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The thesis work is devoted to the synthesis of NiTiO3-based semiconductive structures, i.e. powders and thin films, and the investigation of their related properties with the aim of their applications in photocatalysis. Theoretical approach and numerical simulations of the electronic, vibrational and optical properties of bulk and nanosized NiTiO3 structures have been carried out in order to deepen the understanding of the experimental results. The synthesis of NiTiO3 powders has been achieved by sol-gel and solid state reaction, while NiTiO3 thin films have been grown by rf-sputtering.Characterizations on their structural, vibrational and optical properties confirm the stabilization of polycrystalline NiTiO3 in its ilmenite phase in both powders and thin films as well. The determination of a band gap at 2.25 eV suggests the feasibility to implement the synthesized materials as visible-light-active photocatalysts. This feature has been tested in thedegradation of methylene blue in aqueous solution using rf-sputtered NiTiO3 thin films irradiated with visible light,achieving the degradation of 60% of the initial concentration of the colorant in 300 minutes. In addition, the electro-oxidation of methanol has been accomplished by applying an external voltage on an electrode containing NiTiO3 powders in alkaline media. The Ni ions present in the catalyst have been identified as the active species with the oxidation of the organic molecules on the surface of Ni3+ sites. As a main achievement, NiTiO3 has been synthesized as powders and thin films with suitable characteristics for efficient heterogeneous photocatalysis and the catalytic capabilities of NiTiO3 have beendemonstrated on the photodegradation of Methylene Blue and the electro-oxidation of methanol., Structures semi-conductrices à base de NiTiO3, et l'étude de leurs propriétés dans le but de les appliquer en photocatalyse. Une étude théorique et des simulations numériques ont été effectuées pour analyser les propriétés électroniques, vibrationnelles et optiques de NiTiO3 massif ou sous forme de clusters nanométriques. Les poudres NiTiO3 ont été synthétisées par sol-gel par réaction en phase solide, tandis que les films minces ont été obtenus par pulvérisation cathodique rf-magnétron. Les caractérisations de leurs propriétés physiques confirment l'obtention de NiTiO3 polycristallin dans sa phase ilménite. La détermination du gap électronique à 2,25 eV suggère la faisabilité de mise en oeuvre des matériaux synthétisés comme photocatalyseurs actifs sous irradiation en lumière visible. Cette fonctionnalité a été testée par la dégradation du bleu de méthylène en solution aqueuse en utilisant les couches minces de NiTiO3 sous irradiation visible, atteignant la dégradation de 60% de la concentration initiale du colorant en 300 minutes. En outre, l'électro-oxydation du méthanol a été réalisée en appliquant une tension externe sur une électrode contenant des poudres NiTiO3 dans des milieux alcalins. Les ions de Ni présents dans le catalyseur ont été identifiés comme des espèces actives et que l'oxydation des molécules organiques se produit sur la surface des sites de Ni3+. En résumé, NiTiO3 a été synthétisé sous forme de poudres et de films minces ayant des caractéristiques appropriées pour la photocatalyse hétérogène efficace et les capacités catalytiques de NiTiO3 ont été démontrées sur la photodégradation du bleu de méthylène et l'électrooxydation de méthanol.

The thesis work is devoted to the synthesis of NiTiO3-based semiconductive structures, i.e. powders and thin films, and the investigation of their related properties with the aim of their applications in photocatalysis. Theoretical approach and numerical simulations of the electronic, vibrational and optical properties of bulk and nanosized NiTiO3 structures have been carried out in order to deepen the understanding of the experimental results. The synthesis of NiTiO3 powders has been achieved by sol-gel and solid state reaction, while NiTiO3 thin films have been grown by rf-sputtering.Characterizations on their structural, vibrational and optical properties confirm the stabilization of polycrystalline NiTiO3 in its ilmenite phase in both powders and thin films as well. The determination of a band gap at 2.25 eV suggests the feasibility to implement the synthesized materials as visible-light-active photocatalysts. This feature has been tested in thedegradation of methylene blue in aqueous solution using rf-sputtered NiTiO3 thin films irradiated with visible light,achieving the degradation of 60% of the initial concentration of the colorant in 300 minutes. In addition, the electro-oxidation of methanol has been accomplished by applying an external voltage on an electrode containing NiTiO3 powders in alkaline media. The Ni ions present in the catalyst have been identified as the active species with the oxidation of the organic molecules on the surface of Ni3+ sites. As a main achievement, NiTiO3 has been synthesized as powders and thin films with suitable characteristics for efficient heterogeneous photocatalysis and the catalytic capabilities of NiTiO3 have beendemonstrated on the photodegradation of Methylene Blue and the electro-oxidation of methanol.; Structures semi-conductrices à base de NiTiO3, et l'étude de leurs propriétés dans le but de les appliquer en photocatalyse. Une étude théorique et des simulations numériques ont été effectuées pour analyser les propriétés électroniques, vibrationnelles et optiques de NiTiO3 massif ou sous forme de clusters nanométriques. Les poudres NiTiO3 ont été synthétisées par sol-gel par réaction en phase solide, tandis que les films minces ont été obtenus par pulvérisation cathodique rf-magnétron. Les caractérisations de leurs propriétés physiques confirment l'obtention de NiTiO3 polycristallin dans sa phase ilménite. La détermination du gap électronique à 2,25 eV suggère la faisabilité de mise en oeuvre des matériaux synthétisés comme photocatalyseurs actifs sous irradiation en lumière visible. Cette fonctionnalité a été testée par la dégradation du bleu de méthylène en solution aqueuse en utilisant les couches minces de NiTiO3 sous irradiation visible, atteignant la dégradation de 60% de la concentration initiale du colorant en 300 minutes. En outre, l'électro-oxydation du méthanol a été réalisée en appliquant une tension externe sur une électrode contenant des poudres NiTiO3 dans des milieux alcalins. Les ions de Ni présents dans le catalyseur ont été identifiés comme des espèces actives et que l'oxydation des molécules organiques se produit sur la surface des sites de Ni3+. En résumé, NiTiO3 a été synthétisé sous forme de poudres et de films minces ayant des caractéristiques appropriées pour la photocatalyse hétérogène efficace et les capacités catalytiques de NiTiO3 ont été démontrées sur la photodégradation du bleu de méthylène et l'électrooxydation de méthanol.

Tesis de maestría en ciencias especialidad física El mundo en el que vivimos sería inconcebible sin la electrónica. En la actualidad, el uso de dispositivos electrónicos se ha convertido en una necesidad. Muchos de nosotros vivios nuestras vidas cotidianas ligadso a una gran varidad de aparatos tecnológicos los cuales facilitan enormemente las actividades del día a día, por lo que el obtener dispositivos capaces de realizar más tareas y más rápidamente o mejor es ahora una ambición tanto individual como colectiva del ser humano. Es por ello que la investigación en materiales es hoy una de las ramas de la ciencia de más interés a nivel mundial. Especificamente dentro del campo de la electronica, la investigación en materiales ha conllevado a la creación de dispositivos cada vez más pequeños y a la vez más capaces y muchas veces menos costosos en su fabricación que sus predecesores. El silicio es el material semiconductor en el que la mayoría de los dispositivos electrónicos basan su estructura, debido a su abundancia en la naturaleza y a sus propiedades físicas. Pero existen también otros materiales semiconductores que poco a poco han ido atrayendo la atención de los investigadores y ganado terreno en la industria electrónica por diversas razones, como por ejemplo que sus propiedades son óptimas para determinada tarea, que presentan ventajas cualitativas superiores a la tecnología del silicio o que simplemente son más baratos. Universidad de Sonora. División de Ciencias Exactas y Naturales, 2013.

Four ZnPc-dimers with 2,5-thienyl (ZnPc-th-ZnPc 1), 2,7-fluorenyl (ZnPc-flu-ZnPc 2), 3,6-bisthienylldiketopyrrolopyrrole (ZnPc-DPP-ZnPc 3) and 1,4-phenyl (ZnPc-p-ZnPc 4) bridges have been studied as dopant-free hole transporting materials (HTMs) in perovskite solar cells (PSCs). The synthesis and characterization of ZnPc-th-ZnPc 1 and ZnPc-flu-ZnPc 2 dimers are reported for the first time. Steady state and time resolved photoluminescence demonstrate the good hole-extraction capability of these materials. The best efficiencies obtained for dimers 1, 2, 3 and 4 are 15.5 %, 15.6 %, 16.8 % and 15.7 %, respectively, without the addition of dopants. Besides, these derivatives demonstrated better stability both in dark storage conditions with a relative humidity 60 % for 160 h when compared to doped spiro-OMeTAD. The push-pull nature of dimer ZnPc-DPP-ZnPc 3 has led to the highest efficiency among the ZnPc derivatives under study demonstrating that donor-acceptor-donor systems can be good alternatives to commonly used materials due their energy levels, low cost and the final morphology of the hole transporting layer.

Perovskite solar cells are one of the most promising photovoltaic technologies, although their molecular level design and stability toward environmental factors remain a challenge. Layered 2D Ruddlesden-Popper perovskite phases feature an organic spacer bilayer that enhances their environmental stability. Here, the concept of supramolecular engineering of 2D perovskite materials is demonstrated in the case of formamidinium (FA) containing A(2)FA(n-1)Pb(n)I(3n+1) formulations by employing (adamantan-1-yl)methanammonium (A) spacers exhibiting propensity for strong Van der Waals interactions complemented by structural adaptability. The molecular design translates into desirable structural features and phases with different compositions and dimensionalities, identified uniquely at the atomic level by solid-state NMR spectroscopy. For A(2)FA(2)Pb(3)I(10), efficiencies exceeding 7% in mesoscopic device architectures without any additional treatment or use of antisolvents for ambient temperature film deposition are achieved. This performance improvement over the state-of-the-art FA-based 2D perovskites is accompanied by high operational stability under humid ambient conditions, which illustrates the utility of the approach in perovskite solar cells and sets the basis for advanced supramolecular design in the future.

One of the most prominent hole-transporting material (HTM) for hybrid perovskite solar cells has been 2,2″,7,7″-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), which is commonly doped with metal bis(trifluoromethylsulfonyl)imide (M(TFSI)n) salts that contribute to generating the active radical cation HTM species. The underlying role of the metal cation, however, remains elusive. Here, the effect of metal cations (M = Li, Zn, Ca, Cu, and Sr) on doping spiro-OMeTAD is analyzed by a combination of techniques, including electron paramagnetic resonance spectroscopy and cyclic voltammetry, which is complemented by photovoltaic device and hole mobility analysis. As a result, the authors reveal the superiority of Zn(TFSI)2 salts in device performances as compared to the others, including redox-active Cu(TFSI)2. This analysis thereby unravels new design principles for dopant engineering in HTMs for hybrid perovskite photovoltaics.

Despite the outstanding role of mesoscopic structures on the efficiency and stability of perovskite solar cells (PSCs) in the regular (n-i-p) architecture, mesoscopic PSCs in inverted (p-i-n) architecture have rarely been reported. Herein, an efficient and stable mesoscopic NiOx (mp-NiOx) scaffold formed via a simple and low-cost triblock copolymer template-assisted strategy is employed, and this mp-NiOx film is utilized as a hole transport layer (HTL) in PSCs, for the first time. Promisingly, this approach allows the fabrication of homogenous, crack-free, and robust 150 nm thick mp-NiOx HTLs through a facile chemical approach. Such a high-quality templated mp-NiOx structure promotes the growth of the perovskite film yielding better surface coverage and enlarged grains. These desired structural and morphological features effectively translate into improved charge extraction, accelerated charge transportation, and suppressed trap-assisted recombination. Ultimately, a considerable efficiency of 20.2% is achieved with negligible hysteresis which is among the highest efficiencies for mp-NiOx based inverted PSCs so far. Moreover, mesoscopic devices indicate higher long-term stability under ambient conditions compared to planar devices. Overall, these results may set new benchmarks in terms of performance for mesoscopic inverted PSCs employing templated mp-NiOx films as highly efficient, stable, and easy fabricated HTLs.

Low-dimensional hybrid perovskites have emerged as promising materials for optoelectronic applications. Although these materials have already demonstrated enhanced stability as compared to their three-dimensional perovskite analogues, their functionality has been limited by the insulating character of the organic moieties that primarily play a structure-directing role. This is particularly the case for the layered (2D) perovskite materials based on formamidinium lead iodide (FAPbI3) that remain scarce. We demonstrate a low-dimensional hybrid perovskite material based on a SPbI4 composition incorporating an electroactive naphthalenediimide (NDI) moiety as an organic spacer (S) between the perovskite slabs and evidence the propensity of the spacer to stabilize the α-FAPbI3 perovskite phase in hybrid low-dimensional SFAn–1PbnI3n+1 perovskite compositions. This has been investigated by means of solid-state nuclear magnetic resonance spectroscopy in conjunction with molecular dynamics simulations and density functional theory calculations. Theoretical calculations suggest an electronic contribution of the organic spacer to the resulting optoelectronic properties, which was confirmed by transient absorption spectroscopy. We have further analyzed these materials by time-resolved microwave conductivity measurements, revealing challenges for their application in photovoltaics.

The electron transport layer (ETL) is a key constituent in perovskite solar cells (PSCs). It should provide efficient and selective electron extraction, low resistivity and high stability. Here, zinc stannate (Zn2SnO4, ZSO) is employed as an ETL in planar PSCs. A surface treatment of a compact ZSO layer is introduced based on chemical bath deposition (CBD). CBD results in a dense and uniform surface morphology that promotes the formation of a perovskite film with better surface coverage and enlarged grains, which lead to reduced recombination losses. Such improvements effectively increase the charge extraction at ETL/perovskite interface and reduce trapassisted recombination, which results in a remarkable photovoltaic performance, low hysteresis index, and good reproducibility. The efficiency of PSCs based on CBD-modified ZSO ETL has been dramatically increased from 19.3% to 21.3% with a notable increase in open circuit voltage of 60 mV compared to bare ZSO-based devices. This value is among the highest for ZSO-based PSCs. More importantly, the CBD-treated PSCs exhibited good stability, retaining more than 90% of its initial efficiency over 1000 h under continuous illumination at maximum power point. These results demonstrate that CBD can significantly improve the performance and stability of ZSO-based planar PSCs, a crucial requirement for commercialization.