Yannan Mu

High catalytic activity of a PbS counter electrode prepared via chemical bath deposition for quantum dots-sensitized solar cells

A PbS counter electrode (CE) has been fabricated by a chemical bath deposition method, and can function as a counter electrode with high catalytic activity for quantum dots-sensitized solar cells (QDSSCs). The PbS nanoparticles can act as an excellent electrical tunnel for fast electron transport from an external circuit to the CE. Electrochemical impedance spectroscopy reveals a low charge transfer resistance (Rct1) between polysulfide and PbS, the optimized PbS CE shows an Rct1 as low as 15.42 Ω cm2. The current density–voltage curves of the QDSSCs were investigated under AM 1.5 light at 100 mW cm−2. CdS quantum dots-sensitized solar cells with the PbS CE achieved a power energy conversion efficiency of 2.91% and showed no obvious degradation of current density over 72 h under ambient conditions.

The enhanced photoelectrochemical performance of CdS quantum dots sensitized TiO2 nanotube/nanowire/nanoparticle arrays hybrid nanostructures

This study aims at improving the photoelectrochemical performance mainly from two aspects: the increased number of heterojunctions and the advantages of nanotube/nanowire/nanoparticle arrays hybrid nanostructures. TiO2 nanoparticles porous layer was sensitized by CdS quantum dots (QDs), and coated on the top of the material, hydrogen-treated TiO2 nanotubes with nanowires, which was also sensitized by CdS QDs (This nanostructure is defined as CdS/H:TTWP). CdS/H:TTWP was successfully fabricated by the methods of electrochemical anodization, successive ionic layer adsorption and reaction (SILAR) and sol–gel. The data from the photoelectrochemical (PEC) performance test shows that the photocurrent density of CdS/H:TTWP is 7.6 mA cm−2 at −0.43 V vs. Ag–AgCl under AM 1.5 G illuminations.

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.

The effects of CTAB concentration on the properties of electrodeposited cadmium telluride films

The effects of cetyltrimethylammonium bromide (CTAB) concentrations on the properties of electrochemically deposited cadmium telluride films have been investigated using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and photoelectrochemical measurements. The results show that CTAB concentration plays a very important role in directing the morphology evolution of thick films from cabbage-shaped CdTe arrays to high density nanoneedle structures. Various CdTe structures can be obtained by changing the CTAB concentration in the electrolyte. Meanwhile, it was observed that the Te/Cd ratio of the as-deposited thin film decreased with the increase of CTAB concentration. When CTAB concentrations are 0.02 M, the composition of CdTe film is near stoichiometric and Te is in excess. Growth mechanisms for shape-selective CdTe synthesis are proposed based on these results. In addition, we found that the device based on the aligned cabbage-shaped CdTe array-on-Ni configuration prepared at 0.02 M CTAB demonstrates excellent photoelectrical properties, which is ascribed to the large absorption coefficient of the material and also suggests a good electronic structure quality of the cabbage-shaped rods.

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.

Embedded CdS nanorod arrays in PbS absorber layers: enhanced energy conversion efficiency in bulk heterojunction solar cells

Oriented and high-density n-type CdS nanorod arrays were successfully embedded in p-type PbS absorber layers by a facile and low-cost hydrothermal method and a chemical bath deposition method. The structural, optical and electrical properties of these samples were examined, and the results demonstrated that the high quality three-dimensional heterostructure was obtained. Further investigation revealed that the three-dimensional heterostructure possessed superior optical absorption property due to the optical scattering from the nanorod array. In addition, photovoltaic property measurements demonstrated that the energy conversion efficiency of the novel three-dimensional heterojunction solar cell was increasing by 35% in comparison with the standard planar heterojunction solar cell. The observed improvement is mostly attributed to the three-dimensional heterostructure enabling increased heterojunction area, improved charge carrier collection and enhanced optical absorption ability. This study demonstrates that the three-dimensional heterostructure has potential application in thin film solar cells, and the solution process represents a promising technique for large-scale fabrication of these novel solar cells.

Ag–Cu2O composite microstructures with tunable Ag contents: synthesis and surface-enhanced (resonance) Raman scattering (SE(R)RS) properties

Metal–semiconductor composite microstructures have recently been demonstrated to possess potential applications due to their unique structures. Ag–Cu2O composite microstructures (Ag–Cu2O CMSs) with tunable silver content have been synthesized with a facile in situ method. Ag contents on the surface of Cu2O can be tuned through the variation of the concentration of AgNO3, which further greatly affected the surface-enhanced (resonance) Raman scattering (SE(R)RS) performance. The Ag–Cu2O CMSs prepared with 0.4 mM AgNO3 show the optimum SE(R)RS properties, better than pure Ag NPs. Furthermore, the enhancement mechanism and uniformity of Ag–Cu2O CMSs are investigated in detail.

Synthesis of ZnO nanosheet array film with dominant {0001} facets and enhanced photoelectrochemical performance co-sensitized by CdS/CdSe

In this work, [110] oriented ZnO nanosheet (ZnONS) array films with a large percentage of high-energy {0001} surfaces were prepared for the first time with the assistance of sodium citrate. ZnONS array films possess prominent UV–visible absorption with an absorption edge at ~405 nm, indicating that the optical property of the semiconductor is dependent on a specific crystal structure and crystal plane. CdS and CdSe quantum dots (QDs) were assembled onto ZnONS array films to form a cascade structure of ZnONS/CdS/CdSe by the successive ionic layer adsorption and reaction method. The as-fabricated photoanode exhibits strong absorption in the visible spectrum up to 735 nm. With light illumination, the optimum photoanode yields a photocurrent of ~4.40 mA cm−2 at 0 V versus SCE, which is about 4.6 times of that of pure ZnONS samples. The excellent photoelectrochemical (PEC) properties of our photoanodes suggest that the QDs sensitized ZnONS array films with a large percentage of high-energy surfaces have potential applications in PEC solar cells.

Electrodeposition of a novel CdTe array on Ni foils and photoelectrochemical performance

A novel perpendicularly aligned CdTe array with cauliflower-like morphology was fabricated on a Ni substrate using a simple electrochemical synthesis method. The samples were characterized by XRD, EDX and FESEM, and the results demonstrate that a high-purity, uniform cauliflower-like CdTe array was obtained. Rod lengths can reach to 3.0 μm, with nanoparticles stacking along the rod growth direction, keeping the diameter at 1.5 μm. A schematic diagram of the possible growth process and evolution from CdTe seed nuclei to the cauliflower-like CdTe array was proposed. The device based on the aligned array-on-Ni configuration demonstrates excellent photoelectrical properties, which is ascribed to the large absorption coefficient of the material and also suggests good electronic structure quality of the cauliflower-like rods. The technique described is applicable to fabricate highly aligned cauliflower-like semiconductor arrays on other conductive substrates.

Effect of sodium chloride on the electrochemistry activity of electrodeposited CdTe films with various morphologies

In this paper, a cadmium telluride (CdTe) film is successfully synthesized on Ni foils via a simple electrochemical deposition method. Especially, with sodium chloride (NaCl) being added into the electrolyte directly, an interesting morphology evolution from spherical CdTe film to rod-shaped CdTe film, then to clustered CdTe film, and finally to double-layered film is observed with the increase of the NaCl concentration. The products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis spectroscopy, and photoelectrochemical measurements. It is found that the amount of NaCl played an important role in determining the morphology of CdTe film. The possible growth mechanism is discussed as well. Photoelectrochemical measurements reveal that the morphology of CdTe film can affect their photoelectrical properties greatly, and the uniform CdTe nanorod arrays prepared at 0.05 mol L−1 NaCl exhibit excellent photoelectrical properties, which is meaningful to the investigation of CdTe solar cells. According to the experiments, this simple but effective method can also be extended to the control of the growth of other nanostructures.