TiO2 Nanorod Array Films Research Articles

Efficient Perovskite Solar Cells Depending on TiO2 Nanorod Arrays.

Perovskite solar cells (PSCs) with TiO2 materials have attracted much attention due to their high photovoltaic performance. Aligned TiO2 nanorods have long been used for potential application in highly efficient perovskite solar cells, but the previously reported efficiencies of perovskite solar cells based on TiO2 nanorod arrays were underrated. Here we show a solvothermal method based on a modified ketone-HCl system with the addition of organic acids suitable for modulation of the TiO2 nanorod array films to fabricate highly efficient perovskite solar cells. Photovoltaic measurements indicated that efficient nanorod-structured perovskite solar cells can be achieved with the length of the nanorods as long as approximately 200 nm. A record efficiency of 18.22% under the reverse scan direction has been optimized by avoiding direct contact between the TiO2 nanorods and the hole transport materials, eliminating the organic residues on the nanorod surfaces using UV-ozone treatment and tuning the nanorod array morphologies through addition of different organic acids in the solvothermal process.

Silver-Decorated TiO2 Nanorod Array Films with Enhanced Photoelectrochemical and Photocatalytic Properties

Highly ordered TiO2 nanorod (TNR) array films decorated with Ag nanoparticles (NPs) were synthesized on fluorine-doped tin oxide (FTO) by a hydrothermal treatment and a successive ionic layer adsorption reaction (SILAR) technique. The amount of Ag NPs on the TNR can be controlled by changing the number of cycles in silver nitrate (AgNO3) solution. The morphology, structure, composition, optical, photoelectrochemical and photocatalytic properties of the Ag/TNR films were investigated in detail. The Ag/TNR films exhibit larger redshift of the absorption edges and higher absorption intensities in the visible light range. Furthermore, the Ag/TNR films sensitized with 5 SILAR cycles show the best photocurrent density (32 μA/cm2) and photodegradation efficiency (95.52%), which is 5.7 and 1.3 times higher than that of pure TNR, respectively. The excellent properties can be ascribed to localized surface plasmon resonance (LSPR) effect of Ag NPs. The stability and reusability of the Ag/TNR films were also investigated. Therefore, the Ag/TNR films with high performance and stability can be used in potential applications.

Preparation and characterization of CuCrO2/TiO2 heterostructure photocatalyst with enhanced photocatalytic activity

A series of novel p-type CuCrO2/n-type TiO2 heterostructure photocatalysts were fabricated for the first time by depositing CuCrO2 nanoparticles on TiO2 nanorod-array film through a facile spin-coating method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photocurrent response were employed to characterize the as-synthesized composites. The photocatalytic activity of CuCrO2/TiO2 for degradation of methylene blue (MB) aqueous solution was much higher than pure TiO2, which could be ascribed to the formation of p–n heterojunctions between CuCrO2 nanoparticles and TiO2 nanorods. In particular, the best degradation efficiency of CuCrO2/TiO2 heterojunction was 85.3%, about 1.14 times higher than pure TiO2 (74.6%), which could be attributed to their high separation efficiency of photogenerated electrons and holes. It is expected this strategy of p–n junction for enhancing photocatalytic activity can have considerable impact to promote the development of high efficient photocatalyst and industrial application for degrading pollutant, treating waste water and other environmental protection fields.

Enhanced Photoelectrocatalytic Activity of Oriented Rutile TiO<sub>2</sub> Nanorod Array Film through Nb Doping

TiO2 nanorod array films with or without Nb doping grown directly on transparent conductive glass (FTO) were prepared by a facile hydrothermal method. The films were characterized by means of field emission scanning electron microscopy (FE-SEM) with energy-dispersive x-ray spectra (EDS), X-ray diffraction (XRD) and the X-ray photoelectron spectroscoy (XPS). The electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV) and transient photocurrent were investigated in a three-electrode system with TiO2 nanorod array film served as the photoanode. The photoelectrocatalytic activity of the films was evaluated by the oxidation of glucose under UV irradiation. The results show that both the pure and Nb-doped TiO2 nanorods perpendicularly grown on FTO substrate are rutile phase. The resistance of the TiO2 nanorod array photoanode is decreased significantly by Nb doping. The steady-state photocurrent (iss) for glucose oxidation at Nb-doped TiO2 nanorod array film is much higher than that at the pure one. The enhanced photoelectrocatalytic activity of the Nb-doped TiO2 nanorods could be attributed to the enhanced charge transport ability.

Significant effects of reaction temperature on morphology, crystallinity, and photoelectrical properties of rutile TiO2 nanorod array films

Oriented single-crystalline TiO2 nanorod arrays have been extensively studied as the electrode of photoelectrochemical cells due to their unique properties. In this study, oriented rutile TiO2 nanorod arrays were directly synthesized on fluorine-doped tin oxide glass substrates by a facile hydrothermal method, and the effects of growth conditions (i.e. reaction temperature, growth time and titanium precursor) on their morphologies, crystal structures and photoelectrical properties were investigated. Reaction temperature played a more critical role in tailoring the surface morphology, crystal structures (i.e. length, diameter and crystallinity of nanorods) and photoelectrical properties of the nanorods than growth time did. With the increase in reaction temperature from 140 °C to 200 °C, both photocurrent density and external quantum efficiency (EQE) increased initially and then decreased, with a maximum value of 5.6 × 10−2 mA cm−2 at 170 °C and 2.7% at 160 °C, respectively. In addition, photoelectric measurements demonstrated that TiO2 nanorod arrays synthesized from TiCl4 at a relatively low reaction temperature exhibited a much higher EQE value than those obtained from titanium isopropoxide.

TiO2 Nanorod Arrays Sensitized with CdS Quantum Dots for Solar Cell Applications: Effects of Rod Geometry on Photoelectrochemical Performance

CdS quantum dot (QD) sensitized TiO2 nanorod array (NRA) film electrodes with different rod geometries were fabricated via a solvothermal route followed by a sequentialchemical bath deposition (S-CBD) process. By controlling the solution growth conditions, the rod geometries, especially the tip structures, of the TiO2 NRAs were tuned. The results indicated that the vertically aligned hierarchical NRAs possessed conically shaped tip geometry, which was favorable for film electrodes due to the reduced reflectance, enhanced light harvesting, fast charge-carrier separation and transfer, suppression of carrier recombination, sufficient electrolyte penetration and subsequent efficient QD assembly. CdS QD sensitized TiO2 NRA film electrodes with tapered tips exhibited an enhanced photoelectrochemical (PEC) performance, a photocurrent intensity of 5.13 mA/cm2 at a potential of 0 V vs. saturated calomel electrode, an open-circuit potential of −0.68 V vs. saturated calomel electrode and an incident photon to current conversion efficiency (IPCE) of 22% in the visible-light region from 400 to 500 nm. The effects of rod geometry on the optical absorption, reflectance, hydrophilic properties and PEC performance of bare TiO2 and CdS QD sensitized TiO2 NRA film electrodes were investigated. The mechanism of charge-carrier generation and transfer in these CdS QD sensitized solar cells based on vertically aligned TiO2 nanorods is discussed.

Nanostructured homogenous CdSe–TiO2 composite visible light photoanodes fabricated by oblique angle codeposition

A unique fabrication method, oblique angle codeposition, is used to deposit well-aligned nanorod arrays and thick films of homogenously mixed CdSe–TiO2 composites. The composite films are characterized structurally, optically, and photoelectrochemically using a variety of experimental techniques. The CdSe–TiO2 composites are compared with pure CdSe and TiO2 films in order to determine their utility for photoelectrochemical (PEC) applications and to understand the mechanisms underlying the observed behaviors. The evaporation process of CdSe creates three different cluster types within the TiO2 film structures: isolated Se, Se-deficient CdSe, and Se-rich CdSe. The prevalence of each cluster type is dependent on predicted film composition, and each is affected differently by open-air annealing. Isolated Se can be incorporated into the TiO2 lattice, resulting in low energy rutile phase. Se-deficient CdSe clusters crystallize preferentially into cubic CdSe and are easily oxidized into CdO, while Se-rich CdSe clusters crystallize into hexagonal CdSe and are more stable. Furthermore, each of these cluster types interacts differently with the surrounding TiO2 matrix, resulting in diverse optical and PEC behaviors. Importantly, the composite nanorod structure is a more efficient photoanode under visible light illumination than both the pure CdSe and TiO2 nanorod array films. The stoichiometry of the CdSe domains is more important than overall CdSe content within the film in determining the structural, optical, and PEC properties of the films.

TiO2 nanorod arrays grown from a mixed acid medium for efficient dye-sensitized solar cells

A series of oriented rutile TiO2 nanorod-array films are in-situ grown on fluorine-doped tin oxide (FTO) coated glass substrates from a mixed acid solution containing titanium tetraisopropoxide (TTIP), hydrochloric acid (HCl), acetic acid (HOAc), and water (H2O) by means of hydrothermal reaction at 150 °C. The effect of HOAc in the titania growth solution on the structure and micro-morphology of TiO2 nanorod array films, as well as the photoelectric conversion properties in dye-sensitized solar cells (DSSCs) has been fully investigated. It is found that HOAc can facilitate the formation of uniform, dense, and vertically oriented TiO2 nanorods and hence improves the dye adsorption, electron diffusion coefficient, and the photovoltaic performance of DSSCs, typically in short-circuit photocurrent and power conversion efficiency. A power conversion efficiency of 4.03% has been achieved on a DSSC based on a 2.3 µm-long nanorod array film obtained from a mixed acid solution with the TTIP:HCl:HOAc:H2O ratio of 0.8:4:8:8 by volume.

Substrate-free, large-scale, free-standing and two-side oriented single crystal TiO2 nanorod array films with photocatalytic properties

A substrate-free, large-scale, free-standing and two-side oriented single crystal rutile TiO(2) nanorod array film with a thickness of over ten micrometers, self-assembled via a facile hydrothermal reaction of titanium powder in a mixture solution of H(2)O(2) and HCl, exhibits high activity for the photocatalytic degradation of methyl orange.

CdS Quantum Dots-Sensitized TiO2 Nanorod Array on Transparent Conductive Glass Photoelectrodes

An oriented single-crystalline TiO2 nanorod or wire array on transparent conductive substrates would be the most desirable nanostructure in preparing photoelectrochemical solar cells because of its efficient charge separation and transport properties as well as superior light harvesting efficiency. In this study, a TiO2 nanorod array film grown directly on transparent conductive glass (FTO) was prepared by a simple hydrothermal method. The formation of CdS quantum dots (QDs) on the vertically aligned TiO2 nanorods photoelectrode was carried out by chemical bath deposition. The as-prepared materials were characterized by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction. The results indicate that CdS QDs with a diameter smaller than 10 nm are uniformly covered on the surface of the single-crystalline TiO2 nanorods. Under AM 1.5 G illumination, the photoelectrode was found with a photocurrent intensity of 5.778 mA/cm2 at a potential of 0 V versus Ag/AgCl and an open-circuit photovoltage of 1.292 V versus Ag/AgCl. The photocurrent is 28.6 times higher than that of a bare TiO2 nanorod array, and the photoelectrochemical properties are comparable to those of a CdS QDs-sensitized TiO2 nanotube array, suggesting that the CdS QDs-sensitized TiO2 nanorod array on FTO photoelectrodes has a potential application in solar cells.