Semiconductor photocatalysis has emerged as an interesting area of research since the discovery of Honda-Fujishima effect. In this study, TiO2/MoO2/graphene composites have been prepared by a solar radiation-assisted co-reduction method, wherein ammonium tetrathiomolybdate salt and graphite oxide are reduced to MoO2 and graphene respectively along with TiO2. The method involved the utilization of focused pulses of natural sunlight using a simple convex lens, thereby eliminating the need for harmful reducing agents. The compound was characterized by XRD and SEM for phase identification and morphology. The TiO2/MoO2/graphene composite exhibits superior photocatalytic water splitting activity without using a co-catalyst. In addition, we demonstrate the electrocatalytic hydrogen production using this earth abundant catalyst, which shows high current density (60 mA/cm2) and low Tafel slope (47 mV/dec). The hydrogen evolved during photocatalysis was detected by gas chromatography.

Present study investigates the system of small and large band gap materials for their use in Photoelectrochemical splitting of water. Electrodeposited Zr doped hematite (α-Fe2O3) films were subjected to ZnO quantum dots sensitization for 24, 48, and 72 hours which later on characterized for optical, structural, morphological and photoelectrochemical properties. These sensitized films, when used as photoelectrode in PEC cell, showed a significant increase in the photocurrent density as compared to unsensitized films. This may be attributed to reduction in carrier recombination rate along with photocatalytic effect of ZnO. The enhanced photo response has also been supported by increased negative value of flat band potential from -0.29V/SCE for unsensitized film to -0.8V/SCE for ZnO QDs sensitized hematite film, as examined by Mott-Schottky curve. In the present system, small band gap hematite has been chosen as a main solar energy absorber, while wide band gap ZnO QDs decorated over it, as an efficient electron transport across the interface by reducing charge carrier recombination rate.

Composite photocatalysts comprised of two semiconducting oxides, with suitable band gaps and band positions, have been reported as an effective approach to enhance photocatalytic activity in the visible region of the electromagnetic spectrum. Here, we report the synthesis, characterization, and photocatalytic evaluations of semiconducting composites made by combing bismuth oxide with either tantalum oxynitride or tantalum nitride. Visible light active composites were synthesized using solution chemistry synthesis method. The composites were characterized by powder X- ray diffraction (PXRD), diffuse reflectance UV-Vis spectroscopy, and photoluminescence (PL). Their photocatalytic activities were evaluated for generation of hydrogen from an aqueous methanol solution under visible light irradiation (λ≥ 420 nm). The as-prepared composite catalysts are found to have longer photogenerated charge-carrier life time, resulting in enhanced photocatalytic activities.

An inline metal organic chemical vapor deposition system was used to deposit tin sulfide at temperatures >500 °C. Tetramethyltin was used as the tin source and diethyldisulfide as the sulfur source. An overhead injector configuration was used delivering both precursors directly over the substrate. The tin and sulfur precursors were premixed before injection to improve chemical reaction in the gas phase. Growth temperatures 500 – 540 °C were employed producing films with approximate 1:1 stoichiometry of Sn and S detected by energy dispersive x-ray spectroscopy. X-ray diffraction showed there to be mixed phases with Sn2S3 present with SnS.

Single step synthesis of monophase CuSbS2 thin films by electro-deposition in ionic liquid electrolyte based on choline chloride and urea (ChCl:U) eutectic mixture is described. The formation of binary CuxS and SbxSy film phases using CuCl2 and SbCl3 precursors along with Na2S2O3 as sulfur source in ChCl:U are established as -0.59 V and -0.36 V vs. Pt, respectively by cyclic voltammetry and used to optimize CuSbS2 thin films growth potential and precursor composition. CuSbS2 films deposited at -0.65 V vs Pt with 1:1 Cu to Sb precursor ratio at 80⁰C are highly crystalline in chalcostibite orthorhombic structure. Deviant Cu/Sb ratio at 1:0.71 and 1:1.4 reveal inclusion of Cu3SbS3 and Sb2S3, respectively. Direct 1.65 eV band gap for single phase CuSbS2 film and with inclusive secondary phases at 1.73±0.1 eV and 2.13 eV is observed. As-deposited CuSbS2 films are p-type and n-p hetero-junction device in the n-ZnO/p-CuSbS2/Ag structure shows rectifying I-V curves and dependence on the CuSbS2 film growth conditions.

The wide range of optical band gaps of InGaN thin films led to considerable research in increasing the efficiency of solar cells. In this study, we present electrical, optical and structural properties of InGaN thin films grown by in situ rf sputtering method. Several samples of InGaN were deposited on aluminosilicate glass and silicon(111) substrates at different temperatures and varying N2 flow ratio. Growth temperatures are 35 °C, 150 °C, 200 °C. Aluminum metal contacts are deposited using DC sputtering method. Resistivity, mobility, conductivity values and their changes with respect to temperature are recorded using hall-effect measurement system. Band gap values and their changes with respect to N2 flow ratio in ( Ar+N2) mixture were calculated using UV spectrophotometer and tauc plots. Atomic composition was calculated using Energy-dispersive X-ray spectroscopy (EDX) analysis. Amorphous/crystalline nature of the samples are verified using XRD analysis.

The cadmium chloride annealing treatment is an essential step in the manufacture of efficient thin film CdTe solar cells. In previous work we have shown that the primary effect of the treatment is to remove high densities of stacking faults from the as-deposited material. Use of density functional theory has shown that some of the higher energy stacking faults are hole traps. Removal of these defects dramatically improves cell efficiency. In this study we focus on the effect of the activation treatment on the underlying n-type cadmium sulphide layer. A range of techniques has been used to observe the changes to the microstructure as well as the chemical and crystallographic changes as a function of treatment parameters. Electrical tests that link the device performance with the micro-structural properties of the cells have also been undertaken. Techniques used include High Resolution Transmission Electron Microscopy (HRTEM) for sub-grain analysis, EDX for chemical analysis and XPS and SIMS for composition-depth profiling. By studying the effect of increasing the treatment time and temperature, we will show that the cadmium sulphide layer depletes to the point of complete dissolution into the absorber layer. We will also show that chlorine penetrates and decorates the grain boundaries in the cadmium sulphide. In addition we will show that chlorine builds up at the heterojunction and concentrates in voids at the cadmium telluride/cadmium sulphide interface. A combination of these effects damages the electrical performance of the solar cell.

Surfactant-free SnS nanoparticles were synthesized using continuous spray pyrolysis (CoSP) technique and used as sensitizers on electro-deposited ZnO nanowire arrays for fabrication of extremely thin absorbing (ETA) layers. The high-surface-area nanowire layer on ITO substrate was directly over-coated by SnS nanoparticles. The morphology of the ZnO/SnS nanostructures showed the coverage of orthorhombic SnS nanocrystals on hexagonal ZnO prismatic nanowires. The crystalline phase of the ZnO/SnS nanostructures was studied using X-ray diffraction. Conducting AFM showed a nonlinear characteristics confirming the junction formation.

We investigate the synthesis of kesterite Cu2ZnSnS4 (CZTS) thin films using thermal evaporation from copper, zinc and tin pellets and post-annealing in a sulfur atmosphere. The effects of chemical composition were studied both on the absorber layer properties and on the final solar cell performance. It is confirmed that CZTS thin film chemical composition affects the carrier concentration profile, which then influences the solar cell properties. Solar cells using a CZTS thin film with composition ratio Cu/(Zn+Sn) = 0.87, and Zn/Sn = 1.24 exhibited an open-circuit voltage of 483 mV, a short-circuit current of 14.54 mA/cm2, a fill factor of 37.66 % and a conversion efficiency of 2.64 %. Only a small deviation from the optimal chemical composition can drop device performance to a lower level, which confirms that the CZTS solar cells with high conversion efficiency existed in a relatively narrow composition region.

Using the density functional theory (DFT) and time dependent DFT, within the generalized gradient approximation (GGA), the electronic and optical properties of stoichiometric (ZnS)n nanoparticles (NP) were calculated. The dependence of the gap on the size (n) of the nanoparticle will be presented. The effect of replacing S atoms with P, Se or Te atoms in the (ZnS)n nanoparticles and its influence in the gap will be also shown.

We prepared silicon hyperdoped with sulfur by ion-implantation followed by pulsed laser melting. Effects of laser fluence during pulsed laser melting and of post-annealing on the silicon hyperdoped with sulfur are investigated. The structure of hyperdoped layer changes from poly-to mono-crystal with increasing laser fluence. Interface between sulfur-implanted-layer and single-crystal substrate disappear above 1.1 J/cm2. The spectral intensity of mid-infrared (MIR) optical absorption increases with crystallinity and spectral shape depends on whether the melt depth during pulsed laser melting reaches interface between implanted layer and single-crystal silicon substrate or not. The MIR absorption intensity rapidly decreases with thermal annealing temperature and almost disappears at 750 °C. The activation energy of conductivity decreases with increasing laser fluence and further decreases with increasing post thermal-annealing temperature. The insulator-metal transition is observed for the sample annealed at 750 °C. These results indicate that there is no direct correlation between MIR optical absorption band and insulator-metal transition.