Charge transport and trapping in Cs-doped poly(dialkoxy-<i>p</i>-phenylene vinylene) light-emitting diodes

Gommans, Hans; Kemerink, Martijn; Andersson, Gunther G.; Pijper, Ralf

doi:10.1103/physrevb.69.155216

Cited by 68 publications

(47 citation statements)

References 33 publications

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“…This value is not unreasonable given that the maximum applied bias voltage of 3 V is larger than expected to be needed to fully dope the organic semiconductor. Other factors contributing to the absence of large voltage drops at the electrolyteelectrode interface may be related to a large irregular surface area induced by diffusion of Au into the electrolyte during deposition [16] and diffusion of ions through the Au electrode during the experiment, as reported before by Matyba et al [14].…”

Section: Resultsmentioning

confidence: 69%

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Photoluminescence quenching in films of conjugated polymers by electrochemical doping

et al. 2014

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An important loss mechanism in organic electroluminescent devices is exciton quenching by polarons. Gradual electrochemical doping of various conjugated polymer films enabled the determination of the doping density dependence of photoluminescence quenching. Electrochemical doping was achieved by contacting the film with a solid electrochemical gate and an injecting contact. A sharp reduction in photoluminescence was observed for doping densities between 10 18 and 10 19 cm −3 . The doping density dependence is quantitatively modeled by exciton diffusion in a homogeneous density of polarons followed by either Förster resonance energy transfer or charge transfer. Both mechanisms need to be considered to describe polaron-induced exciton quenching. Thus, to reduce exciton-polaron quenching in organic optoelectronic devices, both mechanisms must be prevented by reducing the exciton diffusion, the spectral overlap, the doping density, or a combination thereof.

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Section: Resultsmentioning

confidence: 69%

“…However, for example, in Ref. [16], we have observed a penetration of (more reactive) Cs into a soft polymer layer by only ∼15 nm. The much lower reactivity of Au may, however, increase the penetration depth.…”

Section: Resultsmentioning

confidence: 99%

Photoluminescence quenching in films of conjugated polymers by electrochemical doping

et al. 2014

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“…Alternatively, n-type doping by Cs + may explain the observed results as well in this specifi c case. [ 50 ] In actual devices, where WMLs are typically sandwiched between an organic semiconductor and a metallic electrode, the situation is more complicated than the one studied here. In lowest order, oppositely directed dipoles are expected at both interfaces of the WML.…”

Section: General Considerationsmentioning

confidence: 91%

Origin of Work Function Modification by Ionic and Amine‐Based Interface Layers

Reenen

Kouijzer

Janssen

et al. 2014

Adv Materials Inter

131

138

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can evolve into a successful thin fi lm photovoltaic technology. To this end, further improvements in the sunlight-toelectricity conversion effi ciency are still needed. To do so, not only the optoelectronic, active layer should be considered, but also the connection between this layer and the electrodes. This connection is facilitated by so-called work function modifi cation layers (WMLs) that serve to align the transport levels in the organic semiconductor and the conductor by modifi cation of the work function. Materials that are often used are poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) for improving hole collection and injection in combination with an indium tin oxide (ITO) electrode and LiF for the electron contact in combination with an Al metal electrode. A new generation of WMLs fi rst introduced by Cao et al. is based on polyelectrolytes or tertiary aliphatic amines, such as poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt -2,7-(9,9-dioctylfluorene)] (PFN) and the corresponding ethyl ammonium bromide. [ 1 ] Although these materials improve carrier injection or extraction in different organic diode devices, [1][2][3][4][5][6][7] the mechanism behind this improvement is not completely clear. This ambiguity hinders design, selection and optimization of new WMLs.Mechanisms that are generally considered to result in electric fi elds and concomitant work function shifts at metal-organic interfaces are doping, charge transfer, and dipole formation. [8][9][10] Regarding the work function modifi cation of amine side-groups, Lindell et al. [ 11 ] found by photoelectron spectroscopy and density functional calculations that the electron donor para-phenylenediamine chemisorbs onto atomically clean Ni in vacuum. [ 12 ] Due to partial electron transfer from the amine unit, a work function reduction of 1.55 eV is achieved, resulting in a less deep Fermi level. This explanation is not likely to hold for the technologically more relevant procedure on which we shall focus, being the deposition of WMLs from solution on a metal at atmospheric pressure: the metal is not atomically clean, which likely inhibits chemisorption. In other work by Zhou et al. [ 13 ] it is shown that the work function reduction, at atmospheric pressure, by the amine groups in poly(ethylenimine ethoxylated) (PEIE), is generally the same on different conductors. Work function modifi cation by polyelectrolytes and tertiary aliphatic amines is found to be due to the formation of a net dipole at the electrode interface, induced by interaction with its own image dipole in the electrode. In polyelectrolytes differences in size and side groups between the moving ions lead to differences in approach distance towards the surface. These differences determine magnitude and direction of the resulting dipole. In tertiary aliphatic amines the lone pairs of electrons are anticipated to shift towards their image when close to the interface rather than the nitrogen nuclei, which are sterically hindered by the alkyl side chains. ...

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“…Then the contacts do not absorb or inject any charges and do not play a role in the AC measurement. With this condition fulfilled, this method differs fundamentally from conventional impedance measurements in which the source and drain do need to absorb and inject charge [31][32][33][34][35]. …”

Section: Ac Characterization Methodsmentioning

confidence: 99%

Contactless charge carrier mobility measurement in organic field-effect transistors

Roelofs¹,

Li²,

Janssen³

et al. 2014

Organic Electronics

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a b s t r a c tWith the increasing performance of organic semiconductors, contact resistances become an almost fundamental problem, obstructing the accurate measurement of charge carrier mobilities. Here, a generally applicable method is presented to determine the true charge carrier mobility in an organic field-effect transistor (OFET). The method uses two additional finger-shaped gates that capacitively generate and probe an alternating current in the OFET channel. The time lag between drive and probe can directly be related to the mobility, as is shown experimentally and numerically. As the scheme does not require the injection or uptake of charges it is fundamentally insensitive to contact resistances. Particularly for ambipolar materials the true mobilities are found to be substantially larger than determined by conventional (direct current) schemes.

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Charge transport and trapping in Cs-doped poly(dialkoxy-p-phenylene vinylene) light-emitting diodes

Cited by 68 publications

References 33 publications

Photoluminescence quenching in films of conjugated polymers by electrochemical doping

Photoluminescence quenching in films of conjugated polymers by electrochemical doping

Origin of Work Function Modification by Ionic and Amine‐Based Interface Layers

Contactless charge carrier mobility measurement in organic field-effect transistors

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