Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session U34: Organic Electronics II: Charge Transport and TheoryFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY FIAP DMP Chair: Stephanie Lee, Stevens Inst of Tech Room: 506 |
Thursday, March 5, 2020 2:30PM - 2:42PM |
U34.00001: Electro-reflectance study of low-voltage turn-on in triplet fusion OLED materials Sebastian Engmann, Emily Bittle, Lee Richter, David James Gundlach Coherent spin processes like singlet-fission (SF) and triplet fusion (TF) are gaining in interest to the scientific community, as SF could lead to an increase in performance of organic photovoltaics and TF in the emission efficiency of OLED devices. Recently reported results have suggested that higher order effects such as TF lead to a reduction of the luminescence turn-on voltage and is necessary for what was referred to as “sub-band gap turn-on”. However, we have shown that heterojunction band alignment can describe the low voltage turn-on. In this presentation we will present electro-reflection (ER) studies that elucidate the built-in potentials in 2 prototypical OLED devices based on Rubrene and DiFTES-ADT as the emitting layer. The results are put into context of the low luminescence turn-on, which is observed in both cases, and potential higher order effects. Furthermore, differences in the luminescence - current density-voltage-characteristics, L-J-V and magneto-electro-luminescence, MEL, between the two systems will be presented. A kinetic model captures zero field splitting and various exciton and charge carrier recombination pathways. |
Thursday, March 5, 2020 2:42PM - 2:54PM |
U34.00002: The rationale behind the acceptor-donor-acceptor chemical design of non-fullerene acceptors Anastasia Markina, Frederic Laquai, Denis Andrienko Efficiencies of organic solar cells have seen a rapid increase due to the development of non-fullerene acceptors (NFAs). We explain why excitons dissociation into charge-transfer (CT) states, and the subsequent CT state splitting into charge-separated (CS) states, are efficient in NFAs-based solar cells. |
Thursday, March 5, 2020 2:54PM - 3:06PM |
U34.00003: Engineering Diffusion of Charge-Transfer States at Organic Semiconductor Heterojunctions Nolan Concannon, Tao Zhang, Russell J Holmes Interfacial excited states formed at electron donor-acceptor heterojunctions, called charge-transfer (CT) states, are essential intermediates for organic photovoltaic and light-emitting devices. While CT states are known to diffuse, questions remain around the underlying transport mechanism and the materials parameters that determine the diffusion length. In this work, we examine CT state diffusion in donor-acceptor mixtures via photoluminescence quenching methods. The diffusion length is extracted across donor and acceptor type as well as relative composition. In general, we find that CT states are at least as mobile as their bulk counterparts, despite being confined to an interface. Further, the energy of the CT state, and the presence of low-lying triplet states do not strongly determine the scale of the diffusion length. We instead find a correlation between the diffusion length and the mobility of the slowest component charge carrier. The connection between charge carrier transport and CT state diffusion suggests strategies to engineer CT state migration in various devices. These conclusions may also elucidate CT state transport at hybrid interfaces of organic and inorganic semiconductors. |
Thursday, March 5, 2020 3:06PM - 3:42PM |
U34.00004: First-Principles Theory for Understanding Excitons in Stacked Organic Assemblies Invited Speaker: Sahar Sharifzadeh Organic semiconductors are tunable light absorbers with promise as solar energy conversion materials, with their efficiency highly dependent on the nature and energy of electron-hole pairs or excitons formed upon light absorption. Excitons in these materials are controlled by the interplay between inter- and intra-molecular electronic as well as vibrational interactions, which is not yet well-controlled in devices. Here, we utilize first-principles theory to investigate the optoelectronic and vibrational properties of stacks of functionalized PTCDI DNA base surrogates as a model system to study inter- and intra-molecular interactions. We apply time-dependent density functional theory, along with a Franck-Condon analysis of vibronic effects, to finite stacks of molecules that have been recently synthesized. We determine that the intra- and inter-molecular interactions result in distinct vibrational, electronic, and optical properties. For a periodic assembly of PTCDI, many-body perturbation theory predicts a bandstructure with significant bandwidth (~0.8 eV), consistent with strong inter-molecular electronic interactions, and several spatially delocalizated low-energy optically excited-states. By incorporating electron-phonon interactions, we find that at T = 300K, the optical absorption is altered from T = 0 K due to allowed indirect transitions, while exciton delocalization and binding energy, a measure of intermolecular electronic interactions, remains constant. Overall, this work demonstrates that excitonic properties can be modified via inter-molecular electronic and vibrational interactions. |
Thursday, March 5, 2020 3:42PM - 3:54PM |
U34.00005: Quantum Yield Enhancement of BDMO-PPV During Photo-Degradation Matthew Deutsch, Heungman Park Poly-2,5-bis(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene (BDMO-PPV) is a photoluminescent semiconducting polymer similar to other well-studied polyphenylene vinylenes such as MEH-PPV and MDMO-PPV. This family of organic semiconductors has similar emission spectra and absorption spectra due to their backbone structure. However, side-chain structures between different polyphenylene vinylene (PPV) derivatives can result in different optoelectrical and material properties. PPVs are known for their instability, degradation, and low efficiency - a barrier for use in organic electronic devices. BDMO-PPV exhibits enhanced internal and external quantum yield while degrading in organic solvents such as chloroform and toluene. A proposed highly emissive intermediate state during photodegradation is responsible for an increase in internal and external quantum yield. Using photoluminescence spectroscopy, infrared spectroscopy, and light scattering measurements we intend to define the physical and chemical processes behind the photo-degradation of BDMO-PPV. |
Thursday, March 5, 2020 3:54PM - 4:06PM |
U34.00006: Photospintronics- Light-controlled spin transport in hybrid chiral oligopeptide-nanoparticle structures Rupshali Roy It has been found the transmission of electrons through chiral molecules depends on their spin orientation; this is known as chiral induced spin selectivity.This effect makes it feasible to build spintronic devices without ferromagnetic spin injectors since the chiral molecules themselves serve to choose a specific spin to transfer across the molecules. |
Thursday, March 5, 2020 4:06PM - 4:18PM |
U34.00007: Morphology-Dependent Triplet Exciton Diffusion in Vapor Deposited Pentacene Thin Films Kaicheng Shi, Ian Curtin, Andrew Healy, Tao Zhang, David Blank, Russell J Holmes Singlet exciton fission is among the most efficient multiexciton-generation process reported to date. Materials exhibiting singlet fission can potentially generate two triplets for each photogenerated singlet, and are of interest for a variety of applications in photoconversion and light-emission. While the kinetics of fission have been previously examined, fewer works have sought to probe the diffusion length of the resulting non-luminescent triplet state. Here, we probe triplet exciton diffusion in thin films of the archetypical singlet fission material pentacene using a device-based methodology capable of extracting the intrinsic, materials-relevant exciton diffusion length. The dependence of triplet exciton diffusion on morphology and crystalline grain size is probed by varying thin film deposition rate. Increased grain size leads to an increase in exciton lifetime, and a commensurate improvement in the triplet diffusion length. For a change in growth rate from 10 Å/s to 0.05 Å/s, the triplet diffusion length increases from 16.3 nm to 22.0 nm. These results offer an additional handle on how to maximize the triplet exciton diffusion length with optimization of thin film processing conditions. |
Thursday, March 5, 2020 4:18PM - 4:30PM |
U34.00008: Polaronic effects and charge transport in donor-acceptor semiconducting polymers Xiao Wang, Leonard F Register, Ananth Dodabalapur Molecular polaron theories, when applied to high mobility donor-acceptor semiconducting polymers along the chain, indicate that polaronic effects can be very small. These effects include changes to the electronic bandwidth and effective mass resulting from the strong coupling of phonons with charge carriers.1 The bandwidth and effective mass remain essentially unchanged with increasing temperature and are adequate for band transport to take place along the chain. However, the small mean free path obtained from the polymer mobility is still an obstacle in understanding band transport in polymers. We invoke the statistical distribution of carrier free paths and consider the carriers with small free paths as effectively localized due to strong scattering. Only carriers with adequately large free paths can participate in band transport.2 For such carriers, we are able to apply the Boltzmann Transport Equation with appropriate scattering mechanisms to calculate band mobility and the results are in good agreement with experimental data. |
Thursday, March 5, 2020 4:30PM - 4:42PM |
U34.00009: Switching dynamics in Croconic Acid thin film Xuanyuan Jiang, Pratyush P Buragohain, Shashi Poddar, Haidong Lu, Alexei Gruverman, Xiaoshan Xu Croconic Acid (CA) exhibits ferroelectricity due to proton displacement between molecules. The voltage and pulse duration dependence of polarization switching in CA thin film are studied using piezoresponse force microscopy (PFM). From this study, the microscopic mechanism of CA polarization switching is revealed. And the KAI domain growth model is used to fit with this switching dynamic behavior. From the fitting, the dimensionality of domain wall, the nucleation activation energy and other structural parameters are obtained. Also, the dependence of film thickness and substrate effect for CA switching are investigated. This study should be helpful for the control experiments in the ferroelectric devices and organic spin-valves using CA as the spacer. |
Thursday, March 5, 2020 4:42PM - 4:54PM |
U34.00010: Self-assembled monolayer formation of linear molecules onto a FCC(111) surface Eduardo Cisternas, Gonzalo Dos Santos, Marcos Flores, Eugenio Vogel, Antonio Jose Ramirez-Pastor The self-organization of molecules deposited over different surfaces have intersting technological applications. The adsorption of linear molecules as well the formation of self-assembled monolayers are considered in response to the experimental evidence for curcuminoids over gold surfaces. These processes are mainly controlled by the surface-molecule and molecule-molecule interactions. By performing computational calculations based on the density functional theory, we have obtained interaction energies for different configurations of two adsorbed molecules over a Au(111) surface. Such molecules were approximated to linear pentamers while the gold surface corresponds to a triangular lattice. This model system was investigated under the framework of Grand Canonical Monte Carlo simulations paying special attention to two quantities: the surface coverage and an order parameter reflecting the molecular alignment over the surface. As expected, the surface coverage is directly proportional to the system pressure (chemical potential). However, for critical values of the chemical potential the molecules present patterns evidencing nematic transitions. |
Thursday, March 5, 2020 4:54PM - 5:30PM |
U34.00011: Controlling energy levels and Fermi level en route to fully tailored energetics in organic semiconductors Invited Speaker: Moritz Riede Organic semiconductors have yet to achieve simultaneous control over both the energy levels and Fermi level, which was a key breakthrough for inorganic electronics. Here, we combine two approaches from band engineering and molecular doping to demonstrate controlled shifts in ionisation potential and Fermi level of an organic thin film. We experimentally investigate the doping efficiency of a ternary blend system consisting of two host molecules, ZnPc and F8-ZnPc, and the p-dopant F6–TCNNQ. We explain the observed doping behaviour with a statistical model based on energy level shifts of both host and dopant materials, resulting from the quadrupole moments of all involved molecules. We thereby demonstrate that band tuning crucially affects the doping process in organic semiconductors. The practice of comparing host and dopant energy levels must consider the long-range electrostatic shifts, arising from the quadrupole interactions to consistently explain the doping mechanism in organic semiconductors. |
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