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12 Jan 2009

Volume 94, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 94, 022101 (2009); http://dx.doi.org/10.1063/1.3065067 (3 pages)

Hong Li and Qing Zhang
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Three dimensional metal pattern transfer for replica molded microstructures

Yanzhu Zhao, Yong-Kyu Yoon, Seong-O Choi, Xiaosong Wu, Zhan Liu, and Mark G. Allen

Appl. Phys. Lett. 94, 023301 (2009); http://dx.doi.org/10.1063/1.3063122 (3 pages) | Cited 5 times

Online Publication Date: 13 January 2009

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We report a replica molding process for simultaneously forming a three dimensional metal pattern on the surface of molded polymer microstructures. This technique uses noncovalent surface forces to guide the transfer of thin metal films from the three dimensional features of high aspect ratio poly(dimethylsiloxane) micromolds to polymeric replicates. The utility of this technique has been demonstrated by the fabrication of organic coplanar waveguides integrated with vertical Ka-band monopole antenna radiators. These microwave systems show good performance with over 18% bandwidth and greater than 16 dB return loss, demonstrating the versatility of this process.
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84.40.Az Waveguides, transmission lines, striplines
84.40.Ba Antennas: theory, components and accessories
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High band gap poly(9,9-dihexylfluorene-alt-bithiophene) blended with [6,6]-phenyl C61 butyric acid methyl ester for use in efficient photovoltaic devices

Gisela L. Schulz, Xiwen Chen, and Steven Holdcroft

Appl. Phys. Lett. 94, 023302 (2009); http://dx.doi.org/10.1063/1.3070574 (3 pages) | Cited 15 times

Online Publication Date: 13 January 2009

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This paper reports a study of a high band gap conjugated polymer poly(9,9-dihexylfluorene-alt-bithiophene) (F6T2) in an organic photovoltaic device. F6T2 blended with [6,6]-phenyl C61 butyric acid methyl ester (1:4 weight ratio) produced films exhibiting phase segregated domains ∼ 5 nm in size, and possessing a hole mobility of 3×10−8 m2/V s. Open circuit voltages of photovoltaic devices were greater than 1 V, and power conversion efficiencies of 2.7% based on AM 1.5 G illumination were measured. External quantum efficiencies of up to 48 %, and internal quantum efficiencies of up to 87 % were calculated.
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73.50.Dn Low-field transport and mobility; piezoresistance
85.60.-q Optoelectronic devices
73.61.Ph Polymers; organic compounds
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Transmission and reflection phase gratings formed in azo-dye-doped chiral nematic liquid crystals

Tomoyuki Sasaki, Akira Emoto, Tatsutoshi Shioda, and Hiroshi Ono

Appl. Phys. Lett. 94, 023303 (2009); http://dx.doi.org/10.1063/1.3072363 (3 pages) | Cited 7 times

Online Publication Date: 14 January 2009

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Transmission and reflection gratings were simultaneously formed in azo-dye-doped chiral nematic liquid crystals (N∗LCs) with planar alignment. The formation process is based on a phototuning of the Bragg reflection band of the N∗LC. The helical pitch of the photoreactive N∗LC was spatially controlled with intensity variation of interference light. The resultant periodic structure showed both transmissive and reflective diffractions due to the spatially modulated light intensities. The observed dependence of diffraction efficiencies on the polarization states of the probe beam was well explained by considering a spatial modulation of the helical pitch.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.79.Dj Gratings
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Self-organized patterns by optical nonlinearity in 4-(4-pentenyloxy)benzonitrile

Mónica Trejo-Durán, Edgar Alvarado-Méndez, and Víctor M. Castaño

Appl. Phys. Lett. 94, 023304 (2009); http://dx.doi.org/10.1063/1.3072609 (3 pages)

Online Publication Date: 14 January 2009

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Optical characterization of the organic compound 4-(4-pentenyloxy)benzonitrile under two different conditions was carried out. The experiments show deformation of the scattered light spots upon heating as well as evidence of a thermally self-induced nonlinearity. In consequence, self-diffraction pattern, self-bending, and filamentation of the impinging beam appear as a function of the laser power, creating self-organized patterning during the filamentation due to modulation instabilities.
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42.65.-k Nonlinear optics
42.70.Jk Polymers and organics
42.60.Fc Modulation, tuning, and mode locking
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Ambipolar pentacene/C60-based field-effect transistors with high hole and electron mobilities in ambient atmosphere

Hu Yan, Tsubasa Kagata, and Hidenori Okuzaki

Appl. Phys. Lett. 94, 023305 (2009); http://dx.doi.org/10.1063/1.3072608 (3 pages) | Cited 21 times

Online Publication Date: 16 January 2009

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Ambipolar field-effect transistors (FETs) were fabricated with a heterostructure of pentacene/C60 in which the C60 layer functioned as an n-type channel while the pentacene layer functioned as both a p-type channel and a sealing capsule for the unstable C60 layer. The ambipolar FET, operating in an ambient atmosphere, exhibited a hole mobility of 0.2 cm2/V s with a threshold voltage of −2.3 V and an electron mobility of 0.04 cm2/V s with a threshold voltage of 66 V with moderately good air stability. However, the threshold voltage and gate voltage for the n-channel operation must be improved for practical applications.
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85.30.Tv Field effect devices
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Study of efficient and stable organic light-emitting diodes with 2-methyl-9,10-di(2-naphthyl)anthracene as hole-transport material by admittance spectroscopy

Meng-Huan Ho, Ming-Ta Hsieh, Kuan-Heng Lin, Teng-Ming Chen, Jenn-Fang Chen, and Chin H. Chen

Appl. Phys. Lett. 94, 023306 (2009); http://dx.doi.org/10.1063/1.3072616 (3 pages) | Cited 9 times

Online Publication Date: 16 January 2009

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An organic light-emitting device with enhanced efficiency sby employing 2-methyl-9,10-di(2-naphthyl)anthracene (MADN) as hole-transport material (HTM) has been developed. The admittance spectroscopy studies indicate that using MADN as HTM can reduce the amount of hole carriers injected into the device leading to a well-balanced carrier recombination. The green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]pyrano-[6,7,8-ij]quinolizin-11-one doped tris(8-quinolinolato)aluminum device achieved a current efficiency of 21.8 cd/A and a power efficiency of 10.4 lm/W at 20 mA/cm2 that are 65% higher than those of the control device. The green-doped device also achieved a long half-decay lifetime of 22 000 h at an initial brightness of 500 cd/m2.
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85.60.Jb Light-emitting devices
72.20.Ee Mobility edges; hopping transport
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Open circuit voltage enhancement due to reduced dark current in small molecule photovoltaic cells

Ning Li, Brian E. Lassiter, Richard R. Lunt, Guodan Wei, and Stephen R. Forrest

Appl. Phys. Lett. 94, 023307 (2009); http://dx.doi.org/10.1063/1.3072807 (3 pages) | Cited 58 times

Online Publication Date: 16 January 2009

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We demonstrate high open circuit voltage photovoltaic cells achieved by reducing the electron leakage current through the introduction of both organic and inorganic electron blocking layers between the donor layer and the anode contact. As an example, the blocking layers reduce the dark current in tin (II) phthalocyanine (SnPc)/C60 solar cells with response across the visible and near infrared spectral region up to a wavelength of 1000 nm, is decreased by two orders of magnitude compared to cells lacking the layers, resulting in a doubling of the open circuit voltage. The structure: indium tin oxide/electron blocker/SnPc (100 Å)/C60 (400 Å)/bathocuproine (100 Å)/Al, has a power conversion efficiency of (2.1±0.1)% at 1 sun, standard AM1.5G solar illumination. This work demonstrates the importance of reducing dark current to achieve high organic thin film photovoltaic cell efficiencies.
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84.60.Jt Photoelectric conversion
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