Miguel Mollar

Substrate influences on the properties of SnS thin films deposited by chemical spray pyrolysis technique for photovoltaic applications

Herein, we report on tin monosulfide (SnS) thin films elaborated by the Chemical Spray Pyrolysis (CSP) technique onto various substrates as simple glass, ITO-, and Mo-coated glasses in order to study the influence of substrates on the physical and chemical properties of Sns thin films. Structural analysis revealed that all films crystallize in orthorhombic structure with (111) as the sole preferential direction without secondary phases. In addition, film prepared onto pure glass exhibits a better crystallization compared to films deposited onto coated glass substrates. Raman spectroscopy analysis confirms the results obtained by X-ray diffraction with modes corresponding well to SnS single-crystal orthorhombic ones (47, 65, 94, 160, 186, and 219xa0cm−1) without any additional parasite secondary phase like Sn2S3 or SnS2. Field emission scanning electron microscope revealed that all films have a cornflake-like particles surface morphology, and energy dispersive X-ray spectroscopy analysis showed the presence of sulfur and tin with a nearly stoichiometric ratio in films deposited onto pure glass. High surface roughness and large grains are observable in film deposited onto glass. From optical spectroscopy, it is inferred that band gap energy of SnS/glass and SnS/ITO were 1.64 and 1.82xa0eV, respectively.

High-pressure structural and elastic properties of Tl2O3

The structural properties of Thallium (III) oxide (Tl2O3) have been studied both experimentally and theoretically under compression at room temperature. X-ray powder diffraction measurements up to 37.7u2009GPa have been complemented with ab initio total-energy calculations. The equation of state of Tl2O3 has been determined and compared to related compounds. It has been found experimentally that Tl2O3 remains in its initial cubic bixbyite-type structure up to 22.0u2009GPa. At this pressure, the onset of amorphization is observed, being the sample fully amorphous at 25.2u2009GPa. The sample retains the amorphous state after pressure release. To understand the pressure-induced amorphization process, we have studied theoretically the possible high-pressure phases of Tl2O3. Although a phase transition is theoretically predicted at 5.8u2009GPa to the orthorhombic Rh2O3-II-type structure and at 24.2u2009GPa to the orthorhombic α-Gd2S3-type structure, neither of these phases were observed experimentally, probably due to the hindrance of the pressure-driven phase transitions at room temperature. The theoretical study of the elastic behavior of the cubic bixbyite-type structure at high-pressure shows that amorphization above 22u2009GPa at room temperature might be caused by the mechanical instability of the cubic bixbyite-type structure which is theoretically predicted above 23.5u2009GPa.

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.

SnS Thin Films Prepared by Chemical Spray Pyrolysis at Different Substrate Temperatures for Photovoltaic Applications

The preparation and analysis of morphological, structural, optical, vibrational and compositional properties of tin monosulfide (SnS) thin films deposited on glass substrate by chemical spray pyrolysis is reported herein. The growth conditions were evaluated to reduce the presence of residual phases different to the SnS orthorhombic phase. X-ray diffraction spectra revealed the polycrystalline nature of the SnS films with orthorhombic structure and a preferential grain orientation along the (111) direction. At high substrate temperature (450°C), a crystalline phase corresponding to the Sn2S3 phase was observed. Raman spectroscopy confirmed the dominance of the SnS phase and the presence of an additional Sn2S3 phase. Scanning electron microscopy (SEM) images reveal that the SnS film morphology depends on the substrate temperature. Between 250°C and 350°C, SnS films were shaped as rounded grains with some cracks between them, while at substrate temperatures above 400°C, films were denser and more compact. Energy-dispersive x-ray spectroscopy (EDS) analysis showed that the stoichiometry of sprayed SnS films improved with the increase of substrate temperature and atomic force microscopy micrographs showed films well covered at 350°C resulting in a rougher and bigger grain size. Optical and electrical measurements showed that the optical bandgap and the resistivity decreased when the substrate temperature increased, and smaller values, 1.46xa0eV and 60 Ωxa0cm, respectively, were attained at 450°C. These SnS thin films could be used as an absorber layer for the development of tandem solar cell devices due to their high absorbability in the visible region with optimum bandgap energy.

Synthesis of In2S3 thin films by spray pyrolysis from precursors with different (S)/(In) ratios

Indium sulfide (In2S3) thin films were prepared by chemical spray pyrolysis technique from solutions with different [S]/[In] ratios on glass substrates at a constant temperature of 250 °C. Thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and optical transmittance spectroscopy. All samples exhibit a polycrystalline structure with a preferential orientation along (0, 0, 12). A good stoichiometry was attained for all samples. The morphology of thin film surfaces, as seen by SEM, was dense and no cracks or pinholes were observed. Raman spectroscopy analysis shows active modes belonging to β-ln2S3 phase. The optical transmittance in the visible range is higher than 60% and the band gap energy slightly increases with the sulfur to indium ratio, attaining a value of 2.63 eV for [S]/[In] = 4.5.

Electrodeposition of CuGaSe2 and CuGaS2 thin films for photovoltaic applications

CuGaSe2 and CuGaS2 polycrystalline thin film absorbers were prepared by one-step electrodeposition from an aqueous electrolyte containing CuCl2, GaCl3 and H2SeO3. The pH of the solution was adjusted to 2.3 by adding HCl and KOH. Annealing improved crystallinity of CuGaSe2 and further annealing in sulphur atmosphere was required to obtain CuGaS2 layers. The morphology, topography, chemical composition and crystal structure of the deposited thin films were analysed by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy and X-ray diffraction, respectively. X-Ray diffraction showed that the as-deposited CuGaSe2 film exhibited poor crystallinity, but which improved dramatically when the layers were annealed in forming gas atmosphere for 40xa0min. Subsequent sulphurization of CuGaSe2 films was performed at 400xa0°C for 10xa0min in presence of molecular sulphur and under forming gas atmosphere. The effect of sulphurization was the conversion of CuGaSe2 into CuGaS2. The formation of CuGaS2 thin films was evidenced by the shift observed in the X-ray diffraction pattern and by the blue shift of the optical bandgap. The bandgap of CuGaSe2 was found to be 1.66xa0eV, while for CuGaS2 it raised up to 2.2xa0eV. A broad intermediate absorption band associated to Cr and centred at 1.63xa0eV was observed in Cr-doped CuGaS2 films.

Fabrication of Cd 1−x Zn x S buffer layer deposited by Chemical Bath Deposition for photovoltaic applications

Cd1−xZnxS films suitable for solar cell photovoltaic applications have been deposited by chemical bath deposition (CBD) on to indium tin oxide (ITO) coated glass substrates. An aqueous solution containing cadmium sulfide, zinc sulfide and thiourea were used as sources of Cd+2, Zn+2, and S−2, respectively. Triethenolamine was used as complexing agent to control the Cd+2 and Zn+2 ions concentrations and ammonia to adjust the pH of the solution. The temperature of the bath was kept at 70 °C. The as deposited films are well adherent, homogeneous and free from pinholes. The incorporation of Zn in CdS was found to be dependent on the annealing temperature. The structure of the CdZnS thin films, as observed by X-ray diffraction, was polycrystalline with hexagonal structure. Several diffraction peaks corresponding to crystallographic planes (100), (002), (102), (110) (103) and (004) were observed. According to energy dispersive spectroscopy (EDS) the films are non-stoichiometric due to a deficit of sulfur, which becomes more important as the Zn content increases. The absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases. The values of the absorption edge are found to vary from (Eg ∼ 2.42 eV) for the CdS film and (Eg ∼ 3.30 eV) for the ZnS film. Cd1−xZnxS thin films can be useful as buffer and window layers in Cu(In,Ga)Se2 and Cadmium telluride (CdTe) thin films solar cells due to ability to tune the band gap through the Zn/Cd ratio present in the chemical bath.

β-In 2 S 3 thin films doped by tin (Sn 4+ ) and deposited by Chemical Spray Pyrolysis technique for photovoltaic applications

β-In2S3 thin films doped by tin at different percentages were deposited by Chemical Spray Pyrolysis (CSP) method at 300 °C substrate temperature onto glass substrate. X-ray diffraction (XRD) was used to study structure, Raman spectroscopy analysis for phase, quality and structure, Scanning Electron Microscopy (SEM) for the surface morphology, Energy Dispersive X-Ray Spectroscopy (EDS) for the composition, Atomic Force Microscopy (AFM) for surface topography and transmittance to determine the gap energy. The XRD analysis showed that the crystallographic structure of β-In2S3 is present on the deposited films with a preferential orientation along (0 0 12) and no secondary phase is observed. SEM images presented films well covered without crack and pinholes but different morphologies and AFM micrographs showed very compact films when the percentage of doping increased. Main mode at 327cm-1 is showed by Raman spectroscopy and from optical analysis, the transmission varied from 60% to 70% with band gaps estimated from 2.64 to 2.82 eV.

High-pressure theoretical and experimental study of HgWO4

HgWO4 at ambient pressure is characterized using a combination of ab initio calculations, X-ray diffraction and Raman scattering measurements. The effect of low pressure and temperature on the structural stability is analysed. Extending our ab initio study to the range of higher pressures, a sequence of stable phases up to 30 GPa is proposed.

Synthesis and characterisation of Cu 2 ZnSnS 4 thin films prepared by sol gel method for photovoltaic applications

This study reports the elaboration and characterisation of Cu2ZnSnS4 (CZTS) thin films prepared by low cost sol gel method associated to spin coating technique. The CZTS thin films were prepared on ordinary glass substrates and annealed at 350°C during 4 min, 8 min, 12 min and 16 min of the samples Z1, Z2, Z3 and Z4 respectively, in order to study the effect of annealing times on the structural, optical and electrical properties. The samples were characterized using X-ray diffractometer, Spectrophotometer UV-VIS and 4-points probe system. The optical parameters were measured and calculated from the transmittance and absorbance spectra in the wavelength between 350 and 1000 nm. The sheet resistance and the resistivity were determined by 4-points probe method. The CZTS films showed a kesterite structure of (112), (200), (220) and (312) plans, the preferential orientation along the (112) plan. The band gap energy of sample Z1 is 1.5 eV, the sheet resistance and resistivity of sample Z1 are 3.61 kΩ/square and 0.257 Ω.cm respectively.