Visible Range Of Solar Spectrum Research Articles

Influence of sodium doping on the material properties and photocatalytic activity of anatase titanium dioxide nanotubes prepared by anodization

The properties of semiconducting materials can be altered to meet our needs by tuning their bandgap with suitable methods. Here bandgap tailoring of anatase TiO2 nanotubes prepared by anodization technique is achieved by sodium doping at variant concentrations. The doped nanotubes with their reduced band gaps that match the visible range of solar spectrum exhibit greater photodegradation efficiency of methylene blue dye (97.3% in 180 min) than the undoped (56.8% in 180 min) with band gap in the UV region. Structural and morphological characterizations of the samples by X-ray diffraction, X-ray Photoelectron Spectroscopy, Raman Spectroscopy, Atomic Force Microscopy and Field Emission Scanning Electron Microscopy reveal that the doping-induced surface changes and increased Ti4+ to Ti3+ reduction play an active role in increasing the photocatalytic efficiency of the samples. Analysis of valence band photo emission spectra indicate shifting of fermi level away from conduction band edge with doping of Na1+ at Ti4+ site producing defect induced super radical formation for photocatalysis.

Tetrathiafulvalene Derivatives as Hole-Transporting Materials in Perovskite Solar Cell.

Over a couple of decades perovskite solar cells have become a highly promising photovoltaic technology. Choosing a dopant-free Hole-Transporting Material (HTM) that offers protection to a perovskite layer from oxidation is one of the viable strategies while addressing the stability of perovskite solar cell. In this line of interest, tetrathiafulvale (TTF) derivatives have shown promise in the past. However, studies that focus on small-molecule TTF derivatives as potential HTM options are scarce. The present study is an attempt to explore the applicability of a few TTF derivatives as HTM in a perovskite solar cell. Here four TTF derivatives, namely, TTF-1 (experimentally reported in a previous study), TTF-2, DBTTF1, and TMTSF1, were studied through electronic structure calculations. The properties concerning HTM, such as impact of adsorption on molecular structure, absorption spectra, distribution of frontier molecular orbitals, interaction energy between TTF derivative and MAPbI3 surface, and charge transfer at an interface, were analyzed. Results show that TTF-2 has the expected energy-level alignment, transparency in the visible range of solar spectrum, and good charge-injection ability at the interface with a perovskite layer. Hence, TTF-2 could be a potential hole-transporting material for a perovskite solar cell, and it can perform better than TTF-1.

Numerical simulation of novel lead-free Cs3Sb2Br9 absorber-based highly efficient perovskite solar cell

In this paper, a novel Cs 3 Sb 2 Br 9 perovskite is presented for the absorber layer of perovskite solar cells (PSC). A planar structure as ITO/TiO 2 /Absorber/Spiro-OMeTAD/Au with Cs 3 Sb 2 Br 9 as a light harvesting material is numerically simulated using SCAPS-1D simulation software. Initially, the optimization is performed on the various material parameters of absorber layer such as thickness, bulk defect density, relative permittivity and bandgap. The obtained optimal values for these parameters are 1000 nm, 1 × 10 12 cm −3 , 10, and 2.0 eV, respectively. Finally, the proposed PSC structure with optimized absorber layer is achieved the maximum power conversion efficiency (PCE) of 15.69% whereas V OC as 1.31 V, J SC as 13.67 mA/cm 2 , FF as 87.61%, and QE of ∼100% at 390 nm wavelength near the visible range of solar spectrum. The obtained results of numerical simulations with Cs 3 Sb 2 Br 9 as absorber layer endorse the novel proposed PSC material as the main body of PSC and opens a better route towards the development of a cost effective, highly efficient (Pb) lead-free and environment friendly PSC. • A novel Cs 3 Sb 2 Br 9 absorber layer material is proposed for design of high efficiency lead-free perovskite solar cell. • Numerical analysis and optimization of novel absorber in proposed PSC structure is performed using SCAPS-1D to investigate the effect of bulk defect density, absorber thickness, energy bandgap and permittivity variations on PSC parameters. • A planar structure consisting of charge transport materials TiO 2 and Spiro-OMeTAD used as ETL and HTL, is simulated for the analysis. • The proposed PSC is promising and may offer the PCE of 15.69% with V OC of 1.31 V , J SC of 13.67 mA/cm 2 and FF of 86.78%.

Studies on the photocatalytic activity molybdenum doped cadmium selenide nanoparticles towards indigo carmine dye degradation under solar light

In the present study, molybdenum doped cadmium selenide (Mo-CdSe) nanoparticles photocatalyst has been synthesized and utilized for the degradation of indigo carmine dye under solar light irradiation. Mo-CdSe nanoparticles were characterized by X-ray diffraction (XRD), ultraviolet spectroscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDAX), transmission electron microscopy, thermo gravimetric (TGA) and FTIR studies. The XRD and EDAX spectrum confirms the presence of Mo onto CdSe matrix. Thermal proved that the Mo-CdSe nanoparticles possessed greater thermal stability than CdSe nanoparticles. Photodegradation studies under solar light irradiation revealed that the Mo-doped CdSe nanoparticles exhibit higher photocatalytic activity than that of pure CdSe nanoparticles. This significant improvement in the photocatalytic efficiency of Mo-CdSe nanoparticles photocatalyst under solar light irradiation can be attributed to the presence of Mo on the CdSe nanoparticles which greatly enhances absorption in the visible range of solar spectrum enabled by the Mo and better charge separation.

Tailoring the antifouling agent titanium dioxide in the visible range of solar spectrum for photoelectrochemical activity with hybrid DFT & DFT + U approach

Titanium dioxide (TiO2) doped with several metal dopants has been studied for photoelectrochemical water splitting and as a shielding agent to overcome the impact of biofouling on marine systems. The n-type TiO2 can be potentially used for water splitting; however, its wide band gap, weak light absorption, and low conductivity limit its applications for water splitting. Hybrid density functional theory (DFT) and DFT + U techniques have been used to investigate the structural parameters, light absorption, optical conductivity, thermodynamic stability, position of conduction, and valence-band edge of TiO2 doped with pristine and metal (Co, Fe, Ag, and Rh). The calculated band gap of pristine was 2.99 eV, and it could absorb photon with a wavelength of 414 nm and generate electron–hole pair, which reacted with water molecule and produced hydroxyl and oxygen ions. The presence of hydroxyl and oxygen ions on the pristine surface increased the antibacterial effect, thereby eliminating the biological toxicants in water. The incorporation of dopants, such as Co, Fe, Ag, and Rh, in TiO2 (2.1 %) significantly altered the properties, including the energy band gap from 2.99 eV to 1.25, 1.51, 1.99, and 2.06 eV, respectively. The narrow band gap and modified band positions were attributed to the new electronic states that appeared due to the dopant cations. The doped material showed significant optical absorption and photoconductivity in the entire visible and ultraviolet regions. Conduction- and valence-band edge locations of Ag-TiO2 facilitated water oxidation–reduction process. Moreover, higher negative free energy of Ag-doped TiO2 made it thermodynamically stable than other compounds. Consequently, the use of metal doping in TiO2 enhanced the optical absorption and photoconductivity owing to a lower band gap energy.

Multistep electrophoretic deposition of TiO2 film and its surface modification for dye sensitized solar cells

Abstract TiO2 is a wide bandgap semiconductor commonly used as a photoanode material in dye sensitized solar cells (DSSCs). However, low absorption of TiO2 in visible range of solar spectrum limits its performance in DSSCs. A multistep electrophoretic deposition (EPD) process was used to improve the morphology of the mesoporous films and high quality TiO2 films were fabricated. Meanwhile, the optical absorbance was enhanced by a convenient and simple surface modification method using tin (Sn). The prepared films were subjected to morphological, optical, elemental, and phase analyses. It was observed that multistep EPD produced high quality films at various electric fields. Moreover, the surface modification was achieved using sonochemical deposition of Sn+ on the film which enhanced its photo-absorption. The current density (J) versus voltage (V) characteristics of Sn/TiO2 film deposited at 20 V based DSSC showed approximately twofold increase in the efficiency of the solar cells. Improved open-circuit voltage (Voc), short-circuit current density (Jsc) and efficiency (η) of the DSSCs as well as significantly high fill factor indicated that the surface modified EPD film is a potential candidate as a photoanode film in DSSCs.

Tuning optical properties of TiO2 by dimension reduction: from 3D bulk to 2D sheets along {001} and {101} plane

The use of two-dimensional sheets exclusively composed of reactive facets of TiO2 catalyst to explore the possibility of enhanced photocatalytic activity has been an exciting research frontier recently. Using first principles calculations, in this paper we investigate the optical properties of bulk and two-dimensional TiO2 nanosheets, pointing out to what extent the reduced dimensionality and dimension might enhance the photocatalytic reactivity of TiO2.The detailed optical properties of 2D sheets of TiO2 generated along the two distinct facets like (001) and (101) are studied extensively and compared with the bulk counterpart of TiO2 for electronic and optical properties. The TiO2 along (101) sheet is found to retain the semiconducting phase whereas the sheet along (001) direction found to be metallic. We found the anisotropy in TiO2–101 to be in four directions while TiO2–001 to be in two directions. Hence their applications as good optical materials are inevitable. Among the two, TiO2–101 sheet shows better absorption coefficient and extinction coefficient indicating better absorbance but TiO2–001 shows better reflectivity in the visible range of solar spectrum. Thus, we report that (001) and (101) nanosheets of TiO2 differ in their electronic structures and hence in optical properties and so can be used in different photocatalytic and optoelectronic applications well.

Enhancing Thermal Conductivity and Photo-Driven Thermal Energy Charging/Discharging Rate of Annealed CMK-3 Based Phase Change Material.

In this work, the CMK-3 is successfully prepared with SBA-15 as the template and first annealed to 2000 °C to improve thermal conductivity. The annealed CMK-3 has a thermal conductivity of 6.981 W m−1 K−1 higher than un-annealed CMK-3. The annealed CMK-3 is used to encapsulate the RT44HC, and RT44HC/annealed CMK-3 has 10-fold of thermal conductivity and enhanced thermal stability than RT44HC. The RT44HC/annealed CMK-3 has a large melting enthalpy of 177.8 J g−1 and good thermal stability. The RT44HC/annealed CMK-3 has optical absorptive coefficient of visible range of solar spectrum, which identify seven-fold higher than RT44HC. The RT44HC/annealed CMK-3 has great photo-thermal performance, and the photo-driven energy charging and discharging rate of RT44HC/annealed CMK-3 is almost 30-fold larger than the RT44HC. The results show that the annealed CMK-3 is a great mesoporous carbon nanomaterial for phase change materials and the annealed CMK-3 based phase change material has great potential in solar thermal utilizations such as solar water heating system and solar heating building systems.

Facile synthesis of 1D-architecture of silver-vanadates in carbon nest for enhanced visible light driven photo-oxidation process

Ag/AgCl/V2O5 nanocatalysts with one dimensional (1D) architecture was synthesized in carboxylic acid functionalized multi-walled carbon nanotubes for methylene blue dye degradation. The growth of uniformly distributed nanoparticles along the carbon-nanotubes was revealed from high resolution transmission electron microscopy and atomic force microscopy analyses. Raman spectroscopy and transmission electron microscopy analyses also confirmed for the creation of defects in the multi-walled carbon nanotube. The hybrid nanocomposite appeared as a suitable photocatalyst for degradation of methylene blue dye absorbing the light in the visible range of solar spectrum. The presence of interactions within the nanoparticles and with the nanotubes was believed to enhance the photo-oxidation process. The creation of defects in the carbon nanotube on modification with Ag/AgCl/V2O5 improved the photocatalytic activity by enhancing the photoelectron transfer process. About ∼90% of the total organic carbon of the dye molecule was found to decompose into CO2, H2O and inorganic ions within 25 min under sunlight.

Nano-architecture based photoelectrochemical water oxidation efficiency enhancement by CdS photoanodes

In the present work, 2D nanostructuring has been utilized to impart an efficiency improvement to the hexagonal phase CdS films for the photoelectrochemical (PEC) cells those were deposited by spray pyrolysis technique. By controlling the aerosol droplet- size, population and impingement time during the spray pyrolysis deposition, various nano-features viz. randomly aligned nanorods, nanotubes and nanowires of CdS has been demonstrated for the first time. A growth mechanism has been proposed to predict the temporal evolution of the nanostructures. The prominent nanoscale structures show improved optical properties in the visible range of solar spectrum. The structural studies validate the morphological differences of nanostructures in terms of the texture coefficient analysis as well as 2D micro x-ray diffraction imaging. Electrochemical characterization is carried out to understand the effect of nanostructuring on the PEC performance of the CdS photoanodes in the sulphide (0.1 M Na2S + 0.02 M Na2SO3) electrolyte at applied bias of 0.2 V (versus SCE). The evolution of morphology from randomly aligned rods to nanowire is responsible for improved photocurrent (3.5 times). CdS film morphology can be tuned to nanotubes, nano- rose buds and nanorod bunches even by doping Zn2+ ions in CdS lattice. Nano-structuring of doped CdS has shown enhanced performance of the photoanodes. The nanotubes structures yielded highest photocurrent density of 1.6 mA cm−2. Whereas modifying the 2D-nanostructured CdS film by simple MoO3 spray coating yields the photocurrent enhancement to 2.1 mA cm−2.

Structural, electronic, optical and elastic properties of the complex K2PtCl6-structure hydrides ARuH6 (A = Mg, Ca, Sr and Ba): first-principles study

We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydrides A2RuH6 (A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of the A2RuH6 systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg2RuH6, Ca2RuH6, Sr2RuH6 and Ba2RuH6, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time.

Synthesis of supported silver nano-spheres on zinc oxide nanorods for visible light photocatalytic applications

We report the synthesis of silver (Ag) nano-spheres (NS) supported on zinc oxide (ZnO) nanorods through two step mechanism, using open vessel microwave reactor. Direct reduction of ZnO from zinc nitrates was followed by deposition precipitation of the silver on the ZnO nanorods. The supported Ag/ZnO nanoparticles were then characterized by electron microscopy, X-ray diffraction, FTIR, photoluminescence and UV–vis spectroscopy. The visible light photocatalytic activity of Ag/ZnO system was investigated using a test contaminant, methylene blue (MB). Almost complete removal of MB in about 60min for doses higher than 0.5g/L of the Ag/ZnO photocatalyst was achieved. This significant improvement in the photocatalytic efficiency of Ag/ZnO photocatalyst under visible light irradiation can be attributed to the presence of Ag nanoparticles on the ZnO nanoparticles which greatly enhances absorption in the visible range of solar spectrum enabled by surface plasmon resonance effect from Ag nanoparticles.

Surface analysis of thermally annealed porous silicon

Quasi-monocrystalline porous silicon (QMPS) has high potential for photovoltaic application for its enhanced optical absorption compared to bulk silicon in the visible range of solar spectrum. In this study, QMPS was formed from low porosity (∼20–30%) porous silicon (PS) produced by electrochemical anodization, and thermal annealing in the temperature range 1050–1100 °C under pure hydrogen ambient for a duration of 30 min. We analyzed the material surface by grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and dynamic secondary ion mass spectroscopy (SIMS) study. The crystallinity was confirmed by GIXRD while FESEM studies revealed that the surface layer is pore free with voids embedded inside the body. AFM studies indicated relatively smooth and uniform surface and the dynamic SIMS study showed the depth profiles of impurities present in the material.