This PDF file contains the front matter associated with SPIE Proceedings Volume 9137, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Due to their geometry, optical microcavities allow strong confinement of light between the mirrors and promise single mode operation at lowest possible lasing thresholds. Nevertheless, such devices suffer from losses not only due to parasitic absorption of the active or mirror layers, but especially via outcoupling of leaky and waveguided modes within the active layer. In this work, we present an organic microcavity sandwiched between high quality dielectric distributed Bragg reflectors. A highly conductive silver layer of 40nm thickness is added next to the active layer, leading to the formation of Tamm-Plasmon-Polaritons (TPP), one replacing the original cavity mode and shifting its resonance to the red, another one emerging from the long-wavelength sideband and moving to the blue. To avoid parasitic absorption introduced by such contacts, the silver layer is structured on the micrometer-scale using photolithography, yielding separated areas supporting either original cavity mode or red shifted TPP-resonances. This separation leads to a strong spatial trapping of the modes to only their resonant regions on the sample and can in turn be exploited to achieve complete three-dimensional confinement of photons. In elliptic holes produced in the metal layer, we observe the formation of Mathieu-Modes, leading to a reduction of the lasing threshold by six times. Facilitating triangular cuts in the silver layer, highly confined standing modes develop in the system, allowing a precise optimization of the spatial mode extension and reducing the threshold even further down to one order of magnitude below the threshold of an unstructured organic cavity. These results show that the introduction of absorptive metals, needed for the realization of an electrically driven laser, can in turn be harnessed to improve the characteristics of the device.

Three-dimensional organic microlasers were fabricated and lasing with low threshold was demonstrated. The cavities were fabricated via UV lithography from SU-8 doped with different laser dyes. The fabrication scheme relies on commercially available products and is both cheap and rapid. Cubic and stripe-shaped (Fabry-P´erot) microlasers were investigated. The periodic ray trajectories on which their lasing modes are localized were identified as a first step towards the exploration of general three-dimensional microlasers.

This study demonstrates that attaching micro-lens array films (MAFs) on the substrate and reducing the substrate thickness of OLED can significantly increase the power efficiency, while simultaneously reduce image blurring. Using a point source model, based on Monte-Carlo ray-tracing method, the power efficiency enhancement and reduction of blur effect are respectively discussed in three different regions of the MAFs attached substrate: partially reflecting region, transmitting region, and light guiding region of micro-lenses. According to the equations, derived with regard to the substrate thickness and the displacement from the point source and based on geometric relations corresponding to different regions, reducing the substrate thickness will result in different levels of enhancement for power efficiency in different regions. By comparing OLED with MAFs and bare OLED, the overall enhancement ratio of power efficiency is 1.46, which can be further improved to 1.78 by reducing the substrate thickness from 700 μm to 50 μm, and the blurlength is reduced from 942 μm to 255 μm. The simulation results demonstrate the possibility of applying MAFs to OLED for higher power efficiency without image degradation in display and lighting applications.

Currently, the low yield, high power loss, and poor stability of organic light emitting diodes (OLEDs) panels are remaining as the obstacles to the fast growth of the OLED industry, especially for the lighting application. The p-i-n OLEDs have been widely recognized as the promising method to circumvent these bottleneck factors, due to the unique merit of the electrical doping to enable low power loss. In p-i-n OLEDs, the frequently used n-doped electron transport layers (n-ETL1) such as n-BCP, n-Alq₃ possess markedly lower conductivities but better capabilities of injecting electrons into ETL such as BCP, Alq₃, as compared to another class of n-doped ETLs (n-ETL₂), e.g., n-NTCDA, n-PTCDA, n-C₆₀. Thus, in order to minimize the electron loss, we provide the structure of uniting two n-doped layers, cathode/ n-ETL₂/ n-ETL₁/ ETL. In p-i-n OLEDs, the hole current injected from the single p-doped hole transport layer (p-HTL) into the neat HTL must be limited, because the higher conductivity p-HTL has the higher lying highest occupied molecular orbital (HOMO) level, leading to a larger hole transport energy barrier (φB) at the interface with the neat HTL. Therefore, in order to minimize the hole loss, we suggest the structure of uniting two p-HTLs, anode/ p-HTL2/ p-HTL₁/ HTL. The p-HTL₂ possesses high-lying HOMO level and thereby high conductivity, decreasing the ohmic loss in the hole conduction; the p-HTL₁ features a low-lying HOMO level, reducing the φB.

We present novel numerical techniques for the simulation of the light outcoupling from state of the art organic light-emitting diodes (OLED). For the spatial discretization we use the finite element method which we apply in the frequency domain. To account for the large horizontal extension of the OLED we apply a recently proposed approach based on the Floquet transform which allows to restrict the calculations to the unit cell of a (quasi) periodic structure. Optically thick layers are efficiently treated by a plane wave expansion which we combine with the Finite Element Method by the domain decomposition method. We benchmark the new simulation tools for highly efficient state of the art OLED light extraction structures.

We demonstrate organic imaging sensor arrays fabricated on flexible plastic foil with the solution processing route for both photodiodes and thin film transistors. We used the photovoltaic P3HT:PCBM blend for fabricating the photodiodes using spin coating and pentacene as semiconductor material for the TFTs. Photodiodes fabricated with P3HT:PCBM absorb in the green part of the visible spectrum which matches with the typical scintillator output wavelength. The arrays consist of 32x32 pixels with variation in pixel resolution of 200μmx200μm, 300μmx300μm and of 1mmx1mm. The accurate reproducibility of shadow images of the objects demonstrates the potential of these arrays for imaging purposes. We also demonstrate that the crosstalk is relatively insignificant despite the fact that the active photodiode forms a continuous layer in the array. Since both photodiodes and TFTs are made of organic material, they are processed at low temperatures below 150°C on foil which means that these imaging sensors can be flexible, light weight and low cost when compared to conventional amorphous silicon based imaging sensors on rigid substrates. In combination with a scintillator on top of the arrays, we show the potential of these arrays for the X-ray imaging applications.

Charge transfer (CT) mechanisms are crucial for device performance in organic electronics, but they are still not understood on a fundamental level. Here we want to show that in situ IR spectroscopy is very well suited to investigate CT effects in organic semiconductors in a qualitative and quantitative way. We study the ambipolar transport material 4,4´-bis(N-carbazolyl)-1,1´-biphenyl (CBP) as matrix and cesium carbonate (Cs₂CO₃) as n-dopant. To achieve doped layers, both materials were evaporated simultaneously. The system is one of the rare ones for n-doping of organic layers. In the spectra of the doped layers, additional absorption bands appear in the mid IR range. These can be assigned to the negatively charged matrix molecules that indicate electron transfer. The charged molecules exhibit these different absorption bands, as the charge transfer leads to a change in bond length and bond strength of the molecules. Our results very well agree with density functional theory calculations of the vibrational spectra of both, charged and non-charged molecules. By fitting the spectra of the doped layers as a superposition of the vibrational oscillators of neutral and charged species, we were able to quantify the amount of charged matrix molecules and to determine the doping efficiency of the investigated systems. For CBP n-doped with Cs₂CO₃ a hindrance of the CT due to air exposure could be observed.

In this work, we present patterned water-responsive coatings, which alter both their topological and optical properties. The polymer coatings are based on a hydrogen-bonded cholesteric liquid crystalline polymer network. A two-step photopolymerization procedure leads to a patterned coating with repeating liquid crystalline and isotropic areas. The cholesteric liquid crystalline areas reflect green light, whilst the isotropic areas are transparent for visible light. Treatment with alkaline solution results in a hygroscopic polymer salt coating. When placed in demineralized water, the polymer films swells, leading to an enhancement of the surface topography structure in which the liquid crystalline areas swell more. Moreover, the pitch of the helical organization in the cholesteric areas increases due to this swelling leading to a color change from green to red.

Enabled by the broad spectral gain and the efficient energy conversion in the active material, organic semiconductor lasers are promising for spectroscopic applications and have been recently applied for high resolution absorption and transmission spectroscopy. Here, we present the application of organic semiconductor DFB laser (DFB-OSL) as excitation source in Raman spectroscopy. Utilizing an efficient small molecule blend of tris (8-hydroxyquinoline) aluminum (Alq₃) doped with the laser dye 4-(dicyano-methylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM), our encapsulated DFB-OSL achieved a high slope efficiency of 7.6%. The organic lasers were tested in the inverted and upright Raman microscope setups, using free-beam and fibre coupling, respectively. In the free-beam configuration, the emission beam was guided directly into an inverted microscope. Employing a spectrally tunable DFBOSL as the excitation source, we measured the Raman spectra of sulfur and improved the Raman signals for a given optical filter configuration. In the fibre coupling configuration, the organic laser was coupled into a 50 μm multi-mode optical fibre with an efficiency of 70 %. We utilized a round-to-line fibre-bundle for an efficient collection and transfer of Raman light to a spectrograph, by keeping a sufficient spectral resolution. Raman tests were performed on cadmium sulfide and cyclohexane. Our novel fibre-coupled organic laser provides a modular laboratory Raman system.

Chemically synthesized gold-silica nanorods were incorporated into the active layer of solution processed organic photovoltaic devices to enhance the absorption of light by the surface plasmon resonance effect in metallic nanoparticles. Solution processed polymer:fullerene and small molecule:fullerene bulk heterojunction devices were studied. The polymer donors include regioregular poly(3-hexylthiophene) (P3HT) and low bandgap poly[2,6-(4,4-bis-(2-ethylhexyl)- 4N-cyclopenta[2,1-b:3,4-b’] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT). For the small molecule device, 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']-dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5-yl) benzo[c][1,2,5]thiadiazole) (p-DTS(FBTTh₂)₂) was used as the donor. The donors are blended with either [6,6]-phenyl- C₆₁-butyric acid methyl ester (PC₆₀BM) or [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM). The gold-silica nanorods have an aspect ratio (length/diameter) of 3.2 and 2.3 and a shell thickness of ~10 nm. Prior to spin coating, the nanorods were added directly to the donor:acceptor blend solution in either chlorobenzene or dichlorobenzene at different weight percentage of the total donor:acceptor weight. The transverse and longitudinal surface plasmon resonance peaks of the gold-slica nanorods overlap with the absorption spectra of all three donor:acceptor blends to differing degrees. As a result, the power conversion efficiency of optimized plasmonic P3HT:PC₆₀BM and PCPDTBT:PC₇₀BM devices with conventional structure under AM1.5G illumination at 100mW/cm² were increased by 9.3% (to 3.42%) and 20.8% (to 4.11%) respectively relative to the control device without nanorods. For the p-DTS(FBTTh₂)2:PC₇₀BM device, the relative improvement as compared to the control device was 24.2% (to 8.01%).

Phenomenon of vector polyphotochromism was observed in some high-efficient polarization-sensitive materials dependent on the radiant exposure when material was illuminated with linearly polarized actinic light. The phenomenon has purely vector nature, since under probing by unpolarized light, the transmission spectra of the irradiated and unirradiated area of the material are practically identical. However, an essential change in the transmission spectrum of the material was observed by placing the irradiated area between crossed polarizers when the orientation of the axis of induced anisotropy was of 45 degrees relative to the axes of the polarizers. The dispersion of photoanisotropy was studied at different exposure values. Kinetic curves of the photoanisotropy were obtained for wavelength of 532 nm and 635 nm of probing beam for different values of exposure (30, 60 and 250 J/cm²) with linearly polarized actinic light (457 nm). The dispersion curves of the photoanisotropy were obtained for these values of exposure showing an anomalous behavior for exposures above of 30 J/cm². This phenomenon was observed in specially synthesized organic materials based on azo dyes introduced in a polymer matrix. The difference between optical densities was obtained for polarized light with a wavelength of 532 nm and 635 nm at different exposures, which makes the prospect the dynamic polarization spectral filters controlled by light and the spectrally selective dynamic polarization holographic gratings to be created.

In this work, the P3HT:PCBM:pentacene (1:0.8:0.065 by weight) inverted polymer solar cells with roughened Aldoped ZnO (AZO) nanorod array were fabricated. The pentacene doping could modulate the hole mobility and the electron mobility in the active layer. The optimal hole-electron mobility balance ( µ_h/ µ_e=1.000) was achieved as the pentacene doping ratio of 0.065. The 100-nm-long AZO nanorod array were formed as the carrier collection layer and the carrier transportation layer of the inverted polymer solar cells using the combination techniques of the laser interference photolithography method and the wet etching process. Because the AZO nanorod array was prepared using the wet etching process, more defects were formed on the sidewall surface of the AZO nanorods. In this work, the photoelectrochemical (PEC) method was used to grow Zn(OH)₂ and Al(OH)₃ thin layer on the sidewall surface of the AZO nanorods, which could reduce the carrier recombination path in the inverted polymer solar cells. Compared with the P3HT:PCBM:pentacene (1:0.8:0.065) inverted polymer solar cells without PEC treatment, the short circuit current density and the power conversion efficiency of the inverted polymer solar cells with PEC treatment were increased from 14.56 mA/cm² to 15.85 mA/cm² and from 5.45% to 6.13%, respectively. The enhancement in the performance of the inverted polymer solar cells with PEC treatment could be attributed to that the PEC treatment could effectively passivate the defects on the surface of the AZO nonorods.

Deoxyribonucleic acid (DNA), as one kind of biopolymer, has recently emerged as an attractive optical material, showing promise in making versatile optoelectronic devices. In the present study, we report the fabrication and characterization of DNA biopolymer nanocomposite with tunable conductivities and the application in bistable memory device. DNA nanocomposite consisting of DNA biopolymer and silver nanoparticles is synthesized using a phototriggered method. The nanocomposite exhibits tunable conductivities when exposed to UV light under different periods of time. The electrical conductivity is suggested to be dependent on the quantity and the distribution of silver nanoparticles formed in DNA biopolymer. In addition, a memory device based on DNA biopolymer nanocomposite is demonstrated. The operation of different conductivity states can be adjusted by the concentration of nanoparticles. The device shows bistability of current, and presents a stable write-read-erase cycle. Detailed performance of the DNA-based memory device will be presented and discussed.

Efficiency of an organic solar cell is very sensitive to fabrication procedure. One of the most important parameters is active layer morphology which radically influences several cell properties such as generation rate, layer resistance, charge carrier motilities etc. Meantime, in P3HT:fullerene based solar cells, using PCBM would improve the morphology and increase the cost simultaneously. On the other hand, C₆₀ is way less expensive, but its limited solubility in common solvents would influence cell performance. To benefit from its cost and as the formation of C₆₀ aggregates and P3HT crystallinity significantly depend on the solvent which would influence several cell properties, one should find a proper solvent. To make an in-depth investigation of solvent effects, experimental investigations will not suffice and using a precise model to fit the data and extract hidden parameters would help us to have a deep understanding of the cells physical basis. In this work, an optimization algorithm is employed to fit a numerical model simulation results with experiments and the model benefits from a field dependent series resistance. Simulation results indicate that a suitable solvent mainly improves the cell performance by changing 3 basic parameters which are G, μ_n and μ_p. Additionally, although parameters such as E_g and DC dielectric constant are very crucial in determining power conversion efficiency, they cannot be effectively improved changing the solvent. It is reported that the cell prepared by Cl-naph:CB performs better than the other cells. Considering our results, it can be attributed to its larger G, μ_n and μ_p. It also has the least R_s and the largest R_sh among all other P3HT:C60 based cells (which is caused by its higher mobility-carrier density product). This work gives experimentalists an idea of how they should choose a solvent. The results can also be generalized to find a proper solvent for other active layer materials.

Mesoporous TiO₂ material was synthesized from dissolution ilmenite as well as from titanium chloride precursor via a sol-gel process in acidic aqueous solution. The properties of these materials were characterized with several analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide angle X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and Barrett-Joyner-Halenda (BJH) analysis. The mesoporous TiO₂ materials calcinated at various temperatures were found to have high value surface areas. The photovoltaic of photo-anode build from the mesoporous TiO₂ was characterized with I-V Keitley Multimeter, and it was found that photovoltaics fabricated using the mesoporous TiO₂ have a good performance. Such a high photovoltaic activity is explained with large surface area and small crystal size.

In this work, we present a comparative study of optimized AZO electrodes deposited by Atomic Layer Deposition (ALD) with commercial ITO in terms of electrical, optical and structural properties. Despite a lower figure of merit mainly due to a higher sheet resistance, AZO-based OLEDs are shown to present a current density five times higher than ITO-based ones for the same applied voltage. These AZO electrodes fabricated by ALD could thus be promising substitutes for conventional ITO anodes in organic electronic devices.

4-(dicyanomethylene)-2-methyl- 6-(p-dimethylaminostyryl)-4H-pyran (DCM) is well known red laser dye which can be used also in solid state organic lasers. The lowest threshold value of amplified spontaneous emission was achieved by doping 2wt% of DCM molecule in tris-(8-hydroxy quinoline) aluminium (Alq₃) matrix. Further increase of dye concentration also increases threshold value. It is due to large intermolecular interaction which reduce photoluminescence quantum yield. Compounds with small intermolecular interaction and which exhibit similar amplified spontaneous properties as DCM could be useful for solid state organic lasers. In the work photoluminescence and amplified spontaneous emission properties of two DCM derivatives in poly (methyl methacrylate) (PMMA) matrix were investigated. Bulky trityloxyethyl groups are attached to the donor part of investigated molecules. These groups reduce intermolecular distance wherewith reduce photoluminescence quenching. More than one order of magnitude lower excitation threshold energy of the amplified spontaneous emission was achieved in doped polymer films with investigated compound in comparison to doped polymer with DCM. It means that the investigated compound is more perspective as a laser material compared to previously study.

Organic materials are becoming more popular due to their potential application in electronics. Low molecular weight materials possible produce from solution are in special consideration. It gives the possibility to avoid both thermal evaporation in vacuum, and use of polymers in thin film preparation process. Indandione fragment containing azobenzene compounds are one of such materials. These compounds are good candidates for use in design of novel molecular electronic devices due to their possibility to form amorphous structure from solution thus allowing developing flexible, small size systems with low production costs. In this work three indandione fragment containing azobenzene compounds were investigated. Difference between these compounds is bulky groups which assist formation of amorphous thin film. Absorption spectra of the investigated compounds are similar to P3HT but with higher absorption coefficient. Molecule ionization and electron affinity levels of these compounds are around -5.45eV and -3.80eV, respectively. Combining PCBM with investigated compounds could lead to difference between electron affinity levels maximum of 0.15eV. It is several times less compared to ~1eV for P3HT:PCBM system. Higher difference between the donor ionization level and the acceptor affinity level could also be obtained which should lead to the higher open circuit voltage.

In this paper we present electrical and electro-optical (EO) measurements of polymer thin films on silicon substrates. A method is presented on how to interpret ellipsometric measurements of the (EO) coefficient on silicon substrate by taking into account multiple reflections in each sample layer. The obtained EO coefficients on silicon substrate are compared to measurements for indium tin oxide (ITO) coated glass substrates. Electrical measurements are performed to analyze the conduction mechanisms inside the polymer film. Based on the presented experimental data different models are discussed in order to explain the differences in current density during poling between ITO coated glass substrates and silicon substrates.

Charge injection barriers caused by a misalignment of energy levels are of major concern in organic semiconductor devices. One possibility to improve charge carrier injection is the application of an additional layer at the interface between the contact and the organic semiconductor. Self-assembled monolayers (SAMs) have been proven to form stable and well defined layers on various contact materials. Depending on their molecular dipole they can lower or raise the work function of a material and are therefore very well suited as injection layers. Since SAMs can be processed from solution they form a relevant material for printed organic electronics. The orientation of the SAM and thus important interface properties like the interface dipole and the work-function shift are influenced by various parameters such as concentration of the molecule in solution, immersion time and cleanliness of the solution and of the substrate. Infrared-reflection-absorption-spectroscopy (IRRAS) is a very sensitive tool to measure changes in the orientation of SAMs on metal substrates. We performed IRRAS measurements on SAMs consisting of perfluorinated decanethiol (PFDT) on evaporated gold films in order to probe the orientation, ordering and quality of the SAMs. By systematic variation of immersion time and concentration, we were able to conclude on the process steps of layer formation. Taking into account realistic printing circumstances, we also investigated the impact of oxygen in the solvent and the gold substrate on the layer formation process.