B. Marí

Structural, electrical and optical properties of ZnO thin films deposited by sol-gel method

Thin films of intrinsic and Al-doped ZnO were prepared by the sol-gel technique associated with spin coating onto glass substrates. Zinc acetate dehydrate, ethanol and monoethanolamine were used as a starting material, solvent and stabiliser, respectively. Structural, electrical and optical characterizations of the films have been carried out. All films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction . The four-points technique was used to characterize thin films electrically. All films exhibit a transmittance above 80-90% along the visible range up to 650nm and a sharp absorption onset about 375nm corresponding to the fundamental absorption edge 3.3eV. Intense UV photoluminescence is observed for undoped and 1% Al-doped ZnO films.

Optical properties of nanocolumnar ZnO crystals

Oriented nanocolumnar ZnO single crystals were prepared by the electrodeposition technique on conducting glass substrates by using different growth parameters. A factorial design at two levels of three growth parameters such as current density, exposition time and temperature of the bath has been used to study their influence on the height of ZnO columns. The average height of the Zn nanocolumns was obtained by means of atomic force microscopy. X-ray diffraction and scanning electron microscope were used to characterize the morphology of the nanocolumnar ZnO crystals. The optical properties were investigated by means of transmittance and photoluminescence. It was found that further annealing of the electrodeposited samples was necessary in order to achieve good optical properties which are very sensitive to the duration and temperature of the annealing.

p-Type behaviour of electrodeposited ZnO:Cu films

Cu-doped ZnO (ZnO:Cu) thin films and ZnO/ZnO:Cu homojunction devices were electrodeposited on conductive glass substrates in a non-aqueous electrolyte containing Cu and Zn salts. The Cu content of the films is proportional to the Cu/Zn precursor ratio in the deposition electrolyte. ZnO:Cu was found to be of a hexagonal wurtzite structure with (002) preferred orientation. A transition from n-type to p-type was observed for ZnO:Cu films with a Cu/Zn ratio higher than 2% as inferred from the change in the direction of the photocurrent. The rectifying characteristics shown by homojunction devices further confirm the p-type conductivity of ZnO:Cu layers.

Effect of isotopic mass on the photoluminescence spectra of zinc oxide

Zinc sulfide is a wide bandgap semiconductor which crystallizes in either the wurtzite modification (a-ZnS), the zincblende modification (b-ZnS) or as one of several similar tetrahedrally coordinated polytypes. In this work, we report a photoluminescence study of different samples of isotopically pure b-ZnS crystals, and crystals with the natural isotopic abundances, at 15 and 77 K. The derivatives of the free and bound exciton energies on isotopic mass have been obtained. They allow us to estimate the contribution of the zinc and sulfur vibrations to the bandgap renormalization energy by electron-phonon interaction. A two-oscillator model based on the zinc and sulfur renormalization energies has been used to account for the temperature dependence of the bandgap energy in ZnS. The results are compared with those found for other tetrahedrally coordinated semiconductors.

Nanostructured hybrid ZnO thin films for energy conversion

We report on hybrid films based on ZnO/organic dye prepared by electrodeposition using tetrasulfonated copper phthalocyanines (TS-CuPc) and Eosin-Y (EoY). Both the morphology and porosity of hybrid ZnO films are highly dependent on the type of dyes used in the synthesis. High photosensitivity was observed for ZnO/EoY films, while a very weak photoresponse was obtained for ZnO/TS-CuPc films. Despite a higher absorption coefficient of TS-CuPc than EoY, in ZnO/EoY hybrid films, the excited photoelectrons between the EoY levels can be extracted through ZnO, and the porosity of ZnO/EoY can also be controlled.

Enhancement of the conversion efficiency of thin film kesterite solar cell

C u 2 ZnSn S 4 ( CZTS ) is a non-toxic earth abundant material and a promising quaternary semiconductor compound of groups I − I I − I V − V I having a kesterite symmetrical structure. Due to its optimum direct bandgap, it has been considered as a suitable material for absorber layers for photovoltaic cell applications. This paper presents the numerical simulation and modeling of CZTS based thin film kesterite photovoltaic cells using SCAP-1D software. The influence of device parameters such as the carrier concentration, thickness, densities of absorber, buffer and window layers, defect densities and the temperature effect on the performance of the Z n O / C d S / CZTS / M o photovoltaic cell structure are analyzed. Defect densities are added to the absorber layer and the interface between the buffer layer and the absorber layer. This type of solar cell does not comprise any toxic material and can lead to non-toxic thin film photovoltaic cells with outstanding optical properties. In this work, promising optimized results had been achieved with a conversion efficiency of 23.72%, a fill factor of 82.54%, a short-circuit current ( J s c ) of 44.87 mA / cm 2, and an open circuit voltage ( V o c ) of 0.64V. C u 2 ZnSn S 4 ( CZTS ) is a non-toxic earth abundant material and a promising quaternary semiconductor compound of groups I − I I − I V − V I having a kesterite symmetrical structure. Due to its optimum direct bandgap, it has been considered as a suitable material for absorber layers for photovoltaic cell applications. This paper presents the numerical simulation and modeling of CZTS based thin film kesterite photovoltaic cells using SCAP-1D software. The influence of device parameters such as the carrier concentration, thickness, densities of absorber, buffer and window layers, defect densities and the temperature effect on the performance of the Z n O / C d S / CZTS / M o photovoltaic cell structure are analyzed. Defect densities are added to the absorber layer and the interface between the buffer layer and the absorber layer. This type of solar cell does not comprise any toxic material and can lead to non-toxic thin film photovoltaic cells with outstanding optical properties. In this wor...

Synthesis of Sr(1-x-y)Al4O7:Eux2+,Lny3+ (Ln = Dy, Y, Pr) nanophosphors using rapid gel combustion process and their down conversion characteristics

Eu2+ and Eu2++Ln3+ doped SrAl4O7 nanophosphors were synthesized by rapid gel combustion process. The morphology of prepared phosphors was examined with scanning and transmission electron microscopy. The phase identification and the crystal structures of nanophosphors were studied using X-ray powder diffraction techniques. Luminescence characteristics of the prepared nanophosphors were analyzed on account of excitation, emission and phosphorescence decay analysis. The emission spectra demonstrated the broad green emission attributed to 4f65d1→ 4f7 transition of the Eu2+ ions. The effect of codoping of some trivalent lanthanide (Dy3+, Pr3+ and Y3+) ions were investigated for improving the emission intensity and phosphorescence decay time of the basic lattice of SrAl4O7:Eu2+ phosphors. The synthesized materials had enhanced bright luminescent properties that could suitably be applied for display as well as photovoltaic applications.

Elaboration and characterization of In 2 S 3 thin films by spray pyrolysis with [S]/ [In] = 3 ratio

In2S3 thin films were elaborated onto glass substrate by spray pyrolysis method using sulphur-to-indium ratio ([S]/[In]) of 3 and different substrate temperatures. The as-deposited and annealing films were characterized by X-Ray Diffraction (XRD) for the structural, Energy Dispersive Spectroscopy (EDS) for the composition, Raman spectroscopy for samples quality and optical transmittance to measure gap energy. XRD revealed a β-In2S3 phase with a preferential orientation along (0 0 12) plane. Good stoichiometry was noticed in EDS measurement. Raman spectroscopy analysis shows a prominent of active modes of β-In2S3 films with annealing. This is confirming an improvement of structure cristallinity of all films and optical analysis shows a decrease of gap energy after annealing.

Factorial electrochemical design for tailoring of morphological and optical properties of Cu2O

ABSTRACT The electrodeposition of cuprous oxide (Cu2O) onto FTO-coated glass substrate was studied by using a statistical approach in order to control the Cu2O morphology and optical properties. The factorial design considered four electrodeposition conditions at two representative levels as input variables (electrolyte temperature and pH, deposition potential and duration) and the deposition charge and morphology of obtained Cu2O as the output variables. The morphology analysis showed the highest influence on crystal shape was exhibited by electrolyte temperature and pH, reaching significance levels of 95 and 98%, respectively. Temperature as low as 35°C and pH 12.2 results in cubic morphology, while other parameters result in octahedron shape. The highest absorbance was exhibited by the Cu2O with cubic morphology.

Preparation and Luminescence Properties of MZrO 3 :Eu 3+ ,A (M=Ca 2+ , Ba 2+ ; A=Li + , Na + , K + ) Phosphors with Perovskite Structure

Calcium and barium zirconate powders based upon CaZrO3:Eu 3+ , A and BaZrO3:Eu 3+ , A (A=Li + ,