A. Moses Ezhil Raj

Effect of sputtering power on properties and photovoltaic performance of CIGS thin film solar cells

CuInGaS2 (CIGS) thin films were fabricated by DC magnetron sputtering by varying the sputtering power (70, 90, 110 and 130 W). The X-ray diffraction revealed the formation of tetragonal structure with (1 1 2) preferential orientation. The film prepared at 90 W has better crystallinity with minimum dislocation density and strain. From the scanning electron microscopy analysis, it was found to be a denser and larger in grain formation. The elemental quantification and stoichiometric ratio of the CIGS films were confirmed by energy-dispersive spectra. The optical band gap was found using Tauc plot, and it varied from 1.20 to 1.52 eV. The transport conduction mechanism involved in CIGS films was identified from DC four-probe method. Raman studies reveal that all the films composed of CH and CA ordering. The solar cell measurements indicate that high power conversion efficiency (η) of 0.29% and short-circuit current density of (Jsc) of 4.51 mA/cm2 obtained for the film deposited at 90 W.

Magnesium indium oxide (MgIn2O4) spinel thin films : Chemical spray pyrolysis (CSP) growth and materials characterizations

MgIn(2)O(4), which has an inverse spinel structure, has been adopted as the transparent material in optoelectronic device fabrication due to its high optical transparency and electrical conductivity. Such a technologically important material was prepared by the spray pyrolysis technique. Precursors prepared for the cationic ratio Mg/In=0.5 were thermally sprayed onto glass substrates at 400 and 450 degrees C. We report herein the preparation and characterization of the films by X-ray diffraction (XRD), energy-dispersive absorption X-ray spectroscopy (EDAX), and atomic force microscopy (AFM). The XRD results showed the single phase formation of the material that revealed the presence of Mg(2+) and In(3+) in the inverse spinel-related structure. The FTIR and EDAX results further confirmed that the nanocrystalline films were mainly composed of magnesium, indium, and oxygen, in agreement with XRD analysis. We surmised from the AFM micrographs that the atoms have enough diffusion activation energy to occupy the correct site in the crystal lattice. For the 423-nm-thick magnesium indium oxide films grown at 400 degrees C, the electrical conductivity was 5.63x10(-6) Scm(-1) and the average optical transmittance was 63% in the visible range (400-700 nm). Similar MgIn(2)O(4) films deposited at 450 degrees C have a conductivity value of 1.5x10(-5) Scm(-1) and an average transmittance of 75%. Hall coefficient observations showed n-type electrical conductivity and high electron carrier concentration of 2.7x10(19) cm(-3).

Synthesis and characterization of hematite nanopowders

A facile solution approach was employed to synthesize hematite (α-Fe2O3) nanoparticles by using starting precursor iron (III) chloride (FeCl3) and sodium hydroxide (NaOH) as reducing agent without templates at low temperature. The growth and solubility of iron oxide particle was controlled by adjusting the pH of the solution using ammonium hydroxide. As-prepared powders were subsequently calcined in air for 3 h at three different temperatures ranging from 400 to 800 °C. The precursor and the synthesized particles were characterized using TGA-DTA thermal analysis to study the decomposition pattern. X-ray diffraction (XRD) technique confirmed the nanocrystal formation of α-Fe2O3 and Fourier transform infra-red (FTIR) spectral information identified the metal-oxide phase formation. Scanning electron microscope (SEM) was engaged to study the morphology and the purity of the sample was evaluated from the energy dispersive spectrum (EDS). The optical band gap of the particles and its variations with calcination temperature (2.32–2.49 eV) was obtained from the constructed Tauc plot using the optical absorption data. The electrical parameters of the samples were obtained from two probe measuring technique and the effect of temperature on the electrical properties of α-Fe2O3 was discussed.

CuInS 2 Layer Deposition Through Nebulizer Spray Technique for Solar Cell Fabrication

CuInS2 (CIS ) thin films were fabricated by jet nebulizer spray technique at various substrate temperatures such as 250, 300, 350 and 400 °C. The XRD revealed the formation of chalcopyrite crystalline phase with (1 1 2) preferential orientation. The film prepared at 300 °C has better crystallinity with minimum dislocation density and strain. The microstructure of the prepared CIS thin films was investigated by means of scanning electron microscope (SEM ). The elemental quantification and stoichiometric ratio of the CIS films were confirmed by EDS. The conductivity of CIS thin films was carried out by four probe method and it showed that all the films were in semiconducting nature. The optical band gap was found using Tauc plot and it was varied from 1.3 to 1.45 eV. A peak around 298 cm−1 was observed in Raman spectra attributed to the mixture of both CH- and CA-ordering.

Structural, Optical and Ethanol Gas Sensing Performance of Aluminium Doped Zinc Oxide (AZO) Thin Films by Nebulizer Spray Technique

Aluminium doped zinc oxide (AZO) nano—structured films were deposited by nebulizer spray technique. The role of aluminium dopant concentration over the structural, optical and electrical properties was examined by different analytical techniques. The structural results from X-ray diffraction showed that preferential orientation of films obtained along the (002) direction. The surface morphology of the films showed a hexagonal facet with the nano—structured film. The parameters such as resistivity and activation energy were determined from electrical studies. The sensitivity of the films towards ethanol gas was investigated at room temperature.

Defect engineering and opto electronic property modifications by 1.5 MeV Li+ implantation on nano crystalline MgIn2O4 thin films

Spinel MgIn2O4 thin films were deposited on quartz substrates by the chemical spray pyrolysis technique using metal organic precursors at 450°C. Energetic 1.5 MeV Li+ ions were implanted to various fluences of 1013, 1014 and 1015 ions/cm2 onto insulating MgIn2O4 films using a 9 SDH-2, NEC, 3MV accelerator to modify the material properties and surface nature. X-ray diffraction analysis was carried out to identify the changes in the crystallinity and grain orientations before and after implantations. Before implantation, the grains of polycrystalline MgIn2O4 were randomly oriented [(222), (311), (442) and (511)], and after implantation they exhibited a tendency to realign the crystallites along the even (hkl) planes [(222) and (442)]. On the Li+-implanted sample, one or more grains combine together and form bigger grains along with shallow pits, as observed through the atomic force micrographs. The as-deposited films have a percentage transmittance of 70–80% in the wavelength range 400–800 nm and the observed optical transmittance was less in Li+-implanted MgIn2O4 films. The index of refraction and the extinction co-efficient values were respectively n=1.98 and k=10−2 in the visible region. However, the DC electrical conductivity of Li+-implanted films to a fluence of 1015 ions/cm2 was nearly 0.7 S/cm at room temperature. The efficiency of the carrier generation was increased from 13.41% to 26.81% on annealing the implanted sample to lower fluence (1013 ions/cm2).