| 1. |
- Janssen, FJJ, et al.
(författare)
-
Interface instabilities in polymer light emitting diodes due to annealing
- 2003
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 4:4, s. 209-218
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Tidskriftsartikel (refereegranskat)abstract
- In polymer light emitting diodes (PLEDS) with an (ITO/PPV/Ca) structure we observed a significant reduction of both the current and the light output at constant voltage after heat treatment for only 30 min at 65 degreesC. Electroluminescence spectroscopy experiments showed that the shape as well as the amplitude of the spectra were changed. The reduction of current and light output was investigated by measuring I-V and E-V (current-voltage and brightness-voltage) characteristics of PLEDs, I-V characteristics of single carrier devices, and by performing low energy ion scattering and X-ray photoelectron spectroscopy experiments on the Ca/PPV interface. It was concluded that the current and light output reduction could be ascribed to the degradation of the Ca/PPV and the ITO/PPV interfaces. The degradation of the ITO/PPV interface resulted in a reduction of the zero field hole mobility and a small increase of the field dependence of the mobility. The degradation of the Ca/PPV interface, probably by diffusion of calcium into the PPV, resulted in carrier traps and quenching sites, which influenced the field dependent electron mobility. (C) 2003 Elsevier B.V. All rights reserved.
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| 2. |
- Pettersson, Lars, et al.
(författare)
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Optical anisotropy in thin films of poly(3,4-ethylenedioxythiophene)- poly(4-styrenesulfonate)
- 2002
-
Ingår i: Organic electronics. - 1566-1199 .- 1878-5530. ; 3:3-4, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic optical constants spectrum of spin-coated thin films of poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT-PSS) from 200 to 1700 nm were determined using variable-angle spectroscopic ellipsometry and polarized intensity transmission data together with absorption spectroscopy. PEDOT-PSS was found to be very anisotropic, uniaxial with the optic axis parallel to the surface normal. The result is in good agreement with results obtained of chemically polymerized PEDOT layers doped with toluenesulfonate. By adding sorbitol to the PEDOT-PSS dispersion before spin-coating, layers with a higher conductivity were obtained. A detailed study was made of the optical response of these layers in comparison to the PEDOT-PSS prepared from dispersions without sorbitol. The optical anisotropy is important to consider when using PEDOT-PSS in optoelectronic devices, such as polymer light-emitting diodes and photovoltaic devices. © 2002 Elsevier Science B.V. All rights reserved.
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| 3. |
- Van, Der Gon A.W.D., et al.
(författare)
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Modification of PEDOT-PSS by low-energy electrons
- 2002
-
Ingår i: Organic electronics. - 1566-1199 .- 1878-5530. ; 3:3-4, s. 111-118
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Tidskriftsartikel (refereegranskat)abstract
- The stability of conjugated organic materials under electron transport is of great importance for the lifetime of devices such as polymer light-emitting diodes (PLEDs). Here, the modification of thin films of poly(3,4- ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (known as PEDOT-PSS, often used in the fabrication of PLEDs) by low-energy electrons has been studied using X-ray photo-electron spectroscopy. Thin films of PSSH and molecular solid films of EDOT molecules also have been studied. We find that electrons with kinetic energies as low as 3 eV result in significant modification of the chemical structure of the materials. For thin films of PSSH, the electron bombardment leads to a strong loss of oxygen and a smaller loss of sulfur. In addition, a large amount of the sulfur atoms that remain in the films exhibits a different binding energy because of scissions of the bonds to oxygen atoms. For condensed molecular solid films of EDOT molecules, we find that the carbon atoms bonded to oxygen react and form additional bonds, as evidenced by a new component in the C(1s) peak at a higher binding energy. In the PEDOT-PSS blend, we find both effects. The importance of these observations for light-emitting diodes incorporating PEDOT-PSS films is discussed. This work demonstrates that the combination of in situ low-energy electron bombardment in combination with photo-electron spectroscopy is a powerful method to simulate and study certain processes, associated with low-energy electrons, occurring in organic based devices, which cannot be studied directly otherwise. © 2002 Elsevier Science B.V. All rights reserved.
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| 4. |
- Amruth, C., et al.
(författare)
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Inkjet printing of thermally activated delayed fluorescence (TADF) dendrimer for OLEDs applications
- 2019
-
Ingår i: Organic electronics. - Amsterdam : Elsevier. - 1566-1199 .- 1878-5530. ; 74, s. 218-227
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Tidskriftsartikel (refereegranskat)abstract
- This study presents the inkjet printing of a novel OLED device with fully solution-processed organic layers that employ TADF material as an emitting layer. The ink was formulated using new TADF material, triazine core carbazole dendrimers with tert-butyl group at the periphery (tBuG2TAZ), dissolved in a mixture of two non-chlorinated solvents. The influence of the print resolution and the substrate temperature on morphology of the printed films was studied and optimized in ambient conditions. The optimized TADF dendrimer layer was then incorporated in the OLEDs as the emitting layer. The best-printed OLEDs exhibited a maximum current efficiency of 18 cd/A and maximum luminance of 6900 cd/m(2). Such values are comparable to the values obtained in spin coated devices made of the same TADF dendrimer. Further, the mobility of charge carriers extracted from transient electroluminescence measurements of printed OLEDs, when compared to reference OLEDs made by spin coating technique, showed similar values. Finally, we have demonstrated the possibility of patterning of emission the area of complex shapes merely by selectively printing the emission layer. These results demonstrate the potential application of the new dendrimer TADF emitters for the fabrication of efficient OLEDs by an inkjet printing technique.
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| 5. |
- Andersson Ersman, Peter, et al.
(författare)
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Fast-switching all-printed organic electrochemical transistors
- 2013
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 14:5, s. 1276-1280
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Tidskriftsartikel (refereegranskat)abstract
- Symmetric and fast (∼5 ms) on-to-off and off-to-on drain current switching characteristics have been obtained in screen printed organic electrochemical transistors (OECTs) including PEDOT:PSS (poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid)) as the active transistor channel material. Improvement of the drain current switching characteristics is made possible by including a carbon conductor layer on top of PEDOT:PSS at the drain electrode that is in direct contact with both the channel and the electrolyte of the OECT. This carbon conductor layer suppresses the effects from a reduction front that is generated in these PEDOT:PSS-based OECTs. In the off-state of these devices this reduction front slowly migrate laterally into the PEDOT:PSS drain electrode, which make off-to-on switching slow. The OECT including carbon electrodes was manufactured using only standard printing process steps and may pave the way for fully integrated organic electronic systems that operate at low voltages for applications such as logic circuits, sensors and active matrix addressed displays.
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| 6. |
- Andersson Ersman, Peter, et al.
(författare)
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Printed passive matrix addressed electrochromic displays
- 2013
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 14:12, s. 3371-3378
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Tidskriftsartikel (refereegranskat)abstract
- Flexible displays are attracting considerable attention as a visual interface for applications such as in electronic papers paper electronics. Passive or active matrix addressing of individual pixels require display elements that include proper signal addressability, which is typically provided by non-linear device characteristics or by incorporating transistors into each pixel. Including such additional devices into each pixel element make manufacturing of flexible displays using adequate printing techniques very hard complicated. Here, we report all-printed passive matrix addressed electrochromic displays (PMAD), built up from a very robust three-layer architecture, which can be manufactured using standard printing tools. Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) serves as the conducting electrochromic pixel electrodes carbon paste is used as the pixel counter electrodes. These electrodes sandwich self-assembled layers of a polyelectrolyte that are confined to desired pixel areas via surface energy patterning. The particular choice of materials results in a desired current vs. voltage threshold that enables addressability in electronic cross-point matrices. The resulting PMAD operates at less than 3 V, exhibits high colour switch contrast without cross-talk promises for high-volume low-cost production of flexible displays using reel-to-reel printing tools on paper or plastic foils.
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| 7. |
- Andersson, Lars Mattias, et al.
(författare)
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Non-equilibrium effects on electronic transport in organic field effect transistors
- 2007
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 8:4, s. 423-430
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Tidskriftsartikel (refereegranskat)abstract
- Non-ideal behavior in organic field effect transistors, in particular threshold voltage drift and light sensitivity, is argued to be due to intrinsic carrier dynamics. The discussion is based on the theory for hopping transport within a Gaussian density of states. Carrier concentration is shown to be of fundamental importance, and the time required to reach equilibrium at different bias is responsible for device behavior, with implications for mobility evaluation. Experimental results from various conjugated polymers in a field effect transistor illustrate the theory.
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| 8. |
- Andersson, Mattias, et al.
(författare)
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Intrinsic and extrinsic influences on the temperature dependence of mobility in conjugated polymers
- 2008
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 9:5, s. 569-574
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of charge carrier mobility in conjugated polymers and their blends with fullerenes is investigated with different electrical methods, through field effect transistor (FET), space charge limited current (SCLC) and charge extraction (CELIV) measurements. Simple models, such as the Gaussian disorder model (GDM), are shown to accurately predict the temperature behavior, and a good correlation between the different measurement methods is obtained. Inconsistent charge carrier concentrations in the modeling are explained through intrinsic non-equilibrium effects, and are responsible for the limited applicability of existing numerical models. A severe extrinsic influence from water in FETs with a hydrophilic insulator interface is also demonstrated. The presence of water leads to a significant overestimate of the disorder in the materials from measurements close to room temperature and erratic behavior in the 150-350 K range. To circumvent this problem it is shown to be necessary to measure under ultra high vacuum (UHV) conditions. © 2008 Elsevier B.V. All rights reserved.
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| 9. |
- Andersson, Mattias, et al.
(författare)
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Mixed C60/C70 based fullerene acceptors in polymer bulk-heterojunction solar cells
- 2012
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 13:12, s. 2856-2864
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Tidskriftsartikel (refereegranskat)abstract
- Different mixtures of identically substituted C60 and C70 based fullerens have been used as acceptors in three polymer: fullerene systems that strongly express various performance limiting aspects of bulk heterojunction solar cells. Results are correlated with, and discussed in terms of e.g. morphology, charge separation, and charge transport. In these systems, there appears to be no relevant differences in either mobility or energy level positions between the identically substituted C60 and C70 based fullerenes tested. Examples of how fullerene mixtures influence the nano-morphology of the active layer are given. An upper limit to the open circuit voltage that can be obtained with fullerenes is also suggested.
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| 10. |
- Auroux, Etienne, et al.
(författare)
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Solution -based fabrication of the top electrode in light -emitting electrochemical cells
- 2020
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 84
-
Tidskriftsartikel (refereegranskat)abstract
- The light-emitting electrochemical cell (LEC) has demonstrated capacity for cost- and material-efficient solution-based fabrication of the active material under ambient air. In this context, it is notable that corresponding reports on a scalable solution-based fabrication of the electrodes, particularly the top electrode, are rare. We address this issue through the demonstration of a transparent LEC, which is fabricated under ambient air by sequential spray deposition of a hydrophobic conjugated-polymer:ionic-liquid blend ink as the active material and a hydrophilic poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) ink as the transparent top electrode. Such an optimized LEC delivers a luminance of 360 cd/m2 at a power efficacy of 1.6 lm/W, which is on par with the performance of a corresponding LEC device equipped with a vacuum-deposited and reflective metal top electrode. This implies that the entire LEC device indeed can be fabricated with solution-based processes and deliver a good performance, which is critical if the LEC technology is going to fulfil its low-cost potential.
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| 11. |
- Avila, Harold C., et al.
(författare)
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High hole-mobility of rrP3HT in organic field-effect transistors using low-polarity polyurethane gate dielectric
- 2018
-
Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 58, s. 33-37
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Tidskriftsartikel (refereegranskat)abstract
- We report unusually high charge carrier mobilities for regioregular poly(3-hexyltiophene) (rrP3HT) in organic field-effect transistors (OFETs) using polyurethane (PU) as dielectric layer. Our devices display hole mobilities up to 1.37 cm(2)/V in the saturation regime and an ON/OFF current ratio higher than 10(3), operating at voltages as low as -10 V, with a high I-DS current of 1.5 mu A. We assign the measured high mobilities mainly to the low density of randomly-oriented electric dipoles at the semiconductor/dielectric interface, which leads to a narrow energy distribution of the electronic levels available for charge transport in rrP3HT. This is confirmed by experimental and theoretical techniques: (1) temperature-dependent transport measurements for extraction of disorder-induced distribution of electronic levels; (2) density functional theory (DFT) calculations of electric dipole moments of PU; and (3) liquid contact-angle measurements for the dipolar component of dielectric surface tension.
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| 12. |
- Bernard, L., et al.
(författare)
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Study of the morphology of organic ferroelectric diodes with combined scanning force and scanning transmission X-ray microscopy
- 2018
-
Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 53, s. 242-248
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Tidskriftsartikel (refereegranskat)abstract
- Organic ferroelectric diodes attract increasing interest as they combine non-destructive data read-out and low cost fabrication, two requirements in the development of novel non-volatile memory elements. The macroscopic electrical characteristics and performances of such devices strongly depend on their structural properties. Various studies of their global microscopic morphology have already been reported. Here, a multi-technique approach including different scanning force and X-ray microscopies permitted to reveal and locally study nanometer-scale unexpected sub-structures within a P(VDF-TrFE):F8BT ferroelectric diode. The strong impact of these structures on the local polarizability of the ferroelectric is shown. Two alternative fabrication methods are proposed that prevent the formation of these structures and demonstrate improved macroscopic device performances such as endurance and ON/OFF ratio.
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| 13. |
- Braun, Slawomir, et al.
(författare)
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Fermi level equilibrium at donor-acceptor interfaces in multi-layered thin film stack of TTF and TCNQ
- 2010
-
Ingår i: Organic electronics. - Amsterdam, Netherlands : Elsevier BV. - 1566-1199 .- 1878-5530. ; 11:2, s. 212-217
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Tidskriftsartikel (refereegranskat)abstract
- Organic hetero-junctions in multi-layered thin film stacks comprising alternate layers of the molecular donor-tetrathiafulvalene (TTF) and the acceptor - tetracyanoquinodimethane (TCNQ), have been studied by ultraviolet photoelectron spectroscopy ( UPS). We show that the energy level alignment at the organic-organic interfaces in the stacks depends only upon the relative energy structure of the donor and acceptor molecules, in particular, the molecular integer charge transfer (ICT) states. The observed interfacial dipoles, across the multi-layered organic stacks, correspond to the difference in energy between the positive and the negative charge transfer states of the molecules constituting the interface. Consequently, Fermi level across the multi-layer system is pinned to those states, since the energetic conditions for the charge transfer across the interface are fulfilled. Hence the energy level alignment at donor - acceptor interfaces studied can be rationalized on the basis of integer charge transfer model (ICT-model). Moreover, we present the photoelectron spectra where 0.85 eV shift of the highest occupied molecular orbital (HOMO) of TTF during formation of TCNQ over-layer is directly observed. These studies contribute to the understanding of the nature of the offset between the frontier electronic levels of the donor and acceptor components which is of high importance in the engineering of efficient organic solar cells.
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| 14. |
- Brocks, Geert, et al.
(författare)
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Charge equilibration and potential steps in organic semiconductor multilayers
- 2012
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 13:10, s. 1793-1801
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Tidskriftsartikel (refereegranskat)abstract
- Substantial potential steps similar to 0.5 eV are frequently observed in organic multilayers of donor and acceptor molecules. Often such potential steps depend on the order in which the individual layers are deposited, or on which substrate they are deposited. In this paper we outline a model for these potential steps, based upon integer charge transfer between donors and acceptors, charge equilibration across the multilayer, and simple electrostatics. Each donor, acceptor, or substrate material is characterized by a pinning level, and the potential profile can be deduced from the sequential order of the layers, and the differences between their pinning levels. For particular orderings we predict that intrinsic potential differences lead to electric fields across individual layers, which may falsely be interpreted as band bending.
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| 15. |
- Bucinskas, Audrius, et al.
(författare)
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Can attachment of tert-butyl substituents to methoxycarbazole moiety induce efficient TADF in diphenylsulfone-based blue OLED emitters?
- 2020
-
Ingår i: Organic electronics. - : ELSEVIER. - 1566-1199 .- 1878-5530. ; 86
-
Tidskriftsartikel (refereegranskat)abstract
- A new series of TADF emitters with donor-acceptor or donor-acceptor-donor structure containing 2,7-dimethoxycarbazole donor moiety and diphenylsulfone acceptor unit were synthesized and employed in non-doped sky-blue organic light emitting diodes with the external quantum efficiency reaching 9.0%. Thermal, optical and photophysical properties of for D-A and D-A-D compounds containing one or two tert-butyl groups attached to C-3 and C-6 positions of 2,7-dimethoxycarbazole moiety were studied and compared with those of the corresponding compounds containing no tert-butyl groups. Studies of photophysical properties of the compounds confirmed TADF nature of their emission. Computational studies revealed that small modification of the donor moiety could have a significant impact on the TADF mechanism turning it from vibronically induced TADF mediated by the T-2 state to the common TADF which occurs through the direct reverse intersystem crossing between the S-1 and T-1 states. New principle of purposeful of molecular design of TADF emitters with controlled efficiency of reverse intersystem crossing by only small functionalization of donor fragments is proposed.
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| 16. |
- Carlegrim, Elin, et al.
(författare)
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Characterization of the Ni/V(TCNE)x interface for hybrid spintronics applications
- 2010
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 11:6, s. 1020-1024
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Tidskriftsartikel (refereegranskat)abstract
- Vanadium tetracyanoethylene, V(TCNE)x, is an organic-based magnet with properties suitable for spintronics applications, e.g. spin valves. In this paper we propose a new hybrid organic spin valve design where V(TCNE)x is used as a spin-transporting and spin-filtering layer sandwiched between two ferromagnetic (FM) metal contacts, i.e. FM/V(TCNE)x/FM. As the spin injection and detection of such a device occurs at the interfaces the quality of those are of crucial importance. Therefore, the Ni/V(TCNE)x interface has been investigated by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption spectroscopy (NEXAFS) as well as compared with XPS results from a model system, Ni/TCNE. Ni chemically interact with both the vinyl and cyano groups but there is no evidence for significant diffusion of Ni into the V(TCNE)x film. As the chemical interaction affects the spin injection and detection negatively by modifying the lowest unoccupied molecular orbital (LUMO) and destroying the magnetic ordering network at the surface, these results indicate that there is need for a buffer layer between V(TCNE)x and Ni, and in extension most likely between V(TCNE)x and any FM contact.
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| 17. |
- Charrier, D. S. H., et al.
(författare)
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Bimolecular recombination in ambipolar organic field effect transistors
- 2009
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 10:5, s. 994-997
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Tidskriftsartikel (refereegranskat)abstract
- In ambipolar organic field effect transistors (OFET) the shape of the channel potential is intimately related to the recombination zone width W, and hence to the electron-hole recombination strength. Experimentally, the recombination profile can be assessed by scanning Kelvin probe microscopy (SKPM). However, surface potentials as measured by SKPM are distorted due to spurious capacitive couplings. Here, we present a (de)convolution method with an experimentally calibrated transfer function to reconstruct the actual surface potential from a measured SKPM response and vice versa. Using this scheme, we find W = 0.5 mu m for a nickel dithiolene OFET, which translates into a recombination rate that is two orders of magnitude below the value expected for Langevin recombination. (C) 2009 Elsevier B.V. All rights reserved.
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| 18. |
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| 19. |
- Chen, Zhuoying, et al.
(författare)
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Enhanced charge transport by incorporating additional thiophene units in the poly(fluorene-thienyl-benzothiadiazole) polymer
- 2011
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 12:3, s. 461-471
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Tidskriftsartikel (refereegranskat)abstract
- We report a comparative study of optical properties, structure and morphology, field-effect transistor (FET) and solar cell performance between poly(4-(3,4-dihexyl-2,2-bithiophen-5-yl)-7-(5-(9,9-dioctyl-9H-fluoren-2-yl)-3,4-dihexyl-2,2-bithiophen-5-yl)benzo[c][1,2,5]-thiadiazole) (F8TTBTT), and its predecessor poly((9,9-dioctylfluorene)-2,7-diyl-alt[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,2 -diyl) (F8TBT). Compared to F8TBT, F8TTBTT has two more thiophene units incorporated in its monomer structure. Such a modification leads to a reduced optical band gap, improved charge injection and significantly enhanced ambipolar field-effect mobilities reaching 5 x 10 (2) cm(2) V (1) s (1) for holes and 4 x 10 (3) cm(2) V (1) s (1) for electrons. The enhanced carrier mobilities are most likely a result of an increased backbone planarization and interchain interaction. As a consequence of ambipolar transport, light-emission was observed from the transistor channel during operation. The reduced band gap and improved charge transport make F8TTBTT an interesting candidate also for solar cell applications. Unoptimized solar cells based on F8TTBTT: PCBM blends were found to exhibit power conversion efficiency under AM 1.5 illumination of similar to 1.54%. (C) 2011 Published by Elsevier B.V.
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| 20. |
- Cotrone, Serafina, et al.
(författare)
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Phospholipid film in electrolyte-gated organic field-effect transistors
- 2012
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 13:4, s. 638-644
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Tidskriftsartikel (refereegranskat)abstract
- A totally innovative electrolyte-gated field effect transistor, embedding a phospholipid film at the interface between the organic semiconductor and the gating solution, is described. The electronic properties of OFETs including a phospholipid film are studied in both pure water and in an electrolyte solution and compared to those of an OFET with the organic semiconductor directly in contact with the gating solution. In addition, to investigate the role of the lipid layers in the charge polarization process and quantify the field-effect mobility, impedance spectroscopy was employed. The results indicate that the integration of the biological film minimizes the penetration of ions into the organic semiconductor thus leading to a capacitive operational mode as opposed to an electrochemical one. The OFETs operate at low voltages with a field-effect mobility in the 10−3 cm2 V−1 s−1 range and an on/off current ratio of 103. This achievement opens perspectives to the development of FET biosensors potentially capable to operate in direct contact with physiological fluids.
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| 21. |
- Farinhas, Joana, et al.
(författare)
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Efficient ternary organic solar cells based on immiscible blends
- 2017
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 41, s. 130-136
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Tidskriftsartikel (refereegranskat)abstract
- Organic photovoltaic cells based on ternary blends of materials with complementary properties represent an approach to improve the photon-absorption and/or charge transport within the devices. However, the more complex nature of the ternary system, i.e. in diversity of materials' properties and morphological features, complicates the understanding of the processes behind such optimizations. Here, organic photovoltaic cells with wider absorption spectrum composed of two electron-donor polymers, F8T2, poly(9,9-dioctylfluorene-alt-bithiophene), and PTB7, poly([4,8-bis[(2'-ethylhexyl) oxy] benzo[1,2-b: 4,5-b'] dithiophene-2,6-diyl][3-fluoro-2-[(2'-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl]), mixed with [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) are investigated. We demonstrate an improvement of 25% in power conversion efficiency in comparison with the most efficient binary blend control devices. The active layers of these ternary cells exhibit gross phase separation, as determined by Atomic Force Microscopy (AFM) and Synchrotron-based Scanning Transmission X-ray Microscopy (STXM).
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| 22. |
- Felekidis, Nikolaos, et al.
(författare)
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Automated open-source software for charge transport analysis in single-carrier organic semiconductor diodes
- 2018
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Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 61, s. 318-328
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Forskningsöversikt (refereegranskat)abstract
- Organic electronics is an emerging technology with numerous applications in which the active layer is composed of an organic semiconductor (OSC) or blends of multiple OSC. One of the key performance parameters for such devices is the charge carrier mobility which can be evaluated by different measurement techniques. Here, we review different formalisms for extraction and analysis of hole mobilities from temperature-dependent space-charge limited conductivity (SCLC) measurements for pristine OSC as well as for binary and ternary blends as used in e.g. photovoltaic applications. The model is also applicable to n-type materials. Possible sources of measurement errors, such as the presence of traps and series resistance, are discussed. We show that by a simple method of selecting a proper experimental data range these errors can be avoided. The Murgatroyd-Gill analytical model in combination with the Gaussian Disorder Model is used to extract zero-field hole mobilities as well as estimates of the Gaussian energetic disorder in the HOMO level from experimental data. The resulting mobilities are in excellent agreement with those found from more elaborate fits to a full drift-diffusion model that includes a temperature, field and density dependent charge carrier mobility; the same holds for the Gaussian disorder of pure materials and blends with low fullerene concentration. The zero-field mobilities are also analyzed according to an Arrhenius model that was previously argued to reveal a universal mobility law; for most -but not all- material systems in the present work this framework gave an equally good fit to the experimental data as the other models. An automated fitting freeware, incorporating the different models, is made openly available for download and minimizes error, user input and SCLC data analysis time; e.g. SCLC current-voltage curves at several different temperatures can be globally fitted in a few seconds.
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| 23. |
- Gollu, Sankara Rao, et al.
(författare)
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Incorporation of SiO2 dielectric nanoparticles for performance enhancement in P3HT:PCBM inverted organic solar cells
- 2015
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 24, s. 43-50
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that organic solar cells (OSCs) with inverted geometry have not only demonstrated a better stability and longer device life time but also have shown improved power conversion efficiency (PCE). Recent studies exhibit that incorporation of metal and/or semiconducting nanoparticles (NPs) can further increase the PCE for OSCs. In this present work, we have synthesized SiO2 NPs of various sizes (25, 50, 75 and 100 nm) using the modified Stober method and incorporated them into P3HT:PCBM photoactive layer and ZnO based electron transport layer (ETL) in order to investigate the light trapping effects in an OSC. Absorption studies have shown a considerable increase in photo absorption in both cases. The fabricated devices demonstrated 13% increase in the PCE when SiO2 NPs are incorporated in P3HT: PCBM photoactive layer, whereas PCE was increased by 20% when SiO2 NPs are incorporated in ZnO based ETL. Mott-Schottky analysis and impedance spectroscopy measurements have been carried out to determine the depletion width and global mobility for both the devices. The possible reason for PCE enhancement and the role of SiO2 NPs in active layer and ZnO ETL are explained on the basis of the results obtained from Mott-Schottky analysis and impedance spectroscopy measurements. (C) 2015 Elsevier B.V. All rights reserved.
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| 24. |
- Gudeika, D., et al.
(författare)
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Flexible diphenylsulfone versus rigid dibenzothiophene-dioxide as acceptor moieties in donor-acceptor-donor TADF emitters for highly efficient OLEDs
- 2020
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 83
-
Tidskriftsartikel (refereegranskat)abstract
- Flexible versus rigid molecular structures of donor-acceptor-donor type compounds are investigated with respect to efficiency of thermally activated delayed fluorescence (TADF) by theoretical and experimental approaches. Three highly efficient TADF emitters based on flexible diphenylsulfone and rigid dibenzothiophene-dioxide as acceptor units and di-tert-butyldimethyldihydroacridine as donor moiety were designed and synthesized. Despite they showed similar singlet-triplet splitting (0.01–0.02 eV) and high photoluminescence quantum yields in appropriate hosts, maximum external quantum efficiencies as different as 24.1 and 15.9/19.4% were obtained for organic light emitting devices based on these emitters with, respectively, flexible and rigid molecular structures. The high efficiency of the light-emitting compounds with the flexible molecular structure could be traced to the bi-configurational nature of the lowest singlet and triplet states resulting in higher spin-orbit coupling than for molecules with rigid structures. All derivatives showed bipolar charge transport character. High device efficiency with electron mobility of 3 × 10−5 cm2V−1s−1 and hole mobility of 1.3 × 10−4 cm2V−1s−1 at the electric field of 5 × 105 Vcm−1 was recorded for the layer of para-disubstituted diphenylsulfone with flexible molecular structure. This TADF emitter showed an excellent performance in the organic light emitting device, exhibiting a maximum current efficiency, power efficiency, and external quantum efficiency of 61.1 cdA-1, 64.0 lmW−1, and 24.1%, respectively.
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| 25. |
- Guo, Xuewen, et al.
(författare)
-
Novel small-molecule zwitterionic electrolyte with ultralow work function as cathode modifier for inverted polymer solar cells
- 2018
-
Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 59, s. 15-20
-
Tidskriftsartikel (refereegranskat)abstract
- Interfacial compatibility between the electrode and organic semiconductor plays a critical role in controlling the charge transport and hence efficiency of organic solar cell. Here, we introduce a novel small-molecule zwitterionic electrolyte (S1) combined with ZnO as electron transporting interlayer employed for the inverted PTB7:PC71BM bulk heterojunction solar cell. The resulting device with the S1/ZnO stacked interlayer achieves a high PCE of 8.59%, obtaining a 16.2% improvement over the control device performance of 7.4% without the S1 attributed to the significant increased short-circuit current density and fill factor. The interfacial properties are investigated. It is found that the S1/ZnO interlayer possess an ultralow work function of 3.6 eV, which originates from the interfacial double dipole step induced by the zwitterionic side chain electrostatic realignment at interface. The S1/ZnO interlayer exhibits the excellent charge extraction ability, suppresses the charge recombination loss and decreases the series resistance at the active layer/electrode contact.
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| 26. |
- Guo, Xuewen, et al.
(författare)
-
Understanding the effect of N2200 on performance of J71 : ITIC bulk heterojunction in ternary non-fullerene solar cells
- 2019
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 71, s. 65-71
-
Tidskriftsartikel (refereegranskat)abstract
- None-fullerene solar cells with ternary architecture have attracted much attention because it is an effective approach for boosting the device power conversion efficiency. Here, the crystalline polymer N2200 as the third component is integrated into J71: ITIC bulk heterojunction. A series of characterizations indicate that N2200 could increase photo-harvesting, balanced hole and electron mobilities, enhanced exciton dissociation, and suppressed charge recombination, which result in the comprehensive improvement of open circuit voltage, short circuit current and fill factor in the device. Moreover, after introduction of N2200, the morphology of the ternary active layer is optimized, and the film crystallinity is improved. This work demonstrates that adding a small quantity of high crystallization acceptor into non-fullerene donor: acceptor mixture is a promising strategy toward developing high-performance organic solar cells.
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| 27. |
- Isaksson, Joakim, et al.
(författare)
-
Electronically Controlled pH Gradients and Proton Oscillations
- 2008
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 9:3, s. 303-309
-
Tidskriftsartikel (refereegranskat)abstract
- An organic electronic ion pump, including poly(3,4-ethylenedioxythiophene) as the active material has been used to electronically control the transport of protons between two electrolytes and to change the pH of the target solution from 7 to 3 in a few minutes. The number of transported protons equals the time-integrated current between the two addressing electrodes. If no voltage is applied the leakage due to diffusion is not detectable, which indicates an overall proton delivery on/off ratio exceeding 1000. Locally, the pH drop can be even larger and the relationship between the proton delivery rate of the pump and proton diffusion in the electrolyte forms pH gradients. If the device is instead addressed with short pulses, local pH oscillations are created. The transport of protons presented here can be extended to other small sized ions, which in combination with the biocompatibility of the delivery surface make the device promising for cell communication studies and lab-on-a-chip applications.
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| 28. |
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| 29. |
- Jakobsson, Fredrik L. E., 1974-, et al.
(författare)
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Prediction of the current versus voltage behavior of devices based on organic semiconductor host-guest systems
- 2009
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 10:1, s. 95-106
-
Tidskriftsartikel (refereegranskat)abstract
- Organic semiconductor blends are commonly used in organic based (opto-)electronic devices. They are composed of two types of (macro-) molecules, referredto as the guest and host. To achieve optimum device operation, the chemicalnature, electronic structure, molecular order and the relative concentration of theguests and host are crucial. Here, we present simulation results of the currentdensity versus the voltage (J-V) behavior of a two-terminal device based on avariable-range hopping model in which the electronic states of the guest and hostare represented by two Gaussian distributions. The J-V behavior is investigatedfor various energetic mismatches between guest and host states, widths of thedistribution as well as the guest concentration. Finally, a simple tool enablingeasy prediction of the J-V behavior of organic host-guest diodes is derived.
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| 30. |
- Jasiunas, Rokas, et al.
(författare)
-
Interplay between charge separation and hole back transfer determines the efficiency of non-fullerene organic solar cells with low energy level offset
- 2022
-
Ingår i: Organic electronics. - : ELSEVIER. - 1566-1199 .- 1878-5530. ; 108
-
Tidskriftsartikel (refereegranskat)abstract
- Organic bulk heterojunction solar cells with electron acceptors based on small donor-acceptor type molecules show record efficiencies mainly due to their long wavelength absorption, which enables efficient harvesting of solar light and, thus, causes high current density. Meanwhile, relative positions of HOMO and LUMO levels of donor and acceptor materials determine the open circuit voltage. Here, we apply ultrafast transient absorption and transient luminescence techniques together with specially-designed modelling technique to address charge carrier generation and recombination dynamics in detail. We demonstrate the importance of careful adjustment of the HOMO and LUMO levels, as their positions determine formation and recombination rates of interfacial charge transfer (CT) states. An insufficient donor and acceptor LUMO level offset, lower than -300 meV, leads to slow and inefficient CT state formation, while an offset of the HOMO level below -100 meV leads to fast CT state recombination, which we attribute to the back transfer of a hole from the donor to the acceptor.
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| 31. |
- Jespersen, Kim, et al.
(författare)
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Charge formation and transport in bulk-heterojunction solar cells based on alternating polyfluorene copolymers blended with fullerenes
- 2006
-
Ingår i: Organic Electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 7:4, s. 235-242
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Tidskriftsartikel (refereegranskat)abstract
- We investigate charge formation in bulk-heterojunction solar cells based on conjugated polymers in the form of alternating polyfluorene copolymers and the methanofullerene PCBM. Using transient absorption spectroscopy we show that optimal charge formation is obtained with 20-50 wt% PCBM. This is in contrast to the maximum short circuit current density obtained at similar to 80 wt% PCBM as determined by steady state current density-voltage characterization. Hence, we show explicitly that the solar cell performance of these interpenetrating polymer networks containing PCBM is limited by charge transport rather than by formation of charges. (c) 2006 Elsevier B.V. All rights reserved.
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| 32. |
- Kanbur, Yasin, et al.
(författare)
-
High temperature-stability of organic thin-film transistors based on quinacridone pigments
- 2019
-
Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 66, s. 53-57
-
Tidskriftsartikel (refereegranskat)abstract
- Robust organic thin-film transistors (OTFTs) with high temperature stability allow device integration with mass production methods like thermoforming and injection molding, and enable operation in extreme environment applications. Herein we elaborate a series of materials to make suitable gate dielectric and active semiconductor layers for high temperature stable OTFTs. We employ an anodized aluminum oxide layer passivated with cross-linked low-density polyethylene (LD-PE) to form a temperature-stable gate capacitor. As the semiconductor, we use quinacridone, an industrial organic colorant pigment produced on a mass scale. Evaporated MoOx/Ag source and drain electrodes complete the devices. Here we evaluate the performance of the OTFTs healing them in air from 100 degrees C in 25 degrees C increments up to 225 degrees C, holding each temperature for a period of 30 minutes. We find large differences in stability between quinacridone and its dimethylated derivative, with the former showing the best performance with only a factor of 2 decline in mobility after healing at 225 degrees C, and unaffected on/off ratio and threshold voltage. The approach presented here shows how industriallys calable fabrication of thermally robust OTFTs can be rationalized.
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| 33. |
- Kang, Minji, et al.
(författare)
-
Light-sensitive charge storage medium with spironaphthooxazine molecule-polymer blends for dual-functional organic phototransistor memory
- 2020
-
Ingår i: Organic electronics. - : ELSEVIER. - 1566-1199 .- 1878-5530. ; 78
-
Tidskriftsartikel (refereegranskat)abstract
- Organic phototransistor memory is considered as a promising optoelectronic device owing to its multifunctionality. However, due to the poor reliability of each function and the complexity of the device structure, it is necessary to optimize the thin-film process of functional materials when constructing multiple functions into a single device. Here, we demonstrate a dual-functional device that is both a working memory transistor and a phototransistor by incorporating photochromic spironaphthooxazine molecules into an organic insulating layer. The photochmmic molecules in the polymer matrix not only exhibit nonvolatile charge storage properties similar to nano-floating gates but also feature a reversible electronic band structure upon alternating irradiation with ultraviolet and visible light, which makes the device function as both an electrical memory transistor and a phototransistor. Furthermore, the photoresponsive charge trap layer in the demonstrated device leads to excellent memory performance under both dark and light conditions, which includes a large memory window (-56 V), stable endurance cycles (amp;gt;10(2)), and good retention characteristics (amp;gt;10(4) s). Our findings suggest an alternative strategy to realize organic multifunctional nonvolatile memories.
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| 34. |
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| 35. |
- Kawahara, Jun, et al.
(författare)
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Improving the color switch contrast in PEDOT:PSS-based electrochromic displays
- 2012
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 13:3, s. 469-474
-
Tidskriftsartikel (refereegranskat)abstract
- Poly(3,4-ethylenedioxythiophene) chemically doped with poly(styrene sulfonic acid) (PEDOT:PSS) is a material system commonly used as a conductive and transparent coating in several important electronic applications. The material is also electrochemically active and exhibits electrochromic (EC) properties making it suitable as the active element in EC display applications. In this work uniformly coated PEDOT:PSS layers were used both as the pixel electrode and as the counter electrode in EC display components. The pixel and counter electrodes were separated by a whitish opaque and water-based polyelectrolyte and the thicknesses of the two EC layers were varied independently in order to optimize the color contrast of the display element. A color contrast (ΔE∗, CIE L∗a∗b∗ color space) exceeding 40 was obtained with maintained relatively short switching time at an operational voltage less than 2V.
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| 36. |
- Kawahara, Jun, et al.
(författare)
-
Reconfigurable sticker label electronics manufactured from nanofibrillated cellulose-based self-adhesive organic electronic materials
- 2013
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 14:11, s. 3061-3069
-
Tidskriftsartikel (refereegranskat)abstract
- Low voltage operated electrochemical devices can be produced from electrically conducting polymers and polyelectrolytes. Here, we report how such polymers and polyelectrolytes can be cast together with nanofibrillated cellulose (NFC) derived from wood. The resulting films, which carry ionic or electronic functionalities, are all-organic, disposable, light-weight, flexible, self-adhesive, elastic and self-supporting. The mechanical and self-adhesive properties of the films enable simple and flexible electronic systems by assembling the films into various kinds of components using a "cut and stick" method. Additionally, the self-adhesive surfaces provide a new concept that not only allows for simplified system integration of printed electronic components, but also allows for a unique possibility to detach and reconfigure one or several subcomponents by a "peel and stick" method to create yet another device configuration. This is demonstrated by a stack of two films that first served as the electrolyte layer and the pixel electrode of an electrochromic display, which then was detached from each other and transferred to another configuration, thus becoming the electrolyte and gate electrode of an electrochemical transistor. Further, smart pixels, consisting of the combination of one electrochromic pixel and one electrochemical transistor, have successfully been manufactured with the NFC-hybridized materials. The concept of system reconfiguration was further explored by that a pixel electrode charged to its colored state could be detached and then integrated on top of a transistor channel. This resulted in spontaneous discharging and associated current modulation of the transistor channel without applying any additional gate voltage. Our peel and stick approach promises for novel reconfigurable electronic devices, e.g. in sensor, label and security applications.
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| 37. |
- Kemerink, Martijn, et al.
(författare)
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The operational mechanism of ferroelectric-driven organic resistive switches
- 2012
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 13:1, s. 147-152
-
Tidskriftsartikel (refereegranskat)abstract
- The availability of a reliable memory element is crucial for the fabrication of plastic logic circuits. We use numerical simulations to show that the switching mechanism of ferroelectric-driven organic resistive switches is the stray field of the polarized ferroelectric phase. The stray field modulates the charge injection from a metallic electrode into the organic semiconductor, switching the diode from injection limited to space charge limited. The modeling rationalizes the previously observed exponential dependence of the on/off ratio on injection barrier height. We find a lower limit of about 50 nm for the feature size that can be used in a crossbar array, translating into a rewritable memory with an information density of the order of 1 Gb/cm(2). (C) 2011 Elsevier B. V. All rights reserved.
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| 38. |
- Kergoat, Loig, 1984-, et al.
(författare)
-
DNA detection with a water-gated organic field-effect transistor
- 2012
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 13:1, s. 1-6
-
Tidskriftsartikel (refereegranskat)abstract
- A DNA sensor based on a water-gated organic field-effect transistor is described. The semiconductor is poly [3-(5-carboxypentyl)thiophene-2,5-diyl] onto which DNA probes are covalently grafted via NHS/EDC chemistry. Clear changes in the output characteristic of the device are observed upon DNA immobilization and after DNA hybridization. Experimental data point out the importance of the electrolyte Debye length that can screen negative DNA charges and impede transduction. For this reason, deionized water was used in order to increase the Debye length up to several hundreds of nanometers. In this case, a decrease in the off current was observed upon hybridization, whereas no significant change occurred when using saline solutions.
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| 39. |
- Khikhlovskyi, Vsevolod, et al.
(författare)
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Data retention in organic ferroelectric resistive switches
- 2016
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 31, s. 56-62
-
Tidskriftsartikel (refereegranskat)abstract
- Solution-processed organic ferroelectric resistive switches could become the long-missing non-volatile memory elements in organic electronic devices. To this end, data retention in these devices should be characterized, understood and controlled. First, it is shown that the measurement protocol can strongly affect the apparent retention time and a suitable protocol is identified. Second, it is shown by experimental and theoretical methods that partial depolarization of the ferroelectric is the major mechanism responsible for imperfect data retention. This depolarization occurs in close vicinity to the semiconductor-ferroelectric interface, is driven by energy minimization and is inherently present in this type of phase-separated polymer blends. Third, a direct relation between data retention and the charge injection barrier height of the resistive switch is demonstrated experimentally and numerically. Tuning the injection barrier height allows to improve retention by many orders of magnitude in time, albeit at the cost of a reduced on/off ratio. (c) 2016 Elsevier B.V. All rights reserved.
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| 40. |
- Khikhlovskyi, Vsevolod, et al.
(författare)
-
Multi-bit organic ferroelectric memory
- 2013
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 14:12, s. 3399-3405
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Tidskriftsartikel (refereegranskat)abstract
- Storage of multiple bits per element is a promising alternative to miniaturization for increasing the information data density in memories. Here we introduce a multi-bit organic ferroelectric-based non-volatile memory with binary readout from a simple capacitor structure. The functioning of our multi-bit concept is quite generally applicable and depends on the following properties for the data storage medium: (a) The data storage medium effectively consists of microscopic switching elements (hysterons). (b) The positive and negative coercive fields of each hysteron are equal in magnitude. (c) The distribution of hysteron coercive fields has substantial width. We show that the organic ferroelectric copolymer P(VDF-TrFE) meets these requirements. All basic properties of our device were measured and modeled in the framework of the dipole switching theory (DST). As a first example we show the possibility to independently program and subsequently read out the lower, middle and upper parts of the hysteron distribution function, yielding a 3-bit memory in a single capacitor structure. All measured devices show good state reproducibility, high endurance and potentially great scalability.
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| 41. |
- Koch, N., et al.
(författare)
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Molecular orientation dependent energy levels at interfaces with pentacene and pentacenequinone
- 2006
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 7:6, s. 537-545
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Tidskriftsartikel (refereegranskat)abstract
- We used ultraviolet photoelectron spectroscopy (UPS) to investigate the energy level alignment at contacts between pentacene and Ag(1 1 1) in the presence of interfacial 6,13-pentacenequinone (PQ). Depending on the metal pre-coverage with PQ, we found evidence for three distinctly different interface morphologies and molecular orientations, accompanied by significant changes of the energy level alignment. Consequently, the hole injection barrier between pentacene and Ag(1 1 1) varied between 1.1 eV (pristine Ag) and 0.45 eV (5.4 nm PQ pre-coverage on Ag). In addition, our UPS results suggest that PQ can act as deep trap for electrons in a pentacene matrix. Depending on the exact mutual orientation of PQ and pentacene, the depth of these traps can be in the range of 0.2-0.75 eV. © 2006 Elsevier B.V. All rights reserved.
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| 42. |
- Larsen, Christian, et al.
(författare)
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Design, fabrication and application of organic power converters : Driving light-emitting electrochemical cells from the AC mains
- 2017
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 45, s. 57-64
-
Tidskriftsartikel (refereegranskat)abstract
- The design, fabrication and operation of a range of functional power converter circuits, based on diode configured organic field-effect transistors as the rectifying unit and capable of transforming a high AC input voltage to a selectable DC voltage, are presented. The converter functionality is demonstrated by selecting and tuning its constituents so that it can effectively drive a low-voltage organic electronic device, a light-emitting electrochemical cell (LEC), when connected to high-voltage AC mains. It is established that the preferred converter circuit for this task comprises an organic full-wave rectifier and a regulation resistor but is void of a smoothing capacitor, and that such a circuit connected to the AC mains (230 V, 50 Hz) successfully can drive an LEC to bright luminance (360 cd m(-2)) and high efficiency (6.4 cd A(-1)).
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| 43. |
- Li, Hui, et al.
(författare)
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Trion-induced current anomaly in organic polymer
- 2016
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 34, s. 124-129
-
Tidskriftsartikel (refereegranskat)abstract
- In this report, an anomalous time-evolution of electrical current in organic thin-film transistors, OTFTs, isrevealed by employing a specially tailored semiconductor composite channel. The composite is designedby controlling the density of carbon nanotubes dispersed in a host semiconducting polymer belowelectrical percolation. The current anomaly, which, to the best of our knowledge, has never beenobserved before, is directly correlated to strong many-body interactions instantaneously occurring in thesystem under investigation. In essence, two on-chain positively charged polarons are fused with anelectrochemically generated negative hydroxyl ion, OH, in the H2O/O2redox reaction to form a trion.The trion, which is characteristic of the polymer, is intrinsically metastable and can dissociate to mobilepolarons under the influence of electricfield, temperature and/or light illumination. The rate of trionformation is almost three orders of magnitude higher than that of trion dissociation. The fast formationand slow dissociation of the trions is the cause responsible for the observed current anomaly. Themetastable trion is, hence, of fundamental importance in the operation of OTFTs. Understanding thefundamentals pertaining to the anomalous phenomenon not only is crucial for design of more efficientdevices but also can guide development of future, emerging applications of OTFTs.
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| 44. |
- Li, Weiwei, et al.
(författare)
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The Effect of additive on performance and shelf-stability of HSX-1/PCBM photovoltaic devices
- 2011
-
Ingår i: Organic electronics. - : Elsevier Science B.V., Amsterdam.. - 1566-1199 .- 1878-5530. ; 12:9, s. 1544-1551
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Tidskriftsartikel (refereegranskat)abstract
- How 1,8-diiodooctane (DIO) enhances performance of polymer solar cells based on polymer HXS-1 and fullerene [6,6]-phenyl C(71)-butyric acid methyl ester (PC(71)BM) from 3.6% to 5.4% is scrutinized with several techniques by comparing devices or blend films spin-coated from dichlorobenzene (DCB) to those from DCB/DIO (97.5:2.5 v/v). Morphology of blend films is examined with atomic force microscopy (AFM), transmission electron microscopy (TEM) and electron tomography (3-D TEM), respectively. Charge generation and recombination is studied with photoluminescence, and charge transport with field effect transistors. The morphology with domain size in 10-20 nm and vertical elongated clusters formed in DIO system is supposed to facilitate charge transport and minimize charge carrier recombination, which are the main reasons for enhancing power conversion efficiency (PCE) from 3.6% (without DIO) to 5.4% (with DIO). Furthermore, a two year inspection shows no significant impact of DIO on the shelf-stability of the solar cells. No visible degradation in the second year indicates that the morphology of the active layers in the devices is relatively stable after initial relaxation in the first year.
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| 45. |
- Li, Xiaoran, et al.
(författare)
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Programmable polymer light emitting transistors with ferroelectric polarization-enhanced channel current and light emission
- 2012
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 13:9, s. 1742-1749
-
Tidskriftsartikel (refereegranskat)abstract
- We present a voltage programmable polymer light emitting field-effect transistor (LEFET), consisting of a green emitting polymer (F8BT), and a ferroelectric polymer, P(VDF-TrFE), as the gate dielectric. We show by both experimental observations and numerical modeling that, when the ferroelectric gate dielectric is polarized in opposite directions at the drain and source sides of the channel, respectively, both electron and hole currents are enhanced, resulting in more charge recombination and similar to 10 times higher light emission in a ferroelectric LEFET, compared to the device with non-ferroelectric gate. As a result of the ferroelectric poling, our ferroelectric LEFETs exhibit repeated programmability in light emission, and an external quantum efficiency (EQE) of up to 1.06%. Numerical modeling reveals that the remnant polarization charge of the ferroelectric layer tends to pin the position of the recombination zone, paving the way to integrate specific optical out-coupling structures in the channel of these devices to further increase the brightness. (C) 2012 Elsevier B.V. All rights reserved.
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| 46. |
- Li, Xiaodong, et al.
(författare)
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The effect of external electric field on the performance of perovskite solar cells
- 2015
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 18, s. 107-112
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Tidskriftsartikel (refereegranskat)abstract
- Planar heterojunction perovskite solar cells were fabricated through a low temperature approach. We find that the device performance significantly depends on the external bias before and during measurements. By appropriate optimization of the bias conditions, we could achieve an 8-fold increase in the power conversion efficiency. The significant improvement in device performance might be caused by the ion motion in the perovskite under the external electric field.
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| 47. |
- Liewald, C., et al.
(författare)
-
Scanning photocurrent microscopy of electrons and holes in the pigment semiconductor epindolidione
- 2018
-
Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 60, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- Photocurrent microscopy is used to characterize the kinetics of electrons and holes in organic field-effect transistors (FETs) with the hydrogen-bonded pigment epindolidione as active layer. The method relies on electrons and holes, generated on local illumination, which are provided after exciton splitting, to probe charge trapping. In the dark, hole conduction is observed for negative gate voltage while no electron conduction is observed for positive gate voltage. However, under illumination, a fast displacement current with 60 mu s onset time and 1 ms exponential decay occurs for positive gate voltage, which can be explained by exciton splitting underneath the semitransparent top contact followed by subsequent electron trapping and hole extraction. Afterward, trapped electrons hop via further trap states within the film to the insulator into interface traps (13 ms exponential decay) which induce a positive threshold voltage shift in the FET transfer curves for hole transport. Photocurrent microscopy confirms that the displacement current occurs only for illumination under and near the semitransparent source/drain contacts, which act here as metal-insulator-semiconductor (MIS) diodes. For negative gate voltage instead, the photocurrent comprises an enhanced hole current in the FET channel between the contacts. In the channel region, the detrapping of holes at the interface with the insulator (3 ms time constant) enhances the transistor current at low frequencies amp;lt; 1 kHz, whereas the displacement current between the contacts and the gate is observed only at frequencies amp;gt; 10 kHz. Thus, we show here that photocurrent microscopy allows to identify the kinetics of electrons and holes in traps close to the contacts and in the FET channel of pigment transistors.
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| 48. |
- Lin, Lili, et al.
(författare)
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Theoretical insights into the charge transport in perylene diimides based n-type organic semiconductors
- 2012
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 13:11, s. 2763-2772
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Tidskriftsartikel (refereegranskat)abstract
- We employed a tunneling enabled hopping model to investigate the charge transport properties for four n-type organic semiconductors perylene diimides compounds. The molecular parameters are calculated by density functional theory and the transport is modeled by kinetic Monte Carlo simulation. It is found that the substitutions at the bay positions of the perylene core have large influences on the charge transport properties through modifications in molecular conformation, the charge reorganization energy as well as the stacking networks in the crystals. The temperature dependence of the mobility shows typical "band-like", in agreement with the recent experiment, but we ascribe it to be the characteristic of nuclear tunneling effect for a localized charge, not by a delocalized band. The largest charge mobility is calculated to be 16.96 cm(2)/V s for the cyano substitution, in good comparison with the experimental value of 6 cm(2)/V s.
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| 49. |
- Liu, Jiang, et al.
(författare)
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Half‐Gate Light‐Emitting Electrochemical Transistor to Achieve Centered Emissive Organic p‐n Junction
- 2015
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 18, s. 32-36
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Tidskriftsartikel (refereegranskat)abstract
- Conventional organic light-emitting electrochemical cells show promise for lighting applications but in many cases suffer from unbalanced electrochemical doping. A predominant p-doping over n-doping causes an off-centered emissive p-n junction, which leads to poor power-conversion efficiency. Here, we report a half-gate lightemitting electrochemical transistor (HGLECT), in which a ion-conductive gate made from poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) is employed to combat this problem. The gate material, covering half the channel, is used to enhance the ndoping in this part by employing an appropriate operation protocol. We demonstrate a centered light emission zone, closely following the geometry of the gate material. The HGLECT with centered emission profile is shown to be more efficient than the corresponding LEC without gate electrode, and its n-doping level is measured to be 15%.
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| 50. |
- Malti, Abdellah, et al.
(författare)
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Electromagnetic devices from conducting polymers
- 2017
-
Ingår i: Organic electronics. - : ELSEVIER SCIENCE BV. - 1566-1199 .- 1878-5530. ; 50, s. 304-310
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report macroscopic electromagnetic devices made from conducting polymers. We compare their fundamental properties and device parameters with those of similar devices made from copper wires. By using self-standing supra-ampere conducting polymer wires, we are able to manufacture inductors that generate magnetic fields well over 1 G, and incorporate them in feedback LC oscillators operating at 8.65 MHz. Moreover, by utilizing the unique electrochemical functionality of conducting polymers, we demonstrate electrochemically-tunable electromagnets and electromagnetic chemical sensors. Our findings pave the way to lightweight electromagnetic technologies that can be processed (fromwater dispersions) using low-temperature protocols into flexible shapes and geometries.
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