| 1. |
- Crivillers, N, et al.
(författare)
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Photoinduced work function changes by isomerization of a densely packed azobenzene-based SAM on Au: a joint experimental and theoretical study
- 2011
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 13:32, s. 14302-14310
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Tidskriftsartikel (refereegranskat)abstract
- Responsive monolayers are key building blocks for future applications in organic and molecular electronics in particular because they hold potential for tuning the physico-chemical properties of interfaces, including their energetics. Here we study a photochromic SAM based on a conjugated azobenzene derivative and its influence on the gold work function (Phi(Au)) when chemisorbed on its surface. In particular we show that the Phi(Au) can be modulated with external stimuli by controlling the azobenzene trans/cis isomerization process. This phenomenon is characterized experimentally by four different techniques, kelvin probe, kelvin probe force microscopy, electroabsorption spectroscopy and ultraviolet photoelectron spectroscopy. The use of different techniques implies exposing the SAM to different measurement conditions and different preparation methods, which, remarkably, do not alter the observed work function change (Phi(trans)-Phi(cis)). Theoretical calculations provided a complementary insight crucial to attain a deeper knowledge on the origin of the work function photo-modulation.
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| 2. |
- Fenwick, O., et al.
(författare)
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Efficient red electroluminescence from diketopyrrolopyrrole copolymerised with a polyfluorene
- 2013
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 1:3, s. Art. no. 032108-
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis, characterization, and device incorporation of copolymers based on a common green-emitting polyfluorene but containing a small proportion of a low energy gap donor-acceptor-donor unit for red emission in photo- and electroluminescence. At just 1%-3% random incorporation, the low-gap unit is not present on all chains, yet we demonstrate that efficient charge and energy transfer can yield electroluminescent devices with 1% quantum efficiency and a color that can be tuned by adjusting the density of low-gap units to achieve primary red (National Television System Committee). The high current density tail off in the efficiency is reduced by replacing the hole-injection layer with a photochemically cross-linked electron-blocking layer.
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| 3. |
- Hou, Lili, et al.
(författare)
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Optically switchable organic light-emitting transistors
- 2019
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 14:4, s. 347-353
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Tidskriftsartikel (refereegranskat)abstract
- Organic light-emitting transistors are pivotal components for emerging opto- and nanoelectronics applications, such as logic circuitries and smart displays. Within this technology sector, the integration of multiple functionalities in a single electronic device remains the key challenge. Here we show optically switchable organic light-emitting transistors fabricated through a judicious combination of light-emitting semiconductors and photochromic molecules. Irradiation of the solution-processed films at selected wavelengths enables the efficient and reversible tuning of charge transport and electroluminescence simultaneously, with a high degree of modulation (on/off ratios up to 500) in the three primary colours. Different emitting patterns can be written and erased through a non-invasive and mask-free process, on a length scale of a few micrometres in a single device, thereby rendering this technology potentially promising for optically gated highly integrated full-colour displays and active optical memory.
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| 4. |
- Sforazzini, G., et al.
(författare)
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Synthesis and Photophysics of Coaxial Threaded Molecular Wires: Polyrotaxanes with Triarylamine Jackets
- 2014
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:8, s. 4553-4566
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated polyrotaxanes jacketed with hole-transport groups have been synthesized from water-soluble polyrotaxanes consisting of a polyfluorene-alt-biphenylene (PFBP) conjugated polymer threaded through beta-cyclodextrin macrocycles. The hydroxyl groups of the oligosaccharides were efficiently functionalized with triphenylamine (TPA) so that every polyrotaxane molecule carries a coat of about 200 TPA units, forming a supramolecular coaxial structure. This architecture was characterized using a range of techniques, including small-angle X-ray scattering. Absorption of light by the TPA units results in excitation energy transfer (EET) and photoinduced electron transfer (ET) to the inner conjugated polymer core. These energy- and charge-transfer processes were explored by steady-state and time-resolved fluorescence spectroscopy, femtosecond transient absorption spectroscopy, and molecular modeling. The time-resolved measurements yielded insights into the heterogeneity of the TPA coat: those TPA units which are close to the central polymer core tend to undergo ET, whereas those on the outer surface of the polyrotaxane, far from the core, undergo EET. Sections of the backbone that are excited indirectly via EET tend to be more remote from the TPA units and thus are less susceptible to electron-transfer quenching. The rate of EET from the TPA units to the PFBP core was effectively modeled by taking account of the heterogeneity in the TPA-PFBP distance, using a distributed monopole approach. This work represents a new strategy for building and studying well-defined arrays of >100 covalently linked chromophores.
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| 5. |
- Cacialli, F., et al.
(författare)
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Synthesis and characterisation of poly(distyrylbenzene-block-hexa(ethylene oxide)) and its fluorinated analogue - Two new block copolymers and their application in electroluminescent devices
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:12, s. 3555-3561
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Tidskriftsartikel (refereegranskat)abstract
- Two new soluble block copolymers are reported in which chromophores and hexa(ethylene oxide) units alternate along the polymer backbone. In polymer 1 the chromophore was the distyrylbenzene unit. The polymer was synthesised via the Wittig reaction and the ionization potential of 5.4 ± 0.2 eV was measured by cyclic voltammetry and photoelectron spectroscopy. Polymer 1 showed a high solid-state photoluminescence efficiency (34%) and was used to make efficient (0.5 cd/A) light emitting diodes (LEDs). Polymer 1 was also used in light emitting cells, these showed luminescence in reverse bias and a reduced turn-on voltage compared to the LEDs. Polymer 2, in which the chromophore was dodecafluoro-distryrylbenzene, was prepared via the Horner-Wittig reaction and showed an ionization potential of 6.25 ± 0.15 eV and a solid-state photoluminescence efficiency of 17%. It was used as electron-conducting layer in a LED but failed to give significant electroluminescence. The optical energy gap for both polymers was 3.0 eV. © 2002 Published by Elsevier Science Ltd.
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| 6. |
- Chvojka, Petr, et al.
(författare)
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Expanded Multiband Super-Nyquist CAP Modulation for Highly Bandlimited Organic Visible Light Communications
- 2020
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Ingår i: IEEE Systems Journal. - 1932-8184 .- 1937-9234. ; 14:2, s. 2544-2550
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we experimentally demonstrate a novel expanded nonorthogonal multiband super-Nyquist carrier-less amplitude and phase (m-ESCAP) modulation for bandlimited organic visible light communication (VLC) systems. The proposed scheme has the same bandwidth requirement as the conventional m-CAP while breaking the orthogonality between subcarriers by purposely overlapping them. We compare m-ESCAP with the conventional m-CAP and a compressed nonorthogonal version of m-CAP (m-SCAP) in terms of measured bit error rate (BER) performance, bit rates, and spectral efficiencies. We show that the m-ESCAP system offers improvement in the bit rate of $\sim$10% and 20% compared to the m-CAP and m-SCAP, respectively, and in the spectral efficiency of $\sim$20% compared to m-CAP. These gains are achieved at the cost of increased BER, which, however, remains below the 7% forward error correction limit.
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| 7. |
- Haigh, Paul Anthony, et al.
(författare)
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Experimental demonstration of staggered cap modulation for low bandwidth red-emitting polymer-LED based visible light communications
- 2019
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Ingår i: 2019 IEEE International Conference on Communications Workshops, ICC Workshops 2019 - Proceedings.
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Konferensbidrag (refereegranskat)abstract
- © 2019 IEEE. In this paper we experimentally demonstrate, for the first time, staggered carrier-less amplitude and phase (sCAP) modulation for visible light communication systems based on polymer light-emitting diodes emitting at ∼639 nm. The key advantage offered by sCAP in comparison to conventional multiband CAP is its full use of the available spectrum. In this work, we compare sCAP, which utilises four orthogonal filters to generate the signal, with a conventional 4-band multi-CAP system and on-off keying (OOK). We transmit each modulation format with equal energy and present a record un-coded transmission speed of ∼6 Mb/s. This represents gains of 25% and 65% over the achievable rate using 4-CAP and OOK, respectively.
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| 8. |
- Haigh, Paul Anthony, et al.
(författare)
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Hybrid Super-Nyquist CAP Modulation based VLC with Low Bandwidth Polymer LEDs
- 2019
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Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC. ; 2019-September
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Konferensbidrag (refereegranskat)abstract
- Visible light communication systems often suffer from high frequency attenuation when transmitting out-of-band. This effect has been ameliorated by multi-band modulations such as multi-band carrier-less amplitude and phase (m-CAP), which minimises the effect of decreased high frequency magnitude and maximises signal-to-noise ratio-per-sub-band. On the other hand, in the pass-band region, super-Nyquist CAP (SCAP) can offer throughput improvements with no additional complexity at the receiver, at the cost of bit error rate. We propose, for the first time, a new hybrid SCAP modulation format that takes advantageous of both SCAP (i.e. overlapped sub-bands within the modulation bandwidth) and conventional m-CAP (orthogonally spaced bands outside the modulation bandwidth) while maintaining isolation between noise sources. We show higher baud rates within the passband region whilst supporting out-of-band transmission at lower error vector magnitudes.
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| 9. |
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| 10. |
- Kim, J.S., et al.
(författare)
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Kelvin probe and ultraviolet photoemission measurements of indium tin oxide work function: : a comparison
- 2000
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Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 111-112, s. 311-314
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Tidskriftsartikel (refereegranskat)abstract
- We report a comparison of the work functions of thin films of indium tin oxide (ITO), carried out by means of ultraviolet photoelectron spectroscopy (UPS) and by measurements of the contact potential difference with respect to a gold reference electrode (Kelvin probe (KP) method). We investigated commercially available ITOs both "as-received", and after certain surface treatments, such as oxygen plasma. First, we find measurable discrepancies between KP values measured with three different instruments, and between the KP and the UPS values. Secondly, and unexpectedly, we find that the KP, although more sensitive than UPS, does not detect certain differences between ITOs with different surface treatments. We discuss the results in view of the different environments in which the measurements are carried out (UHV for the UPS and air/Ar for the Kelvin method), of the effects which may be induced by the high-energy photon irradiation in the UPS measurement, and of the stability of the gold probe work function in gas ambient. We conclude that UPS is better-suited for absolute work function determination, although KP remains a convenient and inexpensive tool for fast screening of contact potential differences. (C) 2000 Elsevier Science S.A. All rights reserved.
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| 11. |
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| 12. |
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| 13. |
- Murto, Petri Henrik, 1984, et al.
(författare)
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Triazolobenzothiadiazole-Based Copolymers for Polymer Light-Emitting Diodes: Pure Near-Infrared Emission via Optimized Energy and Charge Transfer
- 2016
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Ingår i: Advanced Optical Materials. - : Wiley. - 2195-1071. ; 4:12, s. 2068-2076
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.A series of new near-infrared (NIR) emitting copolymers, based on a low band gap 6-(2-butyloctyl)-4,8-di(thiophen-2-yl)-[1,2,3]triazolo[4',5':4,5]benzo[1,2-c]-[1,2,5]thiadiazole (TBTTT) fluorophore copolymerized into a high band gap poly[3,3'-ditetradecyl-2,2'-bithiophene-5,5'-diyl-alt-5-(2-ethylhexyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione-1,3-diyl] (P2TTPD) host backbone, for polymer light-emitting diode (PLED) applications is reported. PLEDs fabricated from the host polymer (P2TTPD-0) show external quantum efficiencies (EQEs) up to 0.49% at 690 nm, with turn-on voltage (Von) at only 2.4 V. By incorporating the TBTTT segments into the host polymer backbone, pure NIR emission peaking at ca. 900 nm is obtained with Von remaining below 5 V. This work demonstrates that such a low Von can be attributed to efficient intrachain energy and/or charge transfer to the TBTTT sites. When the NIR emitting copolymer (P2TTPD-10) is blended with P2TTPD-0, the TBTTT are confined to well-separated polymer chains. As a result, the EQE from the blend is lower and the Von higher than that obtained from the pure copolymer (P2TTPD-1.0) with equal content of TBTTT. An analogous copolymer (P4T-1.0), consisting of poly[3,3'-ditetradecyl-2,2':5',2'':5'',2'''-quaterthiophene-5,5'''-diyl] (P4T) as the host and 1% TBTTT as the NIR emitter, further demonstrates that pure NIR emission can be obtained only through optimized molecular orbital energy levels, as in P2TTPD-1.0, which minimizes chances for either charge trapping or exciton splitting.
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| 14. |
- Steckler, Timothy, 1979, et al.
(författare)
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Multifunctional materials for OFETs, LEFETs and NIR PLEDs
- 2014
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 2:26, s. 5133-5141
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Tidskriftsartikel (refereegranskat)abstract
- A family of phthalimide-thiophene copolymers with linear and branched alkyl chains attached to the imide nitrogen have been synthesized. Their optical and electronic properties were investigated along with their applications in OFETs and LEFETs. The phthalimide-thiophene copolymer having a C16 straight alkyl chain on the phthalimide yielded the highest mobilities and PLQE with mobilities of 1 x 10(-3) cm(2) V-1 s(-1) for holes and 1 x 10(-2) cm(2) V-1 s(-1) for electrons with a PLQE of similar to 28% in the solid state. Since these polymers are ambipolar and emissive, they have proven to be useful for applications as a host material for NIR PLEDs. In this study a 1% loading of NIR emitting DAD segments based on bisthienyl(thiadiazoloquinoxaline) or bisthienyl(benzotriazolothiadiazole) were incorporated into the phthalimide-thiophene polymerization. Using the branched CH(C8H17)(2) alkyl chain on the host phthalimide-thiophene copolymer combined with the bisthienyl(benzotriazolothiadiazole) emitter resulted in the most efficient (emission maximum >= 850 nm) single layer NIR-emitting PLED to date with an EQE of 0.27% emitting at 885 nm.
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| 15. |
- Steckler, Timothy, 1979, et al.
(författare)
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Near-Infrared Polymer Light-Emitting Diodes Based on Low-Energy Gap Oligomers Copolymerized into a High-Gap Polymer Host
- 2013
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Ingår i: Macromolecular Rapid Communications. - : Wiley. - 1022-1336 .- 1521-3927. ; 34:12, s. 990-996
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Tidskriftsartikel (refereegranskat)abstract
- Near-infrared (NIR) polymer light-emitting diodes (PLEDs) based on a fluorene-dioctyloxyphenylene wide-gap host material copolymerized with a low-gap emitter are presented. Various loadings (1, 2.5, 10, 20 mol%) of the low-gap emitter are studied, with higher loadings leading to decreased efficiencies likely due to aggregation effects. While the 10 mol% loading resulted in almost pure NIR emission (>99.6%), the 1 mol% loading yielded optimum device performance, which is among the best reported to date for a unblended single-layer pure polymer emitter, with an external quantum efficiencies of 0.04% emitting at 909 nm. The high spectral purity of the PLEDs combined with their performance support the methodology of copolymerization as an effective strategy for developing NIR PLEDs.
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| 16. |
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| 17. |
- Tregnago, G., et al.
(författare)
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Thia- and selena-diazole containing polymers for near-infrared light-emitting diodes
- 2015
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 3:12, s. 2792-2797
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Tidskriftsartikel (refereegranskat)abstract
- We report the optical characterization of near-infrared (NIR) emitters for polymer light-emitting diode (PLEDs) applications based on the copolymerization of a phthalimide-thiophene host polymer with a low-gap emitter containing the bisthienyl(benzotriazolothiadiazole) unit. We investigate different loadings of the low-gap emitter (in the range 1-3% by weight) and the substitution of a sulphur atom with a selenium atom to further extend the emission in the NIR up to 1000 nm. PLEDs based on copolymers with 1% loading give the best efficiency (0.09%) and show an almost pure NIR EL (95% in the NIR) peaking at 895 nm.
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