- 2017 Fall Meeting
- Developing excellence in organic optoelectronics
- Organic Optoelectronics | Electrical Engineering and Computer Science | MIT OpenCourseWare
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Atomic spectroscopy at interfaces. Metrology, molecules and fundamental tests. Biomolecules and spectroscopy. Organic photonics and nanostructures. Optical random media. Group members. Trainees, Thesis, PhD. Organic lasers The main objective is the realization of an electrically pumped organic laser diode. Webmail UP Intranet ENT Within the error margin of the setup no additional spots are generated during operation. The voltage drop inside the ITO anode due to a high resistivity plays an important role for the brightness homogeneity of large area devices.
The voltage drop causes a brightness fall-off towards the center of the device. It is maintaining with increasing average current density and luminance, respectively. The homogeneity of luminance is improved by incorporation of additional metal lines on the anode layer. Montero; Henk J. Bolink Show Abstract. In this paper the methodology used to derive this model and its application to experimental data is presented.
We report on the experimental observation of large magnetoresistance in polyfluorene organic light-emitting diodes OLEDs. Very similar magnetic field effects MFEs of comparable magnitude were also observed in electroluminescence and photocurrent measurements. We provide a comprehensive overview of these three types of MFE. To the best of our knowledge, the mechanism causing these MFE is currently not known.
Moreover, we show that these experiments do not allow determination whether the MFE acts on the carrier density or carrier mobility making any attempt of explaining it ambiguous. As a remedy, we performed magnetoresistance measurements in holeonly OLEDs and show that the MFE acts on the carrier mobility rather than carrier density.
We propose a new electrooptic antenna design using organic polymer to receive microwave signals. In this paper we present the characterization of an electrooptic organic polymer. We measured the dielectric constant at microwave frequencies, and the electrooptic coefficient. We measured values of r 33 of 3. The goal of the electrooptic antenna design is to obtain maximum microwave and optical interaction.
We propose a novel approach based on resonance effect in both optical and microwave domain. For the optical resonance effect we use a Fabry-Perot cavity, and a patch structure as microwave resonator. Delaire Show Abstract. New fluorinated poly arylene ether sulfone s FPAES and poly arylene ether ketone s FPAEK with two types of NLO chromophores as pendant groups were obtained by a polycondensation reaction carried out using very mild reaction conditions.
The physical origin of this drop has been investigated and is possibly attributable to a secondary phase transition of the copolymers. Dye-loaded zeolite L host-guest materials were already successfully used in the realisation of efficient light-harvesting antenna systems. A new hierarchy of structural order is introduced by arranging the zeolite L crystals into densely packed, oriented monolayers on a substrate. In device engineering, a high degree of supramolecular organisation is a prerequisite for achieving desired macroscopic properties.
The methods we developed to synthesise such monolayers, to fill them with dyes and to terminate them with a luminescent stopcock will be discussed as well as their influence on the design of novel materials. By subsequent insertion of two different types of dye molecules in a zeolite L monolayer, the first unidirectional antenna system was realised. We also report a novel concept for the preparation of thin layer, silicon based solar cells. Organic nanofibers as new media for lasing, waveguiding, and photonic sensing Author s : F. Quochi ; V. Bordo ; F.
Cordella; A. Mura; H. Rubahn ; G. Bongiovanni Show Abstract. We report waveguide amplification of spontaneous emission and coherent random laser action in individual self-assembled organic nanofibers grown by high-vacuum deposition. The interpretation of the experimental results is given on the basis of simple models, including transfer matrix calculations in one-dimensionally disordered structures. We present also the numerical results for light scattering from a nanofiber which can be used as a basis for further experiments.
Joshua Kennedy; Z. Single-walled carbon nanotubes dispersed in a polymer matrix are studied via cw photomodulation spectroscopy. The spectrum is dominated by a modulation of the absorption lineshape, which we assigned to electro-absorption caused by local electric fields arising from trapped photoinduced charges. The lack of selectivity in the excitation and the dominance of the contribution by low energies point to an efficient migration of the photoexcited states, either the singlet excitons or the charges resulting from their dissociation. Singh ; G.
Dennler ; S. Koeppe ; H.
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Neugebauer ; N. Sariciftci ; S. Bauer Show Abstract. The devices were characterized both in under dark showing n-type transistor behaviour with linear and saturated mobility of 1. A typical phototransistor behaviour in a wide range of illumination intensities are observed in these devices.
A poly phenyleneethynylene polymer bearing amino acid substituents as active layer in enantioselective solid-state sensors Author s : M.
Tanese ; O. Hassan Omar ; L. Torsi ; F. Marinelli; D. Colangiuli; G. Farinola ; F. Babudri; F. Naso; L. Sabbatini; P. Zambonin Show Abstract. A poly phenyleneethynylene polymer bearing amino acid pendant groups is used as enantioselective active layer in solid-state sensing devices. The polymer bearing amino acid chiral sites is demonstrated to interact more favorably with the natural menthol than the synthetic one in a quartz crystal microbalance revealing system.
Promising perspectives are seen for the use of such polymers in chiral discriminating, chemically sensitive resistors or even transistors. Now organic thin film transistor technology gains growing maturity, high performance organic photodetectors are the missing link towards full organic photosensitive sensor arrays, needed for the realization of applications like organic scanners and organic cameras. In the borderline of the research in organic solar cells, research in organic photodetectors has mainly been limited to organic photodiodes.
However, phototransistors offer the possibility to reach higher sensitivities, thanks to the internal current gain of a transistor structure. This document focuses on organic field-effect phototransistors organic photoFETs where illumination can be used as an optical gate signal in addition to the electrical gate signal. An experimental description of pentacene photoFETs during broadband illumination is given. A distinction between the direct photocurrent and the additional current enhancement by a thresholdshift can be made, and a relation for this thresholdshift in function of time is revealed.
Consequently, the diffculty to compare different organic photoFETs without any information about the illumination time is highlighted and a comparison based on this power law is proposed. Subsequently it is pointed out that by the stability of this thresholdshift after illumination, the pentacene photoFET does not only act as a light detector but also as a memory element, capable to store information about illumination power and duration for an extended amount of time.
An increase in stochastic molecular vibrations of a solid due to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. We report on a light-induced isothermal phase transition of polymer materials from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light.
Whereas during irradiation by circular polarized light the materials behave as an isotropic viscoelastic fluid, they display considerable fluidity only in the direction parallel to the light field vector under linear polarized light. In this case the polymers behave visually as a liquid along one direction and as a solid in others one-direction liquid-state , demonstrating thus extraordinarily anisotropic mechanical properties. The fluidisation phenomenon is related to photoinduced motion of azobenzene-functionalised molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization.
We also show that the selective excitation of chromophores orientated parallel to the light polarization not only has great influence on the anisotropy of the mechanical properties of the materials, but also induces an anisotropic expanding force, which can be used for polarization-selective opto-mechanical actuators and sensors. Molecular nanocrystals grown in sol-gel thin films for ultrabright chemical sensor applications Author s : V. Monnier ; N. Sanz; M. Bacia; R. Pansu; A. Ibanez Show Abstract. Polyaromatic dyes were used to synthesize molecular nanocrystals in sol-gel thin films for sensor applications.
Indeed, we obtained well-dispersed and spherical nanocrystals with a narrow size distribution, exhibiting a good crystallinity. Time-resolved fluorescence spectroscopy allowed us to measure fluorescence lifetimes of nanocrystals in presence of molecular probes. Then, chemical sensoring properties of these molecular nanocrystals were demonstrated. P-F-TSB exhibits good color purity, high luminance of blue light-emission in organic light-emitting devices.
The broad electroluminescence emission band may attribute to long-wavelength excimer and electromer emission in addition to the blue component from singlet excited state of individual TFM-TSB molecule. In this study, we presented high-performance flexible organic light-emitting diodes FOLEDs ; to do so, we prepared indium-tin oxide ITO thin layers by ion beam sputtering IBS on polyethylene terephtalate PET substrates in soft low temperature conditions.
2017 Fall Meeting
The IBS technology seems well adapted to us to adjust the conduction level of the interface films to the one of the various organic materials making up the fabrication processes of the organic optoelectronic components; moreover this technique does not require a high substrate temperature or an annealing after ITO deposition to crystallize the obtained layers. Because of the great number of deposition parameters oxygen flow, substrate temperature, deposition rate The performances of FOLEDs on PET substrate with different ITO thicknesses were investigated and compared to the ones of a conventional organic light-emitting diode realized on glass substrate and according to the same device configuration.
A green organic light-emitting diode based on a rare-earth terbium complex Author s : A. Cheung ; W. Chan Show Abstract. Tris 8-hydroxyquinoline aluminum Alq has been widely used as the electron transporting layer as well as the green emitter layer in organic light emitting diodes OLEDs since it is thermally and morphologically stable to evaporate into thin films. On the other hand, rare-earth metal ions exhibit sharp spectral band which corresponds to 5Dx-7Fx transitions. In the case of terbium, this results in a sharp emission in green.
In this work, organic light emitting diodes based on a rare-earth metal complex [Tris 3-methylphenyl trimethyl-acetylpyrazoline terbium III] were fabricated by thermal evaporation. The terbium Tb complex was doped into the hole transporting material CBP and the electron transporting material Alq to investigate the effect of dopant in different layers on the device performance.
Developing excellence in organic optoelectronics
The effects of different dopant concentration on the photoluminescence PL and electroluminescence EL emission spectra were also investigated. Sharp emission in green nm was observed for optimum device structure and doping concentration. The optical and electronic characteristics of thick OLEDs were examined by varying the thickness of the carrier transport layers NPB and Alq 3 for the first time.
For having better mode guiding, more than nm thickness device was studied in this paper. The experimental results show the threshold voltage is proportional to the total thickness but the breakdown electric fields decrease. I-V curves can be fitted with a second-order polynomial form, and these fit-ting curves can be used for modeling the carrier transport in thick OLEDs. Eventually, a comprehensive model is pro-posed to describe the carrier transport due to the trap effect in bulk organic materials.
It shows this model is in a good agreement with our measured I-V curves. The synthesis and properties of 3,6-bis triphenylsilyl carbazole as an effective host material for blue electrophosphorescence are reported. The electrochemically active C3 and C6 sites of carbazole are non-conjugated blocked with the steric, bulky and large-gap triphenylsilyls, the resulting new compound retains the large triplet energy of carbazole yet exhibits much enhanced morphological stability and electrochemical stability in comparison with previous carbazole-based host materials.
Photophysical studies and photovoltaic devices on a low bandgap, high charge-carrier-mobility Poly Thienylene Vinylene PTV , prepared from a soluble precursor polymer synthesised via the 'dithiocarbamate route', are reported. In composites with an electron acceptor [6,6]-phenyl C 61 - butyric acid methyl ester PCBM , a soluble fullerene derivative photoinduced absorption PIA characteristic for charged excitations together with photoluminescence PL quenching are observed indicating photoinduced electron transfer.
The photocurrent spectrum of the photovoltaic device shows an onset at about 1. Polymer based devices with adaptable infrared reflection and transmission Author s : C. Nilsson; E. Karlsson; H. Kariis Show Abstract. In the present work the infrared-transmission of PEDOT:PSS poly 3,4-ethylenedioxythiophene :poly styrensulfonat is being investigated using three different kind of electrochromic devises.
The doping is achieved by a voltage applied across the cell. The optical properties are reversible if the polarity of the voltage is changed. We report here, to our knowledge, the first cell with adaptive transmission in the infrared wavelength range. The issue for this type of cell is that all the layers in the device must be transmissive in the whole relevant wavelength range. The results were further verified by construction of similar cells with different configuration giving adaptable reflectivity. We investigated organic bulk-heterojunction solar cells based on an absorber blend of poly 3-hexylthiophene P3HT and [6,6]-phenyl Cbutyric acid methyl ester PCBM by electrical impedance spectroscopy EIS.
A strong neck in the modulus plot of the EIS-spectra indicates that the absorber is divided into two regions of different conductivities. A similar behaviour was observed for pure P3HT-diodes. We compared the current-voltage characteristics and impedance spectra before and after consecutive annealing steps. After the annealing an expansion of the depletion region was observed, indicating that volatile dopants were evaporated out of the absorber.
Organic Optoelectronics | Electrical Engineering and Computer Science | MIT OpenCourseWare
This contributes to an improved photovoltaic performance as the separation of the generated charges in the depletion region is more efficient than in the non-depleted region. Also an improved rectification behaviour might be caused by a lower doping level. In this work we study the internal electric field V int present in devices based on an intrinsically semiconducting polymer.
Intermediate layers between the indium-tin-oxide and Al electrodes and the photoactive layer are able to influence and alter this electric field. Their influence is studied with Electroabsorption EA spectroscopy as well as transient photocurrent measurements under applied bias. We interpret the results in terms of the presence of charges at the interface.
Influence of solvents and substrates on the morphology and the performance of low-bandgap polyfluorene: PCBM photovoltaic devices Author s : Cecilia M. Andersson Show Abstract. Spin-coated thin films of poly[ 9,9-dioctylfluorenyl-2,7-diyl -co-5,5- 4',7'-dithienyl-2',1',3'-benzothiadiazole ] APFO-3 blended with [6,6]-phenyl-C 61 -butyric acid methyl ester PCBM are used as the active material in polymer photovoltaic cells. Such blends are known for their tendency to phase separate during film formation. Tuning the morphology of the blend in a controlled way is one possible road towards higher efficiency.
We studied the effect of adding chlorobenzene to chloroform-based blend solutions before spin-coating on the conversion efficiency of APFOPCBM photodiodes, and related that to the lateral and vertical morphology of thin films of the blend. The lateral morphology is imaged by atomic force microscopy AFM and the vertical compositional profile is obtained by dynamic secondary ion mass spectrometry SIMS.
The profiles reveal compositional variations consisting of multilayers of alternating polymer-rich and PCBM-rich domains in the blend film spin-coated from chloroform. The vertical compositional variations are caused by surface-directed spinodal waves and are frozen in during the rapid evaporation of a highly volatile solvent.
With addition of the low-vapour pressure solvent chlorobenzene, a more homogeneous vertical composition is found. The conversion efficiency for solar cells of this blend was found to be optimal for chloroform:chlorobenzene mixtures with a volume-ratio of We have also investigated the role of the substrate on the morphology.
We found that blend films spin-coated from chloroform solutions on PEDOT:PSS-coated ITO show a similar compositional structure as the films on silicon, and that changing the substrate from silicon to gold only affects the vertical phase separation in a region close to the substrate interface. Comparative studies on solar cell structures using zinc phthalocyanine and fullerenes Author s : M.
Egginger ; R. Koeppe ; F. Meghdadi ; P. Troshin; R. Lyubovskaya; D. Meissner; N. Sariciftci Show Abstract. We compare different structures of organic solar cells based on zinc phthalocyanine ZnPc and fullerene derivatives as electron donor and acceptor materials, respectively. Bilayer devices are fabricated and characterized by current-voltage and spectrally resolved photocurrent measurements. In a novel approach, the ZnPc was combined with soluble fullerene derivatives. With a pyrrolidinofullerene bearing chelating pyrridyl-groups we observed a complexation between donor and acceptor molecules.
Due to a favorable structuring of the donor-acceptor interface this leads to a significant enhancement of the solar cell performance compared to similar devices where no complexation takes place. Coevaporated bulk heterojunction mixed-layers are introduced between the pristine layers. Standard organic light emitting diodes OLEDs are usually bottom-emitting, i. Usually, indium tin oxide ITO is used for this purpose. However, as indium is a very expensive metal, replacing it is of vital interest for cheap OLED mass production, especially when it comes to lighting applications.
We suggest the use of a polymer instead of ITO, carrying out both hole transport and injection. In contrast to conventional approaches, which use a conductive polymer on top of ITO as smoothening and hole injection layer, we employ solely a highly conductive polymer in combination with an OLED comprising doped charge transport layers. This allows us to renounce the ITO layer underneath. The use of such a polymeric injection layer and of a doped small-molecule OLED stack results in a low operating voltage of the devices. Although the polymer possesses a somewhat lower conductivity than ITO, efficient devices can be fabricated.
For example, using the blue emitter Spiro-DPVBi 2,2',7,7'-tetrakis 2,2-diphenylvinyl spiro-9,9'-bifluorene , we achieve an efficiency of up to 5. As another example, we discuss green OLEDs based on the triplet emitter Ir ppy 3 fac tris 2-phenylpyridine iridium doped in a wide gap material.
In this work we discuss improvements of organic solar cells based on poly 3-hexylthiophene-2,5-diyl : C butyric acid methyl ester P3HT:PCBM blends. The polymer layer is combined with various electron transport materials and different cathodes. We were able to utilize the good charge carrier separation and transport properties of the P3HT:PCBM blend together with the flexibility of evaporated heterostructures.
In particular we studied the influence of additional layers of electron transport layer consisting of C 60 , lithium doped bathophenanthroline BPhen:Li 2- 4-tert-butylphenyl 4-biphenylyl -1,3,4-oxadiazole PBD and 2,9- dimethyl-4,7-diphenyl-1,phenantrolene BCP on the cell properties. Comparative study of optoelectronic properties of various Europium complexes used in organic electroluminescent structures Author s : M.
Chakaroun ; R. Antony ; R. Demadrille; A. Moliton Show Abstract. In order to obtain a red emission with organic electroluminescent device, we realized multilayer structures using various Europium complexes as emitting layer. The multilayer structures were obtained with the emitting layer deposited on a ITO substrate; a 2,9-dimethyl-4,7-diphenyl-1,phenanthroline BCP layer was used as hole blocking layer and a tris- 8-hydroxyquinoline aluminium Alq3 layer as electron transport layer.
Cathode of the devices was realized with a calcium layer covered with an protective aluminium layer. Europium complexes absorption spectra in chloroform and electroluminescence spectra are presented. Current-voltage and luminance-voltage characteristics are also presented and we discuss about the results obtained with various molar concentration of Europium complexes in the PVK matrix. The active layer morphology of vacuum deposited organic solar cells based on phthalocyanine-perylene donor-acceptor couple have been studied, comparing coevaporated bulk heterojunction with multilayer structures consisting in alternated donor and acceptor very thin layers.
These latter devices show current-voltage behaviour indicating that their active layer acts as an interpenetrated network. They show better photovoltaic parameters, with power conversion efficiencies 2. A compromise with vacuum evaporation growth rate has to be taken in order to realize the multilayer solar cells: high growth rate produces a better bulk interpenetrated structure giving rise to a better external quantum efficiency, but low growth rate favours the planar molecular arrangement that gives a better absorption of the perylene molecules.
From the comparison between measurements held in open air and under dry nitrogen atmosphere, we think that multilayer solar cells seem to be far less sensible to open air condition than the coevaporated solar cells. Three fluorene-based copolymers carrying reactive side groups oxetanes were synthesised and characterised. Their optical properties are essentially controlled by the introduction of either fluorene or lower energy gap benzothiadiazole or terthiophene comonomers, randomly distributed along the polymer chain.
We show that, in the presence of a small amount of a photoacid dispersed in the polymer films, these are converted into insoluble polymeric networks upon UV irradiation and heating. Absorption and emission spectra of the polymeric networks are similar to those of the starting polymers, showing that the cross-linking, due to the polymerisation of the oxetane groups, does not interfere. This ability to induce their insolubility upon UV irradiation is used to fabricate multi-layer light-emitting diodes. Using a transmission electron microscope grid as a shadow mask we show that micrometer-size patterns can be created.
How stable are polymer:PCBM bulk heterojunction solar cells? Author s : S. Bertho ; I. Prime members enjoy FREE Delivery on millions of eligible domestic and international items, in addition to exclusive access to movies, TV shows, and more. Back to top. Get to Know Us. English Choose a language for shopping. Audible Download Audio Books. Alexa Actionable Analytics for the Web.