Studies on Chemical Bath Deposited Semiconducting Copper Selenide and Iron Sulfide Thin Films Useful For Photovoltaic Applications

Chemical bath deposition (CBD)is one of the simplest, very convient and probably the cheapest method for thin film preparation. Photovoltaic is the cleanest and the most efficient mode of conversion of energy to electrical power. Silicon is the most popular material in this field. The present study on chemical bath deposited semiconducting copper selenide and iron sulfide thin films useful for photovoltaic applications. Semiconducting thin films prepared by chemical deposition find applications as photo detectors, solar control coatings and solar cells. Copper selenide is a p-type semiconductor that finds application in photovolitics. Several heterojunction systems such as Cu2-xSe/ZnSe (for injection electro luminescence), Cu2Se/AgInSe2 and Cu2Se/Si (for photodiodes), Cu2-xSe/CdS, Cu2-xSe/CdSe, CuxSe/InP and Cu2-xSe/Si for solar cells are reported. A maximum efficiency of 8.3% was achieved for the Cu2-xSe/Si cell, various preparation techniques are used for copper selenide like vacuum evaporation, direct reaction, electrodeposition and CBD. Instability of the as-prepared films was investigation and is accounted as mainly due to deviation from stoichiometry and the formation of iron oxide impurity. A sulphur annealing chamber was designed and fabricated for this work. These samples wee also analysed using optical absorption technique, XPS (X-ray Photoelectron Spectroscopy) and XRD.(X-Ray Diffraction).The pyrite films obtained by CBD technique showed amorphous nature and the electrical studies carried out showed the films to be of high resistive nature. Future work possible in the material of iron pyrite includes sulphur annealing of the non-stochiometric iron pyrite CBD thin films in the absence of atmospheric oxygen

Systematic trends in self-consistent calculations of linear quantum wires

Systematic trends in the properties of a linear split-gate heterojunction are studied by solving iteratively the Poisson and Schrödinger equations for different gate potentials and temperatures. A two-dimensional approximation is presented that is much simpler in the numerical implementation and that accurately reproduces all significant trends. In deriving this approximation, we provide a rigorous and quantitative basis for the formulation of models that assumes a two-dimensional character for the electron gas at the junction.

Development of p-type transparent semiconducting oxides for thin film transistor applications

Semiconductor physics has developed significantly in the field of re- search and industry in the past few decades due to it’s numerous practical applications. One of the relevant fields of current interest in material science is the fundamental aspects and applications of semi- conducting transparent thin films. Transparent conductors show the properties of transparency and conductivity simultaneously. As far as the band structure is concerned, the combination of the these two properties in the same material is contradictory. Generally a trans- parent material is an insulator having completely filled valence and empty conduction bands. Metallic conductivity come out when the Fermi level lies within a band with a large density of states to provide high carrier concentration. Effective transparent conductors must nec- essarily represent a compromise between a better transmission within the visible spectral range and a controlled but useful electrical con- ductivity [1–6]. Generally oxides like In2O3, SnO2, ZnO, CdO etc, show such a combination. These materials without any doping are insulators with optical band gap of about 3 eV. To become a trans- parent conductor, these materials must be degenerately doped to lift the Fermi level up into the conduction band. Degenerate doping pro- vides high mobility of extra carriers and low optical absorption. The increase in conductivity involves an increase in either carrier concen- tration or mobility. Increase in carrier concentration will enhance the absorption in the visible region while increase in mobility has no re- verse effect on optical properties. Therefore the focus of research for new transparent conducting oxide (TCO) materials is on developing materials with higher carrier mobilities.

Self-assembly and bioactivity of a polymer/peptide conjugate containing the RGD cell adhesion motif and PEG

The self-assembly and bioactivity of the peptide–polymer conjugate DGRFFF–PEG3000 containing the RGD cell adhesion motif has been examined, in aqueous solution. The conjugate is designed to be amphiphilic by incorporation of three hydrophobic phenylalanine residues as well as the RGD unit and a short poly(ethylene glycol) (PEG) chain of molar mass 3000 kg mol-1. Above a critical aggregation concentration, determined by fluorescence measurements, signals of b-sheet structure are revealed by spectroscopic measurements, as well as X-ray diffraction. At high concentration, a self-assembled fibril nanostructure is revealed by electron microscopy. The fibrils are observed despite PEG crystallization which occurs on drying. This suggests that DGRFFF has an aggregation tendency that is sufficiently strong not to be prevented by PEG crystallization. The adhesion, viability and proliferation of human corneal fibroblasts was examined for films of the conjugate on tissue culture plates (TCPs) as well as low attachment plates. On TCP, DGRFFF–PEG3000 films prepared at sufficiently low concentration are viable, and cell proliferation is observed. However, on low attachment surfaces, neither cell adhesion nor proliferation was observed, indicating that the RGD motif was not available to enhance cell adhesion. This was ascribed to the core–shell architecture of the self-assembled fibrils with a peptide core surrounded by a PEG shell which hinders access to the RGD unit.

Photoinduced hole-transfer in semiconducting polymer/low-bandgap cyanine dye blends: evidence for unit charge separation quantum yield

Power-conversion efficiencies of organic heterojunction solar cells can be increased by using semiconducting donor-acceptor materials with complementary absorption spectra extending to the near-infrared region. Here, we used continuous wave fluorescence and absorption, as well as nanosecond transient absorption spectroscopy to study the initial charge transfer step for blends of a donor poly(p-phenylenevinylene) derivative and low-band gap cyanine dyes serving as electron acceptors. Electron transfer is the dominant relaxation process after photoexcitation of the donor. Hole transfer after cyanine photoexcitation occurs with an efficiency close to unity up to dye concentrations of similar to 30 wt%. Cyanines present an efficient self-quenching mechanism of their fluorescence, and for higher dye loadings in the blend, or pure cyanine films, this process effectively reduces the hole transfer. Comparison between dye emission in an inert polystyrene matrix and the donor matrix allowed us to separate the influence of self-quenching and charge transfer mechanisms. Favorable photovoltaic bilayer performance, including high open-circuit voltages of similar to 1 V confirmed the results from optical experiments. The characteristics of solar cells using different dyes also highlighted the need for balanced adjustment of the energy levels and their offsets at the heterojunction when using low-bandgap materials, and accentuated important effects of interface interactions and solid-state packing on charge generation and transport.

Nanostructured organic layers via polymer demixing for interface-enhanced photovoltaic cells

Significant progress is being made in the photovoltaic energy conversion using organic semiconducting materials. One of the focuses of attention is the morphology of the donor-acceptor heterojunction at the nanometer scale, to ensure efficient charge generation and loss-free charge transport at the same time. Here, we present a method for the controlled, sequential design of a bilayer polymer cell architecture that consists of a large interface area with connecting paths to the respective electrodes for both materials. We used the surface-directed demixing of a donor conjugated/guest polymer blend during spin coating to produce a nanostructured interface, which was, after removal of the guest with a selective solvent, covered with an acceptor layer. With use of a donor poly(p-phenylenevinylene) derivative and the acceptor C-60 fullerene, this resulted in much-improved device performance, with external power efficiencies more than 3 times higher than those reported for that particular material combination so far.

Deposição e caracterização de filmes finos de GaAs e 'Al IND. 2''O IND. 3' para potencial utilizado em transistores

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Investigação de propriedades de filmes finos de Sn'O IND. 2' e 'Al IND. 2''O IND. 3' para aplicação em dispositivos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Matrizes semicondutoras GaAs e Sn'X IND. 2' dopado com terras-raras Ce ou Eu: investigação do transporte elétrico

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigação das propriedades elétricas, ópticas e eletroquímicas de filmes finos semicondutores de BiVO4 e NiO para aplicação em fotoeletrocatálise

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estrutura eletrônica e propriedades elétricas fotoinduzidas em filmes finos de SnO2 com dopagem de Sb, e formação de heteroestruturas com TiO2

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Sintese e aplicação de filmes biocomponentes nanoestruturados de 'TI'/'TI''O IND.2'/'W''O IND.3' por template e 'SI'/'TI''O IND.2'/'PT' por heterojunção em conversão de energia solar e remediação ambiental

Pós-graduação em Química - IQ

Deposição de filmes finos de SnO2 e GaAs, visando confecção de dispositivos baseados na heterojunção SnO2/GaAs

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigação das propriedades ópticas, morfológicas e elétricas da heterojunção SnO2: Ce3+/ GaAs

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preparação, caracterização e estudo da eficiência na fotodegradação e adsorção de Rodamina B de heteroestruturas de TiO2/α-Fe2O3

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)