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Intrinsically distinct hole and electron transport in conjugated polymers controlled by intra and intermolecular interactions
摘要： It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. We here isolate the intrinsic factors affecting either electron or hole transport within the same film microstructure of a model copolymer semiconductor. Relatively, holes predominantly bleach inter-chain interactions with H-type electronic coupling character, while electrons’ relaxation more strongly involves intra-chain interactions with J-type character. Holes and electrons mobility correlates with the presence of a charge transfer state, while their ratio is a function of the relative content of intra- and inter-molecular interactions. Such fundamental observation, revealing the specific role of the ground-state intra- and inter-molecular coupling in selectively assisting charge transport, allows predicting a more favorable hole or electron transport already from screening the polymer film ground state optical properties.
关键词： electron transport,organic semiconductors,conjugated polymers,charge transfer state,hole transport
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Identification and Characterization of ‘Killer-Modes’ in Organic Semiconductors with Terahertz Spectroscopy
摘要： Organic semiconductors are promising modern optoelectric materials, with countless potential applications ranging from ?exible displays to photovoltaics. The applicability of these materials is largely driven by their charge carrier mobility, which is strongly in?uenced by low-frequency vibrations. In this work, the speci?c low-frequency vibrations that exhibit strong electron-phonon coupling, deemed ‘killer-modes’, in organic semiconductors are determined using a combination of terahertz time-domain spectroscopy and solid-state density functional theory. The results of this study enable a concerted synthetic effort to rationally design novel materials, utilizing intermolecular forces to stiffen lattice dynamics, to ultimately improve charge carrier mobility.
关键词： electron-phonon coupling,organic semiconductors,charge carrier mobility,solid-state density functional theory,terahertz spectroscopy
更新于2025-09-11 14:15:04
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Optoelectronics - Advanced Device Structures || Hybrid Silicon-Organic Heterojunction Structures for Photovoltaic Applications
摘要： The concept for inorganic-organic device is an attractive technology to develop devices with better characteristics and functionality due to the complementary advantages of inorganic and organic materials. This chapter provides an overview of the principal requirements for organic and inorganic semiconductor properties and their fabrication processes and focus on the compatibility between low temperature plasma enhanced chemical vapor deposition (PECVD) and polymer organic materials deposition. The concept for inorganic-organic device was validated with the fabrication of three hybrid thin film photovoltaic structures, based on hydrogenated silicon (Si:H), organic poly(3-hexythiophene): methano-fullerenephenyl-C61-butyric-acid-methyl-ester (P3HT:PCBM), and poly(3,4ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) films. Optoelectronic characteristics, performance characteristics, and interfaces of the different configurations aspects are discussed. Hybrid ITO/PEDOT:PSS/(i)Si:H/(n)Si:H structure results in a remarkably high short circuit current density as large as 17.74 mA/cm2, which is higher than the values in organic or inorganic reference samples. Although some hybrid structures demonstrated substantial improvement of performance, other hybrid structures showed poor performance, further R&D efforts seem to be promising, and should be focused on deeper study of organic materials and related interface properties.
关键词： thin film devices,hybrid devices,plasma deposited materials,solar cells,organic semiconductors
更新于2025-09-11 14:15:04
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A simple and robust approach to reducing contact resistance in organic transistors
摘要： Efficient injection of charge carriers from the contacts into the semiconductor layer is crucial for achieving high-performance organic devices. The potential drop necessary to accomplish this process yields a resistance associated with the contacts, namely the contact resistance. A large contact resistance can limit the operation of devices and even lead to inaccuracies in the extraction of the device parameters. Here, we demonstrate a simple and efficient strategy for reducing the contact resistance in organic thin-film transistors by more than an order of magnitude by creating high work function domains at the surface of the injecting electrodes to promote channels of enhanced injection. We find that the method is effective for both organic small molecule and polymer semiconductors, where we achieved a contact resistance as low as 200 Ωcm and device charge carrier mobilities as high as 20 cm2V?1s?1, independent of the applied gate voltage.
关键词： contact resistance,organic transistors,charge injection,high work function domains,organic semiconductors
更新于2025-09-10 09:29:36
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Correlation of Coexistent Charge Transfer States in F <sub/>4</sub> TCNQ-Doped P3HT with Microstructure
摘要： Understanding the interaction between organic semiconductors (OSCs) and dopants in thin films is critical for device optimization. The proclivity of a doped OSC to form free charges is predicated on the chemical and electronic interactions that occur between dopant and host. To date, doping has been assumed to occur via one of two mechanistic pathways: an integer charge transfer (ICT) between the OSC and dopant or hybridization of the frontier orbitals of both molecules to form a partial charge transfer complex (CPX). Using a combination of spectroscopies, we demonstrate that CPX and ICT states are present simultaneously in F4TCNQ-doped P3HT films and that the nature of the charge transfer interaction is strongly dependent on the local energetic environment. Our results suggest a multiphase model, where the local charge transfer mechanism is defined by the electronic driving force, governed by local microstructure in regioregular and regiorandom P3HT.
关键词： F4TCNQ,organic semiconductors,dopants,microstructure,charge transfer,P3HT
更新于2025-09-10 09:29:36
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Fundamental Gaps of Condensed-Phase Organic Semiconductors from Single-Molecule Calculations using Polarization-Consistent Optimally Tuned Screened Range-Separated Hybrid Functionals
摘要： Range-separated hybrid (RSH) functionals have been shown to overcome the tendency of traditional density functional theory to underestimate the fundamental orbital gap. More recently, the screened RSH (SRSH) approach has been developed as a means to extend these functionals to address the effect of the electrostatic environment on the fundamental gap. Here, we report a scheme that combines the SRSH formulation with the polarized continuum model (PCM) within a consistent framework for addressing long-range screened electrostatic interactions, which is further improved by optimal tuning (OT). The quantitative predictive power of the new OT-SRSH-PCM scheme is demonstrated by addressing fundamental gaps in thin films of organic semiconducting materials. This is especially impressive as the approach is based on single molecule calculations. We also discuss the advantages of this approach over alternative schemes combining PCM with RSH. In particular, we show that it avoids the well-documented tendency of standard OT to collapse the range separation parameter when performed within a dielectric continuum.
关键词： optimal tuning,organic semiconductors,fundamental gaps,screened RSH,polarized continuum model,Range-separated hybrid functionals
更新于2025-09-10 09:29:36
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Stretchable Conjugated Polymers: A Case Study in Topic Selection for New Research Groups
摘要： The field of π-conjugated (semiconducting) polymers has been underwritten largely because of the promise of flexible (and increasingly, stretchable) devices for energy and health care. Our research group has spent much of the past six years studying the mechanical properties of conjugated polymers. Mechanically robust materials can extend the life spans of devices such as solar cells and organic light-emitting diode (OLED) panels and enable high throughput processing techniques such as roll-to-roll printing. Additionally, wearable and implantable devices, including electronic skin, implantable pressure sensors, and haptic actuators, benefit by having moduli and extensibilities close to those of biological tissue. At the time of our laboratory’s inception, however, the optoelectronic properties of conjugated polymers were understood in much greater depth than their mechanical properties. We therefore set out, as our laboratory’s first research topic, to understand the molecular and microstructural determinants of the mechanical properties of conjugated polymers. This is an Account not only of our scientific findings but also of the pragmatic aspects, including personnel, funding, and time constraints, behind our studies as a nascent research group. We hope that this Account will provide information to newly independent scientists about the process of starting a new research laboratory.
关键词： π-conjugated polymers,stretchable electronics,organic semiconductors,mechanical properties,wearable devices
更新于2025-09-10 09:29:36
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Stochastic Resonance in Bioinspired Electronic Device Using Polymer Field Effect Transistors
摘要： Stochastic resonance (SR) phenomenon is emerged in organic field effect transistors (OFETs) using π-conjugated polymer, where application of external noise to the OFET system enhances signal/information processing performance which is often found in biological systems. The channel conductivity of the OFET is slightly increased by spin-coating using heated semiconductor polymer solution with heated glass substrate. In order to improve frequency responses of OFET, optimal width of the gate electrode is explored. Furthermore, it turns out that scratching and removing semiconductor film outside the source-drain electrodes and the channel enhances the On-Off current ratio of the device. These fabrication processes lead to steeper nonlinearity on the IDS vs. VGS curve, resulting in emergence of SR, which is fingerprinted in increase of correlation value between input and output signals with increase of intensity of external noise.
关键词： Stochastic resonance,Polymer thin films,Organic semiconductors,Bioinspiration,Field effect transistors
更新于2025-09-09 09:28:46
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Unraveling the Role of Multiphonon Excitations and Disorder Concerning the Meyer-Neldel Type Compensation Effect in Organic Semiconductors
摘要： The Meyer-Neldel (MN) compensation rule, implying an exponential increase in the prefactor with increasing activation energy in a thermally activated process, is naturally emerging in two-site transition rates as a result of multiphonon excitation processes. However, it has been recently demonstrated [Phys. Rev. B. 90, 245201 (2014)] that the experimentally observed compensation behavior for the temperature-activated charge transport in thin-film organic field-effect transistors (OFETs) is not a genuine phenomenon, but rather it is an apparent extrapolated effect that arises as a consequence of the partial filling of the Gaussian DOS distribution. To resolve the contradiction, we investigate the impact of different jump-rate models on macroscopic hopping-charge transport in a random organic system using an effective medium analytic approach. The principal result of this study is that the averaging over the individual jump rates in a conventional Gaussian disordered system erodes the genuine thermodynamically determined MN compensation effect, and therefore, the macroscopic transport no longer reflects the microscopic rates. The apparent compensation behavior observed for OFET mobilities upon varying the carrier concentrations can be reproduced regardless of the single-phonon or multiphonon character of activated transitions. Another remarkable finding is that the disorder formalism does predict a genuine MN compensation effect using multiphonon rates if a disordered semiconductor contains a significant concentration of deep traps, so that the cumulative DOS features a double-peak Gaussian. Thus, this study bridges the gap between Gaussian disorder and multi-excitation entropy (MEE) models concerning the MN effect, and has important implications for the interpretation of the isokinetic MN temperature in disordered organic semiconductors.
关键词： disorder,organic semiconductors,multiphonon excitations,charge transport,Meyer-Neldel rule
更新于2025-09-09 09:28:46
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Probing Exciton Delocalization in Organic Semiconductors: Insight from Time-Resolved Electron Paramagnetic Resonance and Magnetophotoselection Experiments
摘要： Delocalization of excited states of organic semiconductors is directly related to their e?ciency in devices. Time-resolved electron paramagnetic resonance spectroscopy provides unique capabilities in this respect because of its high spectral resolution and capability to probe the geometry and extent of excitons. Using magnetophotoselection experiments, the mode of exciton delocalization, along the backbone or parallel to the π?π stacking direction of the conjugated polymers, can be revealed. We demonstrate the robustness of this approach by applying it to building blocks of a prototypical conjugated polymer showing a symmetry of their excited states being far from ideal for this experiment. This renders magnetophotoselection superior to other approaches because it is applicable to a wealth of other organic semiconductors. The insight gained into exciton delocalization is crucial to the structure?function relationship of organic semiconductors and directly relevant for developing highly e?cient materials.
关键词： time-resolved electron paramagnetic resonance,conjugated polymers,exciton delocalization,organic semiconductors,magnetophotoselection
更新于2025-09-09 09:28:46