Le photovoltaïque nécessite de nouveaux matériaux pour diminuer ces coûts et améliorer les rendements. Ces travaux de thèse ont concerné le développement de nouvelles phases d'oxyde de titane pour l'électronique transparente et la conversion de photon appliquée au PV silicium. L'ablation laser pulsé est une méthode de croissance particulièrement adaptée pour la prospection de matériaux aux propriétés innovantes. Le contrôle des phases anatase, rutile et d'une phase de composition TiO1.45 épitaxié en fonction de la pression partielle d'oxygène a permis de réaliser des films aux propriétés électriques, optiques innovantes. Un film biphasé anatase/rutile dopé niobium (TNO1.80) présente ainsi une transition métal-semi-conducteur aux alentours de 68K. Par ailleurs, le film de composition TiO1.45 épitaxié s'est révélé être un oxyde transparent conducteur de type p. La découverte de ce nouveau p-TCOs a été valorisée et validée par l'élaboration d'une homojonction p - n transparente. Les matrices d'oxyde de titane rutile et anatase ont également été utilisées pour accueillir des ions terres rares Ln3+ afin de convertir les photons ultra-violet du spectre solaire incident vers le proche infrarouge (800 > λ > 1100 nm). Le transfert d'énergie des matrices TiO2 vers les dopants Ln3+ a été étudié en fonction de la structure, de la quantité de dopant ainsi que la qualité de la microstructure des films dopés Ln3+ (Ln3+=Pr3+,Tm3+,Eu3+,Yb3+,Nd3+). / New materials are needed to decrease cost and improve photovoltaic cell performance. These thesis works are focused on the development of new titanium oxide phases for transparent electronic and photon conversion applied to silicon solar cell. Pulsed laser deposition is an adapted growth method for the prospection of materials with innovating properties. The control of epitaxial growth of anatase, rutile and a phase with a composition TiO1.45 in function of oxygen partial pressure allowed us to realize films with innovating electrical and optical properties. A two phase anatase/rutile film doped niobium (TNO1.80) have shown a metal-semiconductor transition about 68 K. Moreover, transparent TiO1.45 epitaxial thin film has displayed a p-type semiconduction behaviour which has been confirmed by the elaboration of a transparent p - n homojunction. Rutile and anatase titanium oxide matrix were also used to host rare earths ions in order to convert ultraviolet to near infra-red photon (800 > λ > 1100 nm). TiO2 matrix to dopant transfer has been studied in function of crystal structure, doping content and the quality of microstructure of films doped Ln3+(Ln3+=Pr3+,Tm3+,Eu3+,Yb3+,Nd3+).

Transparent conducting oxides (TCOs) have attracted extensive attention for decades due to their remarkable applications in optoelectronic devices. The development of functional nanostructured TCOs with unique properties, and an expansion of their functionalities are therefore research directions of significant current interest. Among TCOs, In2O3 is widely applied because of its high charge carrier concentration and mobility, as well as the ease with which it can be deposited as a thin film. The important role of surfaces in tuning properties in materials shows the importance of studying nanostructured materials with high surface areas. In this thesis I examined the synthesis of phase-controlled In2O3 nanocrystals (NCs) and showed the effect of doping and composition on the materials properties. Owing to the relevance of size, structure, and composition for manipulating properties of nanomaterials, synthesis of well-defined nanocrystals of pure and doped In2O3 has been of considerable interest for fundamental studies as well as for technological applications. Phase controlled synthesis of colloidal In2O3 NCs was achieved via a size-structure correlation. The study of the morphological and phase transformations of In2O3 NCs during their growth in solution implies that corundum (rh-In2O3) is a transient structure in the formation of cubic bixbyite (bcc-In2O3) phase. The formation of NCs smaller than 5 nm leads to the spontaneous stabilization of metastable phases owing to the surface energy and/or surface stress contributions, both of which are dependent on size. The growth beyond the critical size lowers the potential energy barrier height and causes the nanocrystal phase transformation. In addition, phase transformation of colloidal In2O3 NCs in the temperature range of 210-260 ˚C during their synthesis in solution was studied using a combination of structural and spectroscopic methods, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy, and analyzed data using Johnson-Mehl-Avrami-Erofeyev-Kholmogorov (JMAEK) and interface nucleation models. The phase transformation occurs via nucleation of bcc-In2O3 phase at the interface between contacting rh-In2O3 NCs, and propagates rapidly throughout the NC volume. In situ high temperature XRD patterns collected during nonisothermal treatment of In2O3 NCs reveal that phase transformation of smaller NCs occurs at a faster rate and lower temperature, which is associated with the higher packing density and contact formation probability of smaller nanoparticles. Owing to the fact that NC surfaces and interfaces play a key role in phase transformation, their control through the synthesis conditions and reaction kinetics is an effective route to manipulating NC structure and properties. Although, doping semiconductor NCs is crucial for enhancing and manipulating their functional properties, the doping mechanism and the effects of dopants on the nanocrystal growth and structure are not well understood. We show that dopant adsorption to the surfaces of colloidal In2O3 NCs during incorporation inhibit NC growth and leads to the formation of metastable rh-In2O3 for nanocrystals smaller than ca. 5 nm. Direct comparison between Cr3+ and Mn3+ dopants indicates that the nanocrystal structure directly determines the dopant incorporation limits and the dopant electronic structure, and can be predicted and controlled. These results enable a new approach to designing multifunctional nanostructures and understanding the early stages of crystal growth in the presence of impurities. Nanocrystalline films fabricated from colloidal Cr3+- and Mn3+- doped In2O3 nanocrystals exhibit strong ferromagnetic ordering up to room temperature. The absence of ferromagnetism in the free standing transition metal (TM)-doped In2O3 NCs and appearance of ferromagnetism only in TM:In2O3 films prepared from colloidal NCs, are attributed to the formation of extended structural defects, proposed to be oxygen vacancies at the NC interfaces. In fact, in TM:In2O3 NCs with high surface to volume ratios, more oxygen vacancies are present at the surface of NCs and networking of NCs in the prepared film causes an increase in grain-boundary defects at the interfaces. A comparative study of magnetic circular dichroism (MCD) spectra of Cr3+-doped bcc-In2O3 and Cr3+-doped rh-In2O3 revealed that Cr3+ ions distinctly occupy different symmetry sites in corundum and bixbyite crystal structure of In2O3. In fact, a change in the crystal structure of In2O3 from bixbyite to corundum changes the electronic configuration of Cr3+. By manipulating the NC composition and structure in solution we applied a one-step synthesis of ternary gallium indium oxide (GIO) nanocrystals with variable crystal structures. The structures and sizes of GIO NCs can be simultaneously controlled, owing to the difference in the growth kinetics of In2O3 and Ga2O3 NCs, and the polymorphic nature of both materials. These dependences, induced by the interactions between specific defect sites acting as electron donors and acceptors, were used to achieve broad emission tunability in the visible spectral range at room temperature. The nature of the photoluminescence is identified as donor -acceptor pair (DAP) recombination and changes with increasing indium content owing to the changes in the energy states of, and interactions between, donors and acceptors. Structural analysis of GIO nanocrystals by extended X-ray absorption fine structure spectroscopy reveals that In3+ occupies only octahedral, rather than tetrahedral, sites in the spinel-type γ-Ga2O3 nanocrystal host lattice, until reaching the substitutional incorporation limit of ca. 25%. The emission decay dynamics is also strongly influenced by the nanocrystal structure and composition.

No description available.

Transparent conducting oxides (TCOs) have attracted extensive attention for decades due to their remarkable applications in optoelectronic devices. The development of functional nanostructured TCOs with unique properties, and an expansion of their functionalities are therefore research directions of significant current interest. Among TCOs, In2O3 is widely applied because of its high charge carrier concentration and mobility, as well as the ease with which it can be deposited as a thin film. The important role of surfaces in tuning properties in materials shows the importance of studying nanostructured materials with high surface areas. In this thesis I examined the synthesis of phase-controlled In2O3 nanocrystals (NCs) and showed the effect of doping and composition on the materials properties. Owing to the relevance of size, structure, and composition for manipulating properties of nanomaterials, synthesis of well-defined nanocrystals of pure and doped In2O3 has been of considerable interest for fundamental studies as well as for technological applications. Phase controlled synthesis of colloidal In2O3 NCs was achieved via a size-structure correlation. The study of the morphological and phase transformations of In2O3 NCs during their growth in solution implies that corundum (rh-In2O3) is a transient structure in the formation of cubic bixbyite (bcc-In2O3) phase. The formation of NCs smaller than 5 nm leads to the spontaneous stabilization of metastable phases owing to the surface energy and/or surface stress contributions, both of which are dependent on size. The growth beyond the critical size lowers the potential energy barrier height and causes the nanocrystal phase transformation. In addition, phase transformation of colloidal In2O3 NCs in the temperature range of 210-260 ˚C during their synthesis in solution was studied using a combination of structural and spectroscopic methods, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy, and analyzed data using Johnson-Mehl-Avrami-Erofeyev-Kholmogorov (JMAEK) and interface nucleation models. The phase transformation occurs via nucleation of bcc-In2O3 phase at the interface between contacting rh-In2O3 NCs, and propagates rapidly throughout the NC volume. In situ high temperature XRD patterns collected during nonisothermal treatment of In2O3 NCs reveal that phase transformation of smaller NCs occurs at a faster rate and lower temperature, which is associated with the higher packing density and contact formation probability of smaller nanoparticles. Owing to the fact that NC surfaces and interfaces play a key role in phase transformation, their control through the synthesis conditions and reaction kinetics is an effective route to manipulating NC structure and properties. Although, doping semiconductor NCs is crucial for enhancing and manipulating their functional properties, the doping mechanism and the effects of dopants on the nanocrystal growth and structure are not well understood. We show that dopant adsorption to the surfaces of colloidal In2O3 NCs during incorporation inhibit NC growth and leads to the formation of metastable rh-In2O3 for nanocrystals smaller than ca. 5 nm. Direct comparison between Cr3+ and Mn3+ dopants indicates that the nanocrystal structure directly determines the dopant incorporation limits and the dopant electronic structure, and can be predicted and controlled. These results enable a new approach to designing multifunctional nanostructures and understanding the early stages of crystal growth in the presence of impurities. Nanocrystalline films fabricated from colloidal Cr3+- and Mn3+- doped In2O3 nanocrystals exhibit strong ferromagnetic ordering up to room temperature. The absence of ferromagnetism in the free standing transition metal (TM)-doped In2O3 NCs and appearance of ferromagnetism only in TM:In2O3 films prepared from colloidal NCs, are attributed to the formation of extended structural defects, proposed to be oxygen vacancies at the NC interfaces. In fact, in TM:In2O3 NCs with high surface to volume ratios, more oxygen vacancies are present at the surface of NCs and networking of NCs in the prepared film causes an increase in grain-boundary defects at the interfaces. A comparative study of magnetic circular dichroism (MCD) spectra of Cr3+-doped bcc-In2O3 and Cr3+-doped rh-In2O3 revealed that Cr3+ ions distinctly occupy different symmetry sites in corundum and bixbyite crystal structure of In2O3. In fact, a change in the crystal structure of In2O3 from bixbyite to corundum changes the electronic configuration of Cr3+. By manipulating the NC composition and structure in solution we applied a one-step synthesis of ternary gallium indium oxide (GIO) nanocrystals with variable crystal structures. The structures and sizes of GIO NCs can be simultaneously controlled, owing to the difference in the growth kinetics of In2O3 and Ga2O3 NCs, and the polymorphic nature of both materials. These dependences, induced by the interactions between specific defect sites acting as electron donors and acceptors, were used to achieve broad emission tunability in the visible spectral range at room temperature. The nature of the photoluminescence is identified as donor -acceptor pair (DAP) recombination and changes with increasing indium content owing to the changes in the energy states of, and interactions between, donors and acceptors. Structural analysis of GIO nanocrystals by extended X-ray absorption fine structure spectroscopy reveals that In3+ occupies only octahedral, rather than tetrahedral, sites in the spinel-type γ-Ga2O3 nanocrystal host lattice, until reaching the substitutional incorporation limit of ca. 25%. The emission decay dynamics is also strongly influenced by the nanocrystal structure and composition.

Chemnitz, Techn. Univ., Diss., 2008.

Saarbrücken, Univ., Diss., 2003. / Computerdatei im Fernzugriff.

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

Organic solar cells and organic light emitting diodes are on the forefront of emerging technologies aimed at harnessing light in ways never thought possible. Largear installations of OLED solid state lighting (SSL), as well as organic photovoltaics(OPVs), will become possible as the efficiencies of these devices continue to rise. All organic solar cells and OLEDs require the use of transparent conductive electrodes.Indium oxide (ITO) is currently the transparent conductor of choice for these applications, due to its unique combination of transparency, high conductivity, durability,and favourable surface properties. Indium, however, is a rare and expensive metal; proposed large-area installations of OPV cells and OLEDs will add further strain to global indium supply. Transparent conductive materials that are abundant, inexpensive, and which enable efficient and robust organic devices must therefore be developed. In the present work, suitable ITO anode replacement materials are demonstrated for OLEDS, small-molecule, polymer, and PbS colloidal quantum dot photovoltaics.

Organic solar cells and organic light emitting diodes are on the forefront of emerging technologies aimed at harnessing light in ways never thought possible. Largear installations of OLED solid state lighting (SSL), as well as organic photovoltaics(OPVs), will become possible as the efficiencies of these devices continue to rise. All organic solar cells and OLEDs require the use of transparent conductive electrodes.Indium oxide (ITO) is currently the transparent conductor of choice for these applications, due to its unique combination of transparency, high conductivity, durability,and favourable surface properties. Indium, however, is a rare and expensive metal; proposed large-area installations of OPV cells and OLEDs will add further strain to global indium supply. Transparent conductive materials that are abundant, inexpensive, and which enable efficient and robust organic devices must therefore be developed. In the present work, suitable ITO anode replacement materials are demonstrated for OLEDS, small-molecule, polymer, and PbS colloidal quantum dot photovoltaics.

Since the discovery of transparent conducting oxide (TCO) thin films¡ATCO has been widely used in optoelectronic devices. To increase the potential application of the TCO, this study aims at growing amorphous TCO thin films which possess visible transparency and high electric conductivity. Up to date, only IGZO exhibits these properties. However, the nature resource of indium, the main material in IGZO, is rare and expensive. In this study, searching for new materials that do not contain In, while manifest high transparent and conductivity is our major challenge. ZnO has an energy band gap of 3.4eV, for which visible photon does not have enough energy to excite the electron in ZnO from the valence band to conduction band. Therefore, it reveals itself as transparent. ZnO materials are relative stable in high temperature and chemical environments and thus a good candidate for been developed into amorphous TCO. The reason for the high conductivity in amorphous IGZO thin films is because the S orbital of In is spherical symmetry and has large radius in which can overlap with the next In ions to form a continuous band for conduction. In this study, a similar strategy is employed by use of the large S orbital of the doping tin (Sn) in ZnO. A ceramic ZnO target for the pulse laser deposition system is partially wrapped with tin foil. The optimum growth condition are searching by tuning oxygen partial pressure, laser energy, the distance between the target and substrate, and substrate temperature.