Deposition Of CdSe Quantum Dots Research Articles

Voltage-assisted SILAR deposition of CdSe quantum dots to construct a high performance of ZnS/CdSe/ZnS quantum dot-sensitized solar cells

The charge recombination on the interfaces of TiO2/quantum dots (QDs)/electrolyte is a key factor limiting the efficiency of quantum dot-sensitized solar cells (QDSSCs). Construction of double-layer barrier structure of ZnS/QDs/ZnS is a vital strategy to suppress the interfacial charge recombination. However, a large lattice mismatch (12%) at CdSe/ZnS interfaces causes CdSe to grow slowly on TiO2/ZnS mesoporous film, weakening the interaction between QDs and mesoporous film, which reducing the efficiency of CdSe QDSSCs with double ZnS barrier layers. Applying a voltage of 2 V in successive ionic layer adsorption reaction (VASILAR) to create an electric field, which assists Cd2+ and SeSO32− ions rapidly diffuse into the TiO2/ZnS mesoporous film to react forming CdSe QDs at room temperature. Optimizing the number of CdSe QDs deposition layers and combine with ZnS double-layer barrier structure, a best PCE of 4.34% for ZnS/CdSe/ZnS QDSSCs is achieved. This study gives a fast and simple approach to inhibit interfacial charge recombination to construct high performance CdSe QDSSCs.

Voltage-assisted SILAR deposition of CdSe quantum dots into mesoporous TiO2 film for quantum dot-sensitized solar cells

CdSe quantum dots (QDs) grows slowly in mesoporous TiO2 film deriving from a large lattice mismatch (11%) and poor interaction between the two, which resulting the low power conversion efficiency (PCE) of quantum dot-sensitized solar cells (QDSSCs). An external voltage is applied in the successive ionic layer adsorption reaction (SILAR) process, which drives the Cd2+ and SeSO32− ions quickly diffused into the mesoporous TiO2 film and reacted to form CdSe QDs at room temperature. The CdSe QDSSCs yields a PCE of 3.27%. This work provides an efficient strategy to assemble QDs for enhancing the performance of QDSSCs.

Interfacial passivation mechanism of sulfide towards quantum dot-sensitized nanocrystalline thin films

We report on the interfacial passivation mechanism in CdSe quantum dot-sensitized ZnO nanocrystalline thin film, where different sulfide semiconductors (such as ZnS and CdS) and sulfide ions are used to modify ZnO nanocrystalline thin film before deposition of CdSe quantum dots (QDs). It is noticed that the highest light-to-electric conversion efficiency of CdSe quantum dot-sensitized ZnO nanocrystalline thin film solar cell is attained up to 4.18 % after CdS interfacial modification. Meanwhile, a simple treatment of ZnO nanocrystalline thin film in Na2S solution can also increase the conversion efficiency of CdSe quantum dot-sensitized solar cell up to 3.45 %. The electron transfer and recombination processes occurred in the interface of QD-sensitized nanocrystalline thin films with and without the different interfacial modifications are detected by measuring intensity modulated photovoltage spectroscopy and electrochemical impedance spectroscopy of solar cells. These results indicate that adsorption of S2− ions on the surface active sites of ZnO nanoparticles is the main reason for the conversion efficiency improvement due to the interfacial passivation of sulfide semiconductors.

Cadmium selenide-sensitized upright-standing mesoporous zinc oxide nanosheets for efficient photoelectrochemical H2 production

Cadmium selenide (CdSe)-sensitized upright-standing mesoporous zinc oxide (ZnO) nanosheets were prepared via a chemical bath deposition followed by annealing and electrochemical deposition of CdSe quantum dots (QDs). The CdSe QDs absorb visible photons under sunlight illumination, promoting electrons from the valence band to the conduction band of CdSe, which then quickly transfer to ZnO followed by the external load to the Pt counter electrode for water reduction. The as-prepared CdSe/ZnO nanosheets show promising photoelectrochemical activities for hydrogen generation.

Controllable in situ photo-assisted chemical deposition of CdSe quantum dots on ZnO/CdS nanorod arrays and its photovoltaic application

Compound semiconductors have been widely applied in the energy field as light-harvesting materials, conducting substrates and other functional parts. Nevertheless, to effectively grow them in various forms toward objective applications, limitations have often been met to achieving high growth rate, simplicity of method and controllability of growing processes simultaneously. In this work, we have grown a uniform CdSe layer on ZnO/CdS nanorod arrays by a novel in situ photo-assisted chemical deposition method. The morphology and quality of the as-formed material could be significantly influenced by tuning the optical parameters of the injected light. Due to the effect of injected light on the key reactions during the growth, a modified natural light with removal of the UV and IR components seems to be more suitable than monochromic light. An efficiency of 3.59% was achieved without any additional treatment, significantly higher than the efficiency of 2.88% of the sample by conventional CBD method under similar conditions with growth rate one order of magnitude higher. In general, the result has suggested its potential importance for other compound materials and opto-electronic devices.

Tungsten trioxide nanorods on flexible carbon cloth for photoelectrochemical water splitting

Upon the WO3 seed layer, WO3 nanorods (NRs) were effectively prepared by facile hydrothermal synthesis on the flexible carbon cloth substrate, subsequently followed by the deposition of CdSe quantum dots by successive ionic layer and adsorption reaction (SILAR) process as a light absorbing medium. It was confirmed that WO3 NRs with a diameter of approximately 170nm (±20nm) with a length of 2.2μm (±0.2μm) were uniformly coated on the entire surface area of carbon cloth substrate that consisted of a bundle of carbon fibers having a diameter of 8.9μm. In addition, the optical properties of WO3 NRs and CdSe/WO3 NRs film were also certified by ultraviolet (UV–vis) spectroscopy, thus disclosing the light absorption of intrinsic WO3 electrode as well as the CdSe light absorber. The photocurrent density of CdSe/WO3 NRs film was about 68μA/cm2, displaying a value that was two times enhanced due to the CdSe light absorber.

Bifunctional Effects of CdSe Quantum Dots and Nb2O5 Interlayer for ZnO Nanorods-based Photoelectrochemical Water-Splitting Cells

Single crystalline ZnO nanorods (ZONRs) with a length of 3.6μm and a diameter of 100nm were prepared using a hydrothermal method. Based on photoactive ZONR films, the thin Nb2O5 layers were introduced using spin-coating, followed by the deposition of CdSe quantum dots (QDs) as an absorber. The Nb2O5 layers, denoted as Nb2O5(1) and Nb2O5(2), were spin-coated one and two times, respectively, to demonstrate the thickness effect of Nb2O5. The Nb2O5(1)-coated ZONR (ZONR/Nb2O5(1)) exhibited a higher photoelectrochemical (PEC) response and better stability than the bare ZONR, due to the surface-related defect states passivated by the Nb2O5. In contrast, the PEC response of the ZONR/Nb2O5(2) was reduced about 40% due to the insulating nature of the thicker Nb2O5. CdSe QD-sensitized ZONR and ZONR/Nb2O5 films were compared, revealing that the ZONR/Nb2O5(1)/CdSe film exhibited significantly enhanced PEC performance when compared with the other films. Herein, the CdSe QDs acted as the light absorber and, in addition, the QDs on the exposed ZONR passivated the surface-related defect states of the ZONR. The Nb2O5 layers also passivated the surface-related defect states of the ZONR; furthermore, the Nb2O5 located between the ZONR and the QDs led to the stepwise energy band edge alignment, resulting in the faster charge separation. These binfunctional effects contributed to the significantly enhanced PEC response of the ZONR/Nb2O5(1)/CdSe.

Deposition of CdSe quantum dots on graphene sheets

High-quality TOP/TOPO capped CdSe quantum dots (QDs) displaying a narrow emission band have been grafted on to graphene nanosheets through a simple wet chemical procedure. A significant red-shift of both the broad absorption and narrow emission spectra of the QDs is induced in the resultant hybrid material, presumably by a strong graphene–QD interaction consistent with a quantum tunnelling phenomenon. The optical properties of monodisperse CdSe QDs of 3–4nm in diameter have been determined in UV–vis and photoluminescence spectra and HRTEM and XPS data, demonstrating the successful decoration of graphene sheets with CdSe QDs. The CdSe QD absorption was observed to shift to longer wavelengths by up to 30nm, with a corresponding shift of up to 18nm observed in the emission band. This effect is equivalent to a narrowing of the band gap by 0.094±0.015eV in absorption and 0.033±0.013eV in emission, or an interaction potential of 9.1±1.5kJmol−1. Another is to consider the effective particle growth based upon the narrowed band gap, consistently found to be 28±1%, despite the physical size remaining unchanged. By effectively shifting the absorption and emission of CdSe QDs to longer wavelengths, this type of nanocomposite may have potential applications in the fields of optics, biological imaging and sensing.

Two-step annealed CdS/CdSe co-sensitizers for quantum dot-sensitized solar cells

CdS/CdSe co-sensitizers on TiO2 films were annealed using a two-step procedure; high temperature (300 °C) annealing of TiO2/CdS quantum dots (QDs), followed by low temperature (150 °C) annealing after the deposition of CdSe QDs on the TiO2/CdS. For comparison, two types of films were prepared; CdS/CdSe-assembled TiO2 films conventionally annealed at a single temperature (150 or 300 °C) and non-annealed films. The 300 °C-annealed TiO2/CdS/CdSe showed severe coalescence of CdSe QDs, leading to the blocked pores and hindered ion transport. The QD-sensitized solar cell (QD-SSC) with the 150 °C-annealed TiO2/CdS/CdSe exhibited better overall energy conversion efficiency than that with the non-annealed TiO2/CdS/CdSe because the CdSe QDs annealed at a suitable temperature (150 °C) provided better light absorption over long wavelengths without the hindered ion transport. The QD-SSC using the two-step annealed TiO2/CdS/CdSe increased the cell efficiency further, compared to the QD-SSC with the 150 °C-annealed TiO2/CdS/CdSe. This is because the 300 °C-annealed, highly crystalline CdS in the two-step annealed TiO2/CdS/CdSe improved electron transport through CdS, leading to a significantly hindered recombination rate.

Electrochemical fabrication of ZnO–CdSe core–shell nanorod arrays for efficient photoelectrochemical water splitting

Efficient hydrogen production from photoelectrochemical (PEC) water splitting is a promising route to solve the approaching energy crisis. Herein, we report a facile all-electrochemical approach to fabricate well-aligned ZnO-CdSe core-shell nanorod arrays with excellent uniformity on transparent indium tin oxide (ITO) substrates. The shell thickness of the core-shell nanorods can be tuned precisely by adjusting the charge density passing through the working electrode during the deposition of CdSe quantum dots (QDs). The optimized ZnO-CdSe nanorod arrays showed excellent PEC performance with a significant saturated photocurrent density of 14.9 mA cm(-2) at 0.8 V (vs. RHE) under AM 1.5 illumination, which is, to the best of our knowledge, the highest value ever reported for similar nanostructures, owing to the favourable band alignment and good distribution of CdSe QDs on ZnO nanorods. Our results demonstrate that the electrochemically deposited ZnO-CdSe nanorod arrays can be utilized as efficient photoanodes in PEC water splitting cells.

The Effect of the Dielectric Constant of a Solution of CdSe Quantum Dots on Electrophoretic Deposition of the Dots

ABSTRACTThe effect on film quality of the dielectric constant εb of the bath solution used for electrophoretic deposition of CdSe quantum dots (QDs) was investigated. Various combinations of solvents yielding different εb were tested, with the best films produced by a bath consisting of hexanes and acetone. Two different types of film were observed, depending on the volume fraction of acetone in the bath: thin, but strongly adhered films for εb < 12 and thick but loose films for εb > 12. This behavior is explained in terms of the rate at which QDs arrive at the surface of the electrode, which depends on the electrophoretic mobility of the QDs and therefore also the dielectric constant of the bath.

Functionalized electrophoretic deposition of CdSe quantum dots onto TiO2 electrode for photovoltaic application

We discuss about the utilization of functionalized electrophoretic deposition technique for photovoltaic application encompassing the prospective potential of both functionalization and electrophoretic deposition. We report the fabrication of TiO2 sensitized electrode by electrophoretic deposition of CdSe quantum dots. This method holds the advantage of achieving effective coating of CdSe onto TiO2 electrode by reducing the deposition time to 15min. Cross-sectional and depth profile elemental analysis revealed the even distribution of CdSe across the TiO2 layer. Ninety percentage of light harvesting efficiency was achieved for the CdSe sensitized electrode affirming the efficacy of sensitization by functionalized electrophoretic deposition.

Flexible quantum dot sensitized solar cell by electrophoretic deposition of CdSe quantum dots on ZnO nanorods

We report on a flexible quantum dot-sensitized solar cell (QDSSC) based on ZnO nanorods with a length of 2 μm. Due to the good coverage of CdSe QDs on ZnO by the electrophoretic deposition method, a maximum power conversion efficiency of ∼1% is achieved for the flexible QDSSC.