Carlos Luiz Ferreira

Comparative study of CdTe sources used for deposition of CdTe thin films by close spaced sublimation technique

Unlike other thin film deposition techniques, close spaced sublimation (CSS) requires a short source-substrate distance. The kind of source used in this technique strongly affects the control of the deposition parameters, especially the deposition rate. When depositing CdTe thin films by CSS, the most common CdTe sources are: single-crystal or polycrystalline wafers, powders, pellets or pieces, a thick CdTe film deposited onto glass or molybdenum substrate (CdTe source-plate) and a sintered CdTe powder. In this work, CdTe thin films were deposited by CSS technique from different CdTe sources: particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass). The largest deposition rate was achieved when a paste made of CdTe and propylene glycol was used as the source. CdTe source-plates led to lower rates, probably due to the poor heat transmission, caused by the introduction of the plate substrate. The results also showed that compacting the powder the deposition rate increases due to the better thermal contact between powder particles.

Influence of deposition parameters on the properties of CdTe films deposited by close spaced sublimation

CdTe thin films are used as absorber layer in CdS/CdTe solar cells. The microstructure of this absorber layer plays a fundamental role in photovoltaic conversion and can be controlled by the deposition parameters used during the film growth. In this work, CdTe thin films were deposited by the CSS method onto glass substrates previously covered with In2O3:Sn. The effects of pressure, source temperature and substrate temperature on the microstructural properties of the films were studied. The properties were mainly influenced by the pressure, the presence of oxygen in the reaction chamber, and the substrate temperature. For films deposited under an argon atmosphere, an increase in grain size and a reduction of the texture were observed as the pressure and substrate temperature were increased. The introduction of oxygen in the atmosphere led to a decrease in the deposition rate and affected the microstructure and composition of the film. Films deposited under an argon-oxygen atmosphere have smaller grains than those deposited under argon and are richer in Te. The addition of oxygen to the atmosphere apparently did not result in the formation of oxides.

Fabrication of TCO/CdS/CdTe/Au solar cells using different CdCl 2 treatments

In this work CdS/CdTe solar cells were submitted to solution, sublimation and vapor CdCl2 treatments, followed by NP etch for several periods of time. The influence of these procedures on cell efficiency is discussed. The individual layers are analyzed and the results are compared with similar studies in the literature. The best NP etching time was 20 s for all CdCl2 treatments. The highest efficiency was achieved for the cell submitted to the solution treatment at 380 °C. Although the layers have shown good properties for a high efficiency cell, the maximum overall efficiency was only 7.8%, probably due to high series and low shunt resistances.

Fique Fabric: A Promising Reinforcement for Polymer Composites

A relatively unknown natural fiber extracted from the leaves of the fique plant, native of the South American Andes, has recently shown potential as reinforcement of polymer composites for engineering applications. Preliminary investigations indicated a promising substitute for synthetic fibers, competing with other well-known natural fibers. The fabric made from fique fibers have not yet been investigated as possible composite reinforcement. Therefore, in the present work a more thorough characterization of fique fabric as a reinforcement of composites with a polyester matrix was performed. Thermal mechanical properties of fique fabric composites were determined by dynamic mechanical analysis (DMA). The ballistic performance of plain woven fique fabric-reinforced polyester matrix composites was investigated as a second layer in a multilayered armor system (MAS). The results revealed a sensible improvement in thermal dynamic mechanical behavior. Both viscoelastic stiffness and glass transition temperature were increased with the amount of incorporated fique fabric. In terms of ballistic results, the fique fabric composites present a performance similar to that of the much stronger KevlarTM as an MAS second layer with the same thickness. A cost analysis indicated that armor vests with fique fabric composites as an MAS second layer would be 13 times less expensive than a similar creation made with Kevlar™.

Construction of an in-line system to produce CdS/CdTe solar cells

This work involved the construction of an in-line system, where CdS and CdTe depositions, CdCl2 vapor treatment and ZnTe deposition were performed by close-spaced sublimation technique without the necessity of opening the system. The system allowed easy movement by rotating the substrate to the deposition regions. The time spent to produce solar cells in the new system (up to 120 min) was considerably shorter than those achieved in other works to perform similar steps with vacuum break. The new system allowed the substrate was positioned in the deposition region after the source and substrate graphite blocks were already heated, resulting in a high initial nucleation rate and the production of dense and continuous films, suitable for production of high efficiency cells. The first cells, with an area of 1 cm2, showed efficiencies up to 7%.

Thin film CdS/CdTe solar cells produced in a CSS in-line system

This work shows results for CdS/CdTe photovoltaic cells grown in a homemade in-line close-spaced sublimation equipment. In this system, most of the steps of cell fabrication were carried out continuously, using dry processing, without breaking vacuum. The efficiency values ranged from 3.5 to 7%. These cells were compared with unfinished devices prepared in the in-line system and finished (heat treatment and contact processing) at NREL. The results suggested that some steps in the cell fabrication should be optimized.

Performance of Plain Woven Jute Fabric-Reinforced Polyester Matrix Composite in Multilayered Ballistic System

The ballistic performance of plain woven jute fabric-reinforced polyester matrix composites was investigated as the second layer in a multilayered armor system (MAS). Volume fractions of jute fabric, up to 30 vol %, were mixed with orthophthalic polyester to fabricate laminate composites. Ballistic tests were conducted using high velocity 7.62 mm ammunition. The depth of penetration caused by the bullet in a block of clay witness, simulating a human body, was used to evaluate the MAS ballistic performance according to the international standard. The fractured materials after tests were analyzed by scanning electron microscopy (SEM). The results indicated that jute fabric composites present a performance similar to that of the much stronger Kevlar™, which is an aramid fabric laminate, as MAS second layer with the same thickness. The mechanism of this similar ballistic behavior as well as the comparative advantages of the jute fabric composites over the Kevlar™ are discussed.

Propriedades de filmes finos de ZnO:Al depositados sobre substratos de poliimida à temperatura ambiente para aplicações em dispositivos optoeletrônicos flexíveis

Este trabalho apresenta as propriedades de filmes finos de ZnO:Al crescidos por pulverizacao catodica com radio frequencia sobre substratos de poliimida para serem utilizados como eletrodos flexiveis de dispositivos optoeletronicos. Para efeitos de comparacao, os filmes tambem foram crescidos sobre lâminas de vidro soda-lime. Os filmes foram depositados com diversas potencias de trabalho, sobre substratos mantidos a temperatura ambiente. Os efeitos da potencia e da espessura nas propriedades opticas, eletricas e estruturais do ZnO:Al foram investigados. Imagens de microscopia de forca atomica revelaram que os filmes foram nanocristalinos e de baixa rugosidade. Valores de resistencia de folha de 8 Ω/sq, correspondente a uma resistividade de 6x10-4 W.cm, e de transmitância de 75% na faixa do visivel foram obtidos, os quais podem ser considerados satisfatorios, principalmente quando se considera que a deposicao foi realizada a temperatura ambiente.

DESEMPENHO DO COMPÓSITO DE MATRIZ POLIÉSTER REFORÇADO COM TECIDO DE JUTA EM UM SISTEMA DE BLINDAGEM MULTICAMADA

* Contribuição técnica ao 72o Congresso Anual da ABM – Internacional e ao 17o ENEMET Encontro Nacional de Estudantes de Engenharia Metalúrgica, de Materiais e de Minas, parte integrante da ABM Week, realizada de 02 a 06 de outubro de 2017, São Paulo, SP, Brasil. DESEMPENHO DO COMPÓSITO DE MATRIZ POLIÉSTER REFORÇADO COM TECIDO DE JUTA EM UM SISTEMA DE BLINDAGEM MULTICAMADA* Foluke Salgado de Assis Sérgio Neves Monteiro Fabio Da Costa Garcia Filho Artur Camposo Pereira Édio Pereira Júnior Carlos Luiz Ferreira Resumo O desempenho balístico de compósitos de matriz de poliéster reforçados com tecido de juta foi avaliado como segunda camada em um sistema de blindagem multicamadas (MAS – Multilayered Armor Systems). Diferentes frações volumétricas de tecido de juta, até 30% vol., foram misturadas com poliéster ortoftálica para se fabricar as placas compósitas. Estes compósitos foram ligados a uma camada cerâmica de alumina dianteira e seguidos por uma placa metálica de liga de alumínio como terceira camada do MAS, os testes balísticos foram conduzidos usando munição comercial de alta velocidade de 7,62 mm. A profundidade de penetração causada pela bala em um bloco de plastilina, que simula o corpo humano, foi usada para avaliar o desempenho balístico do MAS de acordo com o padrão internacional. Os materiais fraturados após testes foram analisados por microscopia eletrônica de varredura (MEV). Os resultados indicaram que os compósitos de tecido de juta apresentam um desempenho semelhante ao do tecido de aramida comercialmente utilizado como segunda camada para MAS com mesma espessura, o KevlarTM. O mecanismo que explica este comportamento balístico semelhante, bem como as vantagens econômicas comparativas dos compósitos de tecido de juta foram discutidos. Palavras-chave: Tecido de juta; Compósito de poliéster; Comportamento balístico; Sistema de blindagem multicamada.

Microstructural and optical properties of CSS and CBD-CdS thin films for photovoltaic solar cells

This work compares the properties of CdS films deposited by CBD and CSS techniques. The influence of the deposition parameters on the properties of the films was investigated. The thickness of CBD films ranged from 80 to 100nm and was affected by the concentration of reactants in the solution. For CSS films, the thickness was controlled in the 100-300nm range, being strongly influenced by the source/substrate temperatures and pressure. Grain size in CSS films was larger than in CBD films. Transmittance of CBD and CSS films ranged from 80 to 90%, but the band gap in CSS films was narrower than in CBD films, which means that CSS films transmit less of the blue part of the solar spectrum than CBD films. However, the growth of CdS films by CSS technique may be advantageous because the CdS/CdTe device could be fully manufactured in the same system.