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31.
Characterisation of charge carrier transport in thin organic semiconductor T layers by time-of-flight photocurrent measurements
Gvido Bratina, Egon Pavlica, 2019, pregledni znanstveni članek

Opis: The paper reviews recent advances in characterisation of charge carrier transport in organic semiconductor layers by time-of-flight photocurrent measurements, with the emphasis on the measurements of the samples with co-planar electrodes. These samples comprised an organic semiconductor layer whose thickness is on the order of a μm or less, and thus mimic the structures of organic thin film transistors. In the review we emphasise the importance of considering spatial variation of electric field in these, essentially two-dimensional structures, in interpretation of photocurrent transients. We review the experimental details of this type of measurements and give examples that demonstrate exceptional sensitivity of the method to minute concentration of electrically active defects in the organic semiconductors as well as the capability of probing charge transport along the channels of different mobility that reside in the same sample.
Najdeno v: osebi
Ključne besede: organic semiconductors, time of flight, mobiulity
Objavljeno: 24.10.2018; Ogledov: 480; Prenosov: 0
.pdf Polno besedilo (2,53 MB)

32.
Enhancement of Charge Transport in Polythiophene Semiconducting Polymer by Blending with Graphene Nanoparticles
Egon Pavlica, Gvido Bratina, 2019, izvirni znanstveni članek

Opis: This paper describes a study on the charge transport in a composite of liquid‐exfoliated graphene nanoparticles (GNPs) and a polythiophene semiconducting polymer. While the former component is highly conducting, although it consists of isolated nanostructures, the latter offers an efficient charge transport path between the individual GNPs within the film, overall yielding enhanced charge transport properties of the resulting bi‐component system. The electrical characteristics of the composite layers were investigated by means of measurements of time‐of‐flight photoconductivity and transconductance in field‐effect transistors. In order to analyze both phenomena separately, charge density and charge mobility contributions to the conductivity were singled out. With the increasing GNP concentration, the charge mobility was found to increase, thereby reducing the time spent by the carriers on the polymer chains. In addition, for GNP loading above 0.2 % (wt.), an increase of free charge density was observed that highlights an additional key role played by doping. Variable‐range hopping model of a mixed two‐ and three‐dimensional transport is explained using temperature dependence of mobility and free charge density. The temperature variation of free charge density was related to the electron transfer from polythiophene to GNP, with an energy barrier of 24 meV.
Najdeno v: osebi
Ključne besede: grafen, polimeri, transport električnega naboja, časovno odvisna fotoprevodnost
Objavljeno: 23.08.2019; Ogledov: 122; Prenosov: 0
.pdf Polno besedilo (1,78 MB)

33.
The role of charge transfer at reduced graphene oxide/organic semiconductor interface on the charge transport properties
Gvido Bratina, Egon Pavlica, 2019, izvirni znanstveni članek

Opis: The effect of 1-pyrenesulfonicacid sodium salt (1-PSA), tetracyanoethylene (TCNE) and tetrafluoro- tetracyanoquinodimethane (F4-TCNQ) on charge transport properties of reduced graphene oxide (RGO) is examined by measuring the transfer characteristics of field-effect transistors and co-planar time-of-flight photocurrent technique. Evidence of p-type doping and a reduction of mobility of electrons in RGO upon deposition of these materials is observed. Time-resolved photocurrent measurements show a reduction in elec- tron mobility even at submonolayer coverage of these materials. The variation of transit time with different coverages reveals that electron mobility decreases with increasing the surface coverage of 1-PSA, TCNE and F4- TCNQ to a certain extent, while at higher coverage the electron mobility is slightly recovered. All three molecules show the same trend in charge carrier mobility variation with coverage, but with different magnitude. Among all three molecules, 1-PSA acts as weak electron acceptor compared to TCNE and F4-TCNQ. The additional fluorine moieties in F4-TCNQ provides excellent electron withdrawing capability compared to TCNE. The experimental results are consistent with the density functional theory calculations.
Najdeno v: osebi
Ključne besede: organic semiconductors, reduced graphene oxide, time-resolved photocurrent measurements, organic thin film transistors
Objavljeno: 28.10.2019; Ogledov: 144; Prenosov: 1
.pdf Polno besedilo (2,22 MB)

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