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16 Jul 2012

Volume 101, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages)

Ting-Gang Chen, Bo-Yu Huang, En-Chen Chen, Peichen Yu, and Hsin-Fei Meng
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Micro-textured conductive polymer/silicon heterojunction photovoltaic devices with high efficiency

Ting-Gang Chen, Bo-Yu Huang, En-Chen Chen, Peichen Yu, and Hsin-Fei Meng

Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages) | Cited 7 times

Online Publication Date: 16 July 2012

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In this work, hybrid heterojunction solar cells are demonstrated based on a conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) directly spun-cast on micro-textured n-type crystalline silicon wafers. The fabrication conditions suggest that the organic coverage on the micro-textured surface is excellent and key to achieve high efficiency, leading to an average power conversion efficiency of 9.84%. A one-dimensional drift-diffusion model is then developed based on fitting the device characteristics with experimentally determined PEDOT:PSS parameters and projects an ultimate efficiency above 20% for organic/inorganic hybrid photovoltaics. The simulation results reveal the impacts of defect densities, back surface recombination, doping concentration, and band alignment.
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88.40.H- Solar cells (photovoltaics)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.07.Pr Organic-inorganic hybrid nanostructures
82.35.Cd Conducting polymers
82.45.Wx Polymers and organic materials in electrochemistry
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Top illuminated inverted organic ultraviolet photosensors with single layer graphene electrodes

Martin Burkhardt, Wei Liu, Christopher G. Shuttle, Kaustav Banerjee, and Michael L. Chabinyc

Appl. Phys. Lett. 101, 033302 (2012); http://dx.doi.org/10.1063/1.4733299 (4 pages)

Online Publication Date: 16 July 2012

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Inverted, top-illuminated organic photodiodes are demonstrated using transparent electrodes including single layer graphene (SLG) and thin gold or silver with poly(3-hexylthiophene) and 1 -(3-methoxycarboyl)-propyl-1-phenyl-(6,6)C61 as active layer. The devices are free of both indium-tin-oxide and poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate). The maximum solar power conversion efficiencies were 0.3% for SLG due to its series resistance and ∼2% for gold and silver. The organic photodiodes with SLG electrodes had good external quantum efficiency at incident illumination less than 10 mW/cm2 and better performance than gold and silver at wavelengths below 300 nm making them attractive for ultraviolet photosensors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
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Hysteresis mechanism in low-voltage and high mobility pentacene thin-film transistors with polyvinyl alcohol dielectric

Wei Wang, Dongge Ma, Su Pan, and Yudan Yang

Appl. Phys. Lett. 101, 033303 (2012); http://dx.doi.org/10.1063/1.4737173 (5 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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In this letter, the hysteresis mechanism of organic thin-film transistors (OTFTs) with polyvinyl alcohol (PVA) as gate dielectric is studied. By examining OTFTs with a blocking polymer layer between gate and PVA or between channel and PVA, we confirm that the origin of the hysteresis is caused by the holes injected from the gate and/or from the channel and trapped in the interface of pentacene/PVA and the PVA bulk. A method is proposed to reduce the hysteresis. As a result, a pentacene OTFT with free-hysteresis and high mobility of 1.8 cm2/Vs is achieved by a triple-layer polymer dielectric at low-operating voltages.
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85.30.Tv Field effect devices
77.80.Dj Domain structure; hysteresis
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Origin of multiple memory states in organic ferroelectric field-effect transistors

Benjamin Kam, Xiaoran Li, Claudio Cristoferi, Edsger C. P. Smits, Alexander Mityashin, Sarah Schols, Jan Genoe, Gerwin Gelinck, and Paul Heremans

Appl. Phys. Lett. 101, 033304 (2012); http://dx.doi.org/10.1063/1.4737176 (5 pages) | Cited 3 times

Online Publication Date: 17 July 2012

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In this work, we investigate the ferroelectric polarization state in metal-ferroelectric-semiconductor-metal structures and in ferroelectric field-effect transistors (FeFET). Poly(vinylidene fluoride-trifluoroethylene) and pentacene was used as the ferroelectric and semiconductor, respectively. This material combination in a bottom gate—top contact transistor architecture exhibits three reprogrammable memory states by applying appropriate gate voltages. Scanning Kelvin probe microscopy in conjunction with standard electrical characterization techniques reveals the state of the ferroelectric polarization in the three memory states as well as the device operation of the FeFET.
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85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.30.Sk Pulse and digital circuits
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Surface doping in pentacene thin-film transistors with few monolayer thick channels

Tatjana Hählen, Claudio Vanoni, Christian Wäckerlin, Thomas A. Jung, and Soichiro Tsujino

Appl. Phys. Lett. 101, 033305 (2012); http://dx.doi.org/10.1063/1.4737214 (4 pages)

Online Publication Date: 17 July 2012

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Molecular surface doping was studied for organic thin film transistors consisting of an active layer of few monolayers pentacene, as prepared by physical vapor deposition. In situ transport measurements with different dopants revealed both positive (tetrafluoro-tetracyanoquinodimethane – F4TCNQ) and negative (manganese(III)-tetraphenylporphyrin-chloride), as well as zero value (cobalt(II)-tetraphenylporphyrin and fullerene) gate threshold shifts. For F4TCNQ, a high doping efficiency of 25% was observed. The maximum gate threshold shift was more than halved with pentacene thickness increasing from 2.5 to 5 monolayers, indicating that the doping effect decays above ∼2.5 monolayers. Charge transfer has been discussed based on complementary x-ray photoelectron experiments.
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85.30.Tv Field effect devices
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Controllable threshold voltage shifts of polymer transistors and inverters by utilizing gold nanoparticles

Su-Ting Han, Ye Zhou, Zong-Xiang Xu, and V. A. L. Roy

Appl. Phys. Lett. 101, 033306 (2012); http://dx.doi.org/10.1063/1.4737422 (5 pages) | Cited 3 times

Online Publication Date: 17 July 2012

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We have demonstrated controllable threshold voltage (Vth) shifts of gold nanoparticles (Au NPs)/poly (3-hexylthiophene) (P3HT) based composite transistors that are fabricated through a low temperature facile technique. By varying the doping concentration of gold nanoparticles in P3HT matrix, Vth has been tuned from 12 V to 27 V without device degradation. Using this technique, the switching voltages of unipolar inverters have also been systematically tuned. Efficient hole conduction and a variation in P3HT crystallinity was observed due to different concentrations of Au NPs which eventually shift the threshold voltage of the devices in a controlled manner.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
84.30.Jc Power electronics; power supply circuits
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Post-growth surface smoothing of thin films of diindenoperylene

A. Hinderhofer, T. Hosokai, K. Yonezawa, A. Gerlach, K. Kato, K. Broch, C. Frank, J. Novák, S. Kera, N. Ueno, and F. Schreiber

Appl. Phys. Lett. 101, 033307 (2012); http://dx.doi.org/10.1063/1.4737168 (4 pages) | Cited 3 times

Online Publication Date: 18 July 2012

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We applied in situ x-ray reflectivity and ultraviolet photoelectron spectroscopy to study the impact of annealing on low temperature (200 K) deposited organic thin films of diindenoperylene (DIP) on SiO2 and indium tin oxide (ITO). At 200 K, DIP is crystalline on SiO2 and amorphous on ITO. Upon heating to room temperature, the roughness of DIP is reduced on both substrates, from 1.5 nm to 0.75 nm (SiO2) and from 0.90 nm to 0.45 nm (ITO). The smoothing is accompanied by crystallization of the surface molecules, whereas the bulk structure of the films does not strongly reorganize.
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68.55.A- Nucleation and growth
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing
81.15.Aa Theory and models of film growth
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Efficient, bulk heterojunction organic photovoltaic cells based on boron subphthalocyanine chloride-C70

Richa Pandey, Yunlong Zou, and Russell J. Holmes

Appl. Phys. Lett. 101, 033308 (2012); http://dx.doi.org/10.1063/1.4737902 (4 pages) | Cited 4 times

Online Publication Date: 19 July 2012

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In this work, we describe the performance of organic photovoltaic cells (OPVs) based on the electron donor-acceptor pairing of boron subphthalocyanine chloride (SubPc) and C70. As an acceptor, C70 is a promising alternative to C60 due to its red-shifted absorption edge and large extinction coefficient, permitting increased photocurrent generation. In uniformly mixed OPVs based on SubPc:C70, peak power conversion efficiency is realized in devices containing 80 wt. % C70. Further enhancement in device performance can be realized through the use of a continuously graded donor-acceptor heterojunction. The optimized graded heterojunction OPV shows a power conversion efficiency of ηP = (5.4 ± 0.2)% under simulated AM1.5 G solar illumination at 100 mW/cm2. This efficiency is significantly larger than the value of ηP = (4.5 ± 0.1)% realized using C60 due to a substantial increase in the short-circuit current density.
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84.60.Jt Photoelectric conversion
85.60.-q Optoelectronic devices
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Hybrid graphene/organic semiconductor field-effect transistors

Tae-Jun Ha, Deji Akinwande, and Ananth Dodabalapur

Appl. Phys. Lett. 101, 033309 (2012); http://dx.doi.org/10.1063/1.4737939 (3 pages) | Cited 1 time

Online Publication Date: 19 July 2012

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In this letter, we report on the improvement of the electronic properties of graphene by capping with π-conjugated organic semiconductor molecules. The off-state current is reduced while the on-state current and mobility are either unaffected or increased. The semiconductors employed included α-sexithiophene and hexadecafluorocopperphthallocyanine. Removal of the organic semiconductor layer results in a return to the original electronic properties. This suggests that weak electronic interactions with organic semiconductors can be a promising approach to favorably alter the transport properties of graphene.
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85.30.Tv Field effect devices
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