Zakya H. KafafiLehigh University · Department of Electrical and Computer Engineering
Zakya H. Kafafi
Ph.D.
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Publications (234)
In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors...
The optical and electrical properties of optically thin one-dimensional (1-D) Ag nanogratings and two-dimensional (2-D) Ag nanogrids are studied, and their use as transparent electrodes in organic photovoltaics is explored. A large broadband and polarization-insensitive optical absorption enhancement in the organic light-harvesting layers is theore...
The optical and electrical properties of optically-thin one-dimensional (1D)
Ag nanogratings and two-dimensional (2D) Ag nanogrids are studied, and their
use as transparent electrodes in organic photovoltaics are explored. A large
broadband and polarization-insensitive optical absorption enhancement in the
organic light-harvesting layers is theoret...
We systematically investigate the optical and electrical properties of ultrathin two-dimensional (2D) Ag nanogratings (NGs), and explore their use as plasmonic transparent conducting electrodes in molecular organic photovoltaics (OPVs). A large broadband and polarization-insensitive optical absorption enhancement in the CuPc (copper phthalocyanine)...
We investigate the optical absorption enhancement in molecular OPVs, in which an ultrathin Ag nanogrid is employed as a transparent electrode. A very high total photon absorptivity of 0.49 is predicted for such OPV architecture.
Recent advances in molecular organic photovoltaics (OPVs) have shown 10% power conversion efficiency (PCE) for single-junction cells, which put them in direct competition with PVs based on amorphous silicon. Incorporation of plasmonic nanostructures for light trapping in these thin-film devices offers an attractive solution to realize higher-effici...
Broadband light absorption enhancement is numerically investigated for the active light harvesting layer of an organic photovoltaic (OPV), which consists of a blend of poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). Periodic plasmonic nanostructures placed above and below the active laye...
This paper discusses the third-order nonlinear optical (NLO) properties of metal-free, lead and transition metal phthalocyanines, as well as scandium, yttrium and lanthanide bisphthalocyanines measured by time-resolved degenerate four-wave mixing at 1064 nm. The study focuses on the structure-property relationships and explores the possible mechani...
Incorporation of plasmonic nanostructures for light trapping is an attractive solution to enhance the optical absorption of the active light-harvesting layer(s) in thin-film photovoltaic cells. The latest research highlights on plasmonic-enhanced organic photovoltaics (OPVs), including metallic nanoparticles and periodic nanopatterned structures, a...
Broadband light absorption enhancement is numerically investigated for double plasmonic nanostructures in thin-film organic photovoltaics (OPVs) using Ag, Al, and Au. A spectrally broadband, polarization-insensitive, and wide-angle absorption enhancement in the organic layer is predicted.
Broadband light absorption enhancement is numerically investigated for double plasmonic structures in thin-film organic photovoltaics. Due to the combined excitation of different Surface Plasmon modes, the absorption enhancement of about 67% is obtained.
Time-resolved degenerate four-wave-mixing studies have been conducted on solutions of transition-metal complexes of benzenedithiol using a 35 ps Nd:YAG laser operating at 1.064 μm. The nonlinear optical properties of the first-row Co(d7), Ni(d8), and Cu(d9) and the d8 group Ni and P t transition metal complexes are discussed.
The third order nonlinear optical (NLO) response of metal free tetrakis(cumylphenoxy)-phthalocyanine, (H2Pc(CP)4) was investigated at 597 nm, near resonance with the strong Q band. The second hyperpolarizability, γ, and the figure of merit, χ(3)/α, measured with a 1.2 ps pulse. was approximately independent of concentration between a 4.6×10−4 M sol...
The 41 papers in this special issue focus on next-generation organic and hybrid solar cells.
We theoretically demonstrate a polarization-independent nanopatterned ultra-thin metallic structure supporting short-range surface plasmon polariton (SRSPP) modes to improve the performance of organic solar cells. The physical mechanism and the mode distribution of the SRSPP excited in the cell device were analyzed, and reveal that the SRSPP-assist...
Reactions of monatomic, diatomic, and triatomic carbon with H2O, H218O, and D2O in argon matrices at 12 K have been investigated by Fourier transform infrared spectroscopy. The absence of infrared absorption peaks due to C1,2/H2O product(s) suggest that carbon atoms and diatomic carbon molecules do not react with H2O. However, triatomic carbon was...
The light extraction efficiency of an organic light-emitting diode (OLED) was significantly enhanced upon incorporating a photonic-crystal (PC) pattern consisting of ZnS pillars residing on top of the transparent anode-glass substrate. The luminance efficiency of the PC-OLED is enhanced by a factor of 2.1 to 2.4 depending on the periodicity of the...
Heterojunction organic photovoltaic devices were fabricated using C60 as the electron acceptor and several pentacene derivatives with triisopropylsilylethynyl functional groups as the electron donor. The open circuit voltage (Voc) of functionalized pentacene-based cells is significantly higher (0.57–0.90V) than for cells based on unsubstituted pent...
We report a study on solar cells using pentacene derivatives with triisopropylsilylethynyl substitution at the 6,13-position and 1,3-dioxolane substitution to the terminal benzenoid rings of pentacene as the electron donor and C60 as the electron acceptor. A significant increase in the open circuit voltage (Voc) was obtained in all the pentacene-de...
We studied hole injection from the conducting polymer blend poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) by optical spectroscopy and characterization of organic light-emitting diodes (OLEDs). Electroabsorption (EA) spectroscopy was used to measure the built-in potential of polyfluorene-based OLEDs with indium tin oxide (ITO)...
In order to develop a fundamental understanding for the effect of molecular packing on the carrier transport properties of organic semiconductors, single crystals of 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP) were prepared using the physical vapor transport technique and characterized by X-ray crystallography. There is...
We report a compact light collection scheme suitable for retrofitting a scanning tunneling microscope (STM) for STM-induced light emission experiments. The approach uses a pair of optical fibers with large core diameters and high numerical apertures to maximize light collection efficiency and to moderate the mechanical precision required for alignm...
The electronic structures of two series of end-capped thiophene oligomers, one set containing the electron-deficient dimesitylboryl end-cap and one containing the electron-rich triaryl amine end-cap, have been modeled using semiempirical quantum chemical calculations and the results used to assign features in the photoemission spectra of the materi...
The authors demonstrate efficient molecular organic light-emitting diodes that use direct hole injection from poly(3,4-ethylene-dioxythio-phene):poly(styrene-sulfonate) into a single layer of tris(8-hydroxyquinoline) aluminum (III) for carrier transport and electroluminescence. Single-layer devices have a lower operating bias and higher luminous po...
X-ray crystal structure analysis of a sublimation-grown spiro silabifluorene, that is highly fluorescent in the violet-blue,
established that there are six cocrystallized ordered conformers in the asymmetric unit. Crystals were grown by a vapor transport
method under argon gas flow at temperatures between 255–280°C. As expected, there are no cocrys...
The electronic structures of 2,5-bis(6′-(2′,2″-bipyridyl))-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PyPySPyPy) and 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PPSPP) at their interfaces with Mg were investigated using ultraviolet, inverse, and x-ray photoemission spectroscopies. PyPySPyPy and PPSPP have been used as bot...
Organic light-emitting diodes (OLEDs) containing red-light-emitting dioxolane-substituted pentacene derivatives are fabricated and characterized. The OLEDs feature guest-host emitting layers consisting of either 6,14-bis(triisopropylsilylethynyl)1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (TP-5) or 2,2,10,10-tetraethyl-6,14-bis(triisopropylsilylet...
A series of primary, secondary, and tertiary amines have been examined as cosolvents with trioctylphosphine oxide (TOPO) for the synthesis of CdSe nanoclusters. Syntheses were conducted in 66 mol % hexadecylamine (HDA), dodecylamine (DDA), dioctylamine (DOA), or trioctylamine (TOA) in TOPO and the growth rates and size distributions of the resultin...
We examine the steady-state and time-resolved photoluminescence of guest-host films featuring a dioxolane-substituted pentacene derivative (2,2,10,10-tetraethyl-6,14-bis(triisopropylsilylethynyl)-1,3,9,11-tetraoxadicyclopenta[b,m]pentacene, EtTP-5) dispersed in the hole transporting material (4,4-bis[N-1-naphthyl-N-phenylamino]biphenyl, alpha-NPD)....
Low-temperature laser sintering has been successfully demonstrated to improve the overall conversion efficiency of dye-sensitized solar cells. Mesoporous TiO2 electrodes were prepared from a colloidal solution of TiO2 nanopowders by a laser direct-write technique and then sintered by a quasi-continuous-wave UV laser (λ=355nm) for the fabrication of...
Two novel dioxolane-substituted pentacene derivatives, namely, 6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (TP-5) and 2,2,10,10-tetraethyl-6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (EtTP-5), have been synthesized and spectroscopically characterized. Here, we examine the ste...
This study reports the fabrication and characterization of nanoscale organic light-emitting diodes (nano-OLEDs) based on poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV). The nano-OLEDs were fabricated by spin casting MEH-PPV into cylindrical nanoholes lithographically patterned into silicon nitride. The electroluminescence (EL...
Two aryl-substituted red emitting pentacenes, 5,6,13,14-tetraphenylpentacene (asym-TPP) and 5,14-bis(2,6-dimethylphenyl)-6,13-diphenylpentacene (DMPDPP), have been prepared and spectroscopically characterized. Guest−host films of pentacene derivatives dispersed in tris(quinolin-8-olato)aluminum(III) (Alq3) exhibit narrow red emission (λmax = 663−68...
We have studied energy transfer to a dioxolane-substituted pentacene derivative, 6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (TP-5), from tris(8-hydroxyquin-8-olinato) aluminum(III) (Alq3) by steady state and time-resolved photoluminescence (PL) spectroscopy. The Förster transfer radius is 27 Å, calculated from...
A series of four asymmetrically aryl-substituted 9,9'-spiro-9-silabifluorene (SSF) derivatives, 2,2'-di-tert-butyl-7,7'-diphenyl-9,9'-spiro-9-silabifluorene (PhSSF), 2,2'-di-tert-butyl-7,7'-dipyridin-2-yl-9,9'-spiro-9-silabifluorene (PySSF), 2,2'-di-tert-butyl-7,7'-dibiphenyl-4-yl-9,9'-spiro-9-silabifluorene (BPhSSF), and 2,2'-di-tert-butyl-7,7'-bi...
We investigate the excitation energy transfer in a guest-host molecular system consisting of a pentacene derivative, namely 6,13-bis(2,6-dimethylphenyl)pentacene (DMPP), doped into tris(8-hydroxyquinolinato)aluminum (Alq(3)) using steady-state and time-resolved photoluminescence (PL) spectroscopy. The concentration dependent energy transfer rate an...
We have investigated the initial stages of vacuum-deposited sexithiophene (alpha-6T) adlayer formation on Au(111) vicinal surfaces at room temperature. The in situ scanning tunneling microscopy (STM) and photoemission spectroscopy (PES) reveal a step edge-driven growth of alpha-6T on the Au(111) vicinal surfaces that first leads to the formation of...
Single heterojunction, small-molecule organic photovoltaic devices (OPVs) have been prepared on fully flexible thermoplastic substrates using prepatterned conducting polymer electrodes( ∼ 450 Ω/◻). OPVs were fabricated via sequential vacuum vapor deposition of layers of the organic electron donating/hole transporting material: N,N′-(α-naphthyl)-N,N...
We report on a detailed quantum-chemical study of the geometric structure and electronic properties of 2,5-bis(6(')-(2('),2(")-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy) and 2,5-di- (3-biphenyl)-1,1-dimethyl-3,4-diphenylsilole (PPSPP). These molecular systems are attractive candidates for application as electron-transport materials in...
Single heterojunction and multi-heterojunction, small-molecule organic
photovoltaic devices (OPVs) have been prepared on Glass/ITO and
fully-flexible thermoplastic substrates using pre-patterned, conducting
polymer electrodes (~ 450Ω/). OPVs were fabricated via sequential
vacuum vapor deposition of layers of the organic electron donating/hole
trans...
High luminance organic light-emitting diodes (OLEDs) with a relatively low operating voltage are presented using a conducting polymer [without an indium−tin oxide (ITO) underlayer] as a hole-injecting electrode (anode) and silole derivatives as an emitter and/or an electron transporter. The conducting polymer films of poly(3,4-ethylenedioxythiophen...
Pulsed-laser deposition and laser direct-write have been applied to deposit dense ( 30 nm thick) and porous nanocrystalline TiO <sub>2</sub> ( nc - TiO <sub>2</sub> , 5–20 μ m thick) layers incorporated in dye-sensitized solar cells. Laser direct-write is a laser-induced forward transfer technique that enables the fabrication of conformal structure...
Laser processing techniques, such as laser direct-write (LDW) and laser sintering, have been used to deposit mesoporous nanocrystalline TiO 2 (nc-TiO 2) films for use in dye-sensitized solar cells. LDW enables the fabrication of conformal structures containing metals, ceramics, polymers and composites on rigid and flexible substrates without the us...
A series of three pentacene derivatives featuring substituted aryl groups at the 6,13-position, namely, 6,13-diphenylpentacene, 6,13-bis(2,6-dimethylphenyl)pentacene, and 6,13-bis(4-tert-butylphenyl)pentacene, have been synthesized and characterized. The optical properties of each compound have been determined in solution and in the solid state. Fi...
Photoemission spectroscopy of an interface between Mg and a silole derivative, 2,5-bis[6′-(2′,2″-bipyridyl)]-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PyPySPyPy) reveals the formation of two gap states both at metal-on-organic (Mg/PyPySPyPy) and organic-on-metal (PyPySPyPy/Mg) interfaces. The appearance of gap states is interpreted as the resu...
The electronic structure of the interface formed by Mg deposition onto 2,5-bis(6"-(2",2"-bipyridyl))-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PyPySPyPy) was investigated using ultraviolet, inverse, and X-ray photoemission spectroscopies. PyPySPyPy is of interest for use as an electron injection/transport layer in high efficiency organic light...
We present high efficiency and high luminance molecular organic light-emitting diodes (MOLEDs) using a conducting polymer as a hole-injecting electrode (anode), a CsF/Al bilayer as a cathode, and silole derivatives as an emitter and/or an electron transporter. The conducting polymer films, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PE...
We report on electron injection from two different metal electrodes into three silole derivatives, namely 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP), 1,2-bis(1-methyl-2,3,4,5,-tetraphenylsilacyclopentadienyl) ethane (2PSP) and 2,5-bis-(2', 2''-bipyridin-6-yl)-1, 1-dimethyl-3,4-diphenylsilacyclopentadiene (PyPySPyPy), p...
We report a high luminance and low operating voltage molecular organic light-emitting diode (MOLED) using a conducting polymer hole-injecting electrode (anode) on a plastic substrate. A dramatic improvement in the rectification ratio is observed upon the insertion of a buffer layer between the conducting polymer anode and the organic hole-transport...
Bilayer organic light-emitting diodes based on tris-8-hydroxyquinolinato aluminum III have been fabricated where the thickness of the light-emitting layer was varied between 10 and 80 nm while maintaining a constant total thickness of the organic layers. The electroluminescence quantum efficiency of the devices was measured as a function of the emi...
Zr-doped ZnO (ZZO) thin films have been investigated as an anode material, a potential alternative to indium tin oxide (ITO), for organic light emitting diode (OLED) devices. ZZO films have been deposited on glass substrates by pulsed laser deposition. The electrical and optical properties of these films were studied as a function of substrate temp...
The surface sheet resistance of conducting films of glycerol-doped poly(3,4-ethylenedioxy-thiophene)–poly(styrene sulfonate) is largely dependent on the annealing temperature. The presence of free glycerol in insufficiently baked films, as indicated by infrared spectra and thermogravimetric analysis, results in conducting polymer films with poor mo...
Here, we report the performance of molecular organic light-emitting diodes (MOLEDs) using novel fluorescent silole derivatives as highly efficient blue and green-emitting organic materials. Three silole derivatives, namely 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP), 9-silafluorene-9-spiro-1′-(2′,3′,4′,5′-tetraphenyl)-1...
Photoemission spectroscopy of an interface formed through step-by-step deposition of Mg onto a film of a silole derivative, 2,5- bis [6<sup>′</sup>-(2<sup>′</sup>,2<sup>″</sup>- bipyridyl )]-1,1- dimethyl -3,4- diphenyl silacyclopentadiene (PyPySPyPy), reveals the formation of gap states arising from electron transfer from the metal to the organic....
Highly efficient exciplex emission is observed from molecular organic light-emitting diodes (MOLEDs) based on silole derivatives as emissive and electron transport materials, and a hole transporting amine derivative. A silole derivative, 2,5-di-(3-biphenyl)-1,1-dimethyl- 3,4-diphenylsilacyclopentadiene (PPSPP), which shows blue fluorescence (476 nm...
We report the performance of molecular organic light-emitting diodes (MOLEDs) using silole derivatives as emissive and electron transport materials. Two siloles, namely 2,5-di-(3- biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP) and 1,2-bis(1-methyl-2,3,4,5,- tetraphenylsilacyclopentadienyl)ethane (2PSP), with high PL quantum yields o...
High quality Sn-doped In2O3 (ITO) thin films have been grown by pulsed laser deposition (PLD) on glass, flexible polyethylene terephthalate (PET) and single crystal yttria stabilized zirconia (YSZ) substrates for use in organic light emitting diodes (OLEDs). Critical electrode issues for the OLED are related to the optical transparency, electrical...
It is well known that the centrosymmetric molecules and centrosymmetric materials don’t exhibit, at least within the dipolar scheme, second order nonlinear optical properties useful fore a large class of practical applications, such as frequency conversion through second harmonic generation or parametric processes, light amplification, electro-opti...
Zinc oxide thin films, doped with aluminum (AZO), gallium (GZO) and zirconium (ZZO), have been deposited on glass substrates by pulsed laser deposition. The electrical and optical properties of these films were investigated as a function of oxygen deposition pressure. These doped zinc oxide films were used as an anode contact to fabricate organic l...
Using a combination of ultraviolet and x-ray photoelectron spectroscopies, we have studied the relative energy level alignment of two phosphorescent guest molecules, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (PtOEP) and tris(2-phenylpyridine)iridium (Ir(ppy)3), doped in an electron transport host, tris(8-hydroxyquinolinato) aluminum (...
Films fabricated from commercially available poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) aqueous dispersions have been widely used in many electronic and optoelectronic applications. Previous attempts to utilize them as anodes in organic light-emitting diodes (OLEDs) were not satisfactory due to their low conductivity. In th...
Organic light emitting devices (OLEDs) have been fabricated on various flexible substrates using conducting polymers as anodes. In this paper we report on the performance of OLEDs using films of highly conductive Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) anodes without an indium tin oxide under-layer. The conducting polyme...
Two series of thin films of oligothiophene derivatives grown on Ag substrates have been studied with photoelectron spectroscopy. The oligothiophenes were end-capped with either electron-deficient dismesitylboryl or electron-rich diphenyltolylamine moieties to create molecules with electron-accepting or -donating properties, respectively. The positi...
Highly oriented indium tin oxide (ITO) thin films were grown by pulsed-laser deposition (PLD) on glass and single-crystal yttria-stabilized zirconia (YSZ) substrates. The structural, electrical, and optical properties of these films were investigated as a function of oxygen partial pressure. Films were deposited at substrate temperature of 300 °C i...
We report a photoemission study of the interfaces between spin-cast films of a new variation of a polymer blend consisting of poly(3,4-ethylenedioxy-thiophene) (PEDOT) and poly(4-styrenesulfonate) (PSS) and glycerol as an additive, and vacuum-evaporated hole transport layers (HTL) of 4,4'-bis(carbazol-9-yl)biphenyl (CBP),N,N'-diphenyl-N,N'-bis(1-na...
Using a combination of ultraviolet and x-ray photoelectron spectroscopies (UPS, XPS), we have studied the relative energy level alignment of two phosphorescent guest molecules, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (PtOEP) and tris(2-phenylpyridine)iridium (Ir(ppy)3), doped in an electron transport host, tris(8-hydroxyquinolinato)...
Results based on the electric-field dependence of electro-modulated fluorescence and steady-state photoconduction in films of tris-(8-hydroxyquinolinato) aluminum (III) (Alq3) are consistent with a model where singlet excitons dissociate into electron–hole pairs through charge transfer state. Dissociation into free carriers or predominantly geminat...
Phenyl, ethynyl-silyl and ethynyl-alkyl derivatives of pentacene have been optically characterized and their use as potential red emitters in organic light emitting devices is investigated. Tuning of the red emission wavelength and photoluminescence quantum efficiency ((phi) pl) is achieved by modifying the substituent and its position on the penta...
Investigations into the lithium fluoride and cesium fluoride/tris(quinolin-8-olato) aluminum (LiF-Alq3 or CsF-Alq3) Lewis acid-Lewis base pairs have been undertaken using hybrid density functional calculations. The results of the calculations clearly show that there is a strong interaction that occurs between the metal fluoride and both the facial...
Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) aqueous dispersion (PEDOT:PSS) is a highly conductive polymer. Attempts to utilize them as an anode in an organic light emitting diode have been made but a satisfactory result was not obtained due to low device efficiency caused by the relatively high surface resistance and poor optical transp...
Transparent conducting indium tin oxide (ITO) tin films were grown by pulsed-laser deposition (PLD) on glass and single crystal yttria-stabilized zirconia (YSZ) substrates. The structural, electrical and optical properties of these films were investigated as a function of substrate deposition temperature and background gas pressure. Films were depo...
We report on efficient molecular organic light-emitting diodes (MOLEDs) composed of novel silole derivatives as an electron transporting layer and an emissive layer. The silole derivative, 2,5-bis(2',2″-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene, used for the electron transport layer exhibits fast electron mobility of 2×10^<-4> cm...
Summary form only given. The operation of a molecular organic light-emitting diode (MOLED) involves injection of electrons and holes from the respective cathode and anode, carrier transport through one or more molecular layers and carrier recombination inside the emissive medium. We review various approaches adopted to molecularly tailor materials...
This Volume 4800 of the conference proceedings contains 30 papers. Topics discussed include organic light emitting materials, light emitting devices, polymers and light emitting devices, organic emissive displays, solid state lighting, carrier transporting and luminescent polymers, new fabrication and characterization techniques, spectroscopy and o...
The recombination zone in triple-layer electroluminescent (EL) devices with the structure indium-tin-oxide (ITO)/N,N'-diphenyl-N,N'bis(3-methylphenyl)-1,1'-biphenyl-4,4'diamine (TPD)/(tris-hydroxyquinolinato (Alq3) + dopant)/Alq3/Mg:Ag has been determined based on their emission quantum efficiency (EL), and examined as a function of applied voltage...
We have studied room temperature electron transport in amorphous films of tris (8-hydroxyquinolinolato) aluminum (III) (Alq3) with the time-of-flight technique. Nondispersive photocurrent transients indicate the absence of intrinsic traps in well-purified films. Exposure of the films to ambient atmosphere results in highly dispersive transport, ind...
We determined the work function of indium tin oxide (ITO) films on glass substrates using photoemission spectroscopy (PES). The ITO coated glass substrates were chemically cleaned ex-situ, oxygen plasma treated ex-situ, or sputtered in-situ. Our results suggest that the performance of ultraviolet photoemission spectroscopy (UPS) measurements can in...
We determined the orbital lineup of the tris 8-hydroxyquinolinato gallium (Gaq 3)/Mg interface using combined x-ray and ultraviolet photoemission spectroscopy XPS and UPS measurements. The Gaq 3 /Mg system is a prototypical model structure for organic electron/low work function electrode transporting materials interfaces found in organic light emit...