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C. Subramanian

Bio: C. Subramanian is an academic researcher from Anna University. The author has contributed to research in topics: Tin oxide & Crystal. The author has an hindex of 6, co-authored 6 publications receiving 205 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, a spray pyrolysis technique was used to synthesize thin films of undoped and fluorine doped tin oxide on borosilicate glass plates.
Abstract: Thin films of undoped and fluorine doped tin oxide have been prepared on borosilicate glass plates by a spray pyrolysis technique. The effect of process parameters, such as tin chloride concentration in the precursor solution, substrate to nozzle distance, carrier gas (air) flow rate, substrate temperature, and doping level of fluorine in the spray solution, on the physical properties of the tin oxide thin films have been investigated. The grown films were polycrystalline in nature above 350°C, the [110] reflection having the maximum intensity in all cases. Films of about 10−3 Ω cm resistivity and high visible transparency of about 88% have been obtained at the optimum substrate temperature of 425°C and fluorine doping concentration of 57 at.%. The optical investigations show that the optimized films have a direct allowed bandgap of 4.25 eV and indirect allowed bandgap of 2.71 eV.

74 citations

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TL;DR: In this paper, the optical properties of these films are investigated in the entire UV-Visible-IR region (0.2 - 10 mikrom). The observed absorption edge lies at 3.65 eV for undoped tin oxide and on doping it shifts towards higher energies, which is due to the Moss-Burstein effect.
Abstract: Undoped, fluorine doped and antimony doped tin oxide films are prepared on quartz plates by Spray pyrolysis technique. The films grown at the optimum substrate temperature with different doping levels have been chosen for this study. Optical properties of these films are investigated in the entire UV-Visible -IR region (0.2 - 10 mikrom). The observed absorption edge lies at 3.65 eV for undoped tin oxide and on doping it shifts towards higher energies, which is due to the Moss - Burstein effect. For fluorine doping depending upon the fluorine concentration, the absorption edge lies in the range 3.9 - 4.14 eV and for antimony doping it lies in the range 3.82 - 4.1 eV. In the undoped tin oxide films the direct allowed transition occurs at 4.02 eV and indirect allowed transition occurs at 2.43 eV, whereas for fluorine doped tin oxide and antimony doped tin oxide films, the direct allowed transitions occur in the range 4.18 - 4.28 and 4.13 - 4.22 eV respectively and the indirect allowed transitions occur in the range 2.63 - 2.73 and 2.54 - 2.65 eV respectively. Optical properties near the plasma edge have been analyzed using Drude's theory. The dependence of effective mass on carrier concentration has been explained on the basis of nonparabolicity of the conduction band. The shift in the fermi energy, calculated on the basis of energy dependent effective mass, is consistent with the measured shift in the absorption edge.

65 citations

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TL;DR: In this article, the effects of dopants on the solubility, stability and induction periods were investigated in stirred solutions, and the interfacial energy for pure and doped solutions at 30°C was calculated.

33 citations

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TL;DR: In this article, single crystals of PbMoO4 were grown by Czochralski method and the growth behavior has been studied by taking into consideration the different parameters such as seed rotation rate, pulling rate and the axial temperature gradient above the melt level.
Abstract: Single crystals of PbMoO4 were grown by Czochralski method. The growth behaviour has been studied by taking into consideration the different parameters such as seed rotation rate, pulling rate and the axial temperature gradient above the melt level. It was found that the crystal-melt interface shape is always convex despite low axial temperature gradient and high seed rotation rate and is attributable to the fact that the crystal is transparent in the IR region and hence to internal radiant heat transfer through the crystal. To study the chemical entities, the powder sample was examined with the FTIR spectroscopic method. Differential thermal analysis confirmed the melting point and the composition. Optical microscopic observation of single crystals revealed gas bubbles in the crystals grown at faster pulling rate and strain induced surface cracks upon heat treatment in the crystals grown with more convex crystal—melt interface shape. Microhardness studies were also performed on the as grown and heat-treated samples and the values of microhardness and fracture toughness were calculated.

22 citations

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TL;DR: In this article, the influence of doping of benzophenone and urea on the growth and electrical properties of triglycine sulphate (TGS) crystals has been investigated.
Abstract: Pure and doped (Benzophenone and Urea) triglycine sulphate (TGS) crystals have been grown from aqueous solution by slow cooling method. The influence of doping of benzophenone and urea on the growth and electrical properties have been investigated. The pyroelectric coefficient increases with the addition of benzophenone and urea. It has been observed that the pyroelectric figure of merit of benzophenone doped TGS crystals is less than urea doped crystals. This is attributed to the higher permittivity of benzophenone doped TGS crystals. The Vicker‘s hardness number was found to be increased for doped crystals.

17 citations


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TL;DR: In this article, a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5 nm thick films of hematite.
Abstract: A promising route to increase the performance of hematite (alpha-Fe2O3) photoelectrodes for solar hydrogen production through water-splitting is to use an extremely thin layer of this visible light absorber on a nanostructured scaffold. However, the typically poor performance of ultrathin (ca. 20 nm) films of hematite has been the limiting factor in implementing this approach. Here, the surprising effect of a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5 nm thick films of hematite. These films exhibit a water oxidation photocurrent onset potential at 1.1V versus the reversible hydrogen electrode (vs. RHE) and a plateau current of 0.63 mA cm(-2) at 1.5 V vs. RHE under standard illumination conditions, representing the highest reported performance for ultrathin hematite films. In contrast, almost no photoactivity is observed for the photoanode with the same amount of hematite on an untreated substrate. A detailed study of the effects of the TEOS treatment shows that a monolayer of SiOx is formed, which acts to change the hematite nucleation and growth mechanism, increases its crystallinity, reduces the concentration of carrier trapping states of the ultrathin films, and suggests its further application to quantum-dot and extremely-thin-absorber (ETA)-type solar cells.

355 citations

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TL;DR: This critical review focuses on the solution deposition of transparent conductors with a particular focus on transparent conducting oxide (TCO) thin-films, with an introduction into the applications of and material criteria for TCOs.
Abstract: This critical review focuses on the solution deposition of transparent conductors with a particular focus on transparent conducting oxide (TCO) thin-films TCOs play a critical role in many current and emerging opto-electronic devices due to their unique combination of electronic conductivity and transparency in the visible region of the spectrum Atmospheric-pressure solution processing is an attractive alternative to conventional vacuum-based deposition methods due to its ease of fabrication, scalability, and potential to lower device manufacturing costs An introduction into the applications of and material criteria for TCOs will be presented first, followed by a discussion of solution routes to these systems Recent studies in the field will be reviewed according to their materials system Finally, the challenges and opportunities for further enabling research will be discussed in terms of emerging oxide systems and non-oxide based transparent conductors (341 references)

347 citations

Journal ArticleDOI
TL;DR: In this article, the authors reviewed the recent progress on solution processable metal oxides and metal chelates as buffer layers in conventional and inverted PSCs and drew a conclusion and gave a perspective.
Abstract: The interfaces between the electrodes and the photoactive layer significantly influence the efficiency and stability of polymer solar cells (PSCs). By choosing suitable interfacial materials, the energetic barrier height at the interface could be reduced to form an ohmic contact with less series resistance, inducing high charge collection efficiency of the corresponding electrodes for holes or electrons. Solution-processable metal compounds, especially metal oxides and transition metal chelates, have the advantages of high charge carrier mobility, suitable work function, low cost, and high environmental stability, which make them attractive for applications as cathode and anode interfacial materials for efficient and stable PSCs. In this paper, we reviewed the recent progress on solution processable metal oxides and metal chelates as buffer layers in conventional and inverted PSCs. In the introduction section, we introduced the operating principles of conventional and inverted PSCs, followed by introducing the energy levels, optical properties, processing methods and characterization techniques of the buffer layers. In the second and third parts, we reviewed recent progress in materials for both anode and cathode buffer layers. Finally, we drew a conclusion and gave a perspective. We believe that solution-processable metal oxides and metal chelates will play a key role as buffer layers in the future fabrication of large area and flexible PSCs with high performance and long term stability.

252 citations

Journal ArticleDOI
TL;DR: In this article, the effect of the sized silver (Ag) nanoparticles on the optical property of SPR was studied. And the authors showed that surface plasmon resonance enhanced the absorption by the sample with Ag nanoparticles above that of the sample without nanoparticles.
Abstract: This work studies the effect of the sized silver (Ag) nanoparticles on the optical property of SPR. Nanoparticles were prepared on fluorine-doped-tin-oxide (FTO) coated glass substrates by RF magnetron sputtering with various deposition times and the subsequent rapid thermal annealing (RTA) to control the particle size. To make the Ag films, Ag films of different thicknesses were first deposited on either glass or FTO substrate by a vacuum sputtering technique. Some of the samples founded nanoparticles by rapid thermal annealing. The substrates with and without nanoparticles were then sensitized by immersing them in a 0.2 mM N719 dye solution. Finally, the effect of the absorption coefficient was investigated by adsorbing it on fine silver Ag islands. The surface plasmon resonance enhanced the absorption by the sample with Ag nanoparticles above that of the sample without nanoparticles. In this study, the peak position of the surface plasmon characteristic absorption increased with the grain size of the nanoparticles in a red-shift. The structure and the quantity of Ag particles were very critical to the surface plasmon resonance effect.

244 citations

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TL;DR: In this article, the authors show using density functional theory that incorporation of Pb into SnO2 reduces the band gap through lowering of the conduction band minimum, thereby increasing the electron affinity.
Abstract: Transparent conducting oxides (TCOs) are an essential component in modern optoelectronic devices, such as solar panels and touch screens. Their ability to combine transparency and conductivity, two properties that are normally mutually exclusive, have made them the subject of intense research over the last 50 years. SnO2, doped with F or Sb, is a widely used and relatively inexpensive transparent conducting material, however, its electronic structure leaves scope for improving its properties for use in many TCO applications, especially in solar cell devices. Here we show using density functional theory that incorporation of Pb into SnO2 reduces the band gap through lowering of the conduction band minimum, thereby increasing the electron affinity. The electron effective mass at the conduction band minimum decreases alongside the band gap, indicating improved charge carrier mobilities. Furthermore, the calculated optical absorption properties show the alloys retain their transparency in the visible spectrum. Our results suggest that alloying of PbO2 with SnO2 will enable improved electronic properties, including a highly tuneable workfunction, which will open up the material for other applications, such as hole injection layers in organic photovoltaics.

181 citations