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21 Jan 2008

Volume 92, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages)

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha
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Performance of bulk heterojunction photovoltaic devices prepared by airbrush spray deposition

R. Green, A. Morfa, A. J. Ferguson, N. Kopidakis, G. Rumbles, and S. E. Shaheen

Appl. Phys. Lett. 92, 033301 (2008); http://dx.doi.org/10.1063/1.2836267 (3 pages) | Cited 10 times

Online Publication Date: 22 January 2008

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We have used airbrush spray deposition to fabricate organic photovoltaic devices with an active layer composed of a blend of poly(3-hexylthiophene) and [6,6]-phenyl-C61 butyric acid methyl ester. Working devices were prepared in ambient conditions from a variety of common organic solvents; active layers prepared from chlorobenzene exhibit improved homogeneity, resulting in narrower distributions of the relevant device parameters. Further studies on devices prepared from chlorobenzene showed that annealing at 120 °C for 10 min resulted in optimum performance, and that an active layer thickness of 150 nm resulted in a maximum efficiency of 2.35% under AM1.5 illumination at 1 sun.
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85.60.Bt Optoelectronic device characterization, design, and modeling
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Integrated organic electronic based optochemical sensors using polarization filters

Elke Kraker, Anja Haase, Bernhard Lamprecht, Georg Jakopic, Christian Konrad, and Stefan Köstler

Appl. Phys. Lett. 92, 033302 (2008); http://dx.doi.org/10.1063/1.2837410 (3 pages) | Cited 1 time

Online Publication Date: 23 January 2008

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A compact, integrated photoluminescence based oxygen and pH sensor, utilizing an organic light emitting device (OLED) as the light source and an organic photodiode (OPD) as the detection unit, is described. The main challenge in such an integrated sensor is the suppression of the excitation light at the detector, which is typically by many orders of magnitude higher in intensity than the emitted fluorescence. In our approach, we refrain from utilizing edge filters which require narrow band excitation sources and dyes with an adequate large Stokes shift. We rather developed an integrated sensor concept relying on two polarizers to separate the emission and excitation light. One polarizer is located right after the OLED, while the other one, oriented at 90° to the first, is placed in front of the OPD. The main advantage of this solution is that any combination of excitation and emission light is acceptable, even if the two signals overlap spectrally. This is especially important for the use of OLEDs as the excitation sources, as these devices typically exhibit a broad spectral emission.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
85.60.Jb Light-emitting devices
85.60.Dw Photodiodes; phototransistors; photoresistors
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Cavity effects on light extraction in organic light emitting devices

Jaewon Lee, Neetu Chopra, and Franky So

Appl. Phys. Lett. 92, 033303 (2008); http://dx.doi.org/10.1063/1.2830820 (3 pages) | Cited 12 times

Online Publication Date: 24 January 2008

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We have demonstrated that the light extraction efficiency of an organic light emitting device is a strong function of device geometry. Specifically, we have found that the ratio of the extracted mode to the substrate-guided mode varies from 22% to 55% depending on the location of the recombination zone. Our simulation results also indicate that more light is trapped in the substrate as the optical length of device increases. We further show that the light intensity profile varies from a Lambertian shape to a non-Lambertian shape depending on the device geometry due to the cavity effect.
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85.60.Jb Light-emitting devices
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Millisecond switching in solid state electrochromic polymer devices fabricated from ionic self-assembled multilayers

Vaibhav Jain, Hank M. Yochum, Reza Montazami, and James R. Heflin

Appl. Phys. Lett. 92, 033304 (2008); http://dx.doi.org/10.1063/1.2834818 (3 pages) | Cited 4 times

Online Publication Date: 24 January 2008

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The electrochromic switching times of solid state conducting polymer devices fabricated by the ionic self-assembled multilayer method has been investigated. The devices were composed of bilayers of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) and poly(allylamine hydrochloride) on indium tin oxide substrates. Devices fabricated from 40 bilayer thick films have coloration and decolaration switching times of 31 and 6 ms, respectively, with low applied voltage (1.4 V) for an active area of 0.6 cm2. The switching times have been shown to decrease with the active area of the electrochromic device suggesting that even faster electrochromic switching times are possible for devices with smaller areas.
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42.79.-e Optical elements, devices, and systems
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Simultaneous color and luminance control of organic light-emitting diodes for mood-lighting applications

Anne Köhnen, Klaus Meerholz, Malte Hagemann, Matthias Brinkmann, and Stefan Sinzinger

Appl. Phys. Lett. 92, 033305 (2008); http://dx.doi.org/10.1063/1.2837409 (3 pages) | Cited 7 times

Online Publication Date: 24 January 2008

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Organic light-emitting diodes (OLEDs) using polymer blends as a single emissive layer often suffer from large color shifts with changing operational voltage. Until now, such devices cannot stand the critical demands of lighting industry. In this contribution, we introduce a pulse-width-modulation-based driver concept, enabling the user to simultaneously and independently adjust color and luminance of a single device with two contacts. This concept makes color-shifting OLEDs highly interesting for “mood-light” applications.
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85.60.Jb Light-emitting devices
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Polymer based organic solar cells using ink-jet printed active layers

T. Aernouts, T. Aleksandrov, C. Girotto, J. Genoe, and J. Poortmans

Appl. Phys. Lett. 92, 033306 (2008); http://dx.doi.org/10.1063/1.2833185 (3 pages) | Cited 13 times

Online Publication Date: 25 January 2008

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Ink-jet printing is used to deposit polymer:fullerene blends suitable as active layer for organic solar cells. We show that merging of separately deposited ink droplets into a continuous, pinhole-free organic thin film results from a balance between ink viscosity and surface wetting, whereas for certain of the studied solutions clear coffee drop effect occurs for single droplets; this can be minimized for larger printed areas, yielding smooth layers with minimal surface roughness. Resulting organic films are used as active layer for solar cells with power conversion efficiency of 1.4% under simulated AM1.5 solar illumination.
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84.60.Jt Photoelectric conversion
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High-performance polymer heterojunction solar cells of a polysilafluorene derivative

Ergang Wang, Li Wang, Linfeng Lan, Chan Luo, Wenliu Zhuang, Junbiao Peng, and Yong Cao

Appl. Phys. Lett. 92, 033307 (2008); http://dx.doi.org/10.1063/1.2836266 (3 pages) | Cited 195 times

Online Publication Date: 25 January 2008

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High-performance polymer heterojunction solar cells fabricated from an alternating copolymer of 2,7-silafluorene (SiF) and 4,7-di(2′-thienyl)-2,1,3-benzothiadiazole (DBT) (PSiF-DBT) as the electron donor blended with [6,6]-phenyl-C61-butyric acid methyl ester as the electron acceptor were investigated. A power-conversion efficiency up to 5.4% with an open-circuit voltage of 0.90 V, a short-circuit current of 9.5 mA cm−2, and a fill factor of 50.7% was achieved under the illumination of AM 1.5 G from a calibrated solar simulator (800 W m−2). The field-effect transistors fabricated from PSiF-DBT showed a high hole mobility of ∼ 1×10−3 cm2 V−1 s−1.
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84.60.Jt Photoelectric conversion
85.30.Tv Field effect devices
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All-metal-electrode-type dye sensitized solar cells (transparent conductive oxide-less dye sensitized solar cell) consisting of thick and porous Ti electrode with straight pores

Yohei Kashiwa, Yorikazu Yoshida, and Shuzi Hayase

Appl. Phys. Lett. 92, 033308 (2008); http://dx.doi.org/10.1063/1.2837633 (3 pages) | Cited 14 times

Online Publication Date: 25 January 2008

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Transparent conductive oxide (TCO) layer-less dye sensitized solar cells (DSCs) are reported. The cell is composed of a glass substrate, TiO2 porous layer stained with dye molecules, porous Ti electrode, electrolyte, and a Pt sputtered Ti sheet. The cell exhibits an efficiency of 7.43% which was a little less than that of 8.44% for a DSC consisting of a TCO glass. The high efficiency was brought about by the thick and porous Ti electrode (200–300 nm thickness) which kept high conductivity and swift ionic diffusion. The preparation process for the Ti electrode is reported.
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84.60.Jt Photoelectric conversion
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Continuous control of third-order optical nonlinearity in charge-transfer-type conjugated polymers

Hideo Kishida, Keisuke Hirota, Hiroshi Okamoto, Hisashi Kokubo, and Takakazu Yamamoto

Appl. Phys. Lett. 92, 033309 (2008); http://dx.doi.org/10.1063/1.2837643 (3 pages) | Cited 3 times

Online Publication Date: 25 January 2008

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Third-order optical nonlinearity was investigated in two charge-transfer (CT)-type conjugated polymers, poly(aryleneethynylene) and poly(thiophene-alt-thiazole), using the third-harmonic generation (THG) method. Comparison of the results with previously obtained THG data for polythiophene and the strong CT polymer poly(thiophene-alt-quinoxaline) revealed that the ratio of the maximum value of third-order nonlinear susceptibility and the absorption coefficient max∣χ(3)∣/αmax increased as the degree of CT character increased for the four polymers. This variation in max∣χ(3)∣/αmax is discussed based on the magnitude of the transition dipole moment between the one-photon-allowed and the one-photon-forbidden excited states.
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42.70.Jk Polymers and organics
82.35.Ej Nonlinear optics with polymers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
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