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Zinc oxide (ZnO) and titanium oxide (TiO2) are two widely studied metal oxide semiconductors due to their unique optical, electronic, and catalytic properties. These materials have attracted considerable interest in the development of advanced electronic device like sensors, solar cells, and photocatalysts, among other applications. Nanostructured thin films of ZnO and TiO2, with thicknesses ranging from a few to several hundred nanometres, have received increasing attention in recent years due to their exceptional properties arising from the quantum confinement and large surface area-to-volume ratio. These properties include enhanced optical absorption, improved charge transport, and increased reactivity, making them suitable for the above-mentioned various applications. In this work several chemical and physical methods of synthesis were utilized to produce nanostructured thin films, which were thoroughly characterized by SEM, STEM, TEM, AFM, GIXRD, UV- Vis, DLTS and ss-IS, and used in advanced configurations of thin-film based solar cells (perovskite) and as immobilized photocatalysts.

In fields such as sensing, catalysis, and optoelectronics, it is crucial to find a way to design and fabricate nanocomposites based on semiconducting oxides with improved functional performances. In this context, SnO2 is interesting material, as it is an earth-abundant and widely used semiconductor with a bandgap of 3.6 eV and is known as a part of the transparent conductive oxide (TCO) family used in solar cells. The raw materials required for SnO2 are affordable, thus fostering continuous interest in exploring synthetic routes to SnO2 nanocrystals and nanostructures, including flame pyrolysis, thermal evaporation, hydrothermal synthesis, and various sol-gel methods. In this work, we report on a novel synthesis approach and combination of different methods to characterize SnO2 nanoparticles and nanostructured thin-films in order to control size and morphology through variation of reaction conditions. The samples prepared in the form of bulk and films with diverse morphology were thoroughly (micro)structurally characterized using X-ray diffraction along with AFM and SEM. In view of the potential application of prepared films as a layer in solar cells, the electrical characterization was carried out using Solid-State Impedance Spectroscopy (SS-IS) in a wide range of temperatures and frequencies. The obtained results show a high degree of chemical and structural homogeneity, see Fig. 1. An attempt was made to elucidate the processes behind the formation and growth of nanostructures as a function of the reaction settings. Moreover, the correlation between the (micro)structure and electrical features of prepared materials is discussed in detail. We seek to better control the SnO2 surface properties, including thin-film quality and homogeneity to facilitate charge transfer and mitigate recombination.

Multilayer thin film solar cells properties are dependent not only on the layer compositions but on the layer mutual interplay. The electron transport layer (ETL) is one of the most important layers for a successful charge separation and extraction of the electrons, and therefore the overall cell efficiency. Both titanium and zinc oxide, which are commonly used for ETL, are known to cause degradation of the active perovskite layer which leads to lower stability and loss in efficiency. SnO2 has lower catalytic activity and therefore is less prone to displaying oxygen vacancies and deep level traps that could worsen the electrical properties and degrade the interface. In addition to that SnO2 can easily be derived by various chemical methods in a mesoporous or nanostructured thin-film configuration. In this work by combination of spin coating and hydrothermal synthesis we derived thin-films of nanostructured SnO2 that were thoroughly characterized by X-ray diffraction, scanning electron and atomic force microscopy, and Raman and UV/VIS spectroscopy. The electrical properties were tested by solid state impedance spectroscopy. The samples showed fast electron transport and typical semiconductor behavior. Use of SnO2 as ETL could be a promising way to obtain more efficient and stable perovskite solar cells.

For semiconducting oxides, recent advantages that allowed conducting synthesis to yield materials with the constituent domains in the nano-range, proved beneficial in terms both of greater surface and pore exposure. Among such nanomaterials, materials used for sensing attracted much attention. In this research we derived nanosized ceria powders by a simple hydrothermal method, prepared intermediate slurries and then tape casted them onto conducting glass substrates, to derive planar thin-films with range of thicknesses. The thin-films were thoroughly characterized: structurally (powder and grazing incidence X-ray diffraction), morphologically (scanning electron microscopy and atomic force microscopy) and electrically (solid state impedance spectroscopy) in a wide range of temperature, frequency and humidity. Depth profiling points to monophasic crystalline ceria in form of slightly agglomerated spherical particles and low-roughness thin-films. Interestingly, the electrical measurements were performed employing surface geometry and cross-section geometry. From the dielectric spectroscopy results we elucidated the influence of the composition and film thickness on the electrical properties and derivatively the humidity sensing performance of the samples. Overall the relative humidity increase lead to a shift to higher conductivity, with gradual relaxation of the films. Thus proving the sensitivity and reversibility of the ceria thin films as humidity sensors.

Modern solid-state solar cells are multi-layered composites ; such configuration allows immense area for upgrades but not without struggle. As the main problem of all modern photovoltaic devices we find the mutual dependence of layers, i.e. the difficulty to predict the exact behaviour due to complex transport mechanisms at the boundaries between thin-film interfaced to other layers. Among such constituents, we find transparent electrodes or transparent conducting oxide layers (TCO), primarily aluminium doped zincite (AZO). AZO is a system thought to be well known, yet synthesis and deposition, chemical modifications, nano-morphological and nano-structural organisation parameters are still not unambiguously related to final functionality. For example, it is not clear how nanostructurisation of AZO would affect light trapping and vertical conductivity, while retaining of lateral conductivity for same thickness of films. The questions regarding general compatibility in interfacing of adjacent layers in SC also remain unclear. The benefits of AZO are thermal stability and mild deposition conditions. We follow these benefits and here we show evaluation of various softer chemical deposition methods for preparing AZO in planar configuration, as well as nanostructured, vertically aligned AZNR films that will retain conductivity, transparency and layer interconnectivity. The successfulness of the synthesis method was checked by means of GIXRD, FTIR-ATR and SEM/EDS. PL/DRS-UV-VIS and DLTS monitored compositional parameters behind transparency as well as lateral and perpendicular conductivity. In addition, parameters from profilometry, contact angle and TEM/EELS analysis shed more light on what synthesis seem to be more favourable for specific property. The utilisation of the observed parameters and behaviour was discussed from the point of view of TCO and CTO performing solar cell layers. The concept of developed material may shift the strategies of the solar cell design. This investigation of AZNR may cause the reconsideration of the paradigm of solar cell assembly since the AZNR additionally show conceptual similarities with charge transfer oxide (CTO) layers.

Modern optoelectronic devices such as photovoltaics repose on having a transparent conducting oxide (TCO) layer as a transparent electrode where aluminium doped zincite (AZO) is often used [1]. AZO has attracted a great attention in many applications because of its nontoxicity, abundancy and affordability better than other TCO materials such as indium tin oxide (ITO) [2]. Even though AZO is a well-known material, its chemical modifications in the course of the synthesis and deposition, along with thereof derived morphology and structural parameters are still not offer straight-forward relations with final functionality. This study offers a comparison of various chemical deposition methods suitable for preparing aluminium doped zincite in two configurations: planar thin-films and nanostructured vertically aligned thin-films. Derived transparent electrodes are structurally characterised by FTIR, Raman, and SEM. More important, the electrical properties are studied employing temperature resolved impedance spectroscopy (IS) in a wide frequency (0.04 Hz – 106 Hz) and temperature (303 K – 513 K) range. IS characterisation attempted to clarify the extent of influence of preparation process, along with nano-structuring of the oxide layer and achieving thin-films, on the electrical transport properties in this type of material. Calculations enabled insights into the dynamics of electrical transport, which was further correlated with structural characteristics of obtained thin-films. The possibility to further tune the applicability of these materials was discussed. Consequently, the results show that electrical conductivity is strongly affected by the choice of the synthesis method.