We investigated 0 to 300 Å thick stepped molybdenum trioxide (MoO3) inter-layer between in-situ oxygen plasma treated conducting indium tin oxide (ITO) and chloro-aluminum pthalocyanine (AlPc-Cl) layer-by-layer evaporated up to 228 Å, with ultra-violet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES). The MoO3 inter-layers were observed to increase the surface workfunction. The workfunction increase was observed to saturate at 20 Å of MoO3 coverage. The increased surface workfunction causes hole accumulation and band bending in the subsequently deposited AlPc-Cl. A possible explanation of reduction in series resistance by the insertion of the MoO3 insulating layer is discussed based on these observations and energy level alignment.

White OLEDs (WOLEDTMs) fabricated using energy efficient phosphorescent OLED (PHOLEDTM) technology open up exciting new ways to develop efficient white lighting. WOLEDs have the potential to transform the lighting industry. In this presentation, phosphorescent WOLEDs with high conductivity transport layers will be discussed. White light can be generated by partial energy transfer from blue to green and red. Single WOLED stacks are demonstrated that match the Energy Star® lighting color criteria for 2700K and 3000K with high efficiency (˜80 lm/W) and high color rendering indices (˜80). Both devices had operational lifetimes (LT70%) over 30,000 hours measured from an initial luminance of 1,000 cd/m2. Different techniques to improve optical outcoupling will also be discussed.

Doping polymers with inorganic nanomaterials to form hybrid nanocomposites is an attractive approach to develop new lightweight optoelectronic materials with unique or improved properties. In this work, poly(3-hexylthiophene) (P3HT) Schottky diodes, doped with ZnO nanowires at different P3HT-to-ZnO concentrations, were studied. Device fabrication was carried out by drop casting the nanocomposite on a Pt electrode followed by thermal evaporation of an Al top electrode. ZnO nanowires were prepared via a physical vapor method with Zn as a source. The nanowires were dispersed in chlorobenzene, then the P3HT powder was added. Properties of the diodes were investigated using capacitance-voltage and current-voltage measurements. In addition, electrical resistance of the nanocomposite films was also investigated using a two-point probe measurement with Pt as Ohmic contacts. Results showed that ZnO nanowire doping decreases the built in potential of the diode and the electrical resistance of the nanocomposite film.

Spectroelectrochemistry was used to study the electron trapping and rectifying behavior in several diphenylamine endgroup polymeric bilayers. Various combinations of the following monomers were pairwise sequentially electropolymerized onto ITO transparent electrodes: FD, DNTD, DPTD and Cl4DPTD. Poly(FD) is a p-type material while poly(DNTD), poly(DPTD) and poly(Cl4DPTD) are bipolar materials being both n-type and p-type. Bilayers of ITO|poly(FD)|poly (DNTD) or ITO|poly (FD)|poly (DPTD), block electrons from reducing the outer layer even at -1.0 V vs Ag/AgCl, yet holes effectively oxidize both layers. The LUMO differences between poly(DNTD) and poly(Cl4DPTD) or poly(DPTD) and poly(Cl4DPTD) provide a large enough electronic barrier that electron trapping can occur between these n-type materials. The visible spectra results imply that these polymers, poly(DPTD) or poly(Cl4DPTD) can be used as photovoltaic materials.

We investigated the possibility of doping poly (sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate) (PTEBS) with perylene tetracarboxylicdiimide (PTCDI) nanobelts through ultraviolet photoelectron spectroscopy (UPS) measurements. For our experiment, PTEBS was tuned to absorb maximum light in the range of 450 nm to 550 nm which corresponds to the maximum solar irradiance of the Earth’s atmosphere. Nanobelts of PTCDI were synthesized by gas phase self assembly process. Doping PTEBS with PTCDI nanobelts causes a shift in the Fermi level of the composite material with respect to the vacuum level as observed in the photoemission spectrum. With increased PTCDI doping, PTCDI does not act much like an electron donor, but more like an electron acceptor. The peaks corresponding to the sigma bonds shift towards the vacuum level with higher concentrations of the dopant. Using angled resolved photoemission spectra from a 3m toroidal grating monochromator, PTEBS displays change in the highest occupied molecular orbital in respect to its Fermi level when the side groups were substituted by H+ or OH- groups. The results confirm that the binding energy decreases with increase in activity of the dissolved hydrogen ions. It is evident that there is an increase in the density of states near the Fermi level and shifts to lower binding energies of the occupied molecular orbitals with pH level decrease, which is in agreement with the published optical absorption characteristics of PTEBS. Since UPS data confirm that PTCDI nanobelts dope PTEBS, along with its tunable absorption characteristics, this composite might be a promising material for optoelectronic application.

We report on a high efficiency deep-blue phosphorescent organic light-emitting diode (POLED) based on new electron-transporting host material. The new electron-transporting host material is an adamantane derivative with high triplet energy and high electron mobility. The deep blue POLED that we have developed utilizes a deep-blue phosphorescent guest material, iridium(III)bis(4’,6’,-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate, and exhibits a power efficiency of about 10.2 lm/W at luminance of 100 cd/m2 and maximum external quantum efficiency (EQE) of about 13 %. The power efficiency of our POLED is much higher than that of POLED using p–bis(triphenylsilyly)benzene (UGH2). The maximum EQE of our POLED was also slightly more than that of POLED using UGH2. The obtained difference in power efficiency originates from the new host material having higher electron mobility than that of UGH2.

In this work we have employed UV-Vis absorbance and excitation techniques in addition to quantum chemical calculations to investigate the probable formation of H-type aggregates of zero charged aryl substituted porphyrin in a guest- host solid state structure. The films were factored via casting technique mixing free-base tetrapyridyl porphyrins (H2TPyP) and polymethilmethacrilate polymer (PMMA) chlorophorm solutions. A pathway for the possible formation of H-type aggregate is suggested.

White organic LEDs are seen as one of the next generation light-sources, with their potential to reach internal efficiencies of unity and their unique appearance as large-area and ultrathin devices. However, to replace existing lighting technologies, they have to be at least on par with the state-of-the-art. In terms of efficiency, the fluorescent tube with 60-70 lumen per Watt (lm W-1) in a fixture is the current benchmark. In the scientific literature, so far only values of 44 lm W-1 have been published for white OLEDs.

Here, we present results (Reineke et al., Nature 459, 234 (2009)) of white OLEDs with 90 lm W-1 at an illumination relevant brightness of 1,000 candela per square meter (cd m-2). Extracting all light from the glass substrate using a 3D light extraction system, we even obtain 124 lm W-1. In order to achieve such high efficacy values, we reduced the energetic losses prior to photon emission that include ohmic and thermal relaxation losses, leading to very low operating voltages. This is accomplished by the use of doped transport layers and a novel, very energy efficient emission layer concept. Equally important, we addressed the optics of the OLED architecture, because about 80% of the generated light remains trapped in conventional devices. Therefore, we used high refractive index substrates to couple out more light and placed the emission to the second field antinode to avoid plasmonic losses. Our devices are also characterized by an outstandingly high efficiency at high brightness, reaching 74 lm W-1 at 5,000 cd m-2.

Two donor-acceptor copolymers containing perylene diimide and oligothiophenes linked through triple bonds have been designed and synthesized by palladium catalyzed Sonogashira coupling reaction. The introduction of the triple bond spacer between the electron-acceptor perylene moieties and the electron donating oligothiophene moieties produces an extended conjugation along the main chain, and produces soluble and high molecular weight copolymers.The thermal, optical and electrochemical properties of these copolymers were examined. The HOMO-LUMO energy levels of these copolymers, along with the photoinduced charge transfer process, probed by photoluminescence quenching and by FTIR photoinduced absorption spectroscopy, in blends with poly(3-hexylthiophene) (P3HT), indicate that they are suitable materials for application as electron acceptor and n-type components in bulk heterojunction solar cells with P3HT.

We have successfully investigated degradation-induced variations in electronic band-gap states in the emissive region of the Alq3-based OLEDs by a deep-level optical spectroscopy technique. Through the intrinsic degradation, both deep-level traps and near-band-edge transitions in the Alq3 emissive zone are found to be red-shifted significantly towards their corresponding bulk levels of the Alq3 single layer. These variations in the interfacial electronic states are probably induced by the intrinsic degradation and indicate that initial molecular structures characteristic of the Alq3 emissive zone are transformed into the bulk-like relaxed ones through the degradation.

Indium tin oxide (ITO) is widely used for opto-electronic products such as organic light-emitting diodes, organic photovoltaic devices and liquid crystal displays due to its high transparency and electrical conductivity. Since there is a trade-off between the conductivity and transparency of ITO, it is necessary to optimize performances of opto-electronic products by balancing the sheet resistance and transmittance. Both sheet resistance and transmittance are affected by a number of factors such as working temperature, working pressure, oxygen-to-argon ratio during the fabricating process, and thickness. In our study, ITO thin films were deposited on glass substrates by dc sputtering. Effects of ITO with different thicknesses, sheet resistances, and transmission spectra on the performance of bulk heterojunction photovoltaic devices were investigated.

White OLED consisting of a fluorescent blue emissive layer combined with a phosphorescent green and a phosphorescent red emissive layer were processed by means of Organic Vapor Phase Deposition (OVPD). Different concepts to tune the color coordinates of the device are discussed with respect to the luminous efficiency. Furthermore, the influence of device aging on the emitted spectrum is being investigated by means of spectrally resolved lifetime measurements.

We report on the improved performance of large-area organic solar cells and modules by integrating metal grids directly with the indium tin oxide (ITO), thereby reducing the series resistance contribution from the ITO. Devices with different areas (0.1, 7, and 36.4 cm2) were prepared to study the area-dependency of the organic solar cells based on pentacene and C60 heterojunctions. Modules were prepared in which four individual cells (7 cm2) were connected in series and parallel. For the series connected modules, VOC scales linearly with the number of cells while parallel connected modules exhibited multiplied current density as expected.

Large-scale manufacturing of organic light-emitting diode (OLED) panels for lighting and display has been slowed by several manufacturing factors, prominent among which are low throughput due in part to the fine metal mask technology for patterning the red-, green-, and blue-light-emitting pixels and low materials utilization efficiency of the available vacuum deposition technology. To overcome these impediments to low-cost OLED manufacturing, Kodak developed a blanket white-emitting OLED architecture in combination with a pixilated color filter array to eliminate the need for fine metal masks and developed a vacuum deposition technology capable of high deposition rates and high materials utilization efficiency. These developments, taken together, allow much higher throughput and yield on fifth-generation and larger substrates that promise to enable low-cost manufacturing of OLED displays and lighting panels. This paper focuses on the deposition technology Kodak developed, a flash vaporization process that can deliver very high materials utilization efficiency at high deposition rates for small-molecule OLED materials without increasing material decomposition.

We present an efficient polymer-small molecule triple-tandem organic solar cell (OSC), consisting of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) bulk heterojunction as the first and second cells, and small molecules copper phthalocyanine (CuPc) and fullerene (C60) as the third cell on top. These sub-cells are connected by an intermediate layer of Al(1 nm)/MoO3(15 nm), which appears to be highly transparent, structurally smooth, and electrically functional. Compared to our previous all polymer triple-tandem organic solar cells (2.03%), this polymer-small molecule triple-tandem organic solar cell achieves an improved power conversion efficiency of 2.18% with a short-circuit current density (Jsc) = 3.02 mA/cm2, open-circuit voltage (Voc) = 1.51 V, and fill factor (FF) = 47.7% under simulated solar irradiation of 100 mW/cm2 (AM1.5G), which can be attributed to the increased photocurrent generation in the third cell since the third cell has the complementary absorption with two bottom cells despite a slightly reduced Voc.

A two-dimensional finite element simulation model for the bi-layer heterostructure organic photovoltaic (PV) cell, based on copper phthalocyanine (CuPc) and fullerene (C60) in the presence and absence of electron transport layers (ETLs) is presented. The effect of bathocuproine (BCP), tris(8-hydroxyquinolinato)aluminum (Alq3), and copper phthalocyanine (CuPc) as ETLs on short-circuit current (Jsc), open-circuit voltage (Voc), and power conversion efficiency (PCE) is investigated. The Frenkel-Poole mobility model was employed in describing the conduction mechanisms in the active layers. Singlet exciton and Langevin recombination techniques were employed to describe excitonic generation and recombination, respectively. The obtained simulation results demonstrate that the efficiency of PV cells is primarily dependent on the short-circuit current, the absorption capability of the active layers, and the charge collection efficiency at the electrodes. In addition, significant reduction in power conversion efficiency is observed with increasing thickness of the ETL layer. From among the modeled device designs, PV cells containing a 50Å BCP layer result in the best power conversion efficiencies of 2.05%.

Hybrid solar cells based on conjugated polymers and colloidally synthesized inorganic nanoparticles have been recognized as an alternative to all-organic solar cells due to the intrinsically higher charge transport property in inorganic component. In this work, CdSe nanoparticles with different sizes, served as the electron acceptor, have been used together with poly(3-hexylthiophene) (P3HT) as the active layer for the hybrid solar cells. The power-conversion efficiency (ηp) of these devices strongly depends on the size of the CdSe nanoparticles, increasing from ηp ˜0.5% for 4.0 nm size nanoparticles to ηp ˜2.4% for 6.8 nm size nanoparticles under AM 1.5 G solar illumination. Furthermore, the devices also exhibit an unusual initial aging period when exposed to the air, which results in a significant enhancement in the short-circuit current, open-circuit voltage and power conversion efficiency.