin film transistors. The highest saturated field effect mobility of the series was 3.3 × 10−3 cm2 V−1 s−1. The three polymers showed only a small decrease in performance over the course of one month, while P3HT devices fabricated for comparison no longer functioned after this storage interval. The polymers are stable in air due to a HOMO level of −5.6 eV as measured by CV. Increased crystallinity as measured by XRD and DSC accounts for the highest mobility polymer.

P3HT:PCBM polymer solar cells with TiO2 nanotube aggregates in the active layer

Co-reporter:Pinyi Yang, Xiaoyuan Zhou, Gongzhong Cao and Christine K. Luscombe

Journal of Materials Chemistry A 2010 vol. 20(Issue 13) pp:2612-2616

Publication Date(Web):22 Jan 2010

DOI:10.1039/B921758D

P3HT:PCBM polymer solar cells with a very small amount of TiO2 nanotube aggregates (0.002 mol per 100 mL) in the active layer have been fabricated. Although in dye-sensitized solar cells nanotube aggregates have been shown to increase light absorption of devices, it was found that TiO2 nanotube aggregates reduced the absorbance of the active layer in our case. However, its positive role on the charge collection and transportation maintained the EQE the same as a conventional P3HT:PCBM device and improved the electron mobility from 5.71 × 10−5 cm2 V−1 s−1 to 7.22 × 10−5 cm2 V−1 s−1. The final devices showed a 15% increase in power conversion efficiency compared to conventional P3HT:PCBM devices. The effects of TiO2 nanotube aggregates on the morphology of the active layer were studied by AFM.

Synthesis and Characterization of Thiophene-Containing Naphthalene Diimide n-Type Copolymers for OFET Applications

Co-reporter:Matthew M. Durban, Peter D. Kazarinoff and Christine K. Luscombe

Macromolecules 2010 Volume 43(Issue 15) pp:6348-6352

Publication Date(Web):July 13, 2010

DOI:10.1021/ma100997g

Naphthalene diimide (NDI) copolymers are attractive n-type materials for use in organic electronic devices. Four highly soluble NDI polymers are presented—each differing only in the thiophene content comprising the material. Electron mobilities as high as 0.076 cm2 V−1 s−1 for the novel material PNDI-3Th are reported. Polymer crystallinity and general macromolecular order are shown to effectively improve by increasing the number of thiophene units within the polymer backbone. The structure−property relationship of NDI−thiophene copolymers is presented and discussed as it pertains to organic field effect transistor (OFET) performance.

Externally Initiated Regioregular P3HT with Controlled Molecular Weight and Narrow Polydispersity

Co-reporter:Hugo A. Bronstein

Journal of the American Chemical Society 2009 Volume 131(Issue 36) pp:12894-12895

Publication Date(Web):August 19, 2009

DOI:10.1021/ja9054977

The ability of chemists to design and synthesize π-conjugated organic polymers with precise control remains the key to technological breakthroughs for using polymer materials in electronic and photonic devices. In this communication, the controlled chain-growth polymerization of regioregular poly(3-hexylthiophene) (P3HT) from an external initiator using 1,3-bis(diphenylphosphino)propane (dppp) as a catalyst ligand is reported. The complexes cis-chloro(phenyl)(dppp)nickel(II) and cis-chloro(o-tolyl)(dppp)nickel(II) were synthesized and characterized by 31P NMR spectroscopy. These complexes served as initiators in the polymerization of 2-bromo-5-chloromagnesio-3-hexylthiophene in THF at room temperature, affording fully regioregular P3HT with controlled molecular weights and narrow molecular weight distributions, as demonstrated by gel-permeation chromatography and 1H NMR spectroscopy. MALDI-TOF mass spectrometry revealed that the polymers had almost complete incorporation of the initiating aryl group, and when the aryl group was o-tolyl, only Tol/H end groups were observed. Although external initiators have been used previously with a PPh3 ligand, that methodology led to polymers with broad molecular weight distributions. This is the first example in which complete control over the externally initiated P3HT polymerization has been achieved.

The Effects of Binding Ligand Variation on the Nickel Catalyzed Externally Initiated Polymerization of 2-Bromo-3-hexyl-5-iodothiophene

Co-reporter:Natalia Doubina;Michelina Stoddard;Hugo A. Bronstein;Alex K.-Y. Jen

Macromolecular Chemistry and Physics 2009 Volume 210( Issue 22) pp:1966-1972

Publication Date(Web):

DOI:10.1002/macp.200900375

Organometallic Donor−Acceptor Conjugated Polymer Semiconductors: Tunable Optical, Electrochemical, Charge Transport, and Photovoltaic Properties

Co-reporter:Pei-Tzu Wu, Tricia Bull, Felix S. Kim, Christine K. Luscombe and Samson A. Jenekhe

Macromolecules 2009 Volume 42(Issue 3) pp:671-681

Publication Date(Web):January 13, 2009

DOI:10.1021/ma8016508

A series of 11 organometallic conjugated polymer semiconductors bearing a platinum (Pt) center have been synthesized and their electronic band structures, field-effect charge transport, and use in bulk heterojunction solar cells were evaluated. The Pt-bridged donor−acceptor conjugated poly(aryleneethynylene)s were synthesized by Sonogashira-type polycondensation and are exemplified by poly[4-(5′-trans-bis(tributylphosphine)platinum ethynyl-thiophen-2′-yl)-7-(5′′-ethynyl-thiophen-2′′-yl)-benzo[1,2,5]thiadiazole] (BT-BTPt), poly[5-(5′-trans-bis(tributylphosphine)platinum ethynyl-thiophen-2′-yl)-8-(5′′-ethynyl-thiophen-2′′-yl)-2,3-diheptyl-pyrido[3,4-b]pyrazine] (HPP-BTPt), and poly[5-(5′-trans-bis(tributylphosphine)platinum ethynyl-thiophen-2′-yl)-7-(5′′-ethynyl-thiophen-2′′-yl)-thieno[3,4-b]pyrazine] (TP-BTPt). The Pt-bridged polymers had reversible electrochemical reduction waves from which electron affinities were found to be 2.95 to 3.28 eV. From the onset oxidation potentials of the polymers, we similarly determined ionization potentials to be 4.82 to 5.23 eV. Optical bandgaps of the donor−acceptor polymers were 1.49 to 1.97 eV. The spin coated polymer thin films showed p-channel field-effect charge transport with average hole mobilities of 3.87 × 10−7 to 3.32 × 10−5 cm2/(V s). Bulk heterojunction solar cells based on blends of the polymers with [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) gave power conversion efficiencies as high as 0.68% for HPP-BTPt and 2.41% for BT-BTPt. These results demonstrate the molecular engineering of the electronic band structures and the optical, charge transport, and photovoltaic properties of organometallic donor−acceptor conjugated polymer semiconductors.

Effect of Initiators on the Kumada Catalyst-Transfer Polycondensation Reaction

Co-reporter:Natalia Doubina, Anh Ho, Alex K-Y Jen and Christine K. Luscombe

Macromolecules 2009 Volume 42(Issue 20) pp:7670-7677

Publication Date(Web):July 16, 2009

DOI:10.1021/ma901410k

An investigation for the initiation of a chain-growth polymerization, Kumada catalyst-transfer polycondensation, for the synthesis of poly(3-hexylthiophene) is described. A novel method for the generation of an active catalyst/initiator complex was developed utilizing the inexpensive, air stable Ni(PPh3)2Cl2 precursor to generate the active Ni(PPh3)4 catalyst in situ. Poly(3-hexylthiophene) polymerization reactions were carried out using aryl halides with various substituents on the phenyl ring as external initiators, and it was found that the type of the functional group present on the initiator plays a crucial role in the polymerization. The new method provided a more efficient way to initiate polymerization yielding polymers with higher regioregularity, larger molecular weight, and lower polydispersity than the previously reported methods.

Steric Stabilization Effects in Nickel-Catalyzed Regioregular Poly(3-hexylthiophene) Synthesis

Co-reporter:Shane D. Boyd, Alex K.-Y. Jen and Christine K. Luscombe

Macromolecules 2009 Volume 42(Issue 24) pp:9387-9389

Publication Date(Web):November 19, 2009

DOI:10.1021/ma902190p

The Role of Mesoscopic PCBM Crystallites in Solvent Vapor Annealed Copolymer Solar Cells

Co-reporter:Tricia A. Bull, Liam S. C. Pingree, Samson A. Jenekhe, David S. Ginger and Christine K. Luscombe

ACS Nano 2009 Volume 3(Issue 3) pp:627

Publication Date(Web):February 19, 2009

DOI:10.1021/nn800878c

Solution processable methanofullerene-based solar cells are the most widely studied class of organic photovoltaics (OPVs). The evolution of the electronic properties with solvent vapor annealing (SVA) in polyfluorene-copolymer and [6,6]phenyl-C61-butyric acid methyl ester (PCBM) blended OPVs is studied using various scanning probe techniques: light beam induced current spectroscopy (LBIC), conductive atomic force microscopy (c-AFM), and photoconductive AFM (pc-AFM). We demonstrate that SVA improves the power conversion efficiency by 40% while forming mesoscopic PCBM crystallites and a ∼3 nm copolymer-rich overlayer at the cathode interface. We find that the large crystallites created during annealing do not directly improve the local performance of the device, but instead attribute the performance improvement to the ripened blend morphology and an increase in the hole mobility of the copolymer in comparison to the unannealed blend. The PCBM-rich aggregates act as a sink for excess PCBM, although excess PCBM is initially required to form the appropriate structural features prior to the annealing process.Keywords: light beam induced current microscopy; organic photovoltaic; PCBM; photoconductive atomic force microscopy; solar cell; solvent vapor annealing

Preparation of Titanium Oxide Pillars on Glass Substrates and Ultrathin Titanium Oxide Layer using PMMA/PS Blend Films†

Co-reporter:Dan Liu ; Pinyi Yang

The Journal of Physical Chemistry C 2008 Volume 112(Issue 21) pp:7886-7894

Publication Date(Web):April 30, 2008

DOI:10.1021/jp711686r

In this paper, a simple and inexpensive method of preparing nanosized titanium oxide (TiO2) pillars on glass substrates and ultrathin TiO2 layers is presented, utilizing a blend of commercially available polystyrene (PS) and poly(methyl methacrylate) (PMMA). The surface morphology of PS/PMMA blend films is investigated in terms of the processing parameters including solution concentration, blending ratio, and spin-coating speed. For the first time, a phase inversion was revealed for the PS/PMMA blend films spun coated on conducting substrates (ITO and TiO2), with increasing solution concentration. Atomic force microscopy studies show that PMMA forms vertical cylindrical structures in the matrix of PS on glass substrates and on ultrathin TiO2 layers deposited on indium tin oxide (ITO) substrates. After the PMMA phase is etched away by ultraviolet irradiation and acetic acid, TiO2 pillar structures are successfully created on both types of substrates by infiltration of the sol−gel mixture into the nanosized PS templates followed by calcination at an elevated temperature. The size and shape of the TiO2 pillars were found to be affected by the thickness and phase separation of the initial PS/PMMA films, which depend on the solution concentration and blending ratio of the two polymeric components.

OTFT performance of air-stable ester-functionalized polythiophenes

Co-reporter:Peter D. Kazarinoff, Patrick J. Shamburger, Fumio S. Ohuchi and Christine K. Luscombe

Journal of Materials Chemistry A 2010 - vol. 20(Issue 15) pp:NaN3045-3045

Publication Date(Web):2010/02/19

DOI:10.1039/B927164C

P3HT:PCBM polymer solar cells with TiO2 nanotube aggregates in the active layer

Co-reporter:Pinyi Yang, Xiaoyuan Zhou, Gongzhong Cao and Christine K. Luscombe

Journal of Materials Chemistry A 2010 - vol. 20(Issue 13) pp:NaN2616-2616

Publication Date(Web):2010/01/22

DOI:10.1039/B921758D

Low Bandgap Polymers Based on Silafluorene Containing Multifused Heptacylic Arenes for Photovoltaic Applications

Co-reporter:Mingjian Yuan ; Pinyi Yang ; Matthew M. Durban

Macromolecules () pp:

Publication Date(Web):July 27, 2012

DOI:10.1021/ma300839c

A series of donor–acceptor copolymers based on a new silafluorene containing multifused heptacylic arenes have been designed and synthesized in order to further modulate and optimize their electronic and optical properties. Polymer solar cells based on a blend of these polymers and PC61BM exhibited high open circuit voltages of up to 0.86 V. Through simple and straightforward engineering of molecular structures, the devices based on the PSiFDCTBT:PC61BM (1:3.5 in wt %) blend provided, on average, a Voc of 0.86 V, a Jsc of 8.8 mA/cm2, a FF of 56%, delivering a PCE of 4.2%.