Browse - APL: Organic Electronics and Photonics

Select this Article FREE

Understanding metal doping for organic electron transport layers

Alexander Mityashin, David Cheyns, Barry P. Rand, and Paul Heremans

Appl. Phys. Lett. 100, 053305 (2012); http://dx.doi.org/10.1063/1.3681383 (3 pages)

Online Publication Date: 1 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

This work concerns the physical mechanisms of metal n-doping in charge transport layers for optoelectronic devices, for which the doping level is constrained by transparency requirements so as to avoid parasitic absorption. Comparing various metal dopants, we claim that enhanced conductivity at low doping is initiated by the electrical doping effect, namely, metal-semiconductor charge donation. Electrical measurements show that doping effects at low concentration strongly depend on the work function of the introduced metal, and not every metal works as an efficient dopant. Practical applicability is demonstrated by introducing doped transport layers in prototypical bilayer solar cells in conventional and inverted architectures.

+

Show PACS

61.72.up	Other materials
65.40.gh	Work functions
73.61.Ph	Polymers; organic compounds

Select this Article FREE

Electrical phase transition of poly(4,4′-aminotriphenylene hexafluoroisopropylidenediphthalimide) by photogenerated charged carrier injection

Kyoung-Jae Lee, Dong Min Kim, Kyuwook Ihm, Moonhor Ree, Tai-Hee Kang, and Sukmin Chung

Appl. Phys. Lett. 100, 053306 (2012); http://dx.doi.org/10.1063/1.3681776 (4 pages)

Online Publication Date: 1 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We show a set-up of poly(4,4′-aminotriphenylene hexafluoroisopropylidenediphthalimide) (6F-TPA PI)/Al sample in which holes are injected by photoelectron emission process instead of direct charge carrier injection via metal electrode. In this process, an irreversible electrical phase transition of 6F-TPA PI is found in contrast to the Al/6F-TPA PI/Al structure, leading to a write-once-read-many behavior. The photoelectron spectroscopy results measured before and after the switching process revealed that the irreversible electrical phase transition of 6F-TPA PI is attributed to the chemical modification of the carbonyl group in phthalimide moiety.

+

Show PACS

72.60.+g	Mixed conductivity and conductivity transitions
79.60.Fr	Polymers; organic compounds
78.70.Dm	X-ray absorption spectra

Select this Article FREE

Optimal parameters for morphology of bulk heterojunction solar cells from simulations

Junwei Xue, Tingjun Hou, and Youyong Li

Appl. Phys. Lett. 100, 053307 (2012); http://dx.doi.org/10.1063/1.3681947 (3 pages)

Online Publication Date: 2 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We combine atomistic simulation with mesoscale simulation to predict the morphology of bulk heterojunction (BHJ) solar cells. We show that good morphology is formed for weight fraction of PCBM in the region of 0.41–0.62 for poly(3-hexylthiophene)/[6,6]-phenyl-C₆₁ butyric acid methyl ester BHJ solar cells, which agrees with experimental results. Our simulation results indicate that the enhanced phase separation is achieved by increasing the temperature, which is consistent with transmission electron microscopy results. We find that Flory-Huggins parameter (χ) > 1 is required for phase separation and good morphology. Our simulation method is useful for predicting the morphology of BHJ polymer solar cells.

+

Show PACS

88.40.jr	Organic photovoltaics
88.40.hj	Efficiency and performance of solar cells

Select this Article FREE

Cumulative effects of electrode and dielectric surface modifications on pentacene-based transistors

Mélanie Devynck, Pascal Tardy, Guillaume Wantz, Yohann Nicolas, Luc Vellutini, Christine Labrugère, and Lionel Hirsch

Appl. Phys. Lett. 100, 053308 (2012); http://dx.doi.org/10.1063/1.3681791 (4 pages)

Online Publication Date: 3 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

Surface modifications of the dielectric and the metal of pentacene-based field effect transistors using self-assembled monolayer (SAM) were studied. First, a low interfacial trap density and pentacene 2D-growth were favored by the nonpolar and low surface energy of octadecyltrichlorosilane-based SAM. This treatment leaded to increased mobility up to 0.4 cm² V⁻¹ s⁻¹ and no observable hysteresis on transfer curves. Second, reduced hole injection barrier and contact resistance were achieved by fluorinated thiols deposited on gold contacts resulting in an increased mobility up to 0.6 cm² V⁻¹ s⁻¹. Finally, a high mobility of 2.6 cm² V⁻¹ s⁻¹ was achieved by cumulative effects of both treatments.

+

Show PACS

85.30.Tv

Field effect devices

Select this Article FREE

Cross-linking of a poly(3,4-ethylene dioxythiophene):(polystyrene sulfonic acid) hole injection layer with a bis-azide salt and the effect of atmospheric processing conditions on device properties

Oliver Fenwick, Kate Oliver, and Franco Cacialli

Appl. Phys. Lett. 100, 053309 (2012); http://dx.doi.org/10.1063/1.3680606 (4 pages)

Online Publication Date: 3 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We investigate the role of atmospheric conditions during processing when cross-linking a poly(3,4-ethylene dioxythiophene):(polystyrene sulfonic acid) hole injection layer with a bis-azide salt. In particular, we investigate nitrogen atmosphere and air, since there is a competing reaction of the cross-linker with oxygen. We show enhanced work function when processing under inert conditions, with device properties otherwise unaffected. When processing is done in air, higher irradiation dosages are needed to cross-link and the resulting films show lower work functions. Surprisingly, the finished devices display an unexpected two-fold increase in efficiency which we attribute to increased electron trapping in these films.

+

Show PACS

73.30.+y	Surface double layers, Schottky barriers, and work functions
73.50.Gr	Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.41.+e	Polymers, elastomers, and plastics
68.55.-a	Thin film structure and morphology
72.20.Jv	Charge carriers: generation, recombination, lifetime, and trapping

Select this Article FREE

Four-mode plasmonic structure based on a prism-grating anticrossing bandgap

R. Chuliá-Jordán and D. Santamaría-Pérez

Appl. Phys. Lett. 100, 063301 (2012); http://dx.doi.org/10.1063/1.3682081 (4 pages)

Online Publication Date: 7 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We have developed a plasmonic structure based on an anticrossing bandgap prism-grating coupling technique. We observe that up to four surface plasmons can be excited simultaneously in this plasmonic structure. Initial experiments confirm that such a plasmonic structure can improve sensor performance by tuning the amplitude of the grating. From numerical simulations, we conclude that plasmon modes with equal propagation constants at a different wavelength can only be excited at different grating amplitudes of our plasmonic structure, in such a way that the increase of wavelength implies the increase of the amplitude for a fixed propagation constant.

+

Show PACS

07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Bh	Lenses, prisms and mirrors
42.79.Dj	Gratings

Select this Article FREE

Mixed self-assembled monolayer of molecules with dipolar and acceptor character—Influence on hysteresis and threshold voltage in organic thin-film transistors

Abdesselam Jedaa, Michael Salinas, Christof M. Jäger, Timothy Clark, Alexander Ebel, Andreas Hirsch, and Marcus Halik

Appl. Phys. Lett. 100, 063302 (2012); http://dx.doi.org/10.1063/1.3682301 (4 pages)

Online Publication Date: 7 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

In this report, we investigate the impact of the molecular dipole moment and redox active head groups (C₆₀) in pure and mixed self-assembled monolayers (SAMs), which serve as an ultra-thin hybrid dielectric layer in low-voltage operating organic thin-film transistors. We show that the dipole of the SAM-forming molecules affects the threshold voltage, while the concentration of redox-active C₆₀ moieties determines the hysteresis in devices with α,α′-dihexyl-sexithiophene and pentacene as organic semiconductors.

+

Show PACS

68.47.Pe	Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
85.30.Tv	Field effect devices
77.80.Dj	Domain structure; hysteresis
77.55.-g	Dielectric thin films

Select this Article FREE

Fullerene acceptor for improving open-circuit voltage in inverted organic photovoltaic devices without accompanying decrease in short-circuit current density

Yutaka Matsuo, Junichi Hatano, Takayuki Kuwabara, and Kohshin Takahashi

Appl. Phys. Lett. 100, 063303 (2012); http://dx.doi.org/10.1063/1.3683469 (3 pages)

Online Publication Date: 8 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

A poly(3-hexylthiophene) (P3HT)-based inverted organic photovoltaic (OPV) device with a fullerene electron acceptor, (dimethyl(o-anisyl)silylmethyl)(dimethylphenylsilylmethyl)[60]fullerene (SIMEF2), exhibited 2.9% power conversion efficiency (PCE; J_SC = 7.9 mA/cm², V_OC = 0.66 V, and FF = 0.56) in the device configuration, indium tin oxide/ZnO/P3HT:SIMEF2/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Au under AM1.5 G illumination at 100 mW/cm². Through a comparison with a [6,6]-phenyl-C61-butyric acid methyl ester-based device (PCE = 2.4%, J_SC = 7.8 mA/cm², V_OC = 0.56 V, and FF = 0.55), SIMEF2 was found to give higher V_OC without a decrease in J_SC. This result marks progress toward overcoming the trade-off relationship between V_OC and J_SC in the development of highly efficient OPV devices.

+

Show PACS

85.60.Bt	Optoelectronic device characterization, design, and modeling
85.65.+h	Molecular electronic devices
84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables

Select this Article FREE

Efficient hybrid white polymer light-emitting devices with electroluminescence covered the entire visible range and reduced efficiency roll-off

Sujun Hu, Minrong Zhu, Qinghua Zou, Hongbin Wu, Chuluo Yang, Wai-Yeung Wong, Wei Yang, Junbiao Peng, and Yong Cao

Appl. Phys. Lett. 100, 063304 (2012); http://dx.doi.org/10.1063/1.3682526 (4 pages)

Online Publication Date: 8 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We report efficient hybrid white polymer light emitting devices (WPLEDs) fabricated via simple solution-proceeded process from a newly synthesized wide band-gap fluorene-co-dibenzothiophene-S,S-dioxide copolymer, which dually function as fluorescent blue emitter and host material for electrophosphorescent sky-blue, yellow, and saturated-red dyes. The Commission Internationale d’Énclairage coordinates of the best devices are (0.356, 0.334), with electroluminescence covered the entire visible light spectrum from 400 to 780 nm, resulting in a high color rendering index of 90. Incorporation of a bilayer electrode consisting of water/alcohol-soluble conjugated polymer and Al as electron-injection cathode boosts an enhancement of 50% in device efficiency, leading to external quantum efficiency of 12.6%, and peak power efficiency of 21.4 l m W⁻¹ as measured in an integrating sphere. Both the efficiency and the color quality of the obtained device are ranking among one of the highest values for WPLEDs reported to date. Furthermore, as compared with those all-phosphorescent WPLEDs, the hybrid WPLEDs studied here exhibit a significantly reduced efficiency roll-off due to the very low doping concentration.

+

Show PACS

85.60.Jb

Light-emitting devices

Select this Article FREE

Bloch surface waves-controlled fluorescence emission: Coupling into nanometer-sized polymeric waveguides

Mirko Ballarini, Francesca Frascella, Emanuele Enrico, Pietro Mandracci, Natascia De Leo, Francesco Michelotti, Fabrizio Giorgis, and Emiliano Descrovi

Appl. Phys. Lett. 100, 063305 (2012); http://dx.doi.org/10.1063/1.3684272 (4 pages)

Online Publication Date: 10 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

The lateral confinement of Bloch surface waves on a patterned multilayer is investigated by means of leakage radiation microscopy (LRM). Arrays of nanometric polymeric waveguides are fabricated on a proper silicon-nitride/silicon-oxide multilayer grown on a standard glass coverslip. By exploiting the functional properties of the polymer, fluorescent proteins are grafted onto the waveguides. A fluorescence LRM analysis of both the direct and the Fourier image plane reveals that a substantial amount of emitted radiation couples into a guided mode and then propagates into the nanometric waveguide. The observations of the mode are supported by numerical simulations.

+

Show PACS

42.70.Jk	Polymers and organics
42.79.Gn	Optical waveguides and couplers
42.30.Kq	Fourier optics
42.79.-e	Optical elements, devices, and systems

Select this Article FREE

Investigation of the device instability feature caused by electron trapping in pentacene field effect transistors

Chang Bum Park

Appl. Phys. Lett. 100, 063306 (2012); http://dx.doi.org/10.1063/1.3680248 (3 pages)

Online Publication Date: 10 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

The phenomenon of device instability governed by electron trapping was investigated in pentacene field-effect transistors. We found that the threshold voltage shift (ΔV_T) increases significantly when the device is exposed to photo-irradiation with the depletion gate bias. This effect reveals that a number of electron trapping sites are located in the pentacene band gap, presenting the mechanism of the photo-induced ΔV_T. In addition, we found the specific shift of bias-stressed ΔV_T under a monochromatic of 690-500 nm, which reflects that the electron trap states would be distributed between the energy levels of 1.8 and 2.5 eV in the gap state.

+

Show PACS

85.30.Tv

Field effect devices

Select this Article FREE

Organic photovoltaic cells with nano-fabric heterojunction structure

June Hyoung Park, Austin R. Carter, Lynetta M. Mier, Chi-Yueh Kao, Sharlene A. M. Lewis, Raju P. Nandyala, Yong Min, and Arthur J. Epstein

Appl. Phys. Lett. 100, 073301 (2012); http://dx.doi.org/10.1063/1.3679097 (4 pages)

Online Publication Date: 13 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

Organic photovoltaic cells containing electron-transporting organic nanofibers in the form of “nanofabrics” are investigated. Nano-fabric heterojunctions of poly(3-hexylthiophene) and electron-transporting nanofibers significantly improve short-circuit current density in organic photovoltaic cells. The nanofibers and nanofabric are synthesized from organic electron-transporting material bis(octyl)-perylenediimide (PDI-C₈). The PDI-C₈ based nano-fabric’s electron mobility is measured to be 0.08 cm²/V s. The nanofabric improves charge collection by expanding the interfacial acceptor-donor area while simultaneously providing dedicated electron transport pathways to the LiF/Al electrodes. An increase in fill factor is observed for photovoltaic cells incorporating the nanofabric heterojunctions and is attributed to efficient removal of space charge.

+

Show PACS

88.40.jr	Organic photovoltaics
88.40.H-	Solar cells (photovoltaics)
88.40.jp	Multijunction solar cells

Select this Article FREE

Sign change in the organic magnetoresistance of tris(8-hydroxyquinolinato)aluminum upon annealing

Hoju Kang, Ik-Jae Lee, and Choon Sup Yoon

Appl. Phys. Lett. 100, 073302 (2012); http://dx.doi.org/10.1063/1.3684873 (4 pages)

Online Publication Date: 13 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We report the sign change in the magnetoresistance of a tris(8-hydroxyquinolinato)aluminum film with the morphological change from amorphous to crystalline state upon annealing. The negative component of the magnetoresistance followed power law behavior, whereas the positive one showed non-Lorentzian function behavior. The decreasing absolute values of the negative component with increased annealing temperature may be understood by both intersystem-crossing-based mechanism and quenching of triplet excitons. The increasing values of the positive component with increased annealing temperature may be explained by the increase in the hopping probability of charge carriers with increased crystallinity of the film.

+

Show PACS

73.61.Ph	Polymers; organic compounds
73.50.Jt	Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.40.Gh	Other heat and thermomechanical treatments
73.20.Mf	Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Dn	Low-field transport and mobility; piezoresistance

Select this Article FREE

Electron mobility determination of efficient phosphorescent iridium complexes with tetraphenylimidodiphosphinate ligand via transient electroluminescence method

Ming-Yu Teng, Song Zhang, Sheng-Wei Jiang, Xu Yang, Chen Lin, You-Xuan Zheng, Leyong Wang, Di Wu, Jing-Lin Zuo, and Xiao-Zeng You

Appl. Phys. Lett. 100, 073303 (2012); http://dx.doi.org/10.1063/1.3684971 (4 pages)

Online Publication Date: 13 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

The electron mobility of Alq₃ and iridium complexes was determined via transient electroluminescence (EL) method based on ITO (indium tin oxide)/di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane/complex/LiF/Al with short and rectangular driving voltage pulses. Apparent values of the electron mobility (μ_e) in complexes have been investigated from their onset of EL upon different driving voltages. The result reveals that the μ_e, 4.31 × 10⁻⁶ cm²/V⋅s, of the efficient phosphorescent material Ir(tfmppy)₂(tpip) [1, tfmppy = 4-trifluoromethylphenylpyridine, tpip = tetraphenylimido-diphosphinate] under electric field of 1300 (V/cm)^1/2 is as high as that of Alq₃, which indicates that the good device performances of 1 are partly due to its high electron mobility.

+

Show PACS

85.60.Jb

Light-emitting devices

Select this Article FREE

Magnetic-field effects in illuminated tetracene field-effect transistors

Tobat P. I. Saragi and Thomas Reichert

Appl. Phys. Lett. 100, 073304 (2012); http://dx.doi.org/10.1063/1.3684835 (4 pages)

Online Publication Date: 14 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We report on magnetic-field effects in illuminated tetracene field-effect transistors. A decrease in the photocurrent is observed when an external magnetic field is applied. In this case, the resistance of the conducting channel increases by up to 0.75%, which leads to positive magnetoresistance. This can be attributed to: (1) A magnetic field-induced decrease in the interaction rate between triplet excitons and trapped holes. (2) The coupling between the singlet and the triplet manifold of states is decreased in a magnetic field and, hence, the singlet exciton fission and triplet exciton fusion rate constants are reduced.

+

Show PACS

85.30.Tv

Field effect devices

Select this Article FREE

Kelvin probe microscopic visualization of charge storage at polystyrene interfaces with pentacene and gold

T. J. Dawidczyk, G. L. Johns, R. Ozgun, O. Alley, A. G. Andreou, N. Markovic, and H. E. Katz

Appl. Phys. Lett. 100, 073305 (2012); http://dx.doi.org/10.1063/1.3684977 (3 pages)

Online Publication Date: 14 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

Charge carriers trapped in polystyrene (PS) were investigated with Kelvin probe microscopy (KPM) and thermally stimulated discharge current (TSDC). Lateral heterojunctions of pentacene/PS were scanned using KPM, effectively observing polarization along a side view of a lateral nonvolatile organic field-effect transistor dielectric interface. TSDC was used to observe charge migration out of PS films and to estimate the trap energy level inside the PS, using the initial rise method.

+

Show PACS

73.40.Qv	Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv	Field effect devices
72.20.Jv	Charge carriers: generation, recombination, lifetime, and trapping

Select this Article FREE

Poly-(3-hexylthiophene)/[6,6]-phenyl-C₆₁-butyric-acid-methyl-ester bilayer deposition by matrix-assisted pulsed laser evaporation for organic photovoltaic applications

A. P. Caricato, M. Cesaria, G. Gigli, A. Loiudice, A. Luches, M. Martino, V. Resta, A. Rizzo, and A. Taurino

Appl. Phys. Lett. 100, 073306 (2012); http://dx.doi.org/10.1063/1.3685702 (4 pages)

Online Publication Date: 15 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

A poly-(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C₆₁-butyric-acid-methyl-ester (PCBM) bilayer structure has been realized by single step matrix-assisted pulsed laser evaporation (ss-MAPLE) technique using the same solvent for both the polymers under vacuum conditions. Our ss-MAPLE procedure allows the fabrication of polymeric multilayer device stacks, which are very difficult to realize with the conventional solvent assisted deposition methods. A proof of concept bilayer P3HT/PCBM solar cell based on ss-MAPLE deposition has been realized and characterized. This demonstration qualifies ss-MAPLE as a general and alternative technique for the implementation of polymeric materials in hetero-structure device technology.

+

Show PACS

68.65.Ac	Multilayers
81.15.Fg	Pulsed laser ablation deposition
61.41.+e	Polymers, elastomers, and plastics

Select this Article FREE

ZnO:Al cathode for highly efficient, semitransparent 4% organic solar cells utilizing TiO_x and aluminum interlayers

Andreas Bauer, Tina Wahl, Jonas Hanisch, and Erik Ahlswede

Appl. Phys. Lett. 100, 073307 (2012); http://dx.doi.org/10.1063/1.3685718 (3 pages)

Online Publication Date: 15 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We report on the fabrication of highly efficient, semitransparent bulk heterojunction solar cells comprising poly[[9-(1-octylnonyl)-9h-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) blended with [6,6]-phenyl-C71-butyric acid methyl (PC₇₁BM) esters as active layer. As semitransparent cathode sputtered aluminum doped ZnO was used in combination with a sputter damage preventing, thin (8 nm) TiO_x layer processed from solution and a sputtered aluminum interlayer (ALI). The short circuit current improves for thicker ALIs due to increased reflectance at the cathode leading to average efficiencies of 4.0% for semitransparent solar cells. Comparable results (3.9%) were achieved for devices comprising thick absorbers and thin ALIs.

+

Show PACS

88.40.jm

Thin film III-V and II-VI based solar cells

Select this Article FREE

Publisher’s Note: “Impact of unbalanced charge transport on the efficiency of normal and inverted solar cells” [Appl. Phys. Lett. 100, 013306 (2012)]

J. D. Kotlarski and P. W. M. Blom

Appl. Phys. Lett. 100, 079901 (2012); http://dx.doi.org/10.1063/1.3688479 (1 page)

Online Publication Date: 16 February 2012

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable

+

Show PACS

99.10.Fg	Publisher's note
88.40.J-	Types of solar cells

Select this Article FREE

Spatially resolved spectral mapping of phase mixing and charge transfer excitons in bulk heterojunction solar cell films

I. Riisness, C. Carach, and M. J. Gordon

Appl. Phys. Lett. 100, 073308 (2012); http://dx.doi.org/10.1063/1.3687185 (4 pages)

Online Publication Date: 16 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

Donor-acceptor phase mixing and charge transfer excitons (CTXs) in bulk heterojunction solar cell films have been imaged using confocal photoluminescence (PL) and Raman microscopy. Spatially resolved spectral analysis of PL was used to map fullerene diffusion and agglomeration as well as detect local changes in interfacial contact between donor and acceptor domains due to thermal annealing. CTX emission was most intense at the periphery of micron-sized fullerene agglomerates, which correlates with fullerene depletion in the surrounding film. Raman scattering indicates that the polymer phase is essentially immobile during the annealing process and that fullerene agglomerates reside atop a polymer-rich underlayer.

+

Show PACS

88.40.jr

Organic photovoltaics

Select this Article FREE

Characterizing the charge collection efficiency in bulk heterojunction organic photovoltaic cells

Richa Pandey and Russell J. Holmes

Appl. Phys. Lett. 100, 083303 (2012); http://dx.doi.org/10.1063/1.3686909 (3 pages)

Online Publication Date: 22 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We demonstrate a technique for determining the charge collection efficiency (η_CC) in bulk heterojunction organic photovoltaic cells (OPVs). To extract η_CC, we describe an approach to measure the optical absorption efficiency by examining the external quantum efficiency under reverse bias. Using estimates of the exciton diffusion efficiency obtained from photoluminescence quenching measurements, η_CC is calculated without any input from optical field simulations. For bulk heterojunction OPVs based on the donor-acceptor pairing of boron subphthalocyanine chloride and C₆₀, a peak η_CC of (79 ± 2)% is realized for films containing 80 wt. % C₆₀ under short-circuit conditions. This optimum composition also coincides with a peak in the fill factor and the short-circuit current density.

+

Show PACS

88.40.hj	Efficiency and performance of solar cells
88.40.jr	Organic photovoltaics

Select this Article FREE

Small molecular phosphorescent organic light-emitting diodes using a spin-coated hole blocking layer

Yan Zhao, Lian Duan, Deqiang Zhang, Liudong Hou, Juan Qiao, Liduo Wang, and Yong Qiu

Appl. Phys. Lett. 100, 083304 (2012); http://dx.doi.org/10.1063/1.3688300 (4 pages)

Online Publication Date: 23 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

Small molecular green phosphorescent organic light-emitting diodes (OLEDs) have been studied using a solution processed polyethyleneoxide (PEO) hole blocking layer (HBL) and a Cs₂CO₃/Al cathode. PEO is soluable in alcoholic solvents and allows the fabrication of multilayer OLEDs by successive spin-coating. The current efficiency of the optimized OLED with the PEO HBL increases from 18.8 cd/A to 32.1 cd/A, and the turn-on voltage reduces from 4.8 V to 3.4 V, compared with the device without the PEO HBL. Photovoltaic measurements indicate that the injection barrier for electron is reduced by inserting the PEO layer. X-ray photoelectron spectroscopy measurements further reveal that improvement in device performance is due to the partial penetration of Cs into the PEO layer.

+

Show PACS

85.60.Jb

Light-emitting devices

Select this Article FREE

Solution doping of organic semiconductors using air-stable n-dopants

Yabing Qi, Swagat K. Mohapatra, Sang Bok Kim, Stephen Barlow, Seth R. Marder, and Antoine Kahn

Appl. Phys. Lett. 100, 083305 (2012); http://dx.doi.org/10.1063/1.3689760 (4 pages)

Online Publication Date: 24 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

Solution-based n-doping of the polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI₂OD-T₂)] and the small molecule 6,13-bis(tri(isopropyl)silylethynyl)pentacene (TIPS-pentacene) is realized with the air-stable dimers of rhodocene, [RhCp₂]₂, and ruthenium(pentamethylcyclopentdienyl)(1,3,5-triethylbenzene), [Cp*Ru(TEB)]₂. Fermi level shifts, measured by direct and inverse photoemission spectroscopy, and orders of magnitude increase in current density and film conductivity point to strong n-doping in both materials. The strong reducing power of these air-stable dopants is demonstrated through the n-doping of TIPS-pentacene, a material with low electron affinity (3.0 eV). Doping-induced reduction of the hopping transport activation energy indicates that the increase in film conductivity is due in part to the filling of deep gap states by carriers released by the dopants.

+

Show PACS

81.05.Fb	Organic semiconductors
72.20.Ee	Mobility edges; hopping transport
73.61.Ph	Polymers; organic compounds
78.66.Qn	Polymers; organic compounds
79.60.Bm	Clean metal, semiconductor, and insulator surfaces
61.72.up	Other materials

Select this Article FREE

Efficiency enhancement of organic photovoltaics by addition of carbon nanotubes into both active and hole transport layer

Minas M. Stylianakis and Emmanuel Kymakis

Appl. Phys. Lett. 100, 093301 (2012); http://dx.doi.org/10.1063/1.3690056 (5 pages)

Online Publication Date: 27 February 2012

Full Text: Read Online (HTML) | Download PDF

+

Show Abstract

We investigate the effect of the incorporation of single walled carbon nanotubes (SWNTs) into both the active layer and the hole transport layer (HTL) on bulk heterojunction organic photovoltaic devices. The overall efficiency gain for such a device is 40%, compared with the pristine device. The observed efficiency gain is attributed to a more efficient exciton dissociation due to the SWNTs presence in the photoactive layer and an overall enhanced hole transport and collection through the SWNTs percolation paths, which are extended in both the active layer and the HTL.

+

Show PACS