D. Avellaneda

Cu2SnS3 and Cu4SnS4 Thin Films via Chemical Deposition for Photovoltaic Application

Thin films of copper sulfide (CuS, 200 nm thick) were deposited over thin films of tin sulfide (SnS, 180 nm thick) by sequential chemical deposition. The layers were heated in nitrogen atmosphere at 350 and 400°C. The grazing incidence X-ray diffraction analysis of these layers established the formation of thin films of ternary composition, Cu 2 SnS 3 and Cu 4 SnS 4 . Optical bandgaps of the films are direct, 0.95 eV for Cu 2 SnS 3 and 1.2 eV for Cu 4 SnS 4 , and the electronic transitions are of the forbidden type in both cases. The films are p-type, with electrical conductivities of 0.5-10 Ω ―1 cm ―1 and hole concentrations of 10 17 ―10 18 cm ―3 . Based on the optical absorption coefficients, the light generated current density (J L ) as a solar cell absorber was evaluated for these materials for air mass 1.5 (1000 W/m 2 ) global solar radiation. For a film thickness of 0.5 μm. Cu 2 SnS 3 and Cu 4 SnS 4 could offer J L of 34 and 27 mA/cm 2 , respectively. Corresponding optical conversion efficiencies of solar energy into electron-hole pairs are 32 and 24%. The built-in potential for CdS/Cu 2 SnS 3 and CdS/Cu 4 SnS 4 junctions would be above 0.9 V and above 1.1 V when ZnO replaces CdS as the window layer.

Polymorphic Tin Sulfide Thin Films of Zinc Blende and Orthorhombic Structures by Chemical Deposition

Polycrystalline thin films (100-450 nm in thickness) of SnS formed from chemical baths of Sn(II) in acetic acid/HCl solution, triethanolamine, NH 3 (aq), and thioacetamide are polymorphic consisting of zinc blende (ZB) and orthorhombic (OR) structures. The ZB structure for the SnS film, reported in this work for the first time, has a lattice constant a = 0.579 nm and a direct (forbidden) bandgap of 1.7 eV, which is distinct from that of SnS(ZB), about 1 eV. The electrical conductivity of SnS(ZB) is 6 X 10 -6 (Ω cm) -1 p-type, with activation energies for the conductivity of 0.5 eV at room temperature and 1.6 meV near 10 K. When a SnS(ZB) film is heated in air at 500°C for 30 min, part of it transforms to SnO 2 and to SnS(OR); after 2 h 30 min at 550°C in air the film converts to transparent SnO 2 . Such a film has a bandgap of 3.7 eV and electrical conductivity, ∼ 1 (Ω cm) -1 . Photovoltaic effect in different structures involving these films is presented.

Synthesis and Properties of Platinum Nanoparticles by Pulsed Laser Ablation in Liquid

Platinum Pt nanoparticles were synthesized by pulsed laser ablation in liquid PLAL technique in different liquids acetone, ethanol, and methanol. Ablation was performed using a Q-switched Nd:YAG laser with output energy of 230 mJ/pulse for 532 nm wavelength. Ablation time and laser energy fluence were varied for all the liquids. Effects of laser energy fluence, ablation time, and nature of the liquid were reported. The mean size, size distributions, shape, elemental composition, and optical properties of Pt nanoparticles synthesized by PLAL were examined by transmission electron microscopy TEM, X-ray photoelectron spectroscopy XPS, and UV-Visible absorption spectroscopy.

Effects of Liquid Medium and Ablation Wavelength on the Properties of Cadmium Sulfide Nanoparticles Formed by Pulsed-Laser Ablation

Pulsed-laser ablation in liquid (PLAL) is a green synthesis technique to obtain semiconductor nanomaterials in colloidal form. Herein, cadmium sulfide (CdS) nanoparticles were synthesized by the pulsed-laser ablation of a CdS target in different liquid media by using λ=532 and 1064 nm outputs from a pulsed (10 ns, 10 Hz) Nd:YAG laser at different ablation fluence values. The morphology, structure, crystalline phase, elemental composition, optical, and luminescent properties of CdS nanomaterials were analyzed by using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis absorption spectroscopy, and fluorescence spectroscopy. By changing the liquid medium and ablation wavelength, CdS nanoparticles with different morphology and size were formed, as demonstrated by using TEM analysis. The crystallinity and chemical states of the ablation products were confirmed by using XRD and XPS analyses. The optical bandgap of the CdS nanoparticles was dependent on the ablation wavelength and the fluence. These nanocolloids presented different green emissions, which implied the presence of several emission centers. CdS nanocolloids in distilled water catalyzed the photocatalytic decay of methylene blue dye under light irradiation from a solar simulator.

Synthesis and Properties of Tin Sulfide Thin Films from Nanocolloids Prepared by Pulsed Laser Ablation in Liquid

Tin sulfide (SnS) nanoparticles were synthesized by pulsed laser ablation in liquid (PLAL) technique using an Nd:YAG laser operated at 532 nm. SnS thin films were deposited by spraying the colloidal suspension onto the heated substrates. The influence of different liquid media (dimethyl formamide and isopropyl alcohol) on the thin film properties were studied. Morphology, crystalline structure, and chemical composition of the nanoparticles were identified using transmission electron microscopy with energy dispersive X-ray analysis. The crystalline structure of the thin films was analyzed by using grazing incidence X-ray diffraction, and the chemical states by X-ray photoelectron spectroscopy. Scanning electron microscopy was employed for the morphological analysis of the thin films. Annealing the films at 380 °C improved the crystallinity of the films exhibiting a layered morphology, which may be useful in optoelectronic and sensing applications. Cyclic voltammetry studies showed that the films have good electrochemical properties.

SnS Thin Films in Chemically Deposited Solar Cell Structures

We report photovoltaic cell structures on SnO 2 :F (TCO) coated glass substrates. Thin films of CdS, SnS, and CuS or PbS were deposited sequentially from chemical baths to produce the solar cell structures: SnO 2 :F-CdS- SnS (A)-CuS-Ag; SnO 2 :F-CdS- SnS (A)-PbS-Ag; and SnO 2 :F-CdS- SnS (B)-PbS-Ag. Heating SnS-CuS films results in the formation of Cu 2 SnS 3 , and sequential depositions of SnS and PbS to obtain solar cells produce stratified layers as required for solar cells. The photovoltaic characteristics, Voc 340 mV and J sc 6 mA/cm 2 in these structures suggest that absorber thin films based on tin sulfide are worth investigating as a relatively abundant and non-toxic material for solar cells.

INDIUM SELENIDE THIN FILMS BY LASER IRRADIATION OF In/Se LAYERED STRUCTURE

In this work, we report the formation of In6Se7 thin films by laser irradiation of In/Se layered structure. Indium layer was deposited on glass substrates by thermal evaporation on which selenium thin film was grown by chemical bath deposition from an aqueous solution containing 10 ml of sodium selenosulphate (0.1 M), 1.0 ml acetic acid (25%) and 70 ml distilled water during 5 min. The In/Se coated glass substrates were irradiated using a 532 nm continuous laser for 3–5 min. Structure, morphology, optical and electrical properties of the irradiated thin films were analyzed using various techniques. X-ray diffraction analysis showed that the irradiated thin films were In6Se7 of monoclinic structure. X-ray photoelectron spectroscopic study on the laser irradiated samples provided uniform relative composition of In and Se in the thin films formed after laser irradiation. The morphology, optical and electrical properties of the irradiated samples were investigated. The optical band gap of the In6Se7 thin films was 2.2 eV and also, the thin films were photoconductive.

Copper antimony sulfide thin films for visible to near infrared photodetector applications

Ternary chalcostibite copper antimony sulfide (CuSbS2) is an emerging semiconductor material having applications in photovoltaics, energy storage and optoelectronics due to its high absorption coefficient, suitable bandgap, and it consists of non-toxic and earth abundant elements. CuSbS2 thin films are prepared by combining chemical bath deposition (antimony sulfide (Sb2S3)) and thermal evaporation (copper (Cu)) followed by a heat treatment and their application as visible to near infrared photodetectors is reported. Crystalline structure, elemental composition, chemical state, morphology and optoelectronic properties of the films were characterized by various techniques. The effect of three different Cu thicknesses (CAS 20, CAS 30 and CAS 40 nm) on the photodetection properties are evaluated under illumination using light emitting diodes (LEDs) and a laser. The photodetectors fabricated are successfully tested under different wavelengths, power densities and applied voltage and their photoresponse cyclic stability for each wavelength of illumination was recorded. From the sensitivity calculations, the sample with 20 nm Cu thickness (CAS 20) showed higher detection sensitivity for visible to near infrared wavelengths. Better responsivity results were obtained for CAS 40 because of its improved crystallinity and phase purity. Photodetector properties such as sensitivity and responsivity are evaluated for all the samples. These results are beneficial for cost effective and environment friendly photodetectors and optoelectronic devices based on CuSbS2 thin films.

Nanostructured SnS2 Thin Films from Laser Ablated Nanocolloids: Structure, Morphology, Optoelectronic and Electrochemical Properties

Tin disulfide (SnS2 ) is a binary chalcogenide semiconductor having applications in solar cells, energy storage, and optoelectronics. SnS2 thin films were deposited by spraying the nanocolloids synthesized by pulsed laser ablation in liquid. The structure, morphology, and optoelectronic properties were studied for films obtained from two liquid media (ethanol and isopropanol) and after heat treatments at various temperatures. X-ray diffraction analysis confirmed the hexagonal crystal structure of the films, whereas the 2-H polytype structure was identified by micro-Raman spectroscopy. Oxidation states of Sn (4+) and S (2-) identified from high resolution X-ray photoelectron spectra confirmed the composition and chemical states of the films. The SnS2 thin films exhibited distinct porous surface morphologies as the liquid medium in laser ablation was varied. All as-prepared and annealed films showed photoluminescence with a high intensity peak at 485 nm and a low intensity peak at 545 nm. Thin films annealed at 300 °C showed improved electrochemical properties upon illumination using a blue LED light source. Current-voltage curves recorded in dark and light as well as the photoresponse measurements showed their suitability for utilization in optoelectronic devices. The results of this study may trigger further research towards fabrication of nanostructured thin films in large area for optoelectronic and photoelectrochemical applications in an environment friendly and cost-effective way.

Characteristics of Chemically Deposited Thin Film Solar Cells using SnS and Sb2S3 Absorbers

We use SnS and Sb 2 S 3 thin films of about 500 nm in thickness deposited on glass substrates by chemical deposition to develop solar cell structures: glass-SnO 2 :F/CdS/SnS/CuS/silver paint and SnO2:F/CdS/Sb 2 (S/Se) 3 /PbS/silver paint. Here, SnS and Sb 2 S 3 , and PbS are absorber materials suitable for large scale production, considering their abundance at 0.2 ppm (Sb) and 2 ppm (Sn) and 8ppm (pb) in the earths crust according to published data. SnS films deposited through distinct reaction routes have optical band gap of 1.1 eV or 1.7 eV. In SnO 2 :F/CdS/SnS(1.1eV)/SnS(1.7 eV)/CuS/silver paint, open circuit voltage (V oc ) of ≈ 400 mV, and short circuit current (Jsc)of 7 mA/cm 2 are obtained with a cell efficiency of 1%. Sb 2 S 3 thin films have optical band gap 1.7 eV, but could be reduced through reaction in Se-vapor, upon which solid solutions of Sb 2 (S/Se) 3 are formed. In SnO 2 :F/CdS/Sb 2 (S/Se) 3 /PbS/silver paint, Voc of ≈ 640 mV, Jsc of 7 mA/cm 2 and conversion efficiency of 1.5% are obtained.