Dong Ding

Efficient improvement of photoelectrochemical activity for multiple semiconductor (CdS/PbS/ZnS) co-sensitized TiO2 photoelectrodes by hydrogen treatment

In the present work we report a simple and viable approach to improve the photoelectrochemical activity of TiO2 photoelectrodes. Firstly, a TiO2 nanotube array film with nanowires directly formed on top (denoted as TiO2NTWs) was prepared by a simple electrochemical anodization method on a titanium foil. Then the pristine TiO2NTWs were annealed in a hydrogen atmosphere (denoted as H*TiO2NTWs). Subsequently, the formation of a CdS, PbS, and ZnS quantum dot (QD) sensitized H*TiO2NTW photoelectrode was carried out by successive ionic layer adsorption and reaction (SILAR). The best performance of the photoelectrode was TiO2 NTWs annealed in hydrogen at 350 °C with 4 cycles of CdS plus 2 cycles of PbS and 3 cycles of ZnS. A maximum short-circuit photocurrent density of 3.62 mA cm−2 was obtained under an illumination of AM 1.5 G, which can boost the photocurrent density of the pristine TiO2NTWs by up to 503%. The enhancement was attributed to the extension of the light absorption range by hydrogen treatment and QD sensitization.

Hierarchical TiO2 nanoflowers/nanosheets array film: synthesis, growth mechanism and enhanced photoelectrochemical properties

The possible growth mechanism of a hierarchical TiO2 nanoflower/nanosheet (NFS) array was put forward in the work. The TiO2 NFS array film perpendicularly grown on transparent conductive fluorine-doped tin oxide (FTO) glass substrates was prepared via a one-step template-free hydrothermal method. The NFS array film was formed by the self assembly of nanosheets with exposed highly reactive {001} facets. Titanium butoxide and ammonium hexafluorotitanate ((NH4)2TiF6) were used as titanium precursor and morphology controlling agent, respectively. The growth process of TiO2 NFS array was investigated according to the SEM images and XRD patterns of the products at different reaction stages. The tractable morphology controlling agent played a key role in the preparation of pure anatase TiO2 and affected the thickness of the nanosheets. This study provides new insights into the synthesis of hierarchical anatase TiO2 nanostructures with a high percentage of {001} facets. In addition, the photoelectrochemical performance of the CdS QDs sensitized TiO2 NFS array film was assessed, indicating a variety of applications such as dye-sensitized or quantum dot-sensitized solar cells fields.

Fabrication of NiTe films by transformed electrodeposited Te thin films on Ni foils and their electrical properties

The compact nickel telluride (NiTe) thin film was prepared by two simple steps. High-density tellurium (Te) film with vertical pillar morphology (Te source) was synthesized by a rapid and convenient electrodeposition method without any external agent for the first time. NixTe as the ohmic contact layer material was obtained by a low temperature heat treatment of a Te thin film deposited on a Ni substrate. The structure, morphology, optical and electrical properties of the as-prepared thin films were examined. The current voltage (I–V) characteristic shows that all of the NixTe/Ni samples have already formed ohmic contacts. The NiTe/Ni also shows smaller contact resistance than other samples, which suggests it has potential for application in solar cells as a flexible Ni substrate.

Controlled synthesis of nanotubes and nanowires decorated with TiO2 nanocuboids with exposed highly reactive (111) facets to produce enhanced photoelectrochemical properties

The ability to control the exposure of facets of a crystal has been garnering considerable attention due to the fascinating dependence of the physical properties of crystals on their shapes. Herein, a TiO2WT photoelectrode decorated with anatase TiO2 nanocuboids (TiO2C111WTs) displaying high-energy exposed (111) facets and quantum dot dimensions was prepared for the first time by using a TiCl4 treatment process. F− and NH4+ were introduced together to limit the randomness of the TiCl4 hydrolysates. We propose that both F− and NH4+ were necessary for controlling the exposure of the (111) facets. In comparison with TiO2WT photoelectrodes decorated with either randomly deposited TiO2 nanoparticles (non-facet) or with TiO2 nanofilms or with TiO2 nanocuboids displaying exposed {001} facets (denoted as TiO2PWT, TiO2FWT and TiO2C001WT photoelectrodes, respectively), the hybrid-structured TiO2C111WT photoelectrode achieved superior PEC performances, with Jsc and photoconversion efficiency values of 0.97 mA cm−2 and 0.49%. This enhancement was attributed to the exposure of the highly active (111) facets and the increased specific surface area of TiO2C111WTs. Meanwhile, the photoactive (111) facets offered oxygen vacancies, resulting in an increase of donor density and the enhancement of PEC performances. These facets also promoted the adsorption of CdS QDs and hence further sensitization. The CdS/TiO2C111WTs achieved Jsc and photoconversion efficiency values of 3.95 mA cm−2 and 2.05%, which were about twice those of CdS/TiO2WTs.

A novel cage-like CdTe film with enhanced photoelectrochemical performance

A novel cage-like CdTe film with even porosity size and good connectivity among particles is successfully prepared by a simple technique for the first time. The field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and UV-Vis absorption spectra are used to characterize the morphology, crystallinity and optical property of the new structure. The FESEM observation confirms the formation of cage-like CdTe film after heat treatment. The structural and optical studies reveal that the cage-like CdTe films show better crystallinity and enhanced optical absorption. Based on the characterization results, the possible growth mechanism of the cage-like CdTe film is proposed. Furthermore, the photoelectrochemical property of the film is also investigated by photocurrent and current density–voltage curves and electrochemical impedance spectroscopy (EIS). The cage-like CdTe film yields an enhanced photocurrent and current density of 3.8 mA cm−2, which is significantly higher than other as-prepared CdTe films. Meanwhile, the cage-like CdTe films present improved charge transfer properties and corroborate the photocurrent and current density–voltage measurements. The photostability of the films is also studied. The better photoelectrochemical property of the cage-like CdTe films suggests their potential application in nanostructured solar energy conversion devices.

Enhanced photovoltaic properties of perovskite solar cells by TiO2 homogeneous hybrid structure

In this paper, we fabricated a TiO2 homogeneous hybrid structure for application in perovskite solar cells (PSCs) under ambient conditions. Under the standard air mass 1.5 global (AM 1.5G) illumination, PSCs based on homogeneous hybrid structure present a maximum power conversion efficiency of 5.39% which is higher than that of pure TiO2 nanosheets. The enhanced properties can be explained by the better contact of TiO2 nanosheets/nanoparticles with CH3NH3PbI3 and fewer pinholes in electron transport materials. The advent of such unique structure opens up new avenues for the future development of high-efficiency photovoltaic cells.

Varied crystalline orientation of anatase TiO2 nanotubes from [101] to [001] promoted by TiF6 (2-) ions and their enhanced photoelectrochemical performance

Herein, we report an ionic cross-linkage process of synthesizing [001] preferred oriented anatase TiO2 nanowires and nanotubes hybrid structure (TWTs) based on anodization method wherein varied amounts of TiF62− ions are added in synthetic process. We show how the TiF62− ions switch the growth direction of TWTs from [101] to [001] (denoted as T101WTs and T001WTs, respectively) and change their geometrical morphologies, i.e., small ionic radii TiF62− ions migrate and partly replace the TiO62− octahedra under electric field, which separate out and leave vacancies during annealing process, resulting in a reconstruction of TiO2. Importantly, absorption property and photoelectrochemical (PEC) performance of T001WTs exceed those of T101WTs. Furthermore, CdS QDs are assembled onto TWTs photoelectrodes by successive ionic layer adsorption and reaction technique. Likewise, T001WT/CdS presents superior absorption capability and enhanced PEC performance to those of T101WT/CdS. This could be attributed to their preponderances of improved light absorption capability and decreased electron recombination.

A facile approach for photoelectrochemical performance enhancement of CdS QD-sensitized TiO2 via decorating {001} facet-exposed nano-polyhedrons onto nanotubes

In this study, we report a TiO2 hybrid structure prepared by a facile route, wherein TiF62− ion has been used as both the surfactant and titanium source. Single-crystalline TiO2 nano-polyhedrons with exposed high active {001} facets were grown on a TiO2 nanowire and nanotube (TWTs) films. This hybrid structure served as a model architecture for efficient photoelectrochemical (PEC) devices because it simultaneously offered a large contact area with the electrolyte and direct pathway for photoexcited electron collection. Under simulated sunlight illumination (AM 1.5 light at 100 mW cm−2), this hybrid structure exhibited a photocurrent density of 1.36 mA cm−2 at 0 V vs. Ag/AgCl (JSC) and photoconversion efficiency (η) of 0.81% at −0.51 V vs. Ag/AgCl, nearly 2.4 times higher than those of the bare TWTs. Morphology of the TiO2 nano-polyhedrons in the hybrid structure was greatly influenced by the TiF62− ion concentration, and a proper concentration was determined to be 2.5 mM. Moreover, the CdS QDs were sensitized onto the hybrid structure, and their JSC and η reached 2.31 mA cm−2 & 1.94%, respectively, 1.5 times higher than those of the CdS-sensitized bare TWTs. The TiO2 nano-polyhedrons improved the efficiency via increasing the specific surface area of the electrode, thus facilitating hole transfer into the electrolyte. Moreover, the exposed high reactive {001} facets provided more effective area for the adsorption of CdS, leading to an enhanced photogeneration carrier density.