We present a novel n-type doping technique for organic semiconductors using the metal complex bis(terpyridine)ruthenium as a strong donor. Owing to its low oxidation potential, the reduced neutral form of the donor complex allows an electron transfer to the matrix. This enables n-type conduction that has been seldom reported in metallophthalocyanine systems doped with organic compounds. The n-type zinc-phthalocyanine layers are characterized by the conductivity and the field-effect measurements. By sequential coevaporation of p- and n-doped layers, we have prepared the first stable and reproducible organic homojunction of zinc-phthalocyanine. The diode exhibits surprisingly high built-in voltage attractive e.g. for organic solar cell applications. The temperature dependence of the current-voltage characteristics does not follow the standard Shockley theory of pn-junctions. We explain the behavior of the ideality factor and the saturation current by deviations from the classical Einstein relation at low temperatures.

We use electromodulation (EM) spectroscopy to probe the electric field distribution in polymer light-emitting diodes. The EM spectrum below the turn-on bias is dominated by electroabsorption of the emissive layer but vanishes completely above the turn-on bias. The EM spectrum above turn-on is due entirely to absorption and bleaching effects arising from injected charge. The total elimination of the electroabsorption signal indicates that the internal electric field is effectively screened by the injected charge, and this effect is attributed to accumulation of trapped electrons close to the anode.

Tuning the work functions of metals was demonstrated by chemically modifying the metal surface through the formation of chemisorbed self-assembled monolayers (SAMs) derived from 1H,1H,2H,2H-perfluorinated alkanethiols and hexadecanethiol. The ordering inherent in the SAMs creates an effective, molecular dipole at the metal/SAM interface, which increased the work function of Ag (Φ_Ag ~4.4 eV) to 5.5 eV (ΔΦ ~ 1.1 eV) for 1H,1H,2H,2H-perfluorinated alkanethiols. Hexadecanethiol on the other hand shifted Φ_Ag toward 3.8 eV (ΔΦ ~ 0.6 eV) and raised the energy barrier for hole injection. These SAMs on Au were less efficient. 1H,1H,2H,2H-perfluorodecanethiol raised ΦAu (4.9 eV) by 0.5 eV to 5.4 eV, whereas hexadecanethiol decreased Φ_Au by only 0.1 eV. These chemically modified electrodes were applied in the fabrication of pLEDs and the hole conduction of MEH-PPV was investigated. An ohmic contact for hole injection between a silver electrode functionalized with the perfluorinated SAMs, and MEH-PPV with a HOMO of 5.2 eV was established. Conversely, a silver electrode modified with a SAM of hexadecanethiol lowered Φ_Ag to 3.8 eV, creating an efficient energy barrier for hole injection. This method demonstrates a simple and attractive approach to modify and improve metal/organic contacts in organic electronic devices like LEDs and photovoltaic cells.

We demonstrate high-efficiency organic light-emitting diodes (OLEDs) by incorporating a double emission layer (D-EML) into p-i-n-type cell architecture. The D-EML comprises two layers with ambipolar transport characteristics, both doped with the green phosphorescent dye tris(phenylpyridine)iridium [Ir(ppy)3]. The first EML features a bipolar, but predominantly hole transporting host material, 4,4',4''-tris(N-carbazolyl)-triphenylamine (TCTA), while the second EML is made of an exclusively electron transporting host, e.g. 3-phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole (TAZ); with a weak hole transport capability arising from hopping between dopant sites. The D-EML system of two bipolar layers leads to an expansion of the exciton generation region. Due to its self-balancing character, it avoids accumulation of charge carriers at any interface. Thus, a power efficiency of approximately 77 lm/W and an external quantum efficiency of 19.3% are achieved at 100 cd/m² at an operating voltage of only 2.65V. More importantly, the efficiency decays only weakly with increasing brightness and a power efficiency of 50 lm/W is still obtained even at 4,000 cd/m².

Up to now, most of the optical integrated devices are realized on glass or III-V substrates and the waveguides are usually obtained by photolithography techniques. We present here a new approach based on the use of photopolymerizable compounds. The conditions of self-written channel creation by solitonic propagation inside the bulk of these photopolymerizable formulations are analyzed. Both experimental and theoretical results of the various stages of self-written guide propagation are presented. A further step has been achieved by using a two-photon absorption process for the polymerization via a confocal microscopy technique. Combined with the solitonic guide creation, this technique allows to draw 3D optical circuits. Finally, by doping the photopolymerizable mixtures with push-pull chromophores having a controlled orientation, it will be possible to create active optical integrated devices.

The phoenix project aims to develop all-optical switches based on the combination of inorganic and organic materials in hybrid devices. We present first results in developing low-loss ring resonators fabricated in silicon-on-insulator (SOI) technology, with Q-factors as high as 125.000, and losses of α≈3.5dB/cm in the ring.

The interest for organic molecules in photonics and their use in the conception of new photonic devices, makes necessary a better understanding of their interactions with light. In particular, the modelling of these interactions is complex for biological molecules like proteins or polypeptides. The recent work of a team in our laboratory, using sensitized proteins to carry out holographic memories, has shown this interest of biological materials and the necessity to model their interaction with light. We present a theoretical electromagnetic model for such molecules. The real structure of the molecule is replaced by a theoretical aggregate of sub-wavelength spheres. A T-matrix algorithm is used to calculated the field scattered by these aggregates. The principle of this algorithm is explained. Their advantages and limitations are compared with other rigorous numerical methods used to study electromagnetism problems. The reasons, why we can model a molecule with a theoretical aggregate of spheres, are explained. The choices of the optical parameters of these aggregates are discussed. Some electromagnetic simulations of simple cases are presented in order to illustrate these choices. The experimental validation has to be done.

A new precursor route towards conjugated polymers is presented. Whereas difficulties occurred for the preparation of poly(2,5-thienylene vinylene) (PTV) derivatives via the existing precursor routes, PTV has been synthesised via a new developed "dithiocarbamate route" in good yields and satisfactory molecular weight. Structural characterisations of the conjugated polymers reveal an optical band gap around 1.7 eV. Organic field effect transistors and organic based photovoltaic devices were made and the results are discussed. Solar cells were produced using a blend of the precursor polymer and PCBM at various ratios. The conversion of the precursor polymer towards the conjugated polymer was performed in situ in film spin-coated from the blend. Promising energy conversion efficiencies were observed which were still improved by thermal annealing of the device at 70°C.

This work describes the development of solution processable liquid crystalline semiconductors and their applications in field-effect transistors. The relationship between liquid crystal molecular structure, its corresponding phase behaviour and electrical performance is examined. Molecular design methodology is employed to control the liquid crystalline morphology. The thermal, optical and electrical behaviour of these materials is characterised and X-ray diffraction scattering technique is used to reveal details of morphology and molecular orientation.

We present a theoretical and experimental study of a multilayer organic light emitting device (OLED) with a partially doped emission layer. An extended version of our established "MOLED" device model is used to understand the effects of the partially doped layer on the transport behavior and on the radiative charge recombination distribution as a function of applied bias. A step by step discussion of the possible mechanisms that can be introduced by doping and the resulting changes on the device properties is presented. We have found that under certain conditions the recombination zone is split into two zones leading to an emission color change with increasing voltage. By using the yellow emitting laser dye derivative 4-(dicyanomethylene)-2-methyl-6-{2-[(4-diphenylaminophenyl]ethyl}-4H-pyran (DCM-TPA) with electron trapping capabilities as a dopant in a standard organic light emitting device, we have achieved high quantum efficiency with excellent color saturation. Furthermore, for this special case a blue-shift of the emission color is observed for increasing bias due to the appearance of a double peak structure of the recombination zone.

The contact energy barrier of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS) on poly(9,9-dioctylfluorene) (PFO) amounts to 1 eV, resulting in a hole injection current that is reduced by 6-7 orders of magnitude. However, upon electrical addressing it is demonstrated that the hole contact barrier completely vanishes, resulting in an Ohmic contact. Furthermore, a change of the built-in electric field has been observed with two different techniques. The shift of the built-in electric field is in agreement with a charge dipole layer that reduces the injection energy barrier for the PEDOT:PSS/PFO contact.

We present results and a discussion of highly efficient polymer Light-Emitting Diodes (polymer LEDs, PLEDs). The external quantum efficiency in current standard devices reaches up to 2-4% only. We have explored two routes to enhance this value. In the first route, PEDOT/PSS is replaced with a novel anode or hole injection layer. The efficiency with some Light Emitting Polymers (LEP) is improved significantly, resulting in an efficacy of 35 cd/A for a yellow emitting poly-(para-phenylene-vinylene) and 20 cd/A for a blue emitting poly-(spirobifluorene). We attribute the major improvement compared to standard devices, where about 10 and 5 cd/A are obtained, respectively, to a combination of improved exciton formation efficiency and light out-coupling efficiency, and to less quenching of the radiative decay under actual device operating conditions. In the second route, we developed a new host polymer with high triplet energy such that transition metal-based green-emitting phosphorescent dyes can be used without significant back transfer of triplet excitons to the polymer host. First results using this system showed about 25 cd/A using a soluble green Ir-based emitter. Importantly, all data are obtained in a standard two-layer device of a hole transport/injection layer and the LEP.

The origin of a broad low-energy photo-luminescence (PL) and electro-luminescence (EL) band emerging upon oxidative degradation of hihgly emissive polyfluorenes (PFs) has recently been identified as the emission from on-chain keto defects acting as exciton and/or charge traps. In this work we compare several polyfluorenes with respect to their stability upon thermal degradation, and their stability upon fabrication and operation of PF-based polymer light emitting devices (PLEDs). We show that in addition to the keto emission a second type of defect emission, which is related to the deposition of the metal electrode, can also affect the color purity of PF-PLEDs. Investigated materials are a poly(9,9 dialkylfluorene) with hexahydrofarnesyl sidechains (PF111/12) a poly(9,9 dialkylfluorene) with ethyl-hexyl sidechains (PF 2/6) and two different slightly branched spiro-PFs with and without triphenylamine endcappers, respetively. We find significant differences in the spectral stability of the polymers which may on the one hand be explained by a difference of the chemical stability of the polymers but to some extent must be explained withiin the picture of excited energy migration. Regarding a comparison of the polymers, the end-capped spiro-type PF shows an overall improved performance compared to the other investigated polymers provided that the evaporation process of the metal cathode of an PLED is well controlled to avoid the formation of emissive defects at the interface.

We report on the photophysics of the pristine oligo(ethylene oxide) side-chain grafted polymer PPP-OR11 and the polymer blended with the lithium salt lithiumtriflate. The side-chains render the polymer soluble in common organic solvents and in addition provide ionic conductivity, which is important for the application of the polymer as mixed ionic-electronic conductor for instance in light-emitting electrochemical cells (LECs). The optoelectronic properties of the polymer were studied for two types of light-emitting devices, first in light emitting diodes and secondly in LECs. From these investigations it is evident that in polymer light-emitting diodes (PLEDs) several degradation processes caused by defects on the PPP backbone deteriorate the color stability. These defects are induced either by the oxidation of the polymer or the aluminum deposition process upon device fabrication. Contrarily, LECs fabricated from the same polymer provide color stable blue emission. The color stability of the LEC can be explained by the fact that the recombination zone is shifted from the cathode/polymer interface in PLEDs to the non-doped intrinsic zone between the p- and n-type regions of the LEC, avoiding emission from aluminum evaporation induced defects.

Though being much less efficient than silicon cells, organic solar cells exhibit a unique combination of interesting properties: low cost, flexibility, and the possibility of large surface coverage. Large progresses have been made over the last years using MDMO-PPV (Poly[2-methoxy-5-(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene) reaching efficiencies of 2.9% and recently efficiencies over 3%, using poly(3-hexyl thiophene). A great deal of research however has still to be invested to improve the current state of the art. Among the main key-points to be addressed are namely the stability and lifetime of such devices. We are currently working on bulk heterojunction solar cells made from MDMO-PPV and PCBM (methano-fullerene[6,6]-phenyl C61-butyric acid methyl ester). Different batches of MDMO-PPV, originating from different synthesis modes (classical "Gilch" synthesis and "Sulphinyl" synthesis led by IMEC-IMOMEC) have been tested. Evolution of the power efficiency following continuous illumination (AM1.5, 80 mW.cm^-2) was characterized under controlled atmosphere of nitrogen. In parallel, photodegradation studies are also investigated and electrical modeling is under way in order to get a better understanding of the relations between photochemical and electrical parameters of the diode that can be deduced from I/V curves.

Organic light-emitting diodes (OLED) are rapidly reaching large-scale marketing figures, driven by attractive features like low cost and fast response, being also suitable for application on flexible substrates. All these aspects enable a wide range of applications such as displays, innovative devices in optoelectronics and novel light sources. Furthermore, the benefits expected from OLEDs based devices, if compared to "classical semiconductors" based devices consist of low production costs, lightweight and geometrical flexibility. Novel OLEDs based light sources fulfilling the above-mentioned requirements, call for a considerable effort both in the production processes and in product innovation. Among the variety of possible applicative OLED applications, we focused our research effort on the Automotive sector. Our envisioned approach enabling control of light distribution from an OLED light source include modeling and patterning of the light source, design and fabrication of suitable micro-optics coupled to the flexible transparent Organic Light Emitting Diode (OLED) substrate.

Highly efficiency organic electroluminescent devices employing a phosphorescent dye doped into a wet-processable molecular material have been demonstrated. Methoxy-substituted 1,3,5-tris[4-(diphenylamino)phenyl]benzene (TDAPB) was selected as a host polymer for the phosphorescent dopant fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3], and organic films were fabricated by spin-coating method. The peak external quantum efficiency of 8.2 % (29 cd/A), or luminous power efficiency of 17.3 lm/W, and luminance of 33,000 cd/m2 were achieved at a apply voltage of 9.4 V for a 90nm-thick emissive layer. The emission from the host material of TDAPB was not observed in the electroluminescence or photoluminescence spectra. The decrease in efficiencies at a high current is analyzed using the triplet-triplet annihilation model. The high performance is attributed to the simple device structure, excellent film forming properties of the host material, and the efficient energy transfer from the host to dopant.

Top-emitting organic light-emitting diodes (OLEDS) fornext-generation active-matrix OLED-displays (AM-OLEDs) arediscussed. The emission of light via the conductive transparent top-contact is considered necessary in terms of integrating OLED-technology to standard Si-based driver circuitry. The inverted OLED configuration (IOLED) in particular allows for the incorporation of more powerful n-channel field-effect transistors preferentially used for driver backplanes in AM-OLED displays. The use of the highly conductive polymer PEDOT:PSS as hole injection layer yields anodes with an extremely low contact resistance. The non-destructive spin-coating is enabled by a hydrophobic buffer layer such as pentacene. The overlying transparent electrode was realized employing low-power radio-frequency magnetron sputter-deposition of indium-tin-oxide (ITO). Additionally, a cathode with an interfacially metal-doped electron-injecting layer is proposed. Hybrid inverted OLEDs utilizing the fluorescent emitter system Alq₃:Ph-QAD allowed efficiencies of 2.7 lm/W around 150 cd/m². Device efficiencies are increased by employing a phosphorescent dye Ir(ppy)3 doped into the hole-transporter TCTA. Such phosphorescent hybrid IOLEDs exhibit peak efficiencies of 19.6 cd/A and 5.8 lm/W at 127 cd/m². Thus, the main requirements for a use of hybrid inverted IOLEDs in AM-OLED-displays are satisfied.

This paper presents preliminary synthetic and physical study of a new polythiophene block copolymer. These are conjugated donor (D) block poly(hexylenedithiathiophene) copolymerized with an acceptor (A) block of fluorinated ester derivatized polythiophene via an aliphatic bridge (B) unit. Experimental results show that when -DBAB- type of block copolymer forms, there is strong photoluminescence (PL) quenching in -DBAB- relative to D/A blend or the pristine D or A blocks. PL quenching is attributed to both intra and inter chain photo induced electron transfer or charge separation. Since block copolymer can be easily tailored, this system appears attractive for light harvesting applications including photovoltaic applications.

The progress in the field of organic photodetectors has recently led to the development of very fast and efficient devices, but their spectral sensitivity is mainly limited to the visible, without covering the regions of the spectrum of greater interest for telecommunications. One of the major issues when dealing with long wavelength organic photodetectors is the usually poor environmental stability of low bandgap organic semiconductors. A possible exception to this scenario is represented by coordination complexes with organic ligands. We employ as photosensitive materials transition metal dithiolene and dioxolene complexes which combine high thermal and photochemical stabilities with high molar extinction coefficients in the near infrared. Taking advantage of the broad tuning of electronic absorption spectra which can be exerted by changing the oxidation state of the complexes, we develop planar metal-semiconductor-metal phostodetectors which are spectrally matched to the optical fiber windows and which can detect light pulses with repetition rates in the range of hundreds of kbit/s. This investigation demonstrates the existence of organic materials of potential telecom interest and that the detection of infrared light pulses is feasible, thus representing a first step toward organic photodetectors for telecommunications.

We report on the study of the optical properties of hybrid systems made from molecular aggregates (J-aggregates) and metallic nanoparticles (Au and Ag). Both entities have outstanding optical properties that have been extensively addressed both through experimental and theoretical efforts. The J-aggregates were chosen for their linear and non-linear excitonic response that shows among other intriguing properties, superradiant emission, ultrafast optical switching, and electroluminescence. These J-aggregates form spontaneously on the surface of Au and Ag nanoparticles, used primarily to excite the organic shell through optical near-field interaction. Steady state as well as ultrafast spectroscopic measurements was used to characterize the nature of the interaction between the two constituents as well as to follow the dynamics of the exciton in the aggregate upon near-field excitation from the particle. For both Au and Ag, Mie scattering theory calculations of the hybrid ground state absorption spectra account for the experimental observations and reflect the coherent coupling between the excitonic states in the aggregate and the nanoparticles electronic transition dipoles. Furthermore we show that the dipole-dipole coupling strength between the individual molecules in the aggregate is increased by ~30% on the surface of the particle compared to its value in solution. The different dynamics of these nanosystems have been probed using femtosecond spectroscopy and reveals contrasted relaxation pathways for the exciton when interacting with Ag with respect to Au as well as a delay dependent excitonic coherent length.

Recently there has been considerable interest in the construction of photoactive organic materials designed to exhibit novel forms of optical nonlinearity. By exploiting the unique properties of these nanomaterials at high levels of photon flux, new possibilities emerge for applications in energy harvesting, low-threshold lasing, quantum logic devices, photodynamic therapy, etc. In particular, a detailed appraisal of the theory spotlights novel mechanisms for directed energy transfer and energy pooling in nanophotonic dendrimers. Characterized by a nonlinear dependence on the optical irradiance, these mechanisms fall into two classes: (a) those where two-photon absorption by individual donors is followed by transfer of the sum energy to the acceptor; (b) where the excitation of two electronically distinct but neighbouring donor groups is followed by a collective migration of their energy to a suitable acceptor. In each case these transfer processes are subject to minor dissipative losses, associated with intramolecular vibrational relaxation in the donor species. In this paper we describe in detail the balance of factors and the constraints that determines the favored mechanism, which include the excitation statistics, structure of the energy levels, selection rules, molecular architecture, the distribution of donors and acceptors, spectral overlap and coherence factors. Knowledge of these factors and the means for their optimization offers fresh insights into nanophotonic characteristics, and informs strategies for the design of new photoactive materials.

This paper reports on the synthesis and characterization of a novel class of materials namely, photo-actuating and photo-rheological polymers. The terms photo-actuation and photo-rheological refer to the phenomena, where photo-responsive polymers undergo conformational changes upon UV irradiation. This conformational change can result in changes in the spectral and physical properties of the polymer. For example, its volume and rheological properties. The first part of this paper describes the laboratory-based synthesis and characterization of these materials. The second part describes the experimental methodology and results obtained when characterizing the photo-actuation and photo-rheological behavior of the materials. It was paramount in these experiments to control the temperature of the test specimen; this was necessary as some of the changes in the properties brought about by UV irradiation could also be accounted for by an increase in the temperature of the test specimen. Two classes of photo-responsive material were synthesized and characterized using conventional analytical techniques. The first series of polymers were polymethyl methacrylate (PMMA) based with azobenzene groups in the side chain, the second series contained spiropyran groups in the side chain. The characterization of the photo-rheological behavior of these materials involved the deployment of a custom-modified rheometer, which was operated under isothermal conditions. A liquid light guide was used to enable in-situ irradiation of the test specimen with UV or visible light. The photo-actuation studies involved experiments on liquids and solid films of the above-mentioned co-polymers. A commercially available 3-D surface profiler was used to study their photo-actuating behavior. A couple of unique apparatus were also designed and used to characterize the photo-actuation behavior of the polymers in solution. The effects of irradiation on the photo-rheological and photo-actuating behavior were quantified taking temperature effects into consideration. Potential end-use applications for these polymers are considered.

A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or domes, of the solute on substrates such as silicon, mica, glass, and indium-tin-oxide. The dome size can be controlled by the casting conditions. Higher concentration and slower evaporation of the solvent leads to larger domes. Upon annealing, the dyes may crystallize and form polycrystalline or single crystalline domes or crystalline fibers. Photophysical properties of the domes were investigated and it was found that the absorption and fluorescence spectra depend on the aggregate kind (polycrystalline or single crystalline) and the dome size.

Using ultrafast pump-probe and pump-push-probe spectroscopy we highlight evidence of monodimensional photophysics coming from isolated chains of poly(9,9-dioctylfluorene) (PFO). We identify a large gain band with peak value of 2600 db/cm. By exploiting the peculiar one-dimensional physics of the isolated chain, we envisage a novel principle for ultrafast all-optical gain switching. Experiments suggest that the expected maximum rate of on-off switching over a broad wavelengths range (around 100 nm) can be as high as 300 GHz with large modulation depth.

Two models describing charge extraction from insulators have been used to interpret the experimental photocurrent data of 20:80 wt% blends of poly(2-methoxy-5-(3`,7`-dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells. When only drift of charge carriers is taken into account, a square root dependence on voltage of the photocurrent is expected, governed by the difference between electron and hole mobility. It is demonstrated that both the magnitude and functional dependence of the predicted current are in disagreement with experimental data. However, when both drift and diffusion of charges are taken into account, the predicted photocurrent shows a different behaviour: At low electric fields a linear behaviour is predicted, which results from the diffusion of charges, folllowed by saturation at high fields. The agreement between the theoretical result and the experimental data obtained from MDMO-PPV:PCBM cells is satisfactory when a generation rate of G=1.46 × 10²⁷ electron-hole pairs/m3s is used, showing the importance of diffusion at low fields, i.e., near the open-circuit voltage.

A model of exciton quenching in disordered organic materials is formulated. The model considers the quenching as a diffusion-limited process with the diffusion rate being controlled by energetic relaxation of excitons within the inhomogeneously broadened excitonic density of states. The calculated dependence of the radiative exciton decay rate upon the trap density is used in order to fit experimental data on the trap-induced photoluminescence quenching in methyl-substituted planarized poly-para-phenylene and in alkoxy-substituted poly-phenylenevinylene.

Screen-printing is studied as deposition technique for conjugated material based layers. For light emitting diode applications poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) is applied. For this material, batches with different molecular weight and different solution concentrations are subjected to rheology measurements. Also the influence of several printing parameters like squeegee speed and pressure, snap-off distance and mesh size of the screen on the film formation and final thickness is investigated. It is shown that for each material batch and solution concentration specific printer settings have to be used to obtain active layers that are suitable for opto-electronic applications. Photovoltaics based on the principle of bulk donor-acceptor heterojunction are also tested using a blend of MEH-PPV mixed with the C₆₀-derivative (6,6)-phenyl C61-butyric acid methyl ester (PCBM). Promising results have been obtained showing that screen-printing can be a suitable technique for the deposition of the active layer of polymer solar cells.

A fundamental aim in organic electronics is an implementation of a polymeric laser diode. For this purpose, an essential step towards this goal is the understanding and fabrication of feedback structures for conjugated polymer lasers. In this work we will present the realization and characterization of a directly imprinted distributed feedback structure into a highly luminescent conjugated polymer, poly(2-methoxy-5(2-ethyl-hexyloxy)-1,4-phenylevevinylene, which was utilized as a model polymer for conjugated laser materials. The presented method permits to directly imprint a distributed feedback grating into the conjugated polymer. Such distributed feedback structures may be fabricated either in the substrate or in the active polymer layer itself. Therefore we chose two accomplished techniques from soft lithography, which has proven itself as a useful tool to pattern a wide variety of materials. By the combination of these two techniques, namely micrmolding in capillaries and liquid embossing, we created a novel technique. We called this new technique liquid imprinting. Under photo-excitation of a frequency doubled Nd:YAG laser, our corrugated distributed feedback structures showed lasing. Because of the inexpensiveness and repeatability, this approach is a very promising candidate for the mass production of conjugated polymer laser devices.

The use of lasers as the driving force of information processing for future photonic technologies is almost inevitable. As a direct consequence of this the protecting of targets from high intensity stray optical beams, the most important being the eye, via optical limiting (high suppression of high intensity optical beams whilst allowing high transmission of ambient light) is a task of immediate importance. This contribution will discuss the application of metallo-phthalocyanine compounds doped into organic polymers to produce composite films to act as passive solid-state optical limiters. A range of phthalocyanines with different metals such as zinc, indium and vanadium substituted into the central cavity doped into the comercially available polymer poly(methyl)-methacrylate, PMMA, is investigated. The nonlinear responses exhibited by the systems are modelled and fitted using a three level orbital model to quantify the nonlinear activity in an effort to elucidate certain molecular design rules for the optical limiting application of the solid-state polymer-phthalocyanine composite. In addition to this the nature and physical properties of the films that are processed are also discussed.

We apply the Time of Flight (TOF) technique to study carrier mobility in N, N’-diphenyl-N,N’-bis(3-methylphenyl) -1,1-biphenyl-4,4’-diamine (TPD) and tris(8-hydroxyquinolato) aluminium (Alq₃). These materials are two examples of, respectively, hole and electron transporting molecular materials. Measurements are performed in free air or under vacuum varying the experimental parameters such as laser pulse intensity and single shot irradiation. We observe a transition from dispersive to non dispersive transport changing the experimental conditions.

Light-polarizing films are a basis of sheet polarizers, which are used in liquid crystal systems. A light-polarizing film is generally produced by the formation of a uniaxial stretched film made of polyvinyl alcohol (PVA) or its derivatives containing a light-polarizing element like iodine or dichroic dye. Films with iodine are excellent in their initial polarizing performance but poor in resistance to moisture and heat. In order to improve the durability of polarizers more stable dichroic element are used instead of iodine. Films with dichroic organic dyes first of all azodyes are superior in the resistance to moisture and heat as compared with iodine systems. Searching for thermally stable dyes, which do not change their colour under of the influence of high temperature and humidity and are suitable for the manufacturing of effective polarizers is an actual problem. In this paper we show the results of optical investigations of uniaxial PVA-films with iodine (with and without transparent layer) and dichroic azodye.

We investigated the electrical stability of polythiophene-based organic thin film transistors (OTFTs). The electrical properties of a thin film transistor such as field effect mobility, threshold voltage and on/off current changed vastly when exposed to air. In order to analyze the stability of the transistor, electrical properties were first measured in vacuum for several hours, then air or oxygen gas was introduced and the changes in the electrical properties were observed. Device showed a decrease in field effect mobility from 10^-3 cm²/V•s to 10^-5 cm²/V•s after exposure to air and the on/off ratio was also changed from 10³ to 10¹.

We simulated modification of brightness as electrode, ITO anode and semitransparent cathode in the transparent organic light emitting device (TOLED). Semitransparent cathodes were used thin metal films, Ca-Ag and LiF-Al. Ca-Ag electrode has a higher transmittance 71% and lower reflectance 13% as compared to 32% and 24% of LiF-Al at 530nm. Reflectance of these material affected brightness and spectrum. Ratio of emitted lights intensity through ITO and metal cathode was calculated theoretically to use reflectance and transmittance of each electrode. Calculated ratio of brightness is in agreement with the measured ones to each electrode. Brightness of emitted light through ITO is about 3.2 and 1.5 times higher than through LiF-Al and Ca-Ag cathodes, respectively. In case of LiF-Al, ratio of transmitted light through the electrode was very different and spectra of light through LiF-Al were accompanied with the interference fringes.

The present paper deals with the development of hybrid sol-gel glasses as host matrixes for molecules having quadratic NLO properties. Second order non-linearities can be observed after poling in order to orient these molecules. However, due to their small size, thermal relaxation processes lead to a decrease of the induced orientation with time. Host matrixes showing a high rigidity and corresponding to a final material presenting a reduced free volume should overcome this drawback. An interesting way is to use the rigidity conferred by an organic-inorganic sol-gel matrix that can polymerize under irradiation. Photopatterning of the layer and simultaneous copolymerization of the hybrid precursor with functionalized chromophores should enhance the second order NLO response. The results presented in this paper focus on the formulation and conditioning of laminated hybrid sol-gel layers with a thickness of 100 μm that remain crack-free under condensation and photopolymerization. Results are presented concerning the generation of 1 μm gratings obtained under spatially controlled visible illumination using interference pattern at 514 nm. Diffraction efficiencies up to 90 % are obtained for an incident intensity of 30 mW.cm^-2. The next step is now the incorporation of functionalized chromophores in the hybrid sol-gel matrix leading to a study of NLO properties of the final material.

We show that a very large optical response is obtained in azo-dye doped nematic liquid crystals for low input light intensities (of the order of a few tens of μW/cm² and that this extreme sensitivity of the nematic film results from a combined action of the photoisomerization process of the azo-dye molecules and the light-induced changes of the anchoring energy. The liquid crystal reorientation can be controlled by changing the molecular length of the ionic surfactant which is used as anchoring agent.

The remarkable effect on lifetime improvement of copper phthalocianine (CuPc) coated indium tin oxide (ITO) anode of organic light emitting diodes (OLED's) is experimentally well approved. Also known are the electrode morphology, with and without CuPc coating, the energy levels of the used materials, important for charge injection and conduction, the carrier mobility etc. Based on this knowledge we suggest the model that explains the mechanism behind the lifetime improvement. We argue that the charge accumulation at the interface between the CuPc and the hole transport layer is responsible for screening out of the electric field variations leading to current density homogenization across the OLED surface. The variation of the injection field, introduced by electrode roughness, is estimated for typical indium tin oxide morphology used in OLED production. Without the CuPc hole injection layer a substantial current channeling occurs in OLED's, leading to accelerated device degradation.

Porous thin films have been fabricated by physical vapor deposition at an extremely oblique angle of incidence (85°). This deposition technique, called glancing angle deposition (GLAD), was used to create thin films composed of isolated helical columns. By investigating a variety of dielectrics, we found that helical GLAD films fabricated from titanium dioxide produce the strongest chiral optical response because of its large refractive index. Further improvements were made by using post-deposition annealing to form anatase and rutile polycrystalline phases of TiO₂. By tailoring the pitch of the helical structures, the circular Bragg reflection band was tuned to preferentially reflect red, green, and blue light. The high porosity of a GLAD film (>50%) permits liquid crystals (LC) to be incorporated into the pores of the helical nanostructure, which creates chiral alignment in otherwise non-chiral LCs. This technique improves circular Bragg reflection and can create addressable hybrid materials with potential applications to high-efficiency reflective displays.

Holographic memories are expected to be used as high capacity portable media. The memory capacity of holographic memories can be made higher than that of the conventional optical disks vecause the holographic memories can use 3D memory storing. Also, the data transfer rate of holographic memories can be easily increased by the use of batch recording/reconstruction of 2D digital data. Recently, photopolymer has been studied as a candidate memory medium. However, this medium shows shrinkage after recording, which makes it difficult to do multiple recording. This paper clarifies the degree of this medium shrinkage that occurs after recording and its effect on bit error rate. Also, the paper explains how the bit error is greatly reduced when the image distortion caused by the shrinkage is corrected.

Different types of polymers are proposed for holographic data storage : photopolymers like PMMA where bonds form or break in the polymer network under illumination, photochromic polymers containing for example azobenzene groups (proposed for high resolution nanolithography), and photopolymerizable systems using inhomogeneous polymerization of one or more monomers for holographic data storage. The material proposed in this work enters in the last family, giving rise to thick phase holograms. The coupling betwween polymerization and diffusion processes is extensively studied in order to characterize the photoinduced microstructuration. Diffusion processes are generated by the concentration gradients due to a disappearance of dye and monomer molecules at different rates in the reactive medium. Creation of gratings with spatial frequencies ranging from 10 to 4000 lines/mm was studied. The formulations are suited to be photopolymerized by illumination around 500 nm, allowing the polymerization of thick samples (thickness of a few hundred microns) with a good optical quality. In order to obtain a reversible process and to improve the storage capicity of the matrix, the medium is doped by a photochromic molecule while the polymerization is used for the photostructuration of the host matrix. The process needs at first the creation of tubular regions corresponding to the highest refractive index of the matrix. By entering in such a fiber, light is guided in the thickness of the material. In each microfiber, bits are recorded in the second stage one after the other one. Several bits can be stored in a same fiber by wavelength multiplexing.

The hole transport in various poly(p-phenylene vinylene) (PPV) derivatives has been investigated in hole-only diodes as function of temperature T and applied electric field E. A difference of three decades has been found in the hole mobility between a random copolymer with asymmetric sidechains and a PPV-derivative with symmetric sidechains. The temperature dependence of the hole mobility has been analysed within the correlated Gaussian disorder model. The large differences in the mobility values of these PPV derivatives are governed by a strong decrease of the energetic disorder. The high mobility PPV-based polymers are interesting candidates for being used as hole transport layers in heterojunction light-emitting diodes.

In this work we present an innovative structure for organic Thin Film Transistors (TFTs) that is transparent, flexible, and optimized for a good behaviour at relatively high frequencies. Starting from a basic structure, several possible options for building such kind of structure can be implemented. In this work, material, technology, and measurement issues will be discussed.

To realize organic solar cells with high performance, we developed a novel way of stable n-doping using cationic dyes in electron transport materials. In our approach, the volatile donors are created in-situ from stable precursor compounds. Using the cationic dye pyronin B (PyB) as a model precursor, we carried out conductivity and field effect measurements to characterize the properties of doped naphtalene tetracarboxylic dianhydride (NTCDA) thin film. The results show a strong increase in n-type conductivity. Combined FTIR, UV/VIS/NIR and mass spectroscopic measurements suggest the formation of leuco pyronin B during sublimation of pyronin B chloride, and a subsequent charge transfer between dopant and matrix providing free electrons, which increase the n-type conductivity.

Optical absorption phenomena and in particular sub band gap absorption features are of great importance in the understanding of processes of charge generation and transport in organic pure and composite semiconductor films. To come towards this objective, an alternative and high sensitive spectroscopic approach is introduced to examine the absorption of light in pure and compound organic semiconductors. Because sub band gap absorption features are typically characterized by very low absorption coefficients, it is not possible to resolve them using common transmission and reflection measurements and high sensitive alternatives are needed. Therefore, a combination of photocurrent (Constant Photocurrent Method CPM/Fourier Transform Photocurrent Spectroscopy FT-PS) and photothermal techniques (Photothermal Deflection Spectroscopy PDS) has been used, increasing sensitivity by a factor of thousand, reaching detectable absorption coefficients ((E) down to 0.1 cm^-1. In this way, the dynamic range of measurable absorption coefficients is increased by several orders of magnitude compared to transmission/reflection measurements. These techniques have been used here to characterize ground state absorption of thin films of MDMO-PPV, PCBM and a mixture of both materials in a 1:4 ratio, as typically used in a standard active layer in a fully organic solar cell. The spectra reveal defect related absorption phenomena and significant indication of existing interaction in the ground state between both materials, contrary to the widely spread conviction that this is not the case. Experimental details of the techniques and measurement procedures are explained.

Polymer electronics increasingly needs circuit design tools based on simple but accurate device models. It also needs scaling rules and ultimately its own form of Moore's Law. Such models must include accurate conduction equations. Here we begin the development of device models based on the Universal Mobility Law which is itself the basis of roadmapping. This law is the physical manifestation of variable range hopping and this is widely recognized as a dominant mechanism, except perhaps at the highest doping levels. By interpreting this law in terms of the relationship between mobility and carrier density the gradual channel equation is redeveloped below and above pinch-off. It is immediately apparent that mobility is not an appropriate measure of the speed of circuits. Two new parameters K1 and m are introduced. They can be found from accurate measurements on Schottky barriers and give the maximum possible performance. Real performance is always less than this. The values of K and m for a particular process can be assessed above pinch-off and with stable polymer they can be used to accurately predict the output characteristics.

Photopolymers are already well known as holographic materials. The modulation of the refractive index is patterned by the distribution of the cross-linking rate which depends on the illumination conditions. More recently, it has been demonstrated that the quadratic non linear optical (NLO) properties can be patterned in photopolymerized materials doped with push-pull chromophores. In that case, one takes advantage of the huge increase of the viscosity during the polymerization process to freeze the chromophores orientation. By using adapted sequences of applied electric field to orientate the polar NLO molecules combined with appropriate illumination conditions, it is then possible to create periodic poled structures in such doped photopolymers. The technique is therefore especially adapted for the realization of quasi phase matching structures in organic materials.

In this work the theoretical study of record of holographic gratings of transmitted and reflection type in photopolymeric materials with optical attenuation has been carried out. The analytical model describing spatial-temporal transformation of holographic grating field during record is developed. The model takes into consideration light-induced changing of optical attenuation. The results of numerical simulation on the base of the model are presented.

In this work the results of experimental investigations of holographic grating formation in photopolymer HPPM-633 are presented. On the base of fitting of experimental dependence of kinetics of diffraction efficiency with the theoretical one the photopolymer parameters are determined and presented. The photopolymer parameters such as diffusion coefficient and rate of their changing, optical absorption coefficient and rate of their changing, polymerization time, parameters defining contribution of photopolymerization and diffusion in change of refraction index, have been determined for other samples of photopolymer. On the base of model and numerical simulation it has been shown influence of experimental record conditions on diffraction efficiency, optimal record time, angle and wavelength selectivity of photopolymer gratings. The results obtained enable to define the optimal record time and direction of modification of photopolymer composition and external record parameters for achievement of diffraction characteristics predefined.

A light valve is a key component for optical signal processing. A liquid crystal layer is activated by light due to a proximate photoconducting layer. Contemporary commercial light valves are made with an amorphous silicon photoconducting layer which offers an impedance change between light and dark states of up to three orders of magnitude. One drawback of using amorphous silicon is that the resolution of the valve is limited by lateral photocharge spreading. We hope to overcome this by using thin organic photoconducting layers.

We fabricate the porous silicon/ PMMA/DR1 composite films by spin-coating methods in our work. The influence of the rotation speed of spin-coating and solution concentration on inserting of PMMA/DR1 in the porous silicon pores were studied. Micro-Raman spectrometry technique was used to examine the pores filling with PMMA/DR1. The linear and nonlinear refractive index of porous silicon and PMMA/DR1 composite films were studied by Optical reflectivity measurements and Z-scan technique respectively. The luminescence characteristics and stability emission of PMMA/DR1 impregnated samples were also studied in this paper.

In this paper, we demonstrate organic light emitting devices (OLED) that exhibit high brightness, low driving voltage and long lifetime. Devices with the brightness of 10,000 cd/m² can be achieved at 4 V by the use of the high mobility electron-transport layer (ETL) material, bis(10-hydroxybenzo[h]qinolinato)beryllium (Bebq₂), and the mixing host (MH) technology. Electron mobility of Bebq₂ is two orders of magnitude higher than that of the typical ETL material, tris-(8-hydroxyquinoline) aluminum (Alq₃), from the time-of-flight (TOF) measurement and hence the driving voltage can be decreased. By co-evaporating the hole-transport layer (HTL) material and the ETL material as the host of the emitting layer, it reduces two volts in driving voltage because of its bipolar transport characteristics. MH technology can not only decrease the driving voltage, but also increase the device lifetime since it eliminates the sharp boundary of HTL/ETL interface and decreases the carriers piling up near this interface which causes the organic material degradation. Compared to the conventional heterojunction (HJ) OLED, operation lifetime of MH devices was enhanced by a factor of 4.

In a classical multilayer organic light emitting diode (OLED) structure, almost 80% of the light emitted happens to be lost following guiding through the different layers. Patterning of the OLEDs structure was already proposed and reported as an interesting solution towards the optimization of an OLED external efficiency. As an alternative to classical lithographic patterning methods which appear to be quite complex, we propose here the implementation of a quite direct and easy-to-set light-induced patterning method using azo-dye polymers. When a polymer film containing azobenzene dyes is irradiated by an interference pattern between polarized laser beams at a wavelength near the chromophore absorption band, the film surface undergoes a direct, reversible and controlled topographic modification. More surprisingly, we have recently experimentally evidenced that uniform irradiation of an azo-dye polymer using a single laser beam with normal incidence onto the polymer film surface could lead to a self structuration process resulting in the formation of a quasi hexagonal surface-relief grating. After a description of the main features related to light-induced surface relief gratings, we show here that this original patterning process offers an interesting solution for control and optimisation of optoelectronic devices such as OLEDs. The guiding properties of both 1D and 2D structures have been studied and their effects on the light emission properties of a patterned electroluminescent polymer have been characterized and compared after angle dependent measurement of the photoluminescence spectrum. Quite efficient decoupling is evidenced.

Time-resolved luminescence spectroscopy has been used to investigate exciton diffusion in thin films of poly(p-phenylene vinylene) (PPV) based derivatives. Exciton density distribution upon photoexcitation in polymer/fullerene heterostructures has been modeled and exciton diffusion length values of 5 nm and 6 nm are estimated for two different PPV derivatives, which differ by three orders of magnitude in charge carrier mobility due to reduced energetic disorder. Hence, the exciton diffusion length is not correlated to the charge carrier mobility in this class of materials.