Optics in Energy: the power of optical solutions

© 2010 Optical Society of AmericaThe definitive version of this paper is available at: http://dx.doi.org/110.1364/OE.18.0000A1DOI: 10.1364/OE.18.0000A

High-performance C-60 n-channel organic field-effect transistors through optimization of interfaces

© 2008 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.3020533 |DOI: 10.1063/1.3020533High-performance C-60 organic field-effect transistors (OFETs) have been obtained by engineering the essential electrode/semiconductor and dielectric/semiconductor interfaces. By using calcium (Ca) as the source and drain electrodes, the width-normalized contact resistance (RCW) at the electrode/semiconductor interface for devices with channel lengths ranging from 200 down to 25 mu m could be reduced to a constant value of 2 k Omega cm at a gate-source voltage (V-GS) of 2.6 V, leading to electrical properties that are dominated by gate-modulated resistance of the channel as in conventional metal-oxide-semiconductor field-effect transistors. Channel length scaling of the source-drain current and transconductance is observed. Average charge mobility values of 2.5 cm(2)/V s extracted at V-GS < 5 V are found independent of channel length within the studied range. Besides high mobility, overall high electrical performance and stability at low operating voltages are demonstrated by using a 100-nm-thick high-kappa gate dielectric layer of aluminum oxide (Al₂O₃) fabricated by atomic layer deposition and modified with divinyltetramethyldisiloxane-bis (benzocyclobutene). The combined operating properties of these OFETs, obtained in a N-2-filled glovebox, are comparable to the best p-channel OFETs and outperform those of amorphous silicon thin-film transistors

Encapsulation of pentacene/C₆₀ organic solar cells with Al₂O₃ deposited by atomic layer deposition

© 2007 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.2751108DOI: 10.1063/1.2751108Organic solar cells based on pentacene/C₆₀ heterojunctions were encapsulated using a 200-nm-thick film of Al₂O₃ deposited by atomic layer deposition (ALD). Encapsulated devices maintained power conversion efficiency after exposure to ambient atmosphere for over 6000 h, while devices with no encapsulation degraded rapidly after only 10 h of air exposure. In addition, thermal annealing associated with the ALD deposition is shown to improve the open-circuit voltage and power conversion efficiency of the solar cells

Process of changing the refractive index of a composite containing a polymer and a compound having large dipole moment and polarizability and applications thereof

Fused ring bridge, ring locked dyes that form thermally stable photorfractive compositions. The fused ring bridge structures are .pi.-conjugated bonds in benzene-, naphthalene- or anthracene-derived fused ring systems that connect donor and acceptor groups. The donor and acceptor groups contribute to a high molecular dipole moment and linear polarizability anisotropy. The polarization characteristics of the dye molecules are stabilized since the bonds in the fused ring bridge are not susceptible to rotation, reducing the opportunity for photoisomerization. The dyes are compatible with polymeric compositions, including thermoplastics. The dyes are electrically neutral but have charge transport, electronic and orientational properties such that upon illumination of a composition containing the dye, the dye facilitates refractive index modulation and a photorefractive effect that can be utilized advantageously in numerous applications such as in optical quality devices and biological imaging

Thermally stable molecules with large dipole moments and polarizabilities and applications thereof

Disclosed are fused ring bridge, ring-locked dyes that form thermally stable photorefractive compositions. The fused ring bridge structures are .pi.-conjugated bonds in benzene-, naphthalene- or anthracene-derived fused ring systems that connect donor and acceptor groups. The donor and acceptor groups contribute to a high molecular dipole moment and linear polarizability anisotropy. The polarization characteristics of the dye molecules are stabilized since the bonds in the fused ring bridge are not susceptible to rotation, reducing the opportunity for photoisomerization. The dyes are compatible with polymeric compositions, including thermoplastics. The dyes are electrically neutral but have charge transport, electronic and orientational properties such that upon illumination of a composition containing the dye, the dye facilitates refractive index modulation and a photorefractive effect that can be utilized advantageously in numerous applications such as in optical quality devices and biological imaging

Variable-ratio power splitters using computer-generated planar holograms on multimode interference couplers

© 2009 Optical Society of AmericaThe definitive version of this paper is available at: http://dx.doi.org/10.1364/OL.34.000512DOI: 10.1364/OL.34.000512Variable-ratio power splitters using computer-generated planar holograms on multimode interference couplers are analyzed. The coherent wave at the device input is transformed to the desired output using numerically calculated refractive index perturbations on multimode channel waveguides at half the beat length. Devices are fabricated on the silicon-on-insulator platform and characterized at a wavelength of 1.55 μm . Power-splitting ratios are varied by changing the hologram etch depth and the hologram length

A comprehensive analysis of the contributions to the nonlinear optical properties of thin Ag films

© 2010 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.3429118DOI: 10.1063/1.3429118The nonlinear optical properties of 20 nm thick Ag films are investigated by time-resolved white- light continuum pump-probe experiments in both transmission and reflection mode. The dynamics of changes in permittivity Δε are measured at wavelengths between 500 to 700 nm. The data is fitted to a modified Drude model in the frequency domain and to a two-temperature model in the time domain. Changes in the individual Drude parameters are calculated as a function of time. A single, coherent model is proposed based on these fittings that describes the dynamics of the nonlinear optical properties of Ag, which could be used to model the nonlinear responses of multilayer structures containing thin films of Ag. The physical origins of the observed responses are discussed

ITO-free large-area organic solar cells

© 2010 Optical Society of AmericaThe definitive version of this paper is available at: http://dx.doi.org/10.1364/OE.18.00A458DOI: 10.1364/OE.18.00A458We report on large-area pentacene / C60 organic solar cells in which indium-tin-oxide (ITO) is replaced with a conductive polymer electrode and a 5 μm-thick metal grid is used to reduce resistive power losses. The performance of cells with the polymer electrode was compared with that of pentacene / C₆₀ devices using ITO as the transparent electrode. For large-area devices (7.3 cm²) on glass substrates with an integrated metal grid, the performance of a device with the polymer electrode is comparable to that of a device with an ITO electrode combined with a grid

Synthesis of high-T_g hole-transporting polymers with different redox potentials and their performance in organic two-layer LEDs

Organic hole transport materials are used in organic LEDs, where they substantially improve device performance if placed as a hole transport layer (HTL) between the anode and the electroluminescent layer (EL). Soluble polymeric hole transport materials with high glass transition temperatures are of particular interest, because they allow for efficient device fabrication through spin casting of the HTL, and high glass transition temperatures have been found to improve thermal and long-term stability of the device. The redox potential of the hole transport material determines the facility of charge injection at the anode/HTL and the HTL/EL interfaces, thus affecting the overall device efficiency. We have synthesized a series of soluble hole-transporting polymers with glass transition temperatures in the range of 130 degrees C to 150 degrees C. The synthetic method allows facile substitution of the hole transport functionality with electron-withdrawing and electron-donating groups, which permits tuning of the redox potential of the polymer. These polymers have been used as HTL in tow-layer devices ITO/HTL/Alq/Mg. The maximum external quantum efficiency increase, if the redox potential is changed to facilitate reduction of the hole transport material at the HTL/EL interface. Electron-deficient derivatives show higher external quantum efficiencies. The device stability, however, follows the opposite trend

Columnar Discotic Liquid-Crystalline Oxadiazoles as Electron-Transport Materials

A range of discoid species with benzene or triazine cores and three (trialkoxyaryl)oxadiazole arms have been synthesized. 1,3,5-tris{5-[3,4,5-tris(octyloxy)phenyl]-1,3,4-oxadiazol-2-yl}benzene has been studied in detail; it exhibits a columnar discotic liquid-crystalline mesophase between 38 and about 210 °C. The time-of-flight electron mobility at room-temperature varies from about 10^(-3) to 10^(-4) cm^2 V^(-1) s^(-1), indicating these materials may find applications in organic electronics