Hybrid Organic-inorganic Devices Research Articles

Sequential Reactions of Surface- Tethered Glycolytic Enzymes

The development of complex hybrid organic-inorganic devices faces several challenges, including how they can generate energy. Cells face similar challenges regarding local energy production. Mammalian sperm solve this problem by generating ATP down the flagellar principal piece by means of glycolytic enzymes, several of which are tethered to a cytoskeletal support via germ-cell-specific targeting domains. Inspired by this design, we have produced recombinant hexokinase type 1 and glucose-6-phosphate isomerase capable of oriented immobilization on a nickel-nitrilotriacetic acid modified surface. Specific activities of enzymes tethered via this strategy were substantially higher than when randomly adsorbed. Furthermore, these enzymes showed sequential activities when tethered onto the same surface. This is the first demonstration of surface-tethered pathway components showing sequential enzymatic activities, and it provides a first step toward reconstitution of glycolysis on engineered hybrid devices.

A simple route towards low-temperature processing of nanoporous thin films using UV-irradiation: Application for dye solar cells

Fabrication of anatase TiO 2 porous films at low temperature was achieved by a very simple, straightforward and cheap method involving the connection of oxide particles by UV-irradiation in air. The novelty of the method relies on the direct UV-irradiation of oxide nanoparticles, without the presence of any oxide precursor or any additional treatment to form the nanoparticulate film. As electrodes for dye solar cells (DSCs), the 1–3 μm-thick films modified with Dyesol N3 dye showed high photovoltaic responses, a maximum overall energy conversion efficiency of 2.4–2.5% being measured under AM1.5 illumination at 100 and 140 mW cm −2. This method was extended to other semi-conducting oxides such as SnO 2. Efficiencies as high as 1.8% and 1.5% were measured under AM1.5 illumination at 64 and 140 mW cm −2, respectively. This approach draws new prospects in the field of plastic organic–inorganic hybrid devices.

Enhanced pure red electroluminescence intensity of Eu(o-BBA)3(phen) by red dye co-doping and inorganic semiconductor as charge carrier function layer

There is an emission peak at 494nm in the electroluminescence (EL) of PVK [poly(n-vinylcarbazole)]: Eu(o-BBA)3(phen) besides PVK exciton emission and Eu3+ characteristic emissions. Both the peaking at 494nm emission and PVK emission influenced the color purity of red emission from Eu(o-BBA)3(phen). In order to restrain these emissions and obtain high intensity red emission, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7,-tetramethyljulolidy-9-enyl)-4Hpyran (DCJTB) and Eu(o-BBA)3(phen) were co-doped in PVK solution and used as the active emission layer. The EL intensity of co-doped devices reached to 420cd/m2 at 20V driving voltage. The chromaticity coordinates of EL was invariable (x=0.55, y=0.36) with the increase of driving voltage. For further improvement of EL intensity, organic–inorganic hybrid devices (ITO/active emission layer/ZnS/Al) were fabricated. The EL intensity was increased by a factor of 2.5 [(420cd/m2)/(168cd/m2)] when the Eu complex was doped with an efficient dye DCJTB, and by a factor of ≈4 [(650cd/m2)/(168cd/m2)] when in addition ZnS layer was deposited on such an emitting layer prior to evaporation of the Al cathode.

Direct deposition of magnetite thin films on organic semiconductors

Technological procedures able to produce high quality electrodes from magnetic oxides in vertical organic-inorganic hybrid devices is a challenging task in the field of organic spintronics. Thin films of magnetite (Fe3O4) have been successfully grown directly on top of organic semiconductor layers, tris(8-hydroxyquinoline)aluminium(III) (Alq3), by pulsed-electron ablation technique. The films show ferromagnetic behavior and good structural quality, properties detected by magneto-optical Kerr effect, superconductor quantum interference device, micro-Raman spectroscopy, and Atomic Force Microscopy. The ferromagnetic behavior persists even for 10nm thick films. Charge injection at magnetite-organic interface has been finally demonstrated by detecting electroluminescence from Alq3.

Octadecyltriethoxysilane Surface Modification of Zinc Oxide

AbstractZinc Oxide (ZnO) is actively investigated for hybrid organic inorganic device applications. The interface greatly influences the electronic properties of these devices. Molecular surface modification of ZnO is being investigated for its potential to control the alignment of energy levels, charge transfer, as well as, interfacial chemical characteristics that influence device fabrication. In this study, octadecyltriethoxysilane (OTES) treatments of thin film ZnO produced by sol-gel decomposition were explored. The ZnO films were hydroxylated and then modified using OTES in solution. The condensation reaction of the OTES at the surface was promoted by the addition of a protoamine catalyst. Contact angle and infrared spectroscopy studies confirmed the surface modification and indicated that the coverage of the OTES was submonolayer. The modified ZnO films were reproducible and stable for long periods. The effects of the modification on subsequently spin-cast poly[3-hexylthiophene](P3HT) and on hybrid ZnO/P3HT organic solar cell performance are discussed.

Long‐Range Resonant Energy Transfer for Enhanced Exciton Harvesting for Organic Solar Cells

Exciton harvesting is of fundamental importance for the efficient operation of organic photovoltaic devices. The quantum efficiencies of many organic and hybrid organic-inorganic devices are still limited by low exciton harvesting efficiencies. This problem is most apparent in planar heterostructures that suffer from a direct tradeoff between light absorption and exciton harvesting. The bulk heterojunction concept [1,2] was designed to alleviate the problem of limited exciton migration by intimately blending the donor and acceptor phases on the nanometer length scale. In some polymer/fullerene systems, such as poly(2-methoxy,5-(3,7-dimethyloctyloxy)-1,4phenylenevinylene) (MDMO-PPV)/(6,6)-phenyl C61-butyric acid methyl ester (PCBM), time resolved spectroscopy shows the photoinduced formation of the radical anions and cations on femtosecond timescales. [3] This ultrafast formation of the polaron signature is only possible if every exciton is formed on a polymer chain segment that is immediately adjacent to one or more fullerene molecules. However, in other systems, very large domains prevail and, consequently, exciton harvesting is inefficient. [4] This has made the fabrication of efficient devices incorporating new materials difficult because each new material leads to a new morphology with its own characteristic length scale. The ordered bulk heterojunction architecture is intended to alleviate these issues by using a pre-patterned nanostructured scaffold [5–7] that has been engineered to have both straight pathways to the electrodes to ensure efficient carrier collection, and controlled domain size to ensure efficient exciton harvesting. Recently, chain alignment has been shown to be promoted for regioregular poly(3-hexyl thiophene) (RR-P3HT) in straight nanopores of anodic alumina leading to a 20-fold increase in hole-mobility in these structures. [8] For solar cell applications, higher mobilities reduce the effects of space charge [9] and increase the probability of separating the geminate pair formed immediately after exciton dissociation. [10–13] While the ordered bulk heterojunction architecture shows promise, existing structures have domains too large [14,15] for efficient exciton harvesting with singlet diffusion lengths only ca. 3–8 nm. [16–18] At this time, few alternatives other than nanostructuring have been proposed to increase exciton harvesting. Triplet excitons have been shown to have large diffusion lengths due to their long lifetimes, [18–20] but except in a few examples [21,22] this usually comes at the expense of a loss in energy of 0.4–0.8 eV associated with intersystem crossing between the photoexcited singlet to the first excited triplet. [23–25]

Organic–Inorganic Hybrid Optical Upconverter

We report a hybrid organic-inorganic optical upconverter that converts input 1.5-mum infrared light to output visible light. The device was made by direct tandem integration of an inorganic InGaAs/InP photodetector with an organic light-emitting diode (OLED). Incoming 1.5-mum light optical radiation is absorbed by the semiconductor p-i-n detector. The resultant photocurrent drives the OLED to emit visible light at ~520 nm in wavelength. The ratio of the photocurrent-induced versus dark-current-induced visible light emission was measured to be over 100 at a device bias of 14 V at room temperature. Devices with different configurations of the hole transport layer (HTL) were fabricated and tested. It was found that the devices with an HTL of C60/CuPc/NPB exhibited a lowest turn-on voltage (~3.8 V). The results show that the interfacial structure at the inorganic-organic interface plays a vital role in enabling the integration of the hybrid organic-inorganic devices.

Electrical and photovoltaic properties of devices based on PbPc–TiO 2 thin films

The electrical, optical and photovoltaic properties of organic–inorganic hybrid devices consisting of Al/TiO 2/PbPc/ITO and Al/PbPc/TiO 2/ITO structures have been investigated through analyzing the current–voltage characteristics, optical absorption and photocurrent action spectra of the devices. The combined presence of oxygen, light and an electric field in the photocurrent decay of Al/TiO 2/PbPc/ITO device have been studied. It is observed that under illumination, the oxygen radical anions and excitons are formed, which subsequently drift towards the interface with TiO 2, where an internal electric field is present. The excitons that reach to the interface are subsequently dissociated into free charge carriers due to the electric field present at the interface. The exciton diffusion length for PbPc calculated from the dependence of luminescence with the PbPc film is about 13 nm. We have also studied the effect of PbPc thickness and hole mobility on the device performance of organic photovoltaic device consisting of PbPc as an optically active layer, TiO 2 as the electron–transporting layer and ITO and Al used as electrodes. We have shown that the power conversion efficiency in the device is primarily limited by the short-exciton diffusion length combined with the low-hole mobility in PbPc layer. The model of charge transport in Al/TiO 2/PbPc/ITO device explained the experimental results where the total current density is a function of injected carriers at electrode–organic semiconductor surface, the leakage current through the organic layer and collected photogenerated current that results from the effective dissociation of excitons.

Amplified spontaneous emission light source near 640 nm in an organic–inorganic hybrid device based on a dye-filled hollow optical fiber

A new type of amplified spontaneous emission (ASE) source in the visible range is proposed and experimentally demonstrated using a novel dye-filled hollow optical fiber (HOF) with a ring core, where optical guiding is provided by silica fiber while the gain is obtained by organic dye to form an organic–inorganic hybrid active device. The pump and signal light intensity distributions in the hybrid structure are theoretically analyzed along with experimental results. ASE near 640 nm with 150 nm bandwidth and peak power level of −52.61 dBm has been achieved.

Adsorption of cata-condensed aromatics on a Si(100)–2 × 1 surface investigated by infrared absorption spectroscopy

The analysis and control of interfaces between organic molecules and Si surfaces are basic issues for developing organic–inorganic hybrid devices. In this study, the adsorption of cata-condensed aromatics such as naphthalene, anthracene and pentacene on a Si(1 0 0)–2 × 1 surface was investigated by infrared reflection absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). It was found that the adsorption configuration of naphthalene is strongly dependent on the surface coverage. In contrast, larger aromatics such as anthracene and pentacene show less surface coverage dependence. The details of the adsorption configurations are discussed on the basis of frequency calculations performed with a density functional theory.

Adsorption of cata-condensed aromatics on a Si(1 0 0)–2 × 1 surface investigated by infrared absorption spectroscopy

The analysis and control of interfaces between organic molecules and Si surfaces are basic issues for developing organic–inorganic hybrid devices. In this study, the adsorption of cata-condensed aromatics such as naphthalene, anthracene and pentacene on a Si(100)–2 × 1 surface was investigated by infrared reflection absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). It was found that the adsorption configuration of naphthalene is strongly dependent on the surface coverage. In contrast, larger aromatics such as anthracene and pentacene show less surface coverage dependence. The details of the adsorption configurations are discussed on the basis of frequency calculations performed with a density functional theory.

White emission from polymer/quantum dot ternary nanocomposites by incomplete energytransfer

White light emission was obtained from a light-emitting diode prepared frompolymer/quantum dot nanocomposites consisting of poly(9,-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (PDHFPPV) and two kinds of CdSe nanoparticles with differentparticle size. Blue emission from the polymer, green emission from the nm CdSe and red emission from the nm CdSe, which is triggered by partial excitation energy transfer from the polymer, jointlycontribute to white emission of the organic–inorganic hybrid device. Also, the blue-emittingmatrix polymer makes the device preparation process simpler due to its high processability.By controlling the blend ratio, we could obtain a pure white colour from the hybrid device.

Organic–inorganic hybrid electroluminescence device fabricated by conjugated polymer and ZnS:Mn

An organic–inorganic hybrid device was fabricated. The architecture of the hybrid device consisted of two layers sandwiched between two injecting electrodes, one of which was a conjugated polymer layer and the other was an inorganic material layer. Emission from both the organic and inorganic layers was observed, but the mechanisms of luminescence for the layers were different. Our primary results suggest the possibility of integrating different types of luminescence into one device structure.