Deposition of a thin film of TiOx from a titanium metal target as novel blocking layers at conducting glass/TiO2 interfaces in ionic liquid mesoscopic TiO2 dye-sensitized solar cells

Fabrication of Isolated Iron Nanowires

Nanoscale interconnects are an important component of molecular electronics. Here we use X-ray spectromicroscopy techniques as well as scanning probe methods to explore the self-assembled growth of insulated iron nanowires as a potential means of supplying an earth abundant solution. The intrinsic anisotropy of a TiO2(110) substrate directs the growth of micron length iron wires at elevated temperatures, with a strong metal-support interaction giving rise to ilmenite (FeTiO3) encapsulation. Iron nanoparticles that decorate the nanowires display magnetic properties that suggest other possible applications.

Platinum- and CuOx -Decorated TiO2 Photocatalyst for Oxidative Coupling of Methane to C2 Hydrocarbons in a Flow Reactor

Oxidative coupling of methane (OCM) is considered one of the most promising catalytic technologies to upgrade methane. However, C2 products (C2 H6 /C2 H4 ) from conventional methane conversion have not been produced commercially owing to competition from overoxidation and carbon accumulation at high temperatures. Herein, we report the codeposition of Pt nanoparticles and CuOx clusters on TiO2 (PC-50) and use of the resulting photocatalyst for OCM in a flow reactor operated at room temperature under atmospheric pressure for the first time. The optimized Cu0.1 Pt0.5 /PC-50 sample showed a highest yield of C2 product of 6.8 μmol h-1 at a space velocity of 2400 h-1 , more than twice the sum of the activity of Pt/PC-50 (1.07 μmol h-1 ) and Cu/PC-50 (1.9 μmol h-1 ), it might also be the highest among photocatalytic methane conversions reported so far under atmospheric pressure. A high C2 selectivity of 60 % is also comparable to that attainable by conventional high-temperature (>943 K) thermal catalysis. It is proposed that Pt functions as an electron acceptor to facilitate charge separation, while holes could transfer to CuOx to avoid deep dehydrogenation and the overoxidation of C2 products.

The Investigation for Coating Method of Titanium Dioxide Layer in Perovskite Solar Cells

The effect of conventional Perovskite solar cells (PSCs) by using different concentration and spin-coating speeds of titanium dioxide (TiO2) as an electron transport layer (ETL) was studied. The influence of TiO2 based on device structure: fluorine-doped tin oxide substrate/TiO2/Perovskite (CH3NH3PbI3)/2,2′,7,7′-Tetrakis[N,N-di(4-methoxyp phenyl)amino]-9,9′-spirobifluorene/silver, is also studied. The spin-coating speed is varied in a range from 1000 to 3000 rpm to get optimal performance of device. The optimized power conversion efficiency (PCE) of PSCs with original concentration (OC) and double concentration (DC) TiO2 is 8.74 and 9.93%, respectively. The reason is attributed to excellent absorption in shorter wavelength, compact characteristic, and suitable thickness of TiO2, leading to perfect short-circuit current density (Jsc), lower series resistance (Rs), and higher fill factor (FF) of 0.75. Besides, recombination of electron and hole is also decreased due to the compact feature, leading to higher open-circuit voltage (VOC) of 0.91 V.

Pulsed Laser Fabrication of TiO2 Buffer Layers for Dye Sensitized Solar Cells

We report on the fabrication of dye-sensitized solar cells with a TiO₂ buffer layer between the transparent conductive oxide substrate and the mesoporous TiO₂ film, in order to improve the photovoltaic conversion efficiency of the device. The buffer layer was fabricated by pulsed laser deposition whereas the mesoporous film by the doctor blade method, using TiO₂ paste obtained by the sol–gel technique. The buffer layer was deposited in either oxygen (10 Pa and 50 Pa) or argon (10 Pa and 50 Pa) onto transparent conducting oxide glass kept at room temperature. The cross-section scanning electron microscopy image showed differences in layer morphology and thickness, depending on the deposition conditions. Transmission electron microscopy studies of the TiO₂ buffer layers indicated that films consisted of grains with typical diameters of 10 nm to 30 nm. We found that the photovoltaic conversion efficiencies, determined under standard air mass 1.5 global (AM 1.5G) conditions, of the solar cells with a buffer layer are more than two times larger than those of the standard cells. The best performance was reached for buffer layers deposited at 10 Pa O₂. We discuss the processes that take place in the device and emphasize the role of the brush-like buffer layer in the performance increase.

Fine tuning of compact ZnO blocking layers for enhanced photovoltaic performance in ZnO based DSSCs: a detailed insight using β recombination, EIS, OCVD and IMVS techniques

Ultrathin ZnO BLs preventing recombination enhancing photovoltaic performance.

Atomic Layer Deposition of TiO2 for a High-Efficiency Hole-Blocking Layer in Hole-Conductor-Free Perovskite Solar Cells Processed in Ambient Air

In this study we design and construct high-efficiency, low-cost, highly stable, hole-conductor-free, solid-state perovskite solar cells, with TiO2 as the electron transport layer (ETL) and carbon as the hole collection layer, in ambient air. First, uniform, pinhole-free TiO2 films of various thicknesses were deposited on fluorine-doped tin oxide (FTO) electrodes by atomic layer deposition (ALD) technology. Based on these TiO2 films, a series of hole-conductor-free perovskite solar cells (PSCs) with carbon as the counter electrode were fabricated in ambient air, and the effect of thickness of TiO2 compact film on the device performance was investigated in detail. It was found that the performance of PSCs depends on the thickness of the compact layer due to the difference in surface roughness, transmittance, charge transport resistance, electron-hole recombination rate, and the charge lifetime. The best-performance devices based on optimized TiO2 compact film (by 2000 cycles ALD) can achieve power conversion efficiencies (PCEs) of as high as 7.82%. Furthermore, they can maintain over 96% of their initial PCE after 651 h (about 1 month) storage in ambient air, thus exhibiting excellent long-term stability.

Metal oxide semiconductors for dye- and quantum-dot-sensitized solar cells

This Review provides a brief summary of the most recent research developments in the synthesis and application of nanostructured metal oxide semiconductors for dye sensitized and quantum dot sensitized solar cells. In these devices, the wide bandgap semiconducting oxide acts as the photoanode, which provides the scaffold for light harvesters (either dye molecules or quantum dots) and electron collection. For this reason, proper tailoring of the optical and electronic properties of the photoanode can significantly boost the functionalities of the operating device. Optimization of the functional properties relies with modulation of the shape and structure of the photoanode, as well as on application of different materials (TiO2, ZnO, SnO2) and/or composite systems, which allow fine tuning of electronic band structure. This aspect is critical because it determines exciton and charge dynamics in the photoelectrochemical system and is strictly connected to the photoconversion efficiency of the solar cell. The different strategies for increasing light harvesting and charge collection, inhibiting charge losses due to recombination phenomena, are reviewed thoroughly, highlighting the benefits of proper photoanode preparation, and its crucial role in the development of high efficiency dye sensitized and quantum dot sensitized solar cells.

Role of temperature in the recombination reaction on dye-sensitized solar cells

The DSC recombination kinetics was studied up to 100 °C without electrolyte leakage or external contamination using a unique laser assisted glass sealing process. In addition to temperature having a strong influence on the recombination reaction rate, the energy of the exited electrons was found to be critical for determining the recombination activation energy.

Perovskite solar cell with an efficient TiO₂ compact film

A perovskite solar cell with a thin TiO2 compact film prepared by thermal oxidation of sputtered Ti film achieved a high efficiency of 15.07%. The thin TiO2 film prepared by thermal oxidation is very dense and inhibits the recombination process at the interface. The optimum thickness of the TiO2 compact film prepared by thermal oxidation is thinner than that prepared by spin-coating method. Also, the TiO2 compact film and the TiO2 porous film can be sintered at the same time. This one-step sintering process leads to a lower dark current density, a lower series resistance, and a higher recombination resistance than those of two-step sintering. Therefore, the perovskite solar cell with the TiO2 compact film prepared by thermal oxidation has a higher short-circuit current density and a higher fill factor.

All-nano-TiO2 compact film for high-performance dye-sensitized solar cells

An innovative all-nano-TiO2 thin film capable of enhancing dye-sensitized solar cell (DSC) photoefficiencies was prepared by a layer-by-layer method beneath the meso-TiO2 film, employing acid and basic nano-TiO2 sols as cations and anions, respectively. TiO2 syntheses were performed under absolute control to lead to appropriate morphological and optical properties to yield high-quality compact films using profilometry, tuning, and scanning electron microscopy. A detailed study by photoelectrochemical parameters, incident photon-to-current efficiency, electron lifetime, and electrochemical impedance spectroscopy demonstrates that the physical contact between FTO and the electrolyte is prevented and the role of the compact film has been elucidated. DSCs with TiO2 bilayers on top of FTO improved the conversion efficiency up to 62%, mainly because of the prevention of FTO/I3(-) charge recombination and an improved contact between FTO and TiO2.

Preparation and characterization of TiO2 barrier layers for dye-sensitized solar cells

A TiO2 barrier layer is critical in enhancing the performance of dye-sensitized solar cells (DSSCs). Two methods to prepare the TiO2 barrier layer on fluorine-doped tin dioxide (FTO) surface were systematically studied in order to minimize electron-hole recombination and electron backflow during photovoltaic processes of DSSCs. The film structure and materials properties were correlated with the photovoltaic characteristics and electrochemical properties. In the first approach, a porous TiO2 layer was deposited by wet chemical treatment of the sample with TiCl4 solution for time periods varying from 0 to 60 min. The N719 dye molecules were found to be able to insert into the porous barrier layers. The 20 min treatment formed a nonuniform but intact TiO2 layer of ∼100-300 nm in thickness, which gave the highest open-circuit voltage VOC, short-circuit photocurrent density JSC, and energy conversion efficiency. But thicker TiO2 barrier layers by this method caused a decrease in JSC, possibly limited by lower electrical conductance. In the second approach, a compact TiO2 barrier layer was created by sputter-coating 0-15 nm Ti metal films on FTO/glass and then oxidizing them into TiO2 with thermal treatment at 500 °C in the air for 30 min. The dye molecules were found to only attach at the outer surface of the barrier layer and slightly increased with the layer thickness. These two kinds of barrier layer showed different characteristics and may be tailored for different DSSC studies.

Atomic layer deposition of high performance ultrathin TiO₂ blocking layers for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) often use a thin insulating or semiconducting layer (typically TiO₂) between the transparent conductive oxide and the mesoporous TiO₂ to block electron/hole recombination at the conducting oxide/electrolyte interface. The blocking layer (BL) is essential to maintain efficient charge generation under low light conditions, at which DSSCs perform well compared to common semiconductor-based photovoltaic devices. In this work, we show that atomic layer deposition (ALD) can produce ultrathin (<10 nm) BLs that significantly impede charge recombination in functional DSSCs, leading to improved photocurrents, open-circuit photovoltages, and fill factors; this results in an increase in the overall efficiency from ≈7% to ≈8.4% under AM 1.5G illumination. The 5-10 nm ALD BLs are the thinnest optimized DSSC BLs reported to date. The BL retards the open-circuit voltage decay and extends the electron lifetime from ≈0.2 s to more than 10 s at 0.3 V, confirming that the ALD films significantly impede photogenerated charge recombination. By preparing BLs through other deposition techniques, we directly demonstrate that ALD results in better performance, even with thinner films, which is ascribed to the lower pinhole density of ALD materials.

A hybrid soft solar cell based on the mycobacterial porin MspA linked to a sensitizer-viologen Diad

A prototype of a nano solar cell containing the mycobacterial channel protein MspA has been successfully designed. MspA, an octameric transmembrane channel protein from Mycobacterium smegmatis, is one of the most stable proteins known to date. Eight Ruthenium(II) aminophenanthroline-viologen maleimide Diads (Ru-Diads) have been successfully bound to the MspA mutant MspAA96C via cysteine-maleimide bonds. MspA is known to form double layers in which it acts as nanoscopic surfactant. The nanostructured layer that is formed by (Ru-Diad)8MspA at the TiO2 electrode is photochemically active. The resulting "protein nano solar cell" features an incident photon conversion efficiency of 1% at 400 nm. This can be regarded as a proof-of-principle that stable proteins can be successfully integrated into the design of solar cells.

High-performance plastic dye-sensitized solar cells based on low-cost commercial P25 TiO2 and organic dye

High-performance plastic dye-sensitized solar cells (DSCs) based on low-cost commercial Degussa P25 TiO(2) and organic indoline dye D149 have been fabricated using electrophoretic deposition (EPD) with compression post-treatment at room temperature. The pressed EPD electrode outperformed the sintered EPD electrode and as-prepared EPD electrode in short-circuit current density and power conversion efficiency. About 150% and 180% enhancement in power conversion efficiency have been achieved in DSC devices with sintering and compression post-treatment as compared to the as-prepared electrode, respectively. Several characterizations including intensity modulated photocurrent spectroscopy, incident photon-to-electron conversion efficiency and electrochemical impedance spectra have been employed to reveal the nature of improvement with post-treatment. Experimental results indicate that the sintering and compression post-treatment are beneficial to improve the electron transport and thus lead to the enhancement of photocurrent and power conversion efficiency. In addition, the compression post-treatment is more efficient than sintering post-treatment in improving interparticle connection in the as-prepared EPD electrode. Under optimized conditions, the conversion efficiency of plastic devices with D149-sensitized P25 TiO(2) photoanode has reached 5.76% under illumination of AM 1.5G (100 mW cm(-2)). This study demonstrates that the EPD combined with compression post-treatment provides a way to fabricate highly efficient plastic photovoltaic devices.

Ga-doped ZnO transparent electrodes with TiO2 blocking layer/nanoparticles for dye-sensitized solar cells

Ga-doped ZnO [GZO] thin films were employed for the transparent electrodes in dye-sensitized solar cells [DSSCs]. The electrical property of the deposited GZO films was as good as that of commercially used fluorine-doped tin oxide [FTO]. In order to protect the GZO and enhance the photovoltaic properties, a TiO2 blocking layer was deposited on the GZO surface. Then, TiO2 nanoparticles were coated on the blocking layer, and dye was attached for the fabrication of DSSCs. The fabricated DSSCs with the GZO/TiO2 glasses showed an enhanced conversion efficiency of 4.02% compared to the devices with the normal GZO glasses (3.36%). Furthermore, they showed better characteristics even than those using the FTO glasses, which can be attributed to the reduced charge recombination and series resistance.

Applications of Ionic Liquids in Electrochemical Sensors and Biosensors

Ionic liquids (ILs) are salt that exist in the liquid phase at and around 298 K and are comprised of a bulky, asymmetric organic cation and the anion usually inorganic ion but some ILs also with organic anion. ILs have attracted much attention as a replacement for traditional organic solvents as they possess many attractive properties. Among these properties, intrinsic ion conductivity, low volatility, high chemical and thermal stability, low combustibility, and wide electrochemical windows are few. Due to negligible or nonzero volatility of these solvents, they are considered “greener” for the environment as they do not evaporate like volatile organic compounds (VOCs). ILs have been widely used in electrodeposition, electrosynthesis, electrocatalysis, electrochemical capacitor, lubricants, plasticizers, solvent, lithium batteries, solvents to manufacture nanomaterials, extraction, gas absorption agents, and so forth. Besides a brief discussion of the introduction, history, and properties of ILs the major purpose of this review paper is to provide an overview on the advantages of ILs for the synthesis of conducting polymer and nanoparticle when compared to conventional media and also to focus on the electrochemical sensors and biosensors based on IL/composite modified macrodisk electrodes. Subsequently, recent developments and major strategies for enhancing sensing performance are discussed.

Three-dimensional photonic crystal fluorinated tin oxide (FTO) electrodes: synthesis and optical and electrical properties

Photovoltaic (PV) schemes often encounter a pair of fundamentally opposing requirements on the thickness of semiconductor layer: a thicker PV semiconductor layer provides enhanced optical density, but inevitably increases the charge transport path length. An effective approach to solve this dilemma is to enhance the interface area between the terminal electrode, i.e., transparent conducting oxide (TCO) and the semiconductor layer. As such, we report a facile, template-assisted, and solution chemistry-based synthesis of 3-dimensional inverse opal fluorinated tin oxide (IO-FTO) electrodes. Synergistically, the photonic crystal structure possessed in the IO-FTO exhibits strong light trapping capability. Furthermore, the electrical properties of the IO-FTO electrodes are studied by Hall effect and sheet resistance measurement. Using atomic layer deposition method, an ultrathin TiO(2) layer is coated on all surfaces of the IO-FTO electrodes. Cyclic voltammetry study indicates that the resulting TiO(2)-coated IO-FTO shows excellent potentials as electrodes for electrolyte-based photoelectrochemical solar cells.

Effects of calcination temperatures on photocatalytic activity of SnO2/TiO2 composite films prepared by an EPD method

SnO2/TiO2 composite films were fabricated on transparent electro-conductive glass substrates (F-doped SnO2-coated glass:FTO glass) via an electrophoretic deposition (EPD) method using Degussa P25 as raw materials, and were further characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), UV-vis diffuse reflectance spectra and Photoluminescence spectra (PL). XRD and XPS results confirmed that the films were composed of TiO2 and SnO2. FESEM images indicated that the as-prepared TiO2 films had roughness surfaces, which consisted of nano-sized particles. The effects of calcination temperatures on the surface morphology, microstructures and photocatalytic activity of SnO2/TiO2 composite films were further investigated. All the prepared SnO2/TiO2 composite films exhibited high photocatalytic activities for photocatalytic decolorization of Rhodamine-B aqueous solution. At 400 degrees C, the SnO2/TiO2 composite films showed the highest photocatalytic activity due to synergetic effects of low sodium content, good crystallization, appropriate phase composition and slower recombination rate of photogenerated charge carriers.

Fabrication of a multi-scale nanostructure of TiO(2) for application in dye-sensitized solar cells

We propose a highly ordered multi-scale nanostructure of TiO(2) for applications as an anode in dye-sensitized solar cells (DSSCs). The structure is composed of a TiO(2) blocking layer, a TiO(2) inverse opal main body, regularly arranged transport channels between contacting spherical voids of the TiO(2) inverse opal, and TiO(2) nanoparticles coated on the spherical surfaces of the voids. The ordered and continuous backbone of the inverse opal serves as the fast electron transport pathways while the regularly arranged transport channels enable easy transport of dye and electrolyte within the structure. A multi-cycle procedure was developed to enable fabrication of thick inverse opals and easy adjustment of the inverse opal thickness. An example structure was constructed, involving a blocking layer of 90 nm thickness, an inverse opal of 100 nm voids, transport channels of 30-50 nm openings, and nanoparticles 10-15 nm in size. An open-circuit voltage decay investigation showed a significant improvement in electron lifetime for the proposed multi-scale TiO(2) nanostructure based DSSC than that of a TiO(2) nanoparticle film based DSSC, revealing the superior electron recombination characteristic offered by the proposed TiO(2) nanostructure. The conversion efficiency of the DSSC assembled from such an anode structure can reach 4% with a short-circuit current density (J(sc)) of 8.7 mA cm(-2) and open-circuit potential (V(oc)) of 0.76 V under AM 1.5 (100 mW cm(-2)) illumination.