Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J33: Focus Session: Organic Electronics and Photonics - Photophysics and Charge Transfer |
Hide Abstracts |
Sponsoring Units: DMP Chair: Seth Darling, Argonne National Laboratory Room: 341 |
Tuesday, March 19, 2013 2:30PM - 3:06PM |
J33.00001: DILLON MEDAL BREAK
|
Tuesday, March 19, 2013 3:06PM - 3:18PM |
J33.00002: Investigation of Pyrene Excimer formation in various manufacturing processes and ionic structures Hyun-Sook Jang, Mu-Ping Nieh Electrospun pyrene (Py)/polystyrene/tetrabutylammonium hexafluorophosphate (TBAPF6) thin films can provide high-sensitivity and high-selectivity detection of nitro-aromatic explosives through fluorescence quenching of the Py excimers [1]. However, we have found that the formation of Py excimers in Py/PS/TBAPF6 thin films depends greatly on the manufacturing processes. Our results indicate that high solvent vapor pressure promotes the Py excimer fluorescence, while high temperature (around or greater than Tg of the PS) has an opposite effect in absence of solvent -- reducing the Py excimer fluorescence. Moreover, we have found that salts structure such as cation chain length, anion strength can significantly affect the formation of Py excimer both in solution and solid state, presumably due to self-aggregation of the salts and electrostatic interactions between ions and pyrene excimer. 13C-NMR and steady-state fluorescence result indicate that the salt induces peak shift to the downfield in the spectra and quenches the Py excimer intensity drastically.\\[4pt] [1] Wang, Y.; La, A.; Ding, Y.; Liu, Y.;Lei, Y. Advanced Functional Materials 2012, 22, 3547. [Preview Abstract] |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J33.00003: Photoisomerization dynamics of azobenzene materials for solar thermal fuels David A. Strubbe, Jeffrey C. Grossman A solar thermal fuel absorbs sunlight and stores the energy chemically via an induced structural change, which can later be reversed to release the energy as heat. Azobenzene molecules have a cis-trans photoisomerization with these properties, and hydrogen-bonding and packing via attachment to rigid template structures have shown promise in increasing the energy stored and the length of time it can be stored [A Kolpak et al, Nano Lett. 11, 3156-3162 (2011)]. Other important factors in determining the efficiency of a solar thermal fuel are the absorption cross-section and the quantum yield for photoisomerization, which must also be optimized for a successful material. We employ time-dependent density-functional theory (TDDFT) and the GW/Bethe-Salpeter formalism to calculate the optical absorption and dynamics in the excited-state to address these two factors. We use excited-state forces to map out potential-energy surfaces and follow the structural change after absorption for azobenzene-derived materials, to correlate the efficiency of photoisomerization with the functionalization and template. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J33.00004: Optical absorption in fluorenone-based push-pull molecules Eduardo Cruz-Silva, Paul J. Homnick, Paul M. Lahti, Vincent Meunier Push-pull organic molecules include both electron donor and acceptor substituents, which upon excitation induce a charge separation with potential uses in conductive polymers and light-harvesting materials for use in solar cells. In a recent work, a new set of such molecules using fluorenone as the electron-acceptor unit have been reported [1]. Here we present a comprehensive study of their electronic structure and and optical properties using time-dependent density functional theory (TDDFT) as implemented in the NWChem software suite [2]. The remarkable agreement between experimental and computed spectra among all test systems show that TDDFT can be readily used as a predictive tool for assessing and optimizing the optical properties on these systems. 1. P.J. Homnick and P.M. Lahti, Phys. Chem. Chem. Phys. 14, 11961-11968 (2012). 2. M. Valiev, E.J. Bylaska, N. Govind, K Kowalski, et al., Comput. Phys. Commun. 181, 1477 (2010). [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J33.00005: Exciton-Plasmon Interaction Effects in Individual Carbon Nanotubes Igor Bondarev, Areg Meliksetyan We have recently developed a theory for the electrostatically controlled coupling between excitons and low-energy inter-band plasmons in individual semiconducting carbon nanotubes [1]. Here, we report on our studies towards the applications of this effect of both applied and fundamental interest. One practical application is the electromagnetic absorption/photoluminescence control for individual nanotubes [2]. Another, fundamental one, comes from the fact that the coupling of the excitons to the same inter-band plasmon resonance results in their entanglement, a pre-requisite for strong quantum correlations/quantum phase transitions in many-particle systems [3]. Our coupled exciton-plasmon excitation is a quasi-1D Bose system and could possibly be Bose-condensed in an individual carbon nanotube under appropriately created external conditions --- despite the mathematical statements [4] of the BEC impossibility in ideal 1D and 2D quantum systems and previously reported evidence [5] for no free-exciton BEC in carbon nanotubes.\\[4pt] [1] I.V.Bondarev, et al, PRB80, 085407 (2009).\\[0pt] [2] I.V.Bondarev, PRB85, 035448 (2012).\\[0pt] [3] J.Anders, PRA77, 062102 (2008).\\[0pt] [4] R.K.Pathria, P.D.Beale, Statistical Mechanics (Elsevier, 2011).\\[0pt] [5] Y.Murakami, J.Kono, PRL102, 037401 (2009). [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J33.00006: Quantitative analysis of valence photoemission spectra and quasiparticle excitations at chromophore-semiconductor interfaces Christopher Patrick, Feliciano Giustino Understanding electron energetics at interfaces between solids and molecules is a key challenge in many areas of nanotechnology research. Here we develop a quantitative theory of quasiparticle excitations at these interfaces and apply it to the prototypical dye-sensitized solar cell interface of N3 dye molecules adsorbed on the anatase TiO$_2$ (101) surface.\footnote{C. E. Patrick and F. Giustino, Phys. Rev. Lett. 109, 116801 (2012)} Our approach combines density-functional calculations on large interface models, bulk GW calculations,\footnote{C. E. Patrick and F. Giustino, J. Phys. Condens. Matter 24, 202201 (2012)} image charge renormalization, thermal broadening and configurational disorder to obtain a quasiparticle spectrum in good agreement with experimental photoemission data. Our calculations clarify the atomistic origin of the chromophore peak at low binding energy, and illustrate the dual role played by the TiO$_2$ substrate in screening the quasiparticle states of the N3 molecule through both long-range image-charge effects and direct charge transfer via the covalently-bonded anchor groups. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J33.00007: Two-dimensional Fourier transform spectroscopy of primary excitations, in conjugated polymers Kenan Gundogdu, Cong Mai, Andrew Barrette, Robert Younts, Terry McAfee, Harald Ade Conjugated polymers have tremendous potential for use in cheap, flexible, lightweight, energy efficient opto-electronic applications, Despite years of work, critical fundamental aspects about their optical and electronic properties are still poorly understood. Photo absorption in pure semi-conducting polymer thin films eventually results in both free charges and bound excitons with varying branching ratios. However the identification of the nature of early excitations and charge generation is an unresolved problem. There has been no direct observation of initial excitons or free electron-hole pairs, and competing views persist. Here we use 2D Fourier transform spectroscopy methods to separate the spectral signatures of various processes in the photoabsorption process in a homopolymer and show that initial excitation results in an intrachain electronic coherence that persists more than 200 fs. As these coherences evolve they collapse to transient population states i.e excitons, polarons and bipolarons. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J33.00008: Revealing photoinduced charge transfer mechanism across $\pi $-conjugated heterojunctions Yongwoo Shin, Xi Lin The adapted Su-Schrieffer-Heeger (aSSH) model is extended to the $\pi $-conjugated bulk heterojunction system. The New aSSH Hamiltonian incorporated interchain $\pi $-$\pi $ stacking and dynamic electron-phonon coupling effects. Excellent agreements are found between the computed photoadsorption and photoinduced adsorption spectra and their corresponding experimental measurements. It is found that excitons generated in the bulk poly-(p-phenylene vinylene) (PPV) phase must overcome an energy barrier of 0.23 eV to reach heterojunction interface. These interfacial excitons show clear charge separations, with their electron states leaning towards the interface. Therefore, electron transfers from the D$_1^{\mathrm{\ast }}$ state of PPV to the t$_{\mathrm{1u}}^{\mathrm{\ast }}$ state of C$_{60}$ follow non-adiabatic mechanisms, which are accelerated by the 0.97 eV energy drop, close vicinity of the D$_1^{\mathrm{\ast}}$ state to the C$_{60}$ phase, and suppressed inversion symmetry that doubles the number of electron-accepting states. After non-adiabatic electron transfers, the hole D$_1$ states are screened by the optical phonons in PPV, forming self-localized hole polarons and moving further away from heterojunction interface. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J33.00009: Charge transfer excitations in water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C$_{60}$ Rajendra Zope, Luis Basurto, Marco Olguin, Tunna Baruah We present a study of charge transfer (CT) excited states for a recently synthesized group of water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C$_{60}$. The ZnPcS donors (ZnPcS2, ZnPcS3, and ZnPcS4) are promising materials for achieving solar cell device production with the photoactive area prepared from aqueous solution. Experimentally, decreasing the number of sulfonate substituent groups for ZnPc increased the photocurrent and lowered the open circuit voltage V$_{OC}$. Measurements show that the V$_{OC}$ is largest for ZnPc-S4/C$_{60}$ and lowest for ZnPc-S3/C$_{60}$. The degree of sulfonation and the measured device V$_{OC}$ does not result in the expected pattern of values based on donor-acceptor HOMO/LUMO energy differences. Variations in film morphology may account for the unexpected pattern of V$_{OC}$ values. Our charge transfer excited state calculations show that the lowest CT excitation energy among the group of ZnPcS/C60 donor-acceptor pairs corresponds to the disulfonated ZnPc/C60 system. The largest CT excited state energies belong to the tetrasulfonated ZnPc/C60 complex. We also examine the effect of geometrical orientation on the CT energies for the ZnPcS donor-acceptor pairs. [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J33.00010: Packing effects in charge transfer dynamics in organic molecular heterojunctions consisting of TFB and F8BT Mikiya Fujii, Koichi Yamashita Organic semiconductors have been widely investigated for photovoltaic and light emitting devices. Especially, further improvements for more efficient organic solar cells (OSCs) are desired. Thus, we explored computationally possibilities to make OSCs more efficient by adjusting the packing of molecular heterojunctions. We analyzed a molecular heterojunction that consists of poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylenediamine) (TFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Geometrical optimization of TFB(monomer)/F8BT(monomer) complex was carried out with DFT-D/B3LYP/6-31G*. Excited states were also calculated with CIS/6-31G*. To analyze packing effects, we rotated TFB around a principal axis. Then, charge transfer dynamics is analyzed with a quantum master equation (QME) approach in each packing From the excited states calculations, it is clarified that the packing strongly affects the energy level of the charge transfer state only. This packing dependency arises from a packing dependency of the exciton binding energy that is Coulomb interaction between an electron localized to F8BT and a hole localized to TFB. From the QME approach, it is confirmed that qualitative different electronic relaxation dynamics occurs in each different packing. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J33.00011: Charge-Transfer Complexation Mechanism of Poly (4-Vinyl Pyridine)/[6,6] - Phenyl-C$_{61}$-Butyric Acid Methyl Ester in DMF Solution He Cheng, Guangmin Wei, Charles Han The mechanism of charge-transfer complexation in electron-donor(D)/electron-acceptor(A) active layer was studied for a pseudo-binary blend model system, poly(4-vinyl pyridine) /[6,6]-phenyl-C$_{61}$-butyric acid methyl ester in DMF. The time evolution of the system can be characterized by four distinct stages, i.e., induction, complexation, aggregation and precipitation, respectively. In the induction stage, the conformation of P4VP remained unchanged, while the UV-vis showed that the charge-transfer complexation had almost accomplished. In the complexation stage, each P4VP chains complexed with about 3 PCBM molecules at [4VP]/[PCBM]$=$57:1, and shrinked in size with almost no change in UV-vis spectrum. In the subsequent aggregation stage, P4VP/PCBM complexes aggregated with each other to form spherical aggregates with again unchanged UV-vis signals. FA model can be used to explain this mechanism. In the final precipitation stage, huge P4VP/PCBM agglomerate began to phase out. The almost unchanged UV-vis spectrum after the induction stage indicated that the electronic transition from ground to excited state is not necessarily to be influenced by any inter- or intra-polymer structural transition. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J33.00012: Probing charge transfer complex states in organic solar cells using photocurrent spectroscopy Dhanashree Moghe, Danish Adil, Catherine Kanimozhi, Gitesh Dutta, Satish Patil, Suchismita Guha Diketopyrrolopyrrole (DPP) containing copolymers-fullerene blends have gained a lot of interest in organic optoelectronics with a great potential in organic photovoltaics (OPVs). The interfacial charge transfer complex (CTC) states formed in donor-acceptor blended OPVs play a major role in the overall efficiency of the device. We investigate the spectral photocurrent characteristics of five DPP based copolymers; two of them being benzothiadiazole and carbazole -based statistical copolymers of DPP. These systems provide a wide range of bandgap energies ranging from $\sim$ 1.4 to 1.7 eV. We use Fourier transform photocurrent spectroscopy (FTPS) and monochromatic photocurrent (PC) to identify the CTC states in these DPP copolymer -fullerene blends. The stability of the CTC state is found to be dependent on the band gap energy difference between the donor copolymer and the acceptor. We support our inferences from theoretical results obtained using density-functional theory (DFT) and time-dependent DFT for two DPP based copolymers The theoretical calculations reveal a higher contribution of the CTC states to the lowest excited state in the phenyl-based DPP monomer, which has a larger bandgap energy compared to the thiophene-based DPP system, in the presence of a fullerene molecule. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700