Thesis (M.S.)--Oregon State University, 2004. / Typescript (photocopy). Includes bibliographical references (leaves 73-77). Also available on the World Wide Web.

New transparent p- and n-type semiconductors and luminescent materials have been prepared and characterized. Synthesis, structures, optical and electrical properties of new chalcogenide fluoride p-type transparent semiconductors MCuQF (M=Ba, Sr; Q=S, Se, Te) are described. Band-gap tuning and improvement in conductivity through p-type doping are demonstrated in the family. The new Ag sulfide fluoride BaAgSF has been prepared, and its optical and electrical properties have been examined. Phase stabilization as well as optical and electrical properties of the p-type conductors BaCu₂S₂ and BaCu₂Se₂ are considered. New n-type transparent conducting films of W-doped In₂O₃ and W-doped zinc indium oxide (ZIO) have been prepared by pulsed laser deposition, and their electrical properties have been examined. Results on new transparent thin-film transistors containing SnO₂ or ZIO are also presented. Strong near-infrared luminescence of BaSnO3 is described, and the emission brightness is correlated to the crystallite size of assembled nanoparticles. Syntheses, structures, and optical properties of (La,Y)Sc₃(BO₃)₄:Eu³⁺, (Ba,Sr)Sc₂(BO₃)₄:Eu²⁺, and LuAl₃(BO₃)₄:Ln³⁺ (Ln=Eu, Tb, Ce) have been considered with emphasis on relations between structures and optical properties. Finally, the synthesis and luminescence properties of new potential X-ray phosphors Lu₂O₂S:Ln³⁺ (Ln=Eu, Tb) are summarized. / Graduation date: 2005

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--University of Massachusetts Amherst, 2009. / Includes bibliographical references (p. 103-107). Print copy also available.

Organic solar cells (OSCs) have attracted significant attention due to their potential of large area solution fabrication capability at low-cost. For bulk heterojunction (BHJ) OSCs, a thin film of transparent conducting indium tin oxide (ITO), coated on glass or flexible plastic substrate, is widely used as a front electrode. However, indium is not abundant on Earth. Its price has increased continuously over the past 10 years and will likely become an obstacle for the commercialization of OSCs at low cost. Aluminum-doped zinc oxide (AZO) is a promising ITO alternative due to its advantages of high electric conductivity, optical transparency, non-toxicity and low cost. However, reports on OSCs using AZO electrode are quite limited, due to the relatively lower power conversion efficiency (PCE) of AZO-based OCSs as compared to that of ITO-based OCSs. This work focused on studies of high performance AZO-based OSCs through AZO surface modification, absorption enhancement and process optimization. The optical and electronic properties of AZO film including transmittance, sheet resistance, surface morphology and surface work function were characterized. AZO-based OSCs with conventional and inverted structures were fabricated. It was found that AZO-based OSCs with inverted structure demonstrated superior performance than the ones with conventional structure. The inverted structure avoids the use of acidic PEDOT:PSS hole transporting layer, allows the improving of the absorbance of the OSCs and therefore its efficiency. An AZO front transparent cathode was used for application in high performance inverted BHJ OSCs. The photoactive layer consisted a blend of poly[[4,8-bis[(2- ethylhexyl)oxy] benzo [1,2-b:4,5-b'] dithiophene-2,6- diyl][3-fluoro- 2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophenediyl]](PTB7):3'H-Cyclopropa[8,25][5,6]fullerene- C70- D5h(6)-3'-butanoicacid, 3'-phenyl-, methyl ester (PC70BM). A structurally identical control OSC having an ITO front cathode was also fabricated for comparison studies. The structure of OSCs was optimized to achieving absorption enhancement in the active layer. AZO and ITO were modified with a 10 nm thick solution-processed ZnO interlayer to facilitate the efficient electron extraction. The results revealed that bilayer AZO/ZnO and the ITO/ZnO cathodes possess similar electron extraction property. AZO layer has a transparency cutoff at wavelength < 380 nm, results in a slight decrease in the short-circuit current density (JSC). However, the decrease in JSC is very small because the main energy of solar irradiation falls in the spectrum with wavelength > 380 nm. It shows that AZO-based OSCs have a promising PCE of 6.15%, which is slightly lower than that of a control ITO-based OSC (6.57%). AZO-based OSCs, however, demonstrate an obvious enhancement in the stability under an ultraviolet (UV)-assisted acceleration aging test. The significant enhancement in the stability of AZO-based OSCs arises from the tailored absorption of AZO electrode in wavelength < 380 nm, which serves as a UV filter to inhibit an inevitable degradation process in ITO-based OSCs due to the UV irradiation. In order to further investigate the degradation mechanism of OSCs under UV exposure, the change in charge collection characteristics of the OSCs made with ITO/ZnO and AZO/ZnO front cathode before and after UV exposure was examined. It was found that there was an obvious decrease in the charge extraction efficiency of ITO-based OSCs after UV exposure, while there was no observable change in the charge extraction efficiency of OSCs made with AZO/ZnO cathode under the same acceleration aging test. This work demonstrates that AZO is a suitable ITO alternative for application in OSCs, offering an improved device stability, comparable PCE and cell fabrication processes with an attractive commercial potential.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 67-72). Also available on the World Wide Web.

Submitted by GUILHERME RODRIGUES DE LIMA null (guirodrigueslima@hotmail.com) on 2017-09-15T18:57:55Z No. of bitstreams: 1 Defesa_correção_ficha_catalografica.pdf: 3367275 bytes, checksum: 6a436d913d3a352c3a8ec8e237660a1b (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-09-19T17:42:06Z (GMT) No. of bitstreams: 1 lima_gr_me_sjrp.pdf: 3367275 bytes, checksum: 6a436d913d3a352c3a8ec8e237660a1b (MD5) / Made available in DSpace on 2017-09-19T17:42:06Z (GMT). No. of bitstreams: 1 lima_gr_me_sjrp.pdf: 3367275 bytes, checksum: 6a436d913d3a352c3a8ec8e237660a1b (MD5) Previous issue date: 2017-08-18 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Transistores de filme fino (TFT) são dispositivos presentes em nosso cotidiano, usados em uma ampla variedade de aplicações, desde de processadores, registradores e monitores de tela plana. Estes dispositivos apresentam diversos benefícios, tais como: transparência, flexibilidade, rapidez, baixo custo e confiabilidade, o que faz com que tenham interesse de muitos grupos de pesquisa nas últimas décadas. Este trabalho visa o desenvolvimento de um novo método de deposição por spray, em atmosfera ambiente e a baixa temperatura (350ºC), para produção de filmes finos de óxidos zinco (ZnO) aplicados como camada ativa em TFTs. Os filmes finos transparentes de ZnO foram depositados por solução de um precursor orgânico (acetato de zinco bi-hidratado (Zn(CH3COO) · 2H2O)) sobre substratos de Si-p/SiO2 pelo método de deposição por spray. Este método emprega uma automação própria de controle na deposição para obter filmes altamente homogêneos e reprodutivos. Um grande conjunto de parâmetros na deposição foram testados para otimização dos filmes semicondutores para TFTs, como por exemplo: distância do spray sobre a placa de aquecimento, tempo de deposição, número de camadas, concentração da solução, entre outros. Os resultados obtidos na caracterização dos dispositivos, como, mobilidade de saturação (µsat), tensão de limiar de operação (Vth) e razão entre a corrente de operação e a corrente intrínseca (ION/OFF), foram comparados para diferentes parâmetros de deposição utilizados. Esse trabalho contribui em utilizar um novo método de deposição de baixo custo, para possíveis aplicações industriais e que pode ser expandido facilmente para larga escala de produção na fabricação de outros dispositivos de filme fino, como, OTFTs (Organic Thin Film Transistors), células solares, LCDs (Liquid Crystal Displays), OLEDs (Organic Light Emitting Diodes), LEDs (Light Emitting Diodes) e sensores. / Thin-film transistors (TFT) are every day devices used in a wide variety of applications, like processors, recorders and flat-panel monitors. These devices that present benefits, such as transparency, flexibility, speed, lower-cost and reliability, which have attracted interest in several research groups in recent decades. The aim of this work is the development of a new method of spray deposition, in ambient atmosphere and at low temperature (350ºC), for the production of thin films of zinc oxide (ZnO) applied as active layer in TFTs. The ZnO thin films were deposited from an organic solution of zinc acetate dihydrate (Zn(CH3COO) · 2H2O) on to Si-p/SiO2 substrates by the spray deposition method. This method employs its own automation for the deposition to obtain highly homogeneous and reproducible films. A large set of parameters in the deposition were tested for optimization of the semiconductor films for TFTs, such as: distance of the spray to the hot-plate, deposition time, number of layers, solution concentration, among others. The results obtained in the characterization of the devices, such as, mobility at saturation (μsat), threshold voltage (Vth) and on/off ratio (ION/OFF), were compared for different deposition parameters. This work contributes to the development of a novel, low-cost deposition method for possible industrial applications that can be easily expanded for large scale production of other thin film devices, such as, Organic Thin Film Transistors (OTFTs), solar cells, LCDs (Liquid Crystal Displays), OLEDs (Organic Light Emitting Diodes), LEDs (Light Emitting Diodes) and sensors. / CNPq: 133952/2015-0