Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F41: Focus Session: Organic Electronics and Photonics, Design of Semiconducting Materials |
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Sponsoring Units: DPOLY Chair: Alejandro Briseno, University of Massachusetts, Amherst Room: 214A |
Tuesday, March 3, 2015 8:00AM - 8:36AM |
F41.00001: BREAK |
Tuesday, March 3, 2015 8:36AM - 8:48AM |
F41.00002: Addition of ferrocene controls polymorphism and enhances charge mobilities in poly(3-hexylthiophene) thin-film transistors Brandon Smith, Michael Clark, Christopher Grieco, Alec Larsen, John Asbury, Enrique Gomez Crystalline organic molecules often exhibit the ability to form multiple crystal structures depending on the processing conditions. Exploiting this polymorphism to optimize molecular orbital overlap between adjacent molecules within the unit lattice of conjugated polymers is an approach to enhance charge transport within the material. We have demonstrated the formation of tighter $\pi $-$\pi $ stacking poly(3-hexylthiophene-2,5-diyl) polymorphs in films spin coated from ferrocene-containing solutions using grazing incident X-ray diffraction. As a result, we found that the addition of ferrocene to casting solutions yields thin-film transistors which exhibit significantly higher source-drain current and charge mobilities than neat polymer devices. Insights gleaned from ferrocene/poly(3-hexylthiophene) mixtures can serve as a template for selection and optimization of next generation small molecule/polymer systems possessing greater baseline charge mobilities. Ultimately, the development of such techniques to enhance the characteristics of organic transistors without imparting high costs or loss of advantageous properties will be a critical factor determining the future of organic components within the electronics market. [Preview Abstract] |
Tuesday, March 3, 2015 8:48AM - 9:00AM |
F41.00003: Predicting nematic coupling constants of semiflexible polymers from MD simulations Wenlin Zhang, Enrique Gomez, Scott Milner The nematic phase is important for many semiflexible polymers. For example, semiflexible polymers with nematic phase can be directly used in many applications, including displays and high strength fibers. The existence of nematic phases also enables better processing of functional semiflexible polymers including conducting conjugated polymers. The nematic coupling constant $\alpha$, together with the chain stiffness $\kappa$, governs chain alignment and the isotropic-to-nematic (IN) transition temperature $T_{IN}$ for semiflexible polymers. For many semiflexible chains, crystallization or thermal degradation can preclude the IN transition, so that $T_{IN}$ cannot be used to estimate $\alpha$. We combine self-consistent field theory (SCFT) with atomistic molecular dynamics (MD) simulations of semiflexible chains under external tension in the isotropic phase to estimate the nematic coupling constant $\alpha$. Using our mean-field model, we can obtain the variational free energy of a given polymer, from which the IN transition temperature $T_{IN}$ can be determined. We apply our method to estimate $\alpha$ and $T_{IN}$ of a commonly studied conjugated polymer, poly(3-hexylthiophene) (P3HT). Using the estimated $T_{IN}$, we predict P3HT is nematic after melting from crystal. [Preview Abstract] |
Tuesday, March 3, 2015 9:00AM - 9:12AM |
F41.00004: Heteroatom-Containing Contorted Molecular Semiconductors Nicholas Davy, Gabriel Man, Sean Parkin, Antoine Kahn, Yueh-Lin Loo Contorted polyaromatic hydrocarbons (c-PAHs), such as contorted hexabenzocoronene (c-HBC), are promising active ingredients for organic photovoltaic (OPV) devices due to their inherent stability, tunable frontier energy levels, and synthetic accessibility. The utility of c-HBC derivatives in OPV devices, however, has been limited by the large band gaps of these materials and, as a consequence their limited ability to harvest visible light. Here we report the synthesis, characterization and device integration of tetrabenzofuranyldibenzocoronene (c-TBFDBC) and tetrabenzothienodibenzocoronene (c-TBTDBC) -- a pair of heteroatom-containing c-PAHs that show broader absorption of the solar spectrum compared to c-HBC, with maximum absorptivities above 10$^{5}$ M$^{-1}$ cm$^{-1}$ in both the near-UV and in the visible. Bilayer OPV devices comprising c-TBFDBC or c-TBTDBC and C70 outperform those having c-HBC in photocurrent production and power conversion efficiency. External quantum efficiency spectra indicate improved light harvesting by both donor and acceptor molecules on annealing. Grazing incidence x-ray diffraction experiments reveal increases in the crystallinity of donor and acceptor layers on annealing and a preference for edge-on orientation in c-HBC and c-TBFDBC. [Preview Abstract] |
Tuesday, March 3, 2015 9:12AM - 9:48AM |
F41.00005: Manipulating the backbone structure of semiconducting polymers Invited Speaker: Christine Luscombe Pi-Conjugated polymers 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). The advances made in organic electronics have been driven by the syntheses of pi-conjugated polymers with increasingly complex structures but have heavily relied on an Edisonian approach. Despite these advances, there are many contradictory reports in the literature about our understanding of the performance of $\pi $-conjugated polymers in many applications. Our group has been studying and developing techniques to grow semiconducting polymers using a living polymerization method. This has allowed us to synthesize polymer architectures that we haven't been able to access till now including polythiophene brushes, star-shaped P3HT, as well as hyperbranched P3HT. It also allows us to accurately control the molecular weights of P3HT and produce materials with a narrow molecular weight distribution. In this presentation, our work towards creating brush polymers will be presented where a series of fully conjugated graft copolymers containing poly(3-hexylthiophene) (P3HT) side chains and a p-type carbazole-diketopyrrolopyrrole donor--acceptor backbone were synthesized via a graft through Suzuki polymerization. [Preview Abstract] |
Tuesday, March 3, 2015 9:48AM - 10:00AM |
F41.00006: Synthesis and Self-Assembly of Rod$_{2}$Coil Miktoarm Star Copolymers of Poly(3-dodecxylthiophene) and Poly(methyl methacrylate) with high rod fractions Jicheol Park, Hong Chul Moon, Chung-Royng Choi, Jin Kon Kim Poly(3-dodecylthiophene)-b-poly(methyl methacrylate) diblock copolymer (P3DDT-$b$-PMMA) can self-assembled into various microdomains such as spheres, cylinders, and lamellae depending on weight fraction of P3DDT. However, only filbril morphology was formed when weight fraction of P3DDT ($w_{\mathrm{P3DDT}})$ was major ($w_{\mathrm{P3DDT}}$ $\sim$ 0.76). Here, we introduce a new approach to obtain microdomain structures even at high $w_{\mathrm{P3DDT}}$ by using well-defined A$_{\mathrm{2}}$B miktoarm star copolymer composed of P3DDT and PMMA ((P3DDT)$_{\mathrm{2}}$PMMA. We found via small angle X-ray scattering and transmission electron microscopy that (P3DDT)$_{2}$PMMA showed PMMA cylinder packed hexagonally in the matrix of P3DDT and body-centered-cubic spheres of PMMA for $w_{\mathrm{P3DDT}}$ of 0.66 and 0.75, respectively. This because of much reduction of the rod-rod interaction in (P3DDT)$_{\mathrm{2}}$PMMA compared with P3DDT-$b$-PMMA diblock copolymers. [Preview Abstract] |
Tuesday, March 3, 2015 10:00AM - 10:12AM |
F41.00007: A Quantum Chemical Study of Structural and Electronic Properties of DTBT and DTBT:C70 Complexes Mesfin Tsige, Ram Bhatta Organic photovoltaic (OPV) devices containing the dithienyl-benzothiadiazole (DTBT) based conjugated polymers are promising candidates for solar energy harvesting. Practical realization of OPV devices requires further improving their performance, which relies on the fundamental understanding of the morphology and electronic properties of DTBT-based polymers. Nevertheless, even the conformational properties of DTBT have not been fully revealed yet. Here, we present the quantum chemical calculations of the structural and electronic properties of DTBT as well as DTBT:C70 complexes at the molecular level. These first principles results include the two-dimensional potential energy surface, the band gap, DTBT:C70 equilibrium distance as well as the energy level offset at the interface compared to the energy levels of the individual material. The computed results are compared to the available experimental data. [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F41.00008: Theoretical modelling of high-dielectric constant donors for high-conversion organic film solar cells Kenji Mishima, Koichi Yamashita In this contribution, we report our theoretical design of high dielectric-constant donors based on the DFT and TD-DFT quantum chemistry calculations. The motivation of our study lies in the importance of high-dielectric constant donors and acceptors for purposes of separating photo-generated excitons efficiently and preventing them from recombining, thus leading to high photo-conversion efficiency in the organic film solar cells. Our theoretical design guideline is to bind the conventional thiophene-related one-dimensional donor molecules via benzene rings two-dimensionally, which leads to extended pi-conjugation and their high dielectric constants. Our numerical results indicate that the dielectric constant increases monotonically with the size of the molecule. The dielectric constant of the two-dimensionally extended thiophene donor amounts to 13.6, which is more than three times as much as that of the conventional P3HT donor molecule ($\sim$ 4). By using PCBM molecule as an acceptor, the total amount of photo-induced transferred charge transfer from the donor to the acceptor is comparable to that of the P3HT/PCBM system. [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F41.00009: ABSTRACT WTHDRAWN |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F41.00010: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 10:48AM - 11:00AM |
F41.00011: High-throughput organic semiconductor discovery combining tight-binding and first-principles calculations Andre Leitao Botelho, Tim Mueller We present the combination of a tight-binding model and first-principles calculations as a two-step screening for the accelerated discovery of organic semiconductors. For the tight-binding model, we select the adapted Su-Schrieffer-Heeger Hamiltonian for its ability to provide both the electronic structure and optimized geometry based solely on the structural formula. We produce two sets of parameters, one to match the optical gaps to exciton energies from TDDFT, and another set to match the transport gaps to HOMO/LUMO energies from DFT with an experimental correction factor. Although the fittings use fewer than one thousand oligomers, the predictive results for the remaining one million oligomers agree with DFT (coefficient of determination of up to 0.8) and can be used as a pre-screening step. With the same set of parameters, we also calculate the charged states to predict the Marcus theory reorganizational energies as an estimate the conductivities of holes and electrons. Based on the calculated properties, we discuss materials selection for photovoltaics and transistors. [Preview Abstract] |
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