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An organic phototransistor (OPT) shows nonvolatile memory effect due to its novel optical writing and electrical erasing processes. In this work, we utilize an organic light-emitting diode (OLED) as the light source to investigate OPT-based memory (OPTM) performance. It is found that the OPTM can be used as either flash memory or write-once read-many-times memory by adjusting the properties of the Ta2O5 gate dielectric layer. UV/ozone treatment is applied to effectively change dielectric properties of the Ta2O5 film. The mechanisms for this are examined by X-ray photoelectron spectroscopy and capacitance-voltage measurement. It turns out that the densities of oxygen vacancies and defects in the first 1.8 nm Ta2O5 films near the Ta2O5/semiconductor interface are reduced. Furthermore, for the first time, we use this multifunctional OPTM, which unites the photosensitive and memory properties in one single device, as an optical feedback system to tune the brightness of the OLED. Our study suggests that these OPTMs have potential applications in tuning the brightness uniformity, improving the display quality and prolonging the lifetime of flat panel displays.

Various works on modification of the indium-tin oxide (ITO) substrate have been carried out so as to enhance hole injection in organic light-emitting devices. Herein, a simple and efficient approach to tuning the work function of the ITO substrate is described by surface modification of ITO with an organosiloxane self-assembled monolayer. The influences of the electronegativity on modification of the ITO substrate are systematically investigated by attaching electron-withdrawing groups (Cl, Br, and I) and an electron-donating group (NH2) to the organosiloxane materials. The preparation and modification of the ITO substrate has been studied using primarily atomic force microscopy and X-ray photoelectron spectroscopy and vacuum-ultraviolet spectroscopy, and remarkable changes have been observed after modification. The device based on a 3Cl-Si-ITO-modified anode exhibits the best efficiency among the devices, better than the control devices based on bare ITO, UV-treated ITO, and even Cl-ITO.

Phosphorescent quantum yields have been increased by 12 times by choosing bulky boracic anions as counterions for blue-emitting cationic iridium(III) complexes.

Halogen ions (I(-), Br(-), Cl(-)) were added into a colloidal solution of CdSe and PbS quantum dots (QDs) to form QDs capped with these inorganic ligands. Halogen ions attached to QDs through electrostatic interactions and the varying coordination strength between the inorganic ligands and QDs led to different degrees of redispersion and stabilization in polar solvents. Moreover, we successfully conducted electrophoretic deposition (EPD) of QDs capped with inorganic ligands. Negatively charged QDs were adsorbed onto a positively charged TiO2 anode. The assembled QDs films were used in photovoltaic devices and offered better efficiency than QDs capped with organic ligands. This work demonstrates that halogen ions are indeed promising ligands to improve the stability of QDs with inorganic ligands and the EPD method shows prospects in assembling QDs films for practical applications.

Ir(III) metal complexes with general formula [(C^N)2Ir(P^SiO)], where (C^N)H is 2-phenylisoquinoline (1), 2-phenylpyridine (2) or 2-(2,4-difluorophenyl)pyridine (3), and (P^SiO)H is an organosilanolate ancillary chelate with either diphenylsilyl (a) or dimethylsilyl (b) substituent, were synthesized, among which the structure of 3a was also confirmed using single-crystal X-ray diffraction analyses. These complexes exhibit bright phosphorescence in the region of 489-632 nm in solution at room temperature, showing the first successful example of using organosilanolate as an ancillary chelate. For application, organic light emitting diodes (OLEDs) using phosphors 3a and 3b doped in N,N'-dicarbazolyl-3,5-benzene (mCP) exhibited a maximum brightness of 50,800 cd m(-2) at 800 mA cm(-2) (12 V) with η(ext) of 10.1% and a brightness of 45,900 cd m(-2) at 700 mA cm(-2) (14.5 V) with η(ext) of 10.2%, respectively.

In this paper, ZnO nanorod-nanosheet hierarchical structures were fabricated using a facile method on zinc foil and used as flexible photoanodes in dye-sensitized solar cells (DSCs). Compared to nanorods (NRs) obtained by the dissolution-precipitation method, the nanorod-nanosheet (NR-NS) hierarchical structures obtained by a second-step homogeneous precipitation improved the performance of DSCs by increasing photocurrent density significantly. As a result, the power conversion efficiency of the devices based on such a NR-NS hierarchical structure reached up to 2.4% under 100 mW cm(-2) illumination condition. This represents an enhancement by 108% as compared to DSCs based on NR assembled nanoflowers, for which the efficiency was 1.1%. The enhancement of the photocurrent was due mainly to the much larger specific surface area and resulting dye-loading amount. The electron transport properties in this structure were also investigated by means of electrochemical impedance spectroscopy (EIS). Furthermore, the formation mechanism of the NR-NS hierarchical structures are discussed.

Films of zinc tin oxide (ZTO), grown from solutions with zinc acetate dehydrate and tin(II) 2-ethylhexanoate dissolved in 2-methoxyethanol, have been used to fabricate thin-film transistors in combination with solution-processed aluminum oxide as the gate insulator. And the nonhomogeneity of the single-layer ZTO films, caused by both ZTO film-substrate interaction and surface crystallization, has been studied, which is essential to achieve high performance transistors. In the bottom-contact thin-film transistor based on a Sn-rich layer of ZTO, a high mobility of 78.9 cm(2) V(-1) s(-1) in the saturation region has been obtained, with an on-to-off current ratio of 10(5) and a threshold gate voltage of 1.6 V.

In this paper, 8-hydroxyquinoline aluminium (Alq(3)) was used in interface modification of dye-sensitized solar cells (DSCs). Alq(3) was the first discovered interface modification material with combined effects of retarding charge recombination and Förster resonant energy transfer (FRET). Results of dark current curve and AC impedance showed that Alq(3) could retard charge recombination in DSCs. I-V curves showed that conversion efficiency increased with Alq(3) modification. Besides the interface modification effect, it was discovered that Alq(3) also acted as energy relay dye with the FRET effect between itself and N3, which increased photoresponse and electron injection. The application of Alq(3) with combined effects opened a new door to explore more novel multi-functional interface modification materials to improve the performance of DSCs.

Intramolecular π-π stacking interaction in one kind of phosphorescent cationic iridium complexes has been controlled through fluorination of the pendant phenyl rings on the ancillary ligands. Two blue-green-emitting cationic iridium complexes, [Ir(ppy)(2)(F2phpzpy)]PF(6) (2) and [Ir(ppy)(2)(F5phpzpy)]PF(6) (3), with the pendant phenyl rings on the ancillary ligands substituted with two and five fluorine atoms, respectively, have been synthesized and compared to the parent complex, [Ir(ppy)(2)(phpzpy)]PF(6) (1). Here Hppy is 2-phenylpyridine, F2phpzpy is 2-(1-(3,5-difluorophenyl)-1H-pyrazol-3-yl)pyridine, F5phpzpy is 2-(1-pentafluorophenyl-1H-pyrazol-3-yl)-pyridine, and phpzpy is 2-(1-phenyl-1H-pyrazol-3-yl)pyridine. Single crystal structures reveal that the pendant phenyl rings on the ancillary ligands stack to the phenyl rings of the ppy ligands, with dihedral angles of 21°, 18°, and 5.0° between least-squares planes for complexes 1, 2, and 3, respectively, and centroid-centroid distances of 3.75, 3.65, and 3.52 Å for complexes 1, 2, and 3, respectively, indicating progressively reinforced intramolecular π-π stacking interactions from complexes 1 to 2 and 3. Compared to complex 1, complex 3 with a significantly reinforced intramolecular face-to-face π-π stacking interaction exhibits a significantly enhanced (by 1 order of magnitude) photoluminescent efficiency in solution. Theoretical calculations reveal that in complex 3 it is unfavorable in energy for the pentafluorophenyl ring to swing by a large degree and the intramolecular π-π stacking interaction remains on the lowest triplet state., (© 2012 American Chemical Society)

A novel bipolar host material, which meets the requirements of high triplet energy, good charge carrier transport properties, high solubility, and film-forming ability at the same time, has been designed and synthesized. Utilizing a new compound as host material, high-efficiency solution-processed blue and white phosphorescent organic light-emitting diodes (PHOLEDs) have been achieved., (© 2011 American Chemical Society)

A new cationic iridium complex has been developed with 2-(1-phenyl-1H-pyrazol-3-yl)pyridine as the ancillary ligand, which bears a pendant protective phenyl ring within the molecule; blue-green light-emitting electrochemical cells (LECs) based on the complex show dramatically enhanced stability compared to the LEC based on a similar complex without pendant phenyl rings., (This journal is © The Royal Society of Chemistry 2011)

In this paper, the interface modification effects of 4-tertbutylpyridine (TBP), especially the interaction with dye molecules, were discussed. The results of FTIR showed that TBP interacted with dye molecules, in addition to its interaction with the TiO(2) film. Reaction between N3 and TBP by the interaction force of the H atom in the -COOH group of N3 and the N atom of TBP could retard the aggregation of dye molecules, decreasing the electron quenching and charge recombination. Furthermore, the results of cyclic voltammograms and UV-vis absorption edge revealed the interaction between TBP and dye molecules could cause the energy level of the dye molecules to change, influencing the electron injection efficiency in DSCs. The IPCE results indicated that with TBP modification, the injection efficiency decreased, but the electron collection efficiency was enhanced., (This journal is © the Owner Societies 2011)

PbS QDs have been synthesized by an in situ photocatalysis method using the photocatalytic activity of nanocrystalline TiO(2) films. Both the photovoltaic response and size of the synthesized PbS QDs were analyzed. Compared with the conventional synthesis route, this method is simpler and produces less waste.

Montmorillonite (MMT) added to electrolytes has been reported in the literature to facilitate the transport of I(-)/I(3)(-), and improve the ionic conductivity and consequent photocurrent of dye-sensitized solar cells (DSCs). This paper firstly observes, investigates and reports that MMT addition to a poly(ethylene oxide) (PEO)-based gel electrolyte not only improves the ionic conductivity of the gel electrolyte, but also increases the photovoltage and decreases the dark current. From the results of electrochemical impedance spectroscopy (EIS) and transient photovoltage spectra, we evidence that MMT in the polymer gel electrolyte can efficiently retard the charge recombination that occurs at the TiO(2)/dye/electrolyte interfaces.

The interface modification effect within quasi-solid dye-sensitized solar cells and the photovoltaic performance were investigated after the introduction of Mg(OOCCH(3))(2) as an additive into a polymer gel electrolyte. Electrochemical impedance spectroscopy showed that the addition of Mg(OOCCH(3))(2) into the polymer gel electrolyte can efficiently retard charge recombination at the TiO(2)/electrolyte interface. Mg(OOCCH(3))(2) in the electrolyte can also contribute to the enhancement of the incident photon-to-electron conversion efficiency by modifying the dye molecules. This results in an improvement in the photovoltage and photocurrent due to a barrier layer at the TiO(2)/electrolyte interface and the promotion of charge injection at the dye/TiO(2) interface, respectively. Photovoltaic measurements reveal that a conversion efficiency enhancement from 4.05% to 4.96% under 100 mW cm(-2) is obtained after the amount of Mg(OOCCH(3))(2) added was optimized.

In this paper, a simple yet efficient method is proposed to improve the performance of dye-sensitized solar cells (DSCs) by modification after sensitization using Mg(OOCCH(3))(2). With modification of Mg(OOCCH(3))(2), a blue shift of the absorption peak and optical band gap were observed in the UV-vis spectrum. As shown in the Fourier transform infrared spectrum, the intermolecular hydrogen bonding of N3 dye, which caused the aggregation of dye molecules, was weakened. As shown in the I-V characteristic, the conversion efficiency of the DSCs was improved by the treatment of Mg(OOCCH(3))(2). Furthermore, the charge recombination was retarded as evidenced by the decreased dark current and the slowed decay rate of the dye excited state, which were characterized by the I-V curve in dark and transient photovoltage spectra. The mechanism of this modification process was also proposed further. Modification with Mg(OOCCH(3))(2) facilitated the electron injection from the dye molecule to the conductive band of TiO(2) by raising the excited state energy level of the dye molecule. This energy level rising was evidenced by the results of the cyclic voltammetry test and the blue shift of the optical band gap. Furthermore, Mg(OOCCH(3))(2) worked as an insulating barrier layer at the sensitized TiO(2)/electrolyte interface, thereby retarding the charge recombination in DSCs.

An efficient method using a polymer dispersion (PD) based on a copolymer of styrene and butyl acrylate to prepare TiO2 electrodes for dye-sensitized solar cells (DSCs) was introduced. The obtained TiO2 nanoporous film was investigated by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. A porous structure with pore size distribution from tens of nanometers to several hundred nanometers or even micrometers was characterized. This offered the film a feature of high haze factor and porosity. When using the film as photoanode, a quasi-solid-state DSC was successfully fabricated. The device showed an improved per-weight-efficiency by a factor of 2.7, resulting from the reduced interfacial resistance and the enhanced light scattering effect revealed by electrochemical impedance spectroscopy and transmittance spectroscopy, respectively. The developed PD-based colloid is promising to be applied in production on a large scale as a result of its simple prescription and stability during storage. A proposal to further improve the porous film is also introduced at the end of the paper.

The electrically conductive function of high-molecular weight poly(ethylene oxide) (PEO) (M(w) = 2 x 10(6) g mol(-1)) was investigated when it was used to gelate liquid electrolyte to fabricate a series of polymer gel electrolytes for dye-sensitized solar cells (DSCs). With the PEO weight ratio increasing from 2.5 to 15.0% (vs. liquid electrolyte), rheological behavior measurement showed that the viscosity of the polymer gel electrolytes increased ca 465 times. However, it was observed by steady-state voltammetry and electrochemical impedance spectra (EIS) measurements that the diffusion coefficient of I(3)(-)/I(-) decreased constantly while the conductivity of the polymer gel electrolytes increased initially and then decreased. These two inconsistent behaviours showed that the mobility of Li(+) was enhanced by PEO. EIS measurement revealed that the internal resistance of the DSCs were reduced since the enhanced mobility of Li(+) was helpful for the transport of electrons within the TiO(2) film through an ambipolar diffusion mechanism. When these polymer gel electrolytes were used to assemble DSCs, the conversion efficiency of DSCs increased continuously until it reached its maximum as the PEO weight ratio increased from 2.5 to 10.0%. By optimizing the dye adsorbing time and the thickness of the TiO(2) film, a quasi-solid DSC based on a polymer gel electrolyte with a PEO weight ratio of 10.0% showed a considerable conversion efficiency, 6.12 and 10.11% under 100 and 30 mW cm(-2) illumination, respectively. Finally, a stability test indicated that the more PEO was added into the polymer gel electrolytes, the better stability was obtained for the corresponding DSCs.

An ambipolar transporting naphtho[2,3-c][1,2,5]thiadiazole derivative with both high electron and hole mobilities has been synthesized via Suzuki cross-coupling. The electron and hole mobilities are 1.7 x 10(-3) cm(2)/ (V.s) and 1.9 x 10(-3) cm(2)/ (V.s) at an electric field of 4.5 x 10(5) V/cm, respectively, as measured by using time-of-flight technique.

A new type of organic-inorganic hybrid materials based on cadmium iodide (CdI2) and phenethylamine (PEA) has been synthesized and characterized. The reaction of CdI2 with PEA in a 1:2 molar ratio yields a four-coordinate hybrid material CdI2(PEA)2 (1) with extended 1D (CdI2)n chains, while the reaction of CdI2 with PEA in a 1:4 molar ratio produces a six-coordinate hybrid material CdI2(PEA)4 (2) with a discrete linear structure of CdI2 moiety. By introducing a trace amount of Na2S to the reaction for CdI2(PEA)2, we obtained a new compound [CdI2(PEA)2](CdS)0.038 (3) with uniformly doped CdS nanoparticles. Steady and transient photoluminescence studies reveal that compounds 1 and 2 exhibit bright blue (465 nm) and green (512 nm) fluorescent emissions in solid state at room temperature, respectively, while compound 3 gives a broad and complex emission ranging from 450 to 700 nm. Theoretical studies of electronic structures were carried out using density functional theory in order to gain a good understanding of the luminescent behaviors of these hybrid materials.

A novel miniaturized, integrated whole-column imaging detection (WCID) system on a microchip is presented. In this system, a program controlled organic light emitting diode (OLED) array was used as a spatial-scanning light source, to achieve imaging by the time sequence of the excited fluorescence. By this mechanism, a photomultiplier tube (PMT) instead of a charge coupled detector (CCD) can be applied to the imaging. Unlike conventional systems, no lenses, fibers or any mechanical components are required either. The novel flat light source provides uniform excitation light without size limitations and outputs a stronger power by pulse driving. The scanning mode greatly reduced the power consumption of the light source, which is valuable for a portable system. Meanwhile, this novel simplified system has a broader linear range, higher sensitivity and higher efficiency in data collection. Isoelectric focusing of R-phycoerythrin (PE) and monitoring of the overall process with WCID were performed on this system. The limit of detection (LOD) was 38 ng mL(-1) or 3.2 pg at 85 nL per column injection of PE. The system provides a technique for WCID capillary isoelectric focusing (cIEF) on chip and can be used for throughput analysis.

An integrated and simplified microfluidic device using a 250 microm x 1-4 cm of organic light emitting diode (OLED) array as a two-dimensional light source for single-channel and multichannel whole-column imaging detection was developed. This fluorescence detection system was used for isoelectric focusing (IEF) of R-phycoerythrin in a microchip. The IEF conditions were optimized, and the total analysis time was extremely reduced to 30 s for 2-cm-long microchannels at 700 V/cm of electric field strength without the presence of electroosmotic flow. The compression of pH gradient caused by electrolytes drawing into the microchannels was efficiently restrained when 1% hydroxylpropylmethyl cellulose in 2% ampholyte was used as the carrier for IEF. Under optimized IEF conditions, the detection limit of this system was approximately 0.6 microg/mL or 45 pg at 75 nL/column injection of R-phycoerythrin. This OLED-induced fluorescence detection system for WCID provides a high-speed IEF technique with quantitative ability and the potential for high integration and throughput microchip systems.

The nanoporous TiO2 films utilized in dye-sensitized solar cells (DSSCs) possess a large surface-to-volume ratio, which facilitates the adsorption of sensitizing dye and the recombination due to the high density of surface traps. In this paper, nanosized PbS was fabricated on the TiO2 films. The components of the modified TiO2 film were studied by X-ray diffraction (XRD) and electron probe microanalysis (EPMA), while the structure of the film was characterized with BET physisorption and high-resolution scanning electron microscopy (HRSEM). The results showed that the PbS particles were 2-3 nm and discrete on the surface of TiO2. Diffusion photovoltage (PV) spectroscopy was employed to study the charge separation and diffusion processes inside modified and unmodified TiO2 films. The diffusion PV signals revealed that the traps on the surface of TiO2 were extremely reduced due to the presence of PbS. The results of transient photovoltage and back I-V characteristics showed that the back reaction, that is, the recombination due to the reaction between an electron on TiO2 and the hole-transporting media, was retarded significantly.

Nanotubes composed of layered or nonlayered materials have been synthesized through various methods, among which template-based electrodeposition technology provides a versatile technique for synthesizing one-dimensional nanostructured materials. However, the growth mechanism of nanotubes using the template method is seldom clarified. Herein, we present the systematic preparation of metal nanotube arrays and put forward the growth mechanism, termed current-directed tubular growth (CDTG), for template-based electrodeposition. There are competitive growth rates for metal atoms entering the crystal lattice, that is, v( parallel) (growth rate parallel to current direction) and v( perpendicular) (growth rate perpendicular to current direction). Metal nanotubes can be obtained at v( parallel)>>v( perpendicular), while nanowires can be obtained at v( parallel) approximately v( perpendicular). The as-synthesized metal (Fe, Co, Ni) nanotubes are constructed from nonlayered materials, which are of body-centered cubic iron structure, hexagonal close packed cobalt structure, and face-centered cubic nickel structure, respectively. The CDTG mechanism is expected to have applications in designing and synthesizing other metal nanotubes and even compound nanotubes via template-based electrodeposition technology.

This paper reports the synthesis of well-aligned copper nanowires using an electrochemical deposition template technique. The electrical properties of copper nanowire arrays synthesized within vertical pores of alumina template were measured using a current-sensing atomic force microscope (AFM), with bias voltage applied between the AFM tip and the gold back-electrode. Nonlinear current-voltage (I-V) characteristics of copper nanowire arrays are observed; this is attributed to the impurities near the wire-lead contact region. These vertical copper nanowire arrays are suitable for use in fabricating nanoelectronic devices.

A simply fabricated microfluidic device using a green organic light emitting diode (OLED) and thin film interference filter as integrated excitation source is presented and applied to fluorescence detection of proteins. A layer-by-layer compact system consisting of glass/PDMS microchip, pinhole, excitation filter and OLED is designed and equipped with a coaxial optical fiber and for fluorescence detection a 300 microm thick excitation filter is employed for eliminating nearly 80% of the unwanted light emitted by OLEDs which has overlaped with the fluorescence spectrum of the dyes. The distance between OLED illuminant and microchannels is limited to approximately 1 mm for sensitive detection. The achieved fluorescence signal of 300 microM Rhodamine 6G is about 13 times as high as that without the excitation filter and 3.5 times the result of a perpendicular detection structure. This system has been used for fluorescence detection of Rhodamine 6G, Alexa 532 and BSA conjugates in 4% linear polyacrymide (LPA) buffer (in 1 x TBE, pH 8.3) and 1.4 fmol and 35 fmol mass detection limits at 0.7 nl injection volume for Alexa and Rhodamine dye have been obtained, respectively.

A high-contrast organic light-emitting diode (OLED) structure is presented. Because of poor contrast of conventional OLED resulting from high reflective metal cathode, the hybrid cathode structure was developed for low reflectivity. It consists the semitransparent cathode layers, passivation layers and a thick light-absorbing film. By optical reflectivity measurement and OLED electrical characterization tests for both OLED with the hybrid cathode and conventional OLED, it was found that the spectrum reflectance of OLED with hybrid cathode is among 8%-12%, about eight times lower than the conventional one when the two types of devices have similar turn-on voltages and current-voltage characteristics. The hybrid cathode for the high-contrast OLED is easily fabricated and its optical reflectance is slightly dependent on wavelength.