Operando Characterization of Organic Mixed Ionic/Electronic Conducting Materials (original) (raw)
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Time-Resolved Structural Dynamics of Organic Mixed Ionic Electronic Conductors
The structure and packing of organic mixed ionic-electronic conductors have an outsized effect on transport properties. In operating devices this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Towards this end, the dynamic structure of a model organic mixed conductor is characterized using multimodal time-resolved operando techniques. Time-resolved operando X-ray scattering reveals asymmetric rates of structural change during doping and dedoping that do not directly depend on potential or charging dynamics. Time-resolved spectroscopy establishes a link between structural transients and the complex dynamics of electronic charge carrier subpopulations, in particular the polaron-bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic mixed conductor based devices, and present the first real-time observation of the structural changes during doping and dedoping...
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Elucidating the rate and geometry of molecular dynamics is particularly important for unravelling ion-conduction mechanisms in electrochemical materials. The local molecular motions in the plastic crystal 1-ethyl-1-methylpyrrolidinium tetrafluoroborate ([C 2 mpyr][BF 4 ]) are studied by a combination of quantum chemical calculations and advanced solid-state nuclear magnetic resonance spectroscopy. For the first time, a restricted puckering motion with a small fluctuation angle of 258 in the pyrrolidinium ring has been observed, even in the lowtemperature phase (À45 8C). This local molecular motion is deemed to be particularly important for the material to maintain its plasticity, and hence, its ion mobility at low temperatures.
The interaction between ionic moieties and the electronic properties of organic and hybrid semiconductors can yield a variety of interesting and sometimes surprising effects. Ionic moieties can induce interface dipoles, support electrochemical doping and lead to band-bending. The dynamic motion of ions under electric fields and the induced changes in conductivity can make it difficult to de-convolute the various mechanisms at play. This review attempts to provide a perspective on different types of interactions between ions and semiconductors and goes into depth addressing the application of solution-processed polyelectrolyte and oligoelectrolyte materials to control the energy band structures and behaviour of organic and hybrid semiconducting optoelectronic devices. This review introduces and highlights different types of ionic materials (such as conjugated polyelectrolytes and molecular ionic dopants) that have been used to achieve different effects (such as creating interfacial dipoles, vacuum energy shifts, changes in Fermi energies and doping) in organic and hybrid semiconducting devices before going into greater depth with the emerging class of non-conjugated polyelectrolytes and oligoelectrolytes and provides a comprehensive summary of recent progress using these materials in semiconducting devices. This class of materials has been receiving increasing attention recently and provides insights into the fundamental effects of ionic functionalities on the energy band structures and functions in organic and hybrid semiconductors.
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Some organic small molecules as well as conjugated polymers are attractive organic semiconductors with rich applications in the branch of immerging organic electronics, e.g., in light-emitting, switching and photovoltaic devices. Surprisingly, there is the lack of methods, suitable for elucidation of basic injection and transport properties. This contribution deals with application of several techniques based on charge transient measurements, isothermal charge transient spectroscopy (IQTS) in microscopic mode, electrochemical methods of double step voltcoulometry (DSVCM) and electrochemical impedance spectroscopy (EIS), which are potentially suitable for obtaining information about basic parameters of traps and their influence on the transport properties. To test the characterization methods we first used the prototypical polysilane-poly[methyl(phenyl)silylene] (PMPSi). Phototodegradation of the by UV radiation is known to cause chain scission and creation of dangling bonds and weak bonds by known mechanisms. Next we show the applicability to study the electron structure of presented methods on PPV and blend of PPV and nano-CdS.
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Synthetic Metals - SYNTHET METAL, 1988
Abstract A comprehensive approach to the analysis of the infrared data of a quarter-filled, slightly dimerized organic molecular conductor characterized by narrow optical gaps is proposed. It is based on a model for a one-dimensional molecular chain system with twofold-commensurate charge-density-waves. Analysis of the room temperature infrared spectra of (TMTSF) 2 ClO 4 indicates the presence of electronic correlations strong enough as to effectively exclude the double occupancy of the electronic states. Other important ...
Probing electronic state charging in organic electronic devices using electroabsorption spectroscopy
Synthetic Metals, 1996
In metal/organic-film/metal device structures with different metal contacts there is a built-in electrostatic potential at equilibrium due to the asymmetric contacts. At thermal equilibrium the electrochemical potential is constant across the device structure. The electrochemical potential can be divided into the sum of two parts, the electrostatic potential and the chemical potential. By measuring the built-in electrostatic potential change across a structure at equilibrium, one can determine the change in chemical potential across the structure. Measuring this built-in electrostatic potential for devices with different contact metals provides a way of changing the chemical potential (CL) in the organic material and identifying the values of p at which charged excitations are populated. Such measurements can be used to gain information on the energy spectrum of intrinsic charged excitations, charged trap states and charged interface states. We apply an electroabsorption technique to measure the built-in potentials of metal/organic-film/metal structures fabricated from poly[2-methoxy,5-(2'-ethyl-hexyloxy)-1,4phenylene vinylene] (MEH-PPV), &,doped MEH-PPV, and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) and discuss what is learned about the charged excitations in these materials from the results.
Journal of Physical Chemistry C, 2019
The steps responsible for device charging in organic electrochemical transistors were investigated using in situ infrared spectroscopy. Metal−electrolyte-dielectric−organic semiconductor capacitor structures were fabricated on infrared waveguides and measured using the total internal reflection sampling method. Upon the application of a voltage, charges were induced in the device, creating polaron absorption features in the mid-infrared region. The dynamics of the device charging were investigated by varying the channel length, dielectric layer thickness, and organic semiconductor layer thickness. Device charging was independent of the channel length but depended strongly on the semiconductor and dielectric layer thicknesses, indicating that the movement of ions is the primary determining factor for device charging kinetics. A quantitative model is developed combining an resistor-capacitor (RC) circuit model for the dielectric layer and a mixed ion−carrier diffusion model for the organic semiconductor layer. The model is evaluated against an RC circuit model for electrochemical charging dynamics, which is used in the popular Bernards model. Thickness-dependent dynamics cannot be adequately explained using the RC circuit model. The model presented here is significantly more appropriate for fundamental studies of ion dynamics in piconjugated materials.