This PDF file contains the front matter associated with SPIE Proceedings Volume 8435, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

This paper presents a study of selective ablation of thin organic films (LEP- Light Emitting Polymer, PEDOT:PSS- Poly 3,4-ethylenedioxythiophene: polystyrene sulfonate) by using 248 nm Excimer laser, on various kinds of multilayered SiN barrier foils for the development of Organic Light Emitting Diodes (OLED). Different Silicon Nitride (SiN) barrier foils with dedicated absorption spectra are taken into account for this purpose. The drive for looking into different types of SiN originates from the fact that the laser selective removal of a polymer without damage to the barrier layer underneath is challenging in the dynamic laser processing of thin films. The barrier is solely responsible for the proper encapsulation of the OLED stack. The main limitation of current OLED design is its shorter life span, which is directly related to the moisture or water permeation into the stack, leading to black spots. An optimization of laser parameters like fluence and number of shots has been carried out for the various types of SiN barrier foils. We are able to obtain a wider working process window for the selective removal of LEP and PEDOT:PSS from SiN barrier, by variation of the different types of SiN.

In an electroluminescent excitation, singlet and triplet excitons are generated. In this contribution it is proposed to harvest all excitons in an efficiently emitting singlet state by use of molecules which exhibit distinct thermally activated delayed fluorescence at T = 300K. Highly attractive examples, comprising Cu(I) complexes and the metal-free acridine orange, are presented and discussed with respect to their photophysical properties.

The interfacial charge transfer recombination processes under working conditions that limit the device performance in quantum dot/polymer bulk heterojunction solar cells have been investigated. We have employed spectroscopic techniques as charge extraction (CE), laser transient absorption spectroscopy (L-TAS) and transient photovoltage (TPV). From the CE technique, we have observed an exponential charge accumulation in the device when light intensity is increased, as it has been related to conventional molecular photovoltaic devices. The L-TAS showed that recombination dynamics, in thin films, are dominated by the presence of trap in both, the nanocrystals and the polymer materials. Finally, from the TPV experiments we observed a strong carrier lifetime, in complete devices, upon charge density. This strong dependency of charge concentration vs charge lifetime has been found to be higher than in organic photovoltaics based on polymer and fullerenes. The comparison between the recombination dynamics from TPV and LTAS, performed with and without electrodes, respectively, allow us to exclude any process related with the metal contacts in the strong dependency of the recombination with the charge density.

Neat bi-layer solar cells of a fullerene acceptor and a cyanine dye donor were prepared using meniscus coating. Meniscus coating is very material efficient and leads to high quality pinhole-free films. The cells exhibit high open circuit voltages of 1 volt, only 0.8 eV below the band gap of the cyanine dye. This is one of the smallest differences reported for organic solar cells and illustrates an almost optimal donor-acceptor energy level alignment.

This manuscript reports that conjugated polymers can show a significant hyperpolarizability, as measured by hyper- Rayleigh scattering (HRS). First, a disubstituted poly(phenanthrene) is examined. It is shown that the polymer exhibits an unexpected, but extremely large second-order nonlinear optical (NLO) response, which moreover strongly depends on the solvent conditions. As the molecular structure of the polymer does not at all fit into the classical paradigms, but yet an extremely high hyperpolarizability is measured, these observations put these theories into perspective. An explanation is postulated, which is based on the variation of the conjugation. Second, the hyperpolarizability of regioregular HTcoupled poly(3-hexylthiophene)s (HT-P3HT)s is measured. It is found that also this conjugated polymer shows a significant hyperpolarizability, showing that the observed NLO behavior of conjugated polymers is not restricted to one polymer, but is instead more general. The dependency of the hyperpolarizability on the degree of polymerization is established.

We demonstrate a simple and novel technique to improve the power conversion efficiency of polymer:fullerene solar cells based on the low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and the soluble fullerene derivative PCBM. We dope the blend via cosolution with the electron accepting molecule tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Doping concentrations of F4-CNQ from 0 - 0.3 %, with respect to the weight of the polymer, were investigated. The dark current-voltage (IV) characteristics, the illuminated IV characteristics, the external quantum efficiency, and the hole mobility in dependence of the doping concentration were studied. We observe an increase in the photocurrent resulting in improved solar cell efficiencies, which corresponds to an increase in the hole mobility in the polymer. We explain this enhancement in the solar cell performance in terms of decreased carrier recombination.

The dissociation of excitons at a donor-acceptor interface in organic photovoltaic devices is an important but poorly understood process that takes place over multiple length and time scales. Here, we introduce a method to resolve photoinduced charge movement at an organic heterojunction in both time and space through observation of the Stark shift induced in a nearby J-aggregate probe layer. Using ultrafast transient absorption measurements, we show that this technique provides an opportunity to quantify the recombination and separation dynamics of geminate charge pairs over the entire sub-picosecond to millisecond range of relevant time scales.

We present methods for nanostructuring organic thin films for organic photovoltaic (OPV) devices. Using the glancing angle deposition (GLAD) technique, we fabricate a variety of columnar morphologies of metal phthalocyanine (MPc) materials that can be used as structured donor layers in OPV devices. We leverage this capability with block copolymer surface patterning techniques to achieve perfectly periodic columnar arrays while providing additional control over column dimensions, spacing, and density. Our investigation employs hexagonal seed patterns of platinum on silicon and we vary the seed spacing between 40 nm and 60 nm. We find that pattern resemblance begins to fade when the film thickness exceeds the seed spacing. We compare the film evolution between vertical post and slanted post morphologies, and use advanced substrate motion techniques to constrain column diameters. We conclude by addressing the compatibility of surface patterning with device fabrication. Patterned ITO surfaces and SiO₂ seed patterns are shown.

In order for organic bulk heterojunction solar cells to compete with the traditional inorganic cells, higher power conversion efficiencies are desirable. A characteristic of organic solar cells is their narrow absorption window, compared to the absorption band of inorganic semiconductors. A possible way to capture a wider band of the solar spectrum - and thus increasing the power conversion efficiency - is using two or more solar cells with different bandgaps in a row, referred to as a multi-junction solar cell. In this article, we study the theoretical efficiency potential of three organic cells in a row, i.e. a triple-junction. We study the influence of the energy levels of donor and acceptor, as well as different absorption windows of the subcells. We not only study the light harvesting potential of the usual monolithic configuration, but also consider a stacked set-up. Ideal material characteristics are obtained from these calculations, giving an idea of how the ideal organic triple-junction cell should look like. An interesting result is that it is not necessary to develop photovoltaic organic materials with an absorption window broader than 300 nm for triple-junctions, because hardly any efficiency gain can be achieved by a broader absorption window.

Optimizing the post-production annealing conditions of polymer:fullerene bulk heterojunction solar cells is vitally important, not only for fine-tuning the morphology - thus increasing the efficiency - but also for retaining the desired morphology during long-term operation. However, optimal conditions for annealing temperatures and times can only be chosen, once thermal transition temperatures and annealing kinetics of the blends are well-known. For instance, for systems with glass transition temperatures (T_g) lower than the maximum device operation temperature of 80°C, the mobility needed for morphology coarsening is present, leading to efficiencies decreasing in the course of time. Using advanced fast-scanning thermal analysis techniques, the formation of nuclei and growth of crystals during heating or cooling can be reduced or avoided, and thus, the fast crystallization processes occurring during annealing of the polymer:fullerene blends can be followed. In this study, non-isothermal and isothermal crystallization kinetics of the P3HT:PCBM (poly(3-hexyl thiophene: [6,6] -phenyl C₆₁ - butyric acid methyl ester) and P3HT:bis-PCBM blends are investigated and compared by using Rapid Heating Cooling Calorimetry (RHC).

Sensitized up-conversion (SUC) based on bi-component systems is currently indicated as a potential method to improve the efficiency of PV and PC technologies by photon energy managing. Although high SUC yields have been already demonstrated in solution by using low power non-coherent excitation sources, its application in real devices is still far. Indeed the conversion yield drops dramatically at solid state, where the short diffusion length of excitation energy strongly inhibits the diffusion controlled mechanisms which rule SUC photophysics. A general discussion to analyze the main environmental parameters affecting SUC quantum yield is presented here to find out the guidelines for the fabrication of high performance SUC materials.

The efficiency of organic light-emitting diodes (OLEDs) is limited since only a small fraction of the consumed electrical power is converted into visible light that is finally extracted to air. Most of the efficiency loss is caused by suboptimal radiative quantum efficiency (RQE) of the emitting guest-host system and by dissipating a huge part of the radiated energy to optical modes such as surface plasmons or waveguided modes, which cannot easily be extracted by common outcoupling structures. In order to increase the external quantum efficiency (EQE) of OLEDs new approaches are needed. Recent studies show that the EQE can be enhanced considerably by horizontally oriented emitters, a feature that is well known for fluorescent emitters and has lately been demonstrated in phosphorescent state-of-the-art OLEDs. By means of optical simulations we investigated the influence of non-isotropic emitter orientation on the effective RQE and the outcoupling factor. We show that in order to achieve a consistent efficiency analysis it is indispensable to account for possible deviations from isotropy. Ignoring these orientation effects leads to significant misinterpretation of the RQE and other factors, which determine the external quantum efficiency of a device. Furthermore, we demonstrate the huge potential for efficiency enhancement of mainly parallel dipole emitter orientation in both fluorescent and phosphorescent OLEDs.

In this work, we experimentally and theoretically investigate half-wavelength-thick Organic Light Emitting Diode (OLED) in a vertical microcavity. The latter is based on a quarter-wavelength multilayer mirror on one side and a thin aluminum semi-transparent layer on the other side. Two key parameters are studied for an optimal design of a cavity- OLED: the organic layer and the metallic cathode thicknesses. The experimental study shows that a 627 nm peak emission is obtained for a 127 nm-thick OLED hetero-structure. To achieve both desired optical transmission and effective electron injection, we investigate the influence of the Al cathode thickness on the performance of the microcavity devices. The experimental results are compared to those obtained by simulations of the emission spectra using the transfer matrix method and taking into account the organic emitter position inside the cavity.

Part of the light rays generated within a luminescent medium with a higher refractive index than that of the exit medium, typically air, undergo total internal reflection phenomenon (TIR); these rays will be trapped and guided into the emissive material and will not be extracted out of an OLED device for instance. Trapped light is reabsorbed and eventually converted into heat that will be detrimental to the device performance and lifetime. The amount of trapped energy is highly dependent on the values of the refractive indices involved in the multilayer stack constituting the light emitting device. The amount of trapped energy can be extensive and can even reach as much as 75% in certain cases. Solutions to improve the outcoupling efficiency are therefore attractive. In this paper we propose to use laser speckle to produce a random surface with controlled parameters to enhance the OLED outcoupling. A laser speckle pattern is transferred onto a photoresist which will be subsequently converted into a surface relief profile. The optical setup parameters drive the properties of such surface and thus the outcoupling properties. The resulting surface has a quasi-random shape which could be assimilated to a corrugated surface. We will show that these typical surfaces exhibit light extraction enhancement properties. The generated pattern is then transferred onto the exit interfaces of the emitting device. An extraction improvement close to a factor 3 is measured. We finally discuss a practical case for which the laser speckle shape is applied to texture the surface of encapsulating cover glasses in a top-emitting OLED on steel substrates.

We present the results of our research into the charge carrier dynamics of hybrid LEDs. For this, we have used, for the first time in these type of devices, Transient Electroluminescent measurements (TEL) that permit the calculation of charge mobilities from the slow rise of the transient signal originated by single pulses at different voltages.

Light-emitting transistors based on organic semiconductors have a range of potential advantages incl. tunability, flexibility, and high energy efficiency. A remaining challenge is the required high driving voltages that are caused by energy barriers at the interfaces between the metal electrodes and the organic material that hinder efficient charge carrier injection. In this work, we study the influence of two different self-assembled monolayers based on polar molecules deposited on the metal electrodes in terms of electrical and light-emitting properties of such organic transistors. The dipoles of the two monolayers are in opposite directions, so one monolayer is expected to lower the electrode work function while the other is expected to increase the work function. From an energy barrier perspective, it is thus expected that one monolayer should increase charge carrier injection while the other should reduce it. We find, however, that both types of monolayers improve both the electrical conductance and the emitted light intensity significantly. This is attributed to a change in interfacial microstructure due to the change in surface energy that results from the monolayer. This strategy is therefore a promising route to achieve higher device efficiencies in organic light-emitting transistors.

We describe a high power CW solid-state dye laser setup. With perylene orange in PMMA as gain medium an output power up to 800 mW at 576 nm and a tuning range between 565 and 595 nm is reached. The laser output shows good long time power stability. The durability can be adjusted by variation of the pump power. A feedback loop controls the laser output. At a setpoint of e.g. 100 mW, the laser output can be provided for more than eight hours with a low noise level (RMS < 10%). The spectral width of the laser emission is less than 3 GHz and can be tuned over more than 30 nm. A circular mode-profile is achieved with M2 < 1.4 [1]. Via intra-cavity second harmonic generation more than 1 mW of 290 nm UV-radiation is achieved. As nonlinear element a 7 mm BBO (Beta-Barium Borate) crystal is used. The UV laser radiation can be tuned over 10 nm. The theoretical limit of UV output is estimated to 3.5 mW. To our knowledge we present the first tunable CW polymer UV laser. While the output stability at the fundamental wavelength is reasonably good, in the UV region a significant enhancement of the noise level is observed. In addition to this the long time stability is reduced to few minutes. The limitation is mainly given by the photo-decomposition of the organic dye molecules.

We have studied the optical properties of a hybrid system consisting of cyanine dye J-aggregates (both PIC and TDBC) attached to a spherical microcavity. Instead of the commonly accepted chemical bonding of dye molecules to the surface of microspheres or deposition of dye-doped sol-gel film, in our experiments microspheres were coated with J-aggregate shell utilizing the layer-by-layer assembly of the ultrathin films. In this approach we aimed to take advantage of light confinement in the Whispering Gallery Modes (WGMs) microcavity by placing the emitter (shell of J-aggregates) just at the rim of the microsphere, where the resonant electromagnetic field reaches its maximum. A periodic structure of narrow peaks was observed in the photoluminescence spectrum of the J-aggregates, arising from the coupling between the emission of J-aggregates and the WGMs of the microcavity. The most striking result of our study is the observation of polarization sensitive mode damping caused by re-absorption of J-aggregate emission. This effect manifests itself in dominating emission from the transverse magnetic modes in the spectral region of J-aggregates absorption band where the transverse electric (TE) modes are strongly suppressed. Strong suppression of TE modes reflects preferential tangential orientation of transition dipole moment of J-aggregates in deposited microcavity shell. Observed polarization sensitive mode damping observed in the spectral region of high J-aggregate absorption can be used for suppression of unwanted modes in high Q optical resonators. We also demonstrate that the emission intensity can be further enhanced by depositing a hybrid layer of J-aggregates and Ag nanoparticles onto the spherical microcavity. Owing to the concerted action of WGMs and plasmonic hot spots in the Ag aggregates, we observe strongly enhanced Raman signal from the Jaggregates. Microcavities covered by J-aggregates and plasmonic nanoparticles could be thus useful for a variety of photonic applications in basic science and technology.

We examined the thermal crystallization of deposited films made of 2,5-bis(4-biphenylyl)thiophene (BP1T) and 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5), which are thiophene/phenylene co-oligomers (TPCOs). The deposited films of both BP1T and AC5 showed a microcrystalline phase, and initial microcrystals got larger 10 - 100 times with thermal treatment. Furthermore, we measured the optical properties of microcrystals of BP1T and AC5. At the energy density below the spontaneous amplified emission threshold, it was found that there was a big fluorescent difference between femtosecond laser irradiation and continuous lamp irradiation.

In this paper, we report the investigation of two-dimensional organic photonic crystal microcavity laser (2D OPCM). The gain medium consists of an Alq3:DCJTB layer deposited on a planar Si₃N4 photonic crystal microcavity. Both H2 and L3 photonic crystal cavities are studied in terms of quality factor and the resonance wavelength by 3D FDTD simulations. The structures are characterized under optical pumping by using a Nd:YAG frequency-tripled laser emitting at 355 nm with a repetition frequency of 10 Hz and a pulse duration of 6 ns. A laser peak at 652 nm is observed for both cavities with lasing thresholds of 0.014 nJ and 0.017 nJ for the H2 and the L3 cavities, respectively.

The help of the measurements (the methods are the NMR ¹H and ¹³C, infrared (IR) and the UV-absorption, Raman scattering of light, the fluorescence and the phosphorescence, the pumping of the lasers and lamps, the low-temperature of the spectroscopy in the solutions (77 K) and the Jet-spectroscopy of vapor (2,6 K) and others) and the calculations with application of the developed new complex of the computer of the programs realizing of the quantum-chemical LCAO-MO SCF extended-CI INDO / S of methods are investigated of the photophysical properties of some news and also some known the organic compounds for variations of the electronic and the spatial structures in the series is the mono-, bi-, three, penta- and quincli-cyclic and the bi- and the bis- phenyl, furyl- and tienyl- oxazoles and - oxadiazoles have been studied of the spectroscopy properties in the wavelength range max λ ^max _abs,osc = 208 ÷ 760 nm.

Absorption peak maxima of two organic dyes differing by the position of the methine unit differ by 61 nm in dioxane and 128 nm in acetonnitrile. The difference is not reproduced by TDDFT using ab initio or hybrid functionals. TDDFT errors are different between the molecules due to a different albeit small extent of charge transfer, leading to a qualitative failure of TDDFT to predict relative energetics of the dyes. The TDDFT errors in non-polar solvents (such as dioxane) could be corrected based on the approach of Peach et al. (J. Chem. Phy. 128, 044118 (2008)). Here, we focus on the effect on the absorption spectrum of a polar solvent, specifically of the different between the two molecules sign of the solvatochromic shift vs. dioxane. Using the corrrection due to Peach et al, the absolute TDDFT errors can be brought within accetable ranges of 0.2-0.3 eV with the PCM solvent model, and the blue shift vs.dioxane is reporoduced, although both dyes are predicted to exhibit positive solvatochromism. The inclusion of explicit solvent molecules forming hydrogen bonds with the dye did not appreciably change neither TDDFT energies nor the correction term. These results show the importance of a more careful assessment of computational errors in the strategy of computationaly dye design by changing the conjugation order, where they are expected to be more important than in the case of an extension of the size of conjugation, and more so when polar solvents are used.

The highest external quantum efficiency (EQE) of organic light emitting transistors (OLETs) to date has been achieved by using a 3-layer heterostructure configuration introduced by R. Capelli et al1. In this work, the behaviour of electron and hole currents in the 3-layer heterostructure OLET were investigated: the effect of the film properties of the dielectric and the active layers on the hole and electron currents were analysed. In the fabricated OLETs, electrons showed higher mobilities than holes. In contradiction, the 2-layer organic field effect transistor (OFET) consisting of two charge transporting layers with no light emitting layer indicated higher hole mobility. The results confirm that the light emitting layer significantly hinders the hole transport in the fabricated 3-layer heterostructure OLETs. Finally, the experimental results prove that reduced evaporation rate of the light emitting layer has a positive effect on the electron mobility within the device.

The polymer-based photonic devices have promise as optical components integrated in convenient microchip systems because of ease in the deposition and microfabrication of polymer materials. Furthermore, since the polymers can be easily doped with luminescent materials such as organic dyes, the organic light source devices are also considerable as the integrated optical components. Especially the self-formation method of the fiber type waveguide using the dyedoped photopolymers, called as self-written active (SWA) waveguide technique, brings a simple fabrication scheme of the light sources integrated in the polymer photonic circuit. It has been demonstrated that an in-line optical amplifier and a Fabry-Perot type lasing cavity can be obtained by using the SWA waveguide technique. In this study we have employed this technique to fabricate an incoherent light source with a wideband emission. A serially cascaded SWA waveguide doped with the different organic dyes could be fabricated with a single exposure process. The cascaded SWA waveguide could act as an incoherent light source under UV light irradiation. This device can be expected as a probing light source for the label-free microchip system, which would be available for the biological sensing, environmental measurements, and medical diagnosis.

Surface enhanced Raman spectroscopy (SERs) of functionalization HiPco single wall carbon nanotubes are performed. SWCNTs with covalently bonded amine groups were investigated using SERs assessing the impact of altering the electronic arrangement of the nanotube surface. The Raman frequencies of tangential, disorder modes and radial breathing modes have been used to make comparison between SWCNTs conjugated with Fluoresceinamine. Excitation of nanotube samples at wavelengths in resonance with both metallic and semiconductor nanotubes was undertaken.

In this work we present simple preparation of original trityl group containing glassy luminescent 6-styryl substituted derivatives of 2-(2-tert-butyl-4H-pyran-4-ylidene)malononitrile (DWK-1TB), 2-(2-tert-butyl-4H-pyran-4-ylidene)-2- ethyl-2-cyanoacetate (KWK-1TB), 2-(2-tert-butyl-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK-1TB) and 5-(2-tert-butyl-4H-pyran-4-ylidene)pyrimidine-2,4,6(1H,3H,5H)-trione (JWK-1TB). Their optical properties have been investigated. The absorption maxima of synthesized glasses is in region from 425 nm to 515 nm and emission maxima is from 470 nm to 625 nm in solution of dichloromethane. But absorption maxima of their solid films is from 425 nm to 500 nm and emission maxima is in range from 570 nm to 710 nm. Incorporation of bulky trityloxy ethyl groups combining with existing tert-butyl groups results in thin solid films formation of synthesized glasses from volatile organic solvents (chloroform, dichloromethane) without them being doped in any polymer. This makes them perspective for potential applications in organic light-emitting diodes and organic lasers by simple luminescent layer composition with cheap wet-casting approaches. All glasses show good thermal stability with thermal decomposition temperatures from 264° to 318°C and glass transition values up to 158°C for DWK-1TB. These thermal properties of synthesized glasses could make them also useful for potential applications in other optical materials such as materials for nonlinear optics.

Second-order nonlinear optical (NLO) polymers are emerging materials for next generation photonic and optoelectronic devices. The synthesis of high figure of merit (μ.β0) chromophores is crucial to the preparation of such materials, and we have previously reported the facile synthesis of a suite of chromophores with μ.β0 values of approx. 10,000 x 10-48 esu. These chromophores possess high permanent dipole moments, a property that, when combined with the high first order polarisability of these molecules, results in high NLO susceptibilities in a spatially ordered arrays of these compounds. However, their high permanent dipole moment renders them susceptible to dimerization and aggregation which has the undesirable effect of cancelling the hyperpolarizability vector associated with these molecules thereby reducing the bulk second order NLO susceptibility. Theoretical and experimental investigations have determined that the electro optical activity of NLO chromophores can be maximised through shape modification. The introduction of bulky substituents onto selected chromophore has been shown to cause the molecular shape to become more spherical (oblate) in nature, and in doing so, this limits intermolecular interactions. Previous work has focussed on the introduction of bulky substituents in order to diminish aggregation. We report here on the synthesis of thiazole based zwitterionic chromophores containing bulky substituents and their spectroscopic properties.

In this work we report the recent results of our investigation on visible emission properties of the polymer nanocomposites doped with oxide and fluoride nanopowders activated with praseodymium ions. The set of LaAlO3 and YF3 nanopowders differing in active ions concentration, was carefully characterized with respect of their structural and luminescent properties. Also the PMMA-based nanocomposites doped with these nanopowders were manufactured and characterized. The measurements of excitation and emission spectra as well as fluorescence decays enabled comparison of emission properties of nano-composites and original nanopowders and discussion of the main excitation and deexcitation mechanisms, responsible for the optical properties of developed materials. This, in turn will enable optimization of developed manufacturing technology.

The transport properties of two photovoltaic polymers, poly(3-hexylthiophene) (P3HT) and poly(2,7-carbazole) derivative (PCDTBT), and their polymer:fullerene bulk heterojunction (BHJ) are studied by space-charge-limited current (SCLC), dark-injection space-charge-limited current (DI-SCLC), and admittance spectroscopy(AS). For a nominally hole-only device, electrons leakage occurs. This results in a current larger than the theoretical SCLC and ill-defined DI-SCLC and AS signals. In order to prevent electron leakage, a hole-transporting but electron blocking/trapping thin layer is added between active layer and Au. The layer composed of copper phthalocyanine (CuPc) doped into an amine-based small molecule. Using this interlayer, well-defined carrier transit time can be obtained for mobility extraction. With a suitable interlayer to suppress undesirable carrier injection and transport, these techniques should find broad applications in the transport characterization of narrow gap photovoltaic polymers and BHJ blends.

The electrical behavior of organic solar cell (OSC) has been analyzed using a simple circuital model consisting on an ideal diode together with a series and parallel resistances (R_S and R_P respectively). Applying Kirchhoff's Laws to the circuit leads to a transcendental equation that can be solved numerically without approximations using the Lambert W function. Theoretical expression has been fitted to experimental current-voltage (I-V) curves under forward bias, obtaining fairly accurate values for the electrical parameters. This model has been validated comparing the extracted parameters for dark and illumination conditions of different devices. Results show good agreement for R_S, and ideality factor (η). Electrical parameters obtained in this work are also compared to those ones extracted using an approximated method often employed by other authors ¹. We conclude that approximated method leads to reasonable good values for R_S, R_P and η. However, in the case of R_p the voltage range chosen to fit the data with the exact method must be constrained to the fourth quadrant, where the role of parallel resistance is more critical. To validate the model, a bunch of organic solar cells with structure ITO/ poly(3,4-ethylenedioxythiophene)-poly (4-styrene sulfonate (PEDOT:PSS)/ poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6)C61 (PCBM)/Al has been fabricated in inert atmosphere. Different active layers were deposited varying the P3HT:PCBM ratio (1:0.64, 1:1, 1:1.55) and the active layer thickness (ranging from 100 to 280 nm). Devices are encapsulated inside the glove-box prior its characterization outside the glove-box. Electro optical characterization has been performed with a halogen lamp. Values extracted for RS range from 142 Ω to 273 Ω, values for RP range from 25 kΩ to 331 kΩ. Ideality factor ranges from 5 to 17.

While investigating polymer light emitting diodes (polymer-LEDs) fabricated by solution process, surface roughness influences electro-optical (E-O) characteristics. We expect that E-O characteristics such as luminance and power efficiency related to surface roughness and layer thickness of emitting layer with poly-9-Vinylcarbazole. In this study, we fabricated polymer organic light emitting diodes by solution process which guarantees easy, eco-friendly and low cost manufacturing for flexible display applications. In order to obtain high luminescence efficiency, E-O characteristics of these devices by varying parameters for printing process have been investigated. Therefore, we optimized process condition for polymer-LEDs by adjusting annealing temperatures of emission, thickness of emission layer showing efficiency (10.8 cd/A) at 10 mA/cm₂. We also checked wavelength dependent electroluminescence spectrum in order to find the correlation between the variation of efficiency and the thickness of the layer.

In-situ grown organic nanofibers have been prepared on metal electrodes patterned by electron beam lithography. A systematic investigation shows that the light emission from these nanofibers driven by an AC gate voltage depends nonlinearly on the amplitude of the AC gate voltage and linearly on the frequency of the gate voltage, which indicates that a model involving thermally assisted charge-carrier tunneling can be applied. The photoluminescence spectra of parahexaphenylene (p6P) and α-sexithiophene (6T) nanofibers illustrate that the emission color of the in-situ grown nanofibers can be tuned by depositing two types of discontinuous organic layers on the same platform. Electroluminescence from two nanofiber thin films suggests that the relative light emission contribution from the two organic molecules can be varied by changing, e.g., the nominal thickness of the two materials.

In photorefractive composites, we replace the commonly used fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) by the perylene bisimide dimer DiPBI. In samples, wherein poly-n-vinylcarbazole (PVK) is the charge transporting agent and 4-cyano-4-n-pentylbiphenyl (5CB) the nonlinear optical unit, we observe dramatic enhancements in the overall performance of the composites. When we replace PVK by N,N-diphenyl-N, N-bis(3-methylphenyl)-[1, 1-biphenyl]-4, 4-diamine (TPD) doped polystyrene (PS), the internal photocurrent efficiency is further improved by a factor 11.

Low molecular mass organic compounds which make thin films from volatile organic solutions would be great benefit in future organic light emitting systems. Two most important advantages could be mentioned. First - the repetition of synthesis of small molecules is better than for polymers. Second - wet casting methods could be used. In this work we are presenting optical, electroluminescence and amplified spontaneous emission properties of four original glassy forming compounds containing 2-tert-butyl-6-methyl-4H-pyran-4-ylidene fragment as backbone of the molecule. They has the same N,N-dialkylamino electron donating group with incorporated bulky trityloxy ethyl groups. The difference of these compounds is in electron acceptor group. One has 1H-indene-1,3(2H)-dione group, second has pyrimidine-2,4,6(1H,3H,5H)-trione group, third has malononitrile group and fourth has 2-ethyl-2-cyanoacetate. Absorption maximum of the compounds is between 420 and 500 nm and is red shifted from weaker acceptor group to stronger one. The electroluminescence efficiency for simple device ITO/PEDOT:PSS/Organic compound/BaF/Al is low. For the best one with malononitrile group it was 0.13 cd/A and 0.036 lm/W. It could be increased by optimising the sample geometry or adding addition layers for charge carrier transport and exciton blocking. But nevertheless the use of these compounds in organic light emitting devices in neat films is unlikely. Attached bulky trityloxy ethyl groups and tert-butyl group decrease interaction between the molecules thus allowing to obtain amplified spontaneous emission in neat thin films for all investigated compounds.

We present the most recent results of EU funded project P3SENS (FP7-ICT-2009.3.8) aimed at the development of a low-cost and medium sensitivity polymer based photonic biosensor for point of care applications in proteomics. The fabrication of the polymer photonic chip (biosensor) using thermal nanoimprint lithography (NIL) is described. This technique offers the potential for very large production at reduced cost. However several technical challenges arise due to the properties of the used materials. We believe that, once the NIL technique has been optimised to the specific materials, it could be even transferred to a kind of roll-to-roll production for manufacturing a very large number of photonic devices at reduced cost.

In this work we report the recent results of our investigations on synthesis of RE³⁺:Al₂O₃ nanopowders prepared by a method, in which organic compounds are used as a solvent and lanthanide organic derivatives, and discuss structural and luminescent properties of the powders and PMMA-based composites doped with these powders. The set of the Al₂O₃ nanopowder samples doped with RE³⁺ ions (where RE = Yb and Er) was manufactured and examined with respect of their structural and optical properties. The first PMMA-based composites doped with In this work we report the recent results of our investigations on synthesis of RE³⁺:Al₂O₃ nanopowders prepared by a method, in which organic compounds are used as a solvent and lanthanide organic derivatives, and discuss structural and luminescent properties of the powders and PMMA-based composites doped with these powders. The set of the Al₂O₃ nanopowder samples doped with RE³⁺ ions (where RE = Yb and Er) was manufactured and examined with respect of their structural and optical properties. The first PMMA-based composites doped with Al₂O₃:RE³⁺ nanopowders have been manufactured and characterized in the context of their mechanical, structural and luminescent properties. The investigations have confirmed applicability of developed synthesis method to manufacturing of optically active nanopowders of reasonably good structural quality and homogeneity, consisting of nanoparticles with average size in the range of several tens of nanometers as well as possibility of developing the active composite material, based on PMMA polymer host.

In this work we have compared the effect of using solvents with different boiling temperature on the spectroscopic emission proprieties of poly(n vinylcarbazole) (PVK) and PVK doped with Iridium complexes tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)₃) films, due to the different organization of the polymer on the substrate during the spin coating process. The modified molecular rearrangement affects the emission properties of the PVK material and the consequent energy transfer to the doping molecules. Both Static and dynamic emissions proprieties have been studied, for the case of pure PVK and PVK doped with different weight percentage of Ir(ppy)₃. Different devices have been prepared to test the change in electroluminescence spectral shape and in electrical characteristic and the final efficiencies of the devices have been evaluated.

This study used novel fluorescence based deep-blue-emitting molecules, namely BPVPDA, an organic fluorescence color thin film using BPVPDA exhibit deep blue fluorine with CIE coordinates of (0.13,0.16). The developed original Organic RGB color thin film technology enables the optimization of the distinctive features of an organic light emitting diode (OLED) and (TFT) LCD display. The color filter structure maintains the same high resolution to obtain a higher level of brightness, in comparison with conventional organic RGB color thin film. The image-processing engine is designed to achieve a sharp text image for a thin-film-transistor (TFT) LCD with organic color thin films. The organic color thin films structure uses organic dye dopent in limpid photo resist. With this technology , the following characteristics can be obtained: (1) high color reproduction of gamut ratio, and (2) improved luminous efficiency with organic color fluorescence thin film. This performance is among the best results ever reported for a color-filter used on TFT-LCD and OLED.

We report here on two stable polymorphs of the dinuclear complex [Re₂(μ-Cl)₂(CO)₆(μ-4,5- (Me₃Si)₂pyridazine)]. The compound belongs to the recently reported class of dinuclear luminescent Re(I) complexes of general formula [Re₂(μ-Cl)₂(CO)₆(μ-1,2-diazine)]. In the solid state, the complex exhibits a unique combination of unusual properties: (i) concomitant formation of two highly luminescent polymorphs, and single crystal-to-single-crystal conversion of one form into the other, (ii) remarkable differences in the absorption properties of the two polymorphs due to different redistribution of oscillator strength among the different excitons, and (iii) remarkable differences among the emission properties. In particular, a higher emission quantum yield was found in the solid state than in solution (measured to be 0.52 and 0.56 for the two polymorphs, almost one order of magnitude higher than that of the molecule in solution). Interest in luminescent materials able to efficiently emit in the solid state is continuously growing, because in most applications the dyes are used as solid films. Although rigid environments are expected to freeze rotovibrational relaxation pathways, luminescence efficiency often decreases in the solid state with respect to liquid solution due to concentration quenching, affecting both organic and organometallic emitters. However, an increasing number of molecular-based emitters exhibit enhanced solid state emission. Apart from the importance of bulky substituents in reducing concentration quenching effects, other intra- or inter-molecular phenomena have been invoked as well, such as conformational changes, π-π stacking, hydrogen bonds, or Jaggregates, which cause rearrangements of the energy levels and population. In these two polymorphs the enhancement of the emission with respect to the solution is most likely due to the restricted rotation of the Me3Si groups in the crystals, providing an interesting example of aggregation-induced emission effect (AIE). To provide more insight into the optical properties of the two polymorphs, we present a combined computational and experimental study in the framework of crystal optics in the aim to explore the role of molecular packing on the UV-visible absorption properties of the two known polymorphs of [Re2(μ-Cl)₂(CO)₆ (μ-4,5-(Me₃Si)₂pyridazine)].

In this paper, a combined experimental and theoretical study was performed on the P3HT:PCBM system used in organic photovoltaics. Fast-scanning differential chip calorimetry, an advanced thermal analysis technique, was used to simulate the thermal annealing used in the production of P3HT:PCBM solar cells to increase the degree of crystallinity, and thus efficiency. The main advantage of this technique for stuying the thermal annealing are the very high rates of heating and cooling that can be used, up to 10⁶ K.s^-1, permitting one to avoid crystallization during cooling. In parallel with the experimental study, the charge transfer between donor (P3HT) and acceptor (PCBM) at the interface is studied using density functional theory. The charge separation between donor and acceptor present for the ground state of the combined system, diminished when the first triplet was investigated. This was explained by the formation of a bridge state, formed after population by the LUMO with one electron. Such a molecular orbital can facilitate charge transfer.

Nanocrystalline semiconductor metal oxides have achieved a great importance in our industrial world today. They may be defined as metal oxides with crystal size between 1 and 100 nm. TiO2 nanosize particles have attracted significant interest of materials scientists and physicists due to their special properties and have attained a great importance in several technological applications such as photocatalysis, sensors, solar cells and memory devices. TiO2 nanoparticles can be produced by a variety of techniques ranging from simple chemical to mechanical to vacuum methods, including many variants of physical and chemical vapour deposition techniques. In the present research work we report the synthesis of TiO2 nanoparticles by Sol-Gel technique. The characterization of particles was carried out by XRD and XRF techniques. The importance and applications of these nanoparticles for solar cells are also discussed in this work.

We study the component composition of cyanine dye layers on different substrates (glass, mica, and sapphire) by the absorption spectroscopy. We found that the molecular layer contains isomers of the molecules being coated and aggregated components (dimers and J-aggregates). The relative concentrations of the components depend on the structure of dye and its surface concentration. The single laser pulses of several nanosecond length lead to irreversible changes in the structure of molecular nanolayers and result in the change of the relative concentrations of the layer components. Two types of the spatial orientation of the nanocomponents with different orientations with respect to the surface are formed. One of these types of the orientation transforms into another type under the action of pulsed laser radiation. The above changes were found for all the dielectric substrates studied.