Capacitance, spectroelectrochemistry and conductivity of polarons and bipolarons in a polydicarbazole based conducting polymer

Pomerantz, Zvika; Zaban, Arie; Ghosh, Subrata; Lellouche, Jean‐Paul; García-Belmonte, Germà; Bisquert, Juan

doi:10.1016/j.jelechem.2007.11.005

Cited by 47 publications

(51 citation statements)

References 60 publications

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“…(3) Eqn (34) shows that the conductivity is determined exclusively by the transport level and is completely independent of the presence and distribution of traps. The steady-state conduction is not affected by the trapping process, because the traps remain in equilibrium.…”

Section: Interpretation Of Multiple Trapping Modelsmentioning

confidence: 99%

“…The fit to straight lines gives values close to the thermal energies, k B T = 0.0236 and 0.0288 eV at 273 and 333 K, respectively. Therefore, the conductivity is thermally activated as expected from eqn (34), assuming that the free electrons diffusion coefficient, D 0 , depends weakly on the temperature. Despite this observation, the value of D 0 cannot be clearly identified, due to uncertainties about the carrier transport mechanism above the measured potential range (i.e., band transport or hopping to the transport energy), 103 and this is discussed in the next section.…”

mentioning

confidence: 91%

“…This is most appropriate for electrochemical and photoelectrochemical systems, where the Fermi level can be directly monitored by potentiostatic control. [32][33][34] A system that played a key role in our understanding is the electrochemistry of redox polymers. 35,36 In the work of Chidsey and Murray 35 the main concepts used here were clearly formulated.…”

Section: Introductionmentioning

confidence: 99%

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Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states

Bisquert

2008

Phys. Chem. Chem. Phys.

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183

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The carrier transport properties in nanocrystalline semiconductors and organic materials play a key role for modern organic/inorganic devices such as dye-sensitized (DSC) and organic solar cells, organic and hybrid light-emitting diodes (OLEDs), organic field-effect transistors, and electrochemical sensors and displays. Carrier transport in these materials usually occurs by transitions in a broad distribution of localized states. As a result the transport is dominated by thermal activation to a band of extended states (multiple trapping), or if these do not exist, by hopping via localized states. We provide a general view of the physical interpretation of the variations of carrier transport coefficients (diffusion coefficient and mobility) with respect to the carrier concentration, or Fermi level, examining in detail models for carrier transport in nanocrystalline semiconductors and organic materials with the following distributions: single and two-level systems, exponential and Gaussian density of states. We treat both the multiple trapping models and the hopping model in the transport energy approximation. The analysis is simplified by thermodynamic properties: the chemical capacitance, C m , and the thermodynamic factor, w n , that allow us to derive many properties of the chemical diffusion coefficient, D n , used in Fick's law. The formulation of the generalized Einstein relation for the mobility to diffusion ratio shows that the carrier mobility is proportional to the jump diffusion coefficient, D J , that is derived from single particle random walk. Characteristic experimental data for nanocrystalline TiO 2 in DSC and electrochemically doped conducting polymers are discussed in the light of these models.

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Section: Interpretation Of Multiple Trapping Modelsmentioning

confidence: 99%

mentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states

Bisquert

2008

Phys. Chem. Chem. Phys.

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183

175

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mentioning

confidence: 99%

“…Recently, CV analysis has been improved by including the formation of both polarons and bipolarons and taking their respective DOS values into account. 8 Other techniques use organic thin-film transistor structures to derive the DOS by Kelvin probe force microscopy. 9 In this letter, we present an energy resolved EIS (ER-EIS) method based on the interaction between an organic semiconductor and an electrolyte at an interface via a oxidation/reduction (redox) reaction.…”

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confidence: 99%

Energy resolved electrochemical impedance spectroscopy for electronic structure mapping in organic semiconductors

Nádaždy

Schauer

Gmucová

2014

Applied Physics Letters

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We introduce an energy resolved electrochemical impedance spectroscopy method to map the electronic density of states (DOS) in organic semiconductor materials. The method consists in measurement of the charge transfer resistance of a semiconductor/electrolyte interface at a frequency where the redox reactions determine the real component of the impedance. The charge transfer resistance value provides direct information about the electronic DOS at the energy given by the electrochemical potential of the electrolyte, which can be adjusted using an external voltage. A simple theory for experimental data evaluation is proposed, along with an explanation of the corresponding experimental conditions. The method allows mapping over unprecedentedly wide energy and DOS ranges. Also, important DOS parameters can be determined directly from the raw experimental data without the lengthy analysis required in other techniques. The potential of the proposed method is illustrated by tracing weak bond defect states induced by ultraviolet treatment above the highest occupied molecular orbital in a prototypical r-conjugated polymer, poly[methyl(phenyl)silylene]. The results agree well with those of our previous DOS reconstruction by post-transient space-charge-limited-current spectroscopy, which was, however, limited to a narrow energy range. In addition, good agreement of the DOS values measured on two common p-conjugated organic polymer semiconductors, polyphenylene vinylene and poly(3-hexylthiophene), with the rather rare previously published data demonstrate the accuracy of the proposed method. Determination of the electronic structures of organic semiconductors has major relevance for studies of charge/ energy transport and recombination phenomena in organic electronics. However, weak molecular coupling and disordered structures often preclude application of the spectroscopic methods used for inorganic semiconductors. Electrochemical spectroscopic methods tend to fill this gap. Electrochemical impedance spectroscopy (EIS) has been known for decades and has served many purposes, from studies of electrochemical reaction mechanisms to investigations of passive surfaces.2 EIS development has also been positively influenced by activities related to clarification of solid-electrolyte processes over the last 40 to 50 years.3 A cumulative paper describing progress in the examination of various nanostructured and organic materials by EIS was published by Bisquert et al. 4 Additionally, several other electrochemical methods exist for study of electronic structures in organic semiconductors, based on direct determination of the density of states (DOS) at the Fermi energy. 5,6 Electrochemical cyclic voltammetry (CV) of conducting polymers and molecular solid films has also been interpreted in terms of the electronic DOS. 7 The CV of organic films is generally characterized by a broad non-Nernstian signal, which is interpreted as an indication of the underlying Gaussian DOS that is common in disordered organic materials. Recently, CV anal...

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Unifying Energetic Disorder from Charge Transport and Band Bending in Organic Semiconductors

Karki

Wetzelaer

Reddy

et al. 2019

Adv Funct Materials

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Characterizing the density of states (DOS) width accurately is critical in understanding the charge-transport properties of organic semiconducting materials as broader DOS distributions lead to an inferior transport. From a morphological standpoint, the relative densities of ordered and disordered regions are known to affect charge-transport properties in films; however, a comparison between molecular structures showing quantifiable ordered and disordered regions at an atomic level and its impact on DOS widths and charge-transport properties has yet to be made. In this work, for the first time, the DOS distribution widths of two model conjugated polymer systems are characterized using three different techniques. A quantitative correlation between energetic disorder from band-bending measurements and charge transport is established, providing direct experimental evidence that chargecarrier mobility in disordered materials is compromised due to the relaxation of carriers into the tail states of the DOS. Distinction and quantification of ordered and disordered regions of thin films at an atomic level is achieved using solid-state NMR spectroscopy. An ability to compare solid-state film morphologies of organic semiconducting polymers to energetic disorder, and in turn charge transport, can provide useful guidelines for applications of organic conjugated polymers in pertinent devices.

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Capacitance, spectroelectrochemistry and conductivity of polarons and bipolarons in a polydicarbazole based conducting polymer

Cited by 47 publications

References 60 publications

Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states

Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states

Energy resolved electrochemical impedance spectroscopy for electronic structure mapping in organic semiconductors

Unifying Energetic Disorder from Charge Transport and Band Bending in Organic Semiconductors

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