Direct Determination of the Hole Density of States in Undoped and Doped Amorphous Organic Films with High Lateral Resolution

Tal, Oren; Rosenwaks, Y.; Preezant, Yevgeni; Tessler, Nir; Chan, Catherine; Kahn, Antoine

doi:10.1103/physrevlett.95.256405

Cited by 154 publications

(116 citation statements)

References 25 publications

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“…20 The DOS distribution has been also extracted from space-charge-limited-current spectroscopy and Kelvin probe microscopy. [34][35][36] Recently, the DOS distribution has been estimated from the analysis of ESR lineshape, 37,38 where the existence of significant discrete states has been concluded. However, since the shallow states mainly influence the transport properties, the exponential model is a good approximation to understand the transistor characteristics.…”

Section: Introductionmentioning

confidence: 99%

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

et al. 2013

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We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N ’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge

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Section: Introductionmentioning

confidence: 99%

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

et al. 2013

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“…9(a)). The presence of such a discrete state, probably due to the influence of oxygen, has been indicated in other organic semiconductors from the transistor characteristics, 27 space-charge-limited-current spectroscopy, 56 Kelvin probe microscopy, 57 and ESR. 69,70 The simulated characteristics depicted in Fig.…”

Section: Localized Statementioning

confidence: 99%

“…Similar exponential DOS has been obtained not only from transistor characteristics but also from space-charge-limited-current spectroscopy and Kelvin probe microscopy. [56][57][58] Note that this method is based on the interface approximation because it simply assumes Q = CV G .…”

Section: B Trap Dosmentioning

confidence: 99%

Analysing organic transistors based on interface approximation

Akiyama

Mori

2014

AIP Advances

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Temperature-dependent characteristics of organic transistors are analysed thoroughly using interface approximation. In contrast to amorphous silicon transistors, it is characteristic of organic transistors that the accumulation layer is concentrated on the first monolayer, and it is appropriate to consider interface charge rather than band bending. On the basis of this model, observed characteristics of hexamethylenetetrathiafulvalene (HMTTF) and dibenzotetrathiafulvalene (DBTTF) transistors with various surface treatments are analysed, and the trap distribution is extracted. In turn, starting from a simple exponential distribution, we can reproduce the temperature-dependent transistor characteristics as well as the gate voltage dependence of the activation energy, so we can investigate various aspects of organic transistors self-consistently under the interface approximation. Small deviation from such an ideal transistor operation is discussed assuming the presence of an energetically discrete trap level, which leads to a hump in the transfer characteristics. The contact resistance is estimated by measuring the transfer characteristics up to the linear region.

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“…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. Measurement of the charge transfer resistance via the redox reaction gives direct information about the DOS in organic semiconductors.…”

mentioning

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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Direct Determination of the Hole Density of States in Undoped and Doped Amorphous Organic Films with High Lateral Resolution

Cited by 154 publications

References 25 publications

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

Analysing organic transistors based on interface approximation

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

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