Spectral broadening in quantum dots-sensitized photoelectrochemical solar cells based on CdSe and Mg-doped CdSe nanocrystals

In order to absorb a broad spectrum in visible region, a co-sensitized TiO₂ electrode was prepared by CdSe and Mg-doped CdSe quantum dots (Q dots). The power conversion efficiency of the co-sensitized Q dots photoelectrochemical solar cells (PECs) showed 1.03% under air mass 1.5 condition (I = 100 mW/cm²), which is higher than that of individual Q dots-sensitized PECs. The incident-photon-to-current conversion efficiency of the co-sensitized PECs showed absorption peaks at 541 and 578 nm corresponding to the two Q dots and displayed a broad spectral response over the entire visible spectrum in the 500–600 nm wavelength domains.     

Chemical bath deposition of CdS quantum dots on vertically aligned ZnO nanorods for quantum dots-sensitized solar cells

Formation of CdS quantum dots (Q dots) on the vertically aligned ZnO nanorods electrode was carried out by chemical bath deposition. The diameter and thickness of ZnO nanorods are ～100–150 nm and ～1.6 μm, respectively, and CdS Q dots on ZnO nanorods have a diameter of smaller than 15 nm. In application of the Q dots-sensitized solar cells, composite film exhibited a power conversion efficiency of 0.54% under air mass 1.5 condition (80 mW/cm²), and incident-photon-to-current conversion efficiency showed 18.6%.     

Ag2S quantum dot-sensitized solar cells

We present a new photosensitizer – Ag₂S quantum dots (QDs) – for solar cells. The QDs were grown by the successive ionic layer adsorption and reaction deposition method. The assembled Ag₂S-QD solar cells yield a best power conversion efficiency of 1.70% and a short-circuit current of 1.54 mA/cm² under 10.8% sun. The solar cells have a maximal external quantum efficiency (EQE) of 50% at λ = 530 nm and an average EQE of ～ 42% over the spectral range of 400–1000 nm. The effective photovoltaic range covers the visible and near-infrared spectral regions and is ～ 2–4 times broader than that of the cadmium chalcogenide systems — CdS and CdSe. The results show that Ag₂S QDs can be used as a highly efficient and broadband sensitizer for solar cells.     

Photocurrent generated on a carotenoid-sensitized TiO2 nanocrystalline mesoporous electrode

Photocurrent was observed upon monochromatic illumination of an ITO electrode coated with a TiO₂ nanocrystalline mesoporous membrane with carotenoid 8′-apo-β-caroten-8′-oic acid (ACOA) deposited as a sensitizer (illuminated area 0.25 cm²) and immersed in an aqueous 10 mM hydroquinone (H₂Q), 0.1 M NaH₂PO₄ solution (pH = 7.4) purged with argon, using a platinum flag counter electrode (area 3.3 cm²) and a SCE reference electrode. The carotenoid-sensitized short-circuit photocurrent reached 4.6 μA/cm² upon a 40 μW/cm² incident light beam at 426 nm, with an IPCE (%, incident monochromatic photon-to-photocurrent conversion efficiency) as high as 34%. The short-circuit photocurrent was stable during 1 h of continuous illumination with only a 10% decrease. An open-circuit voltage of 0.15 V was obtained (upon 426 nm, 40 μW/cm² illumination) which remained at a constant value for hours. The observed open-circuit voltage is close to the theoretical value (0.22 V) expected in such a system. The action spectrum resembled the absorption spectrum of ACOA bound on the TiO₂ membrane with a maximum near 426 nm. No decay of the ACOA on the TiO₂ surface was observed after 12 h, presumably because of rapid regeneration of ACOA from ACOA⁺ at the surface by electron transfer from H₂Q.     

AgSbS2 semiconductor-sensitized solar cells

We present a ternary semiconductor nanoparticle sensitizer – AgSbS₂ – for solar cells. AgSbS₂ nanoparticles were grown using a two-stage successive ionic layer adsorption and reaction process. First, Ag₂S nanoparticles were grown on the surface of a nanoporous TiO₂ electrode. Secondly, a Sb–S film was coated on top of the Ag₂S. The double-layered structure was transformed into AgSbS₂ nanoparticles ~ 40 nm in diameter, after post-deposition heating at 350 °C. The AgSbS₂-sensitized TiO₂ electrodes were fabricated into liquid-junction solar cells. The best cell yielded a power conversion efficiency of 0.34% at 1 sun and 0.42% at 0.1 sun. The external quantum efficiency (EQE) spectrum covered the range of 380–680 nm with a maximal EQE of 10.5% at λ = 470 nm. The method can be applied to grow other systems of ternary semiconductor nanoparticles for solar absorbers.     

Synthesis of triphenylamine-based thiophene-(N-aryl)pyrrole-thiophene dyes for dye-sensitized solar cell applications

Two new triphenylamine-based metal-free organic dyes (TPTDYE-1 and TPTDYE-2) containing 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole as a new π-conjugated chromophore were synthesized for dye-sensitized solar cell (DSSC) applications. TPTDYE-1 containing three donor groups around the acceptor group was found to show relatively narrow absorption band from 300 nm to 470 nm while TPTDYE-2 having extended π–π delocalization between the donor and acceptor group showed broad absorption band from 300 nm to 550 nm. The electrochemical studies indicate that the HOMO–LUMO energy gap of TPTDYE-1 is considerably wider than that of TPTDYE-2. The dye-sensitized solar cell performance of each dye was investigated, and the TPTDYE-2-sensitized cell was found to show a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 75%, a short-circuit photocurrent density (J_sc) of 13.50 mA/cm², an open-circuit voltage (V_oc) of 0.72 V, and a fill factor (FF) of 0.69, corresponding to an overall conversion efficiency of 6.71% under simulated AM 1.5 irradiation (100 mW/cm²). Under the same condition the TPTDYE-1-sensitized cell showed the same IPCE value of 75% with a promising conversion efficiency of 6.00%, a J_sc of 11.11 mA/cm², a V_oc of 0.76 V, and a FF of 0.71.     

Preparation and photocatalytic activity of visible light-active sulfur and nitrogen co-doped SrTiO3

Nitrogen and sulfur co-doped SrTiO₃ was prepared by high energy grinding of the mixture of SrTiO₃ and thiourea. A new band gap in visible light region (522 nm) corresponding to 2.37 eV could be formed by the co-doping. The photocatalytic activity for nitrogen monoxide oxidation of SrTiO₃ in visible light region especially in the long wavelength range (λ > 510 nm) could be improved greatly. Under the irradiation of light with wavelength larger than 510 nm, the photocatalytic activity of nitrogen and sulfur co-doped SrTiO₃ was 10.9 times greater than that of pure SrTiO₃. The high visible light photocatalytic activity of this substance may be due to the formation of a new band gap that enables to absorb visible light effectively.     

Highly efficient quasi-solid-state quantum-dot-sensitized solar cell based on hydrogel electrolytes

Chemically crosslinked polyacrylamide-based hydrogel has been first used as the polymer matrix to prepare quasi-solid-state polysulfide electrolyte for CdS/CdSe co-sensitized solar cells (QDSCs). The room temperature ionic conductivity of the gel electrolyte reaches 0.093 S·cm^?1. QDSCs based on this quasi-solid-state electrolyte can present up to 4.0% of light-to-electricity conversion efficiency. Meanwhile, the interfacial recombination at TiO₂/electrolyte interface of the cell is also investigated by Electrochemical Impedance Spectroscopy (EIS).     

Photocatalytic activity of nitrogen and copper doped TiO2 nanoparticles prepared by microwave-assisted sol-gel process

Cu and N-doped TiO₂ photocatalysts were synthesized from titanium (IV) isopropoxide via a microwave-assisted sol-gel method. The synthesized materials were characterized by X-ray diffraction, UV-vis diffuse reflectance, photoluminescence (PL) spectroscopy, SEM, TEM, FT-IR, Raman spectroscopy, photocurrent measurement technique, and nitrogen adsorption–desorption isotherms. Raman spectra and XRD showed an anatase phase structure. The SEM and TEM images revealed the formation of an almost spheroid mono disperse TiO₂ with particle sizes in the range of 9-17 nm. Analysis of N₂ isotherm measurements showed that all investigated TiO₂ samples have mesoporous structures with high surface areas. The optical absorption edge for the doped TiO₂ was significantly shifted to the visible light region. The photocurrent and photocatalytic activity of pure and doped TiO₂ were evaluated with the degradation of methyl orange (MO) and methylene blue (MB) solution under both UV and visible light illumination. The doped TiO₂ nanoparticles exhibit higher catalytic activity under each of visible light and UV irradiation in contrast to pure TiO₂. The photocatalytic activity and photocurrent ability of TiO₂ have been enhanced by doping of the titania in the following order: (Cu, N) - codoped TiO₂ > N-doped TiO₂ > Cu-doped TiO₂ > TiO₂. COD result for (Cu, N)-codoped TiO₂ reveals ∼92% mineralization of the MO dye on six h of visible light irradiation.     

Photoelectrochemical solar cell properties of heteropolytungstic acid-incorporated TiO2 nanodisc thin films

Thin film of heteropolytungstic acid (HPA)-incorporated TiO₂ nanodisc was fabricated, and its photovoltaic performances were observed as a function of irradiation wavelength from 400 nm to 750 nm. Its incident photon-to-current efficiency (IPCE) was determined to be 18.6% around 500 nm, with energy conversion efficiency of 6.9%, which were observed to be further enhanced to 23% and 9%, respectively, by adsorption of ruthenium or porphyrin dyes. Complementary electron transports from both HPA and dyes to TiO₂ nanodisc seems to avoid most of the backward electron or hole transfer reactions to enhance the photoelectrochemical efficiencies of dye-sensitized solar cells.     

Bubble-like CdSe nanoclusters sensitized TiO2 nanotube arrays for improvement in solar cell

Solar cells were fabricated using novel bubble-like CdSe nanoclusters sensitized highly ordered titanium oxide nanotube (TiO₂ NT) array, prepared by anodization technique. The CdSe sensitization of TiO₂ NT arrays was carried out by a chemical bath deposition method with freshly prepared sodium selenosufite, ammonium hydroxide and cadmium acetate dehydrate at different deposition times: 20, 40 and 60 min. The adsorption of CdSe nanoclusters on the upper and inner surface of the TiO₂ NT arrays has been confirmed by field emission scanning electron and transmission electron microscopes. The results show the variation in cell a performance with different deposition times (20, 40, and 60 min) of CdSe on TiO₂ NT arrays. The solar cell with CdSe, deposited for 60 min, shows reasonably high photovoltaic property compared to the reported results of similar studies. This solar cell shows the maximum photoelectric conversion efficiency of 1.56% (photocurrent of 7.19 mA/cm²; photovoltage of 0.438 V; and fill factor of 49.5%) and average incident photon to current efficiency of 50.2%. The photocurrent, incident photon-current efficiency and electron lifetime have been improved due to the increase of covered area and size of bubble-like CdSe nanoclusters on TiO₂ NT arrays with the increase of deposition time.     

Highly efficient CdSe quantum-dot-sensitized TiO2 photoelectrodes for solar cell applications

With 4.2 nm quantum-dots (QDs) as seeds on TiO₂ film, a highly efficient TiO₂ photoelectrode was prepared by a seed-growing process using chemical bath deposition technique, followed by a covering process with ZnS layer, and a post-sintering process at 400 °C. The assembled solar cells presented IPCE peak values of 73% and power conversion efficiency of 3.21% under AM 1.5 G irradiation.     

Au-assisted visible laser MALDI

The excitation of UV-absorbing MALDI matrixes with visible laser (532 nm wavelength) and the desorption/ionization of biomolecules were performed by coating the analytes doped matrix with Au thin film (5–10 nm) using ion sputtering deposition. The Au film was first ablated with the laser of higher fluence, resulting in a crater/hole about the size of the laser beam spot on the target. After a few initial laser shots, analytes and matrix related ions were observed from the crater even at lower laser fluence. Electron microscopy inspection on the laser ablated region revealed the formation of nanoparticles with sizes ranging from <10 to 50 nm. Compared with the infra-red laser (1064 nm) excitation, the visible laser produced much higher abundance of matrix radical ions, and less heating effect as measured by the thermometer molecules. The results suggest the photo-excitation and photo-ionization of matrix molecules by the visible laser, possibly assisted by the gold nanoparticles and nanostructures left on the ablated crater.     

Recognition of DNA based on changes in the fluorescence intensity of CdSe/CD QDs–phenanthroline systems

The CdSe quantum dots (QDs) modified by mercapto-β-cyclodextrin (CD) were synthesized and characterized by transmission electron microscopy, powder X-ray diffraction, excitation and emission spectra, and fluorescence lifetime. When λ_ex = 370 nm, the fluorescence peak of CdSe/CD QDs is at 525 nm. Phenanthroline (Phen) is able to quench their fluorescence, which can be recovered by the addition of DNA. The quenching and restoration of fluorescence intensity were found to be linearly proportional to the amount of Phen and DNA, respectively. The variation of the fluorescence intensity of the CdSe/CD QDs–Phen system was studied, and it was demonstrated to result from a static mechanism due to the formation of a Phen inclusion complex with the CdSe QDs modified by mercapto-β-cyclodextrin. The fluorescence recovery was due to the binding of DNA with Phen in the inclusion complex, leading to the freeing of the CdSe/CD QDs. The binding constants and sizes of the binding sites of the Phen–DNA interaction were calculated to be 1.33 × 10⁷ mol^?1 L and 10.79 bp.     

Growth of gamma glycine crystal and its characterisation

Single crystal of γ-glycine, an organic nonlinear optical material, has been grown by solvent evaporation technique from a mixture of aqueous solutions of glycine and potassium nitrate, lithium nitrate at room temperature. Gamma glycine crystals have been grown up to the dimension of 20 mm × 15 mm × 12 mm. Powder X-ray diffraction of the grown crystal was recorded and indexed. Single crystal X-ray diffraction studies were carried out and the unit cell parameters were compared with the literature values. The γ-phase of glycine is confirmed by single crystal XRD and FTIR spectral analysis. The crystals were characterised by UV–vis–NIR transmission spectrum in the range 200–1100 nm. The second harmonic generation conversion efficiency of γ-glycine crystal was twice the efficiency of KDP crystal. Thermal characteristics of γ-glycine crystals were determined by thermogravimetric analysis (TGA) and differential thermal analysis, which shows the thermal stability of the grown crystals. Dielectric constant and dielectric loss measurements were carried out at different temperatures and frequencies. The microhardness of the grown crystals has been studied using Vicker's microhardness tester.     

All-vanadium redox photoelectrochemical cell: An approach to store solar energy

A highly-efficient all-vanadium photoelectrochemical storage cell has been demonstrated in this work. This storage cell takes advantage of fast electrochemical kinetics of vanadium redox couples of VO₂⁺/VO^2 + and V^3 +/V^2 +, and appears as a promising alternative to photoproduction of hydrogen from water. Continuous photocharging for 25 h revealed a VO^2 + conversion rate of 0.0042 μmol/h and Faradaic efficiency of 95% without external voltage bias. The incident photon-to-current efficiency (IPCE) at 350 nm light was calculated to be ~ 12%.     

Growth and characterization of naphthalene single crystals grown by modified vertical Bridgman method

The large size 20 mm diameter naphthalene single crystals were grown by modified vertical Bridgman method. The optical quality of the grown crystal was analyzed by photoluminescence and ultraviolet visible absorption spectral measurements. Photoluminescence spectrum indicated violet emission at 410 nm. The UV–vis absorption spectrum shows the maximum at 219.32 nm. The microhardness measurements and differential thermal analysis performed to analyze the mechanical and thermal stability of the as grown crystals. The dielectric measurements were carried out at five frequencies, viz., 100 Hz, 1 kHz, 10 kHz, 100 kHz and 1 MHz and at various temperatures, ranging from 308 K to 348 K indicate an increase of the dielectric parameters with the increase of temperature at all the five frequencies. The conductivity of the material is understood to be more of electronic in nature. Also, the increase in the dielectric parameters with that of temperature is due to the temperature variation of electronic polarizability.     

Synthesis of colloidal silver nanoparticles for printed electronics

Colloidal silver particles were successfully prepared by wet chemical synthesis. The pure single phase of silver was confirmed by X-ray diffraction. Transmission electron microscope categorized that the diameters of particles were 100 and 20 nm, depending on the molecular weight of the PVP stabilizer. A schematic drawing model was used to predict the packing efficiency of 1:1 wt% of two mixtures. The mixture of silver solution was deposited as a thin solid film by a desktop inkjet printer. Scanning electron microscope showed that two different sizes of silver particles give higher densely packed structure than the film of single particle size. When a 0–20 V voltage was applied, the current density reached was 0.10 J/cm², suggesting that the silver film has potential to be applied as a cathode layer in organic light emitting diode (OLED) devices.     

Influence of crystal size on the electron–phonon coupling in ZnO nanocrystals investigated by Raman spectroscopy

We have synthesized ZnO nanocrystals of different sizes (25–41 nm) using the sol–gel method and characterized them using different techniques such as: transmission electron microscopy (TEM) and X-ray diffraction (XRD). Raman spectra of different sizes of ZnO nanocrystals were recorded at two excitation wavelengths, 514 and 647 nm, in the spectral range 300–1200 cm⁻¹. The vibrational modes were assigned on the basis of group theory analysis. The influence of mean crystallite size on the strength of the electron–phonon coupling is experimentally estimated by the variation of relative intensities of second order Raman band and the first order Raman band for ZnO nanocrystals of different sizes. We found that the intensity ratio of the 2E₂ and 1E₂ Raman bands decreases almost linearly for both excitation wavelengths with decreasing crystallite size, which reveals that the Fröhlich interaction plays a dominant role in the electron–phonon coupling of the ZnO nanocrystals.     

Chemical generation of iodine atoms

The chemical generation of atomic iodine using a chemical combustor to generate the atomic fluorine intermediate, from the reaction of F₂ + H₂, followed by the production of atomic iodine, from the reaction of F + HI, was investigated. The maximum conversion efficiency of HI into atomic iodine was observed to be approximately 75%, which is in good agreement with the theoretical model. The conversion efficiency is limited by the formation of iodine monofluoride at the walls of the combustor where the gas phase temperature is insufficient to dissociate the IF.