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16 Mar 2009

Volume 94, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 94, 111101 (2009); http://dx.doi.org/10.1063/1.3097278 (3 pages)

Ling Lu, Adam Mock, Tian Yang, Min Hsiung Shih, Eui Hyun Hwang, Mahmood Bagheri, Andrew Stapleton, Stephen Farrell, John O’Brien, and P. Daniel Dapkus
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Light-induced charge transfer in hybrid composites of organic semiconductors and silicon nanocrystals

Roland Dietmueller, Andre R. Stegner, Robert Lechner, Sabrina Niesar, Rui N. Pereira, Martin S. Brandt, André Ebbers, Martin Trocha, Hartmut Wiggers, and Martin Stutzmann

Appl. Phys. Lett. 94, 113301 (2009); http://dx.doi.org/10.1063/1.3086299 (3 pages) | Cited 14 times

Online Publication Date: 17 March 2009

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Charge transfer between silicon nanocrystals (Si-nc) and organic semiconductors has been investigated via light-induced electron spin resonance (LESR). Composites of Si-nc with the hole conductor poly(3-hexylthiophene) (P3HT) and with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been investigated. The LESR measurements allow one to quantify light-induced charge transfer between Si-nc and P3HT, which results in positive P3HT polarons. PCBM, in contrast, acts as an electron acceptor in composites with Si-nc, and after illumination, negative PCBM radicals are created. These results are discussed in terms of light-induced generation and separation of charge carriers in the hybrid composites.
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73.63.Bd Nanocrystalline materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
71.38.-k Polarons and electron-phonon interactions
76.30.Pk Conduction electrons
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Transient photovoltaic behavior of air-stable, inverted organic solar cells with solution-processed electron transport layer

Chang Su Kim, Stephanie S. Lee, Enrique D. Gomez, Jong Bok Kim, and Yueh-Lin Loo

Appl. Phys. Lett. 94, 113302 (2009); http://dx.doi.org/10.1063/1.3099947 (3 pages) | Cited 41 times

Online Publication Date: 17 March 2009

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The short-circuit current density of inverted organic solar cells comprising a solution-processed titania electron transport layer increases with continuous illumination in air and saturates after 10 min. On extended exposure (>2 days), the open-circuit voltage of the devices increases also. The improvement in device characteristics over short time scales is attributed to the filling of shallow electron traps in titania. With an increase in photoconductivity of titania, the short-circuit current increases accordingly. The increase in open-circuit voltage on extended exposure to air is attributed to an increase in the electrostatic field across the diodes when polythiophene is doped by oxygen.
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84.60.Jt Photoelectric conversion
61.72.up Other materials
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Low-voltage organic transistors with titanium oxide/polystyrene bilayer dielectrics

Yingxi Lu, Wi Hyoung Lee, Hwa Sung Lee, Yunseok Jang, and Kilwon Cho

Appl. Phys. Lett. 94, 113303 (2009); http://dx.doi.org/10.1063/1.3097010 (3 pages) | Cited 14 times

Online Publication Date: 19 March 2009

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Pentacene-based low-voltage organic transistors were realized with titanium oxide/polystyrene (TiO2/PS) bilayer dielectrics. Significantly, the TiO2 bottom layer was fabricated by a layer-by-layer deposition procedure and had an ultrathin thickness (<5 nm). The nonpolar PS top layer not only shields out the high polarity TiO2 layer, but also reduces the roughness of the dielectric, which results in low gate leakage of dielectric and the more ordered growth of pentacene film. This organic transistor with a TiO2/PS bilayer dielectric was found to exhibit high performance with a low operating voltage ( ≤ 3 V), and a high on/off ratio (>107).
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.30.Tv Field effect devices
77.55.-g Dielectric thin films
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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Interface dipole at metal-organic interfaces: Contribution of metal induced interface states

C. S. Lee, J. X. Tang, Y. C. Zhou, and S. T. Lee

Appl. Phys. Lett. 94, 113304 (2009); http://dx.doi.org/10.1063/1.3099836 (3 pages) | Cited 7 times

Online Publication Date: 19 March 2009

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Despite the importance of interface dipole on the charge carrier injection at metal/organic contacts, there is yet no estimation of the various contributions to the overall dipole. We propose a simple approach to delineate and estimate the contribution of metal-induced interface states (MISs) toward the overall dipole. The relative contribution of the MIS was found to increase as the slope parameter decreases. By using published results, we estimate the relative MIS contributions in organic-silver contacts for various organic semiconductors to be −30%–80% of the overall dipole.
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73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
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Efficient bilayer phosphorescent organic light-emitting diodes: Direct hole injection into triplet dopants

Z. W. Liu, M. G. Helander, Z. B. Wang, and Z. H. Lu

Appl. Phys. Lett. 94, 113305 (2009); http://dx.doi.org/10.1063/1.3099903 (3 pages) | Cited 11 times

Online Publication Date: 19 March 2009

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In phosphorescent organic light-emitting diodes (OLEDs), a hole transporting layer is traditionally thought to be required to facilitate hole injection into the host molecule. It is found that fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] doped into 4,4′-N,N′-dicarbazole-biphenyl can be used to directly inject and transport holes from an indium tin oxide anode, and thus simplify the device structure and selection of materials. The efficiencies of the simplified bilayer OLEDs exceed 41 lm/W and 57 cd/A at a brightness of 100 cd/m2. We attribute the excellent performance to direct hole injection from the anode to Ir(ppy)3 dopant.
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85.60.Jb Light-emitting devices
72.20.Ht High-field and nonlinear effects
78.60.-b Other luminescence and radiative recombination
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