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Novel nanowire array based highly efficient quantum dot sensitized solar cell

In this communication, a novel CdSe/CdS/ZnO nanowire array fabricated by a 3-step solution-based method was used as a photoanode of a quantum dot sensitized solar cell, which generated a maximum power conversion efficiency of 4.15%.

Self-assembled foam-like graphene networks formed through nucleate boiling

Self-assembled foam-like graphene (SFG) structures were formed using a simple nucleate boiling method, which is governed by the dynamics of bubble generation and departure in the graphene colloid solution. The conductivity and sheet resistance of the calcined (400°C) SFG film were 11.8 S·cm–1 and 91.2 Ω□−1, respectively, and were comparable to those of graphene obtained by chemical vapor deposition (CVD) (~10 S·cm–1). The SFG structures can be directly formed on any substrate, including transparent conductive oxide (TCO) glasses, metals, bare glasses, and flexible polymers. As a potential application, SFG formed on fluorine-doped tin oxide (FTO) exhibited a slightly better overall efficiency (3.6%) than a conventional gold electrode (3.4%) as a cathode of quantum dot sensitized solar cells (QDSSCs).

TiN Nanoparticles on CNT–Graphene Hybrid Support as Noble‐Metal‐Free Counter Electrode for Quantum‐Dot‐Sensitized Solar Cells

The development of an efficient noble-metal-free counter electrode is crucial for possible applications of quantum-dot-sensitized solar cells (QDSSCs). Herein, we present TiN nanoparticles on a carbon nanotube (CNT)-graphene hybrid support as a noble-metal-free counter electrode for QDSSCs employing a polysulfide electrolyte. The resulting TiN/CNT-graphene possesses an extremely high surface roughness, a good metal-support interaction, and less aggregation relative to unsupported TiN; it also has superior solar power conversion efficiency (4.13 %) when applying a metal mask, which is much higher than that of the state-of-the-art Au electrode (3.35 %). Based on electrochemical impedance spectroscopy measurements, the enhancement is ascribed to a synergistic effect between TiN nanoparticles and the CNT-graphene hybrid, the roles of which are to provide active sites for the reduction of polysulfide ions and electron pathways to TiN nanoparticles, respectively. The combination of graphene and CNTs leads to a favorable morphology that prevents stacking of graphene or bundling of CNTs, which maximizes the contact of the support with TiN nanoparticles and improves electron-transfer capability relative to either carbon material alone.

Improvement of photocurrent generation of Ag2S sensitized solar cell through co-sensitization with CdS

In this study, photovoltaic application of Ag2S-CdS heterostructure is reported. The photovoltaic cell generated considerably high photocurrent density (Jsc) of 27.6 mA/cm2, which is over two times larger than that of the Ag2S quantum dot sensitized solar cell (QDSSC) of 11.3 mA/cm2. This improvement is due to the cascade-shaped band structure alignment of ZnO/CdS/Ag2S and to the excellent role of CdS as a buffer layer for relieving lattice mismatch. The power conversion efficiency of the CdS/Ag2S QDSSC, which was attributed to the superior Jsc, was 2.4%, twice as high as the 1.2% efficiency of the Ag2S QDSSC and the CdS QDSSC.

Synthesis and Characterization of ZnO Nanowire–CdO Composite Nanostructures

ZnO nanowire–CdO composite nanostructures were fabricated by a simple two-step process involving ammonia solution method and thermal evaporation. First, ZnO nanowires (NWs) were grown on Si substrate by aqueous ammonia solution method and then CdO was deposited on these ZnO NWs by thermal evaporation of cadmium chloride powder. The surface morphology and structure of the synthesized composite structures were analyzed by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The optical absorbance spectrum showed that ZnO NW–CdO composites can absorb light up to 550 nm. The photoluminescence spectrum of the composite structure does not show any CdO-related emission peak and also there was no band gap modification of ZnO due to CdO. The photocurrent measurements showed that ZnO NW–CdO composite structures have better photocurrent when compared with the bare ZnO NWs.

An exceptionally facile method to produce layered double hydroxides on a conducting substrate and their application for solar water splitting without an external bias

An exceptionally facile process is presented for in situ formation of zinc chromium layered double hydroxide (ZnCr:LDH) nanosheets on a conducting substrate. Thus, ZnCr:LDH nanosheets were synthesized from a metallic Zn film/fluorine-doped tin oxide (FTO) glass by simply dipping into a Cr nitrate solution for only one minute at room temperature. Then, ZnCr:LDHs were converted into zinc chromium mixed metal oxide (ZnCr:MMO) nanoparticles by calcination. Under visible light irradiation (λ > 420 nm), the in situ synthesized ZnCr:MMO photoanode exhibited a stable and an order-of-magnitude higher activity for photoelectrochemical water splitting than that of a ZnCr:MMO film fabricated ex situ by electrophoretic deposition of already-synthesized ZnCr:MMO powders. More significant was that it generated anodic photocurrents even without an externally applied bias potential, which is an unprecedented result for an oxide photoanode-driven PEC system working under visible light.

Freestanding CdS nanotube films as efficient photoanodes for photoelectrochemical cells

Freestanding CdS nanotube films were synthesized for the first time using ZnO nanorod arrays as a sacrificial template. The CdS nanotube films exhibited excellent photo-anodic activities in a photoelectrochemical (PEC) cell.

Molecular conformation dependent emission behaviour (blue, red and white light emissions) of all-trans-β-carotene-ZnS quantum dot hybrid nanostructures

A novel hybrid material consisting of all-trans-β-carotene and ZnS quantum dots (QDs) was prepared by two different controlled experiments and their photophysical properties were investigated in detail. Depending upon the preparation method, the β-carotene molecule had formed either an upright or wrapped conformation around the ZnS QDs and consequently the interaction between these two hybridizing systems was either charge transfer induced or electrostatic in type, respectively. Optical absorption, Raman and FTIR investigations have confirmed the two different conformations of the molecule around the ZnS QDs. Because of the two different conformations and the consequent interactions, different emission colours, such as blue and red wavelengths were obtained from these hybrids. We were also able to obtain white light emission by using cadmium doped ZnS QDs for the hybrid preparation.

Hot electron extraction from CdTe quantum dots via beta carotene molecular energy levels

We report our findings related to hot electron extraction from CdTe quantum dots, and we were able to do this by using beta carotene as an electron acceptor. Transient absorption spectra with two slow recovering negative bleaches at the absorption maximum of the molecule and quantum dot have indicated the slowing down of cooling process and the existence of hot carriers in this hybrid system.