Juan Bautista Carda Castelló

The substrate plays a critical yet often underappreciated role in determining the performance, stability and manufacturability of photovoltaic devices. While conventional glass and polymer films have enabled the rapid development of solar technologies, emerging applications such as building-integrated photovoltaics, wearable systems and large-area conformal devices demand the use of non-conventional substrates, including ceramics, metals, paper, textiles and elastomeric materials. This review provides a comprehensive analysis of the current state of the art of non-conventional substrates for photovoltaic technologies, with particular emphasis on the interplay between material properties, surface chemistry and deposition processes. These substrates introduce distinct mechanical, thermal and interfacial constraints that fundamentally alter thin-film growth, defect formation and device reliability. Key challenges such as porosity, roughness, thermal transport limitations and outgassing are discussed in relation to nucleation, film continuity and interfacial stability. The role of substrate-dependent effects in both chemical and physical deposition techniques is critically examined, highlighting cases where conventional processing approaches are insufficient. Representative device demonstrations are analyzed to illustrate how substrate selection influences performance and integration strategies across different photovoltaic platforms. Finally, common limitations and emerging opportunities are identified, emphasizing the need for the co-design of substrates, materials and processing routes. This work establishes a unified framework to guide the development of next-generation photovoltaic devices on unconventional substrates.

In additive manufacturing technologies, the use of pastes and inks based on materials such as clay to create three-dimensional objects layer by layer has opened new possibilities in fields such as engineering and biomedicine. This review article aims to provide a comprehensive understanding of 3D printing of ceramic pastes through Direct Ink Writing (DIW), also referred to as Robocasting. DIW offers specific advantages for ceramic 3D printing, including the ability to extrude highly loaded pastes with customized rheological properties to accommodate a broad spectrum of ceramic compositions, varying from conventional clays to advanced ceramics. It is characterized by filament deposition control, which facilitates the fabrication of complex, porous, or customized architectures while simultaneously minimizing material waste. Through a bibliometric analysis of the literature published between 2020 and 2024, the most relevant studies regarding printing system architectures, ceramic paste formulations, and adjustment of parameters to obtain high-quality parts were identified. This work presents relevant and accurate explanations of the DIW technology, supporting researchers and industry professionals seeking to initiate or improve ceramic 3D printing processes for a wide range of applications.

The upcoming chapter explores zinc oxide (ZnO) thin films, examining their crystalline and optical properties. It discusses various deposition techniques for creating thin films, defined as layers from nanometers to micrometers thick, used in electronics, optics, and coatings. Thin film deposition methods, crucial for controlling film thickness and properties, include physical vapor deposition (PVD), sputtering, thermal evaporation, electron beam evaporation, and pulsed laser deposition (PLD). These techniques are vital in electronics, optics, and materials research. The chapter also covers ZnO thin films’ applications, emphasizing their photocatalytic abilities. ZnO has a large bandgap energy (3.37 eV), making it effective in UV light absorption and photocatalytic reactions. Upon UV photon absorption, ZnO generates electron-hole pairs, leading to efficient redox processes. ZnO’s chemical stability ensures lasting photocatalytic activity, resisting degradation under harsh conditions. It can be formed into nanostructures like nanoparticles, nanowires, and nanosheets, increasing surface area and catalytic efficiency. ZnO generates reactive oxygen species (ROS) like hydroxyl radicals, superoxide radicals, and hydrogen peroxide during photocatalysis. These ROS degrade organic pollutants, functionalizing substrates to break down fertilizers, pesticides, pharmaceuticals, nitrates, and pollutant gases such as nitrogen oxides and benzene compounds.

This chapter provides a comprehensive review of light-mediated processes in advanced ceramics, emphasizing their role in developing new materials with enhanced properties. The discussion covers photocatalysis for environmental remediation and energy production, ceramic materials in photovoltaic cells for sustainable energy, and the role of ceramics in photonic devices, such as waveguides, lasers, and optical fibers. The analysis also includes ceramic applications in laser technology, focusing on their optical properties, and biocompatible and bioactive ceramic materials in biotechnology for drug delivery, sensors, and theragnosis. Additionally, the chapter examines how light-mediated processes contribute to sustainability and the circular economy by enhancing material properties at the nanoscale and promoting energy-efficient production and recycling methods. The aim is to highlight the transformative potential of light interactions in ceramics, driving advancements in energy efficiency, environmental protection, and medical technology, and inspiring future research and applications in these areas.

In this study, a new red ceramic pigment has been developed within a perovskite structure, and microwave heat treatments have been applied. Those red ceramic pigments within the YAlO₃ system doped with chromium with the nominal composition Y_0.98Al_0.98Cr_0.04O₃ were synthesized by traditional routes and alternative methods like coprecipitation. Also, heat treatment has been studied comparing a traditional electric and microwave kiln. Different flux agents have been incorporated to improve the synthesis reaction. Prepared pigments have been characterized by X-ray diffraction (XRD) as having a predominant phase of perovskite structure, which is responsible for the red shade, and a minority garnet phase that causes more brown colorations. Studies by Ultraviolet-Visible spectroscopy gave rise to a series of absorption bands that indicate the presence of Cr(III) in the octahedral position corresponding to perovskite and Cr(IV) corresponding to garnet in both the octahedral and tetrahedral positions. The perovskite phase is favored with the use of flux mix, corroborating the UV-visible results and being more pronounced in traditional high temperature thermal treatments. The coprecipitation route has been studied to increase the reactivity of the particles given their nanometric size; however, this reactivity favors a greater appearance of undesirable garnet phases with both types of flux. Scanning Electron Microscopy (SEM) micrographs offer information obtained from the secondary electrons of predominantly cubic crystalline phases with sizes between 1 µm and 2 µm in pigments synthesized via the traditional method and sizes less than 1µm together with the glassy phase in pigments synthesized via coprecipitation. Microwave thermal treatments have been studied, obtaining pigments with a majority structure of perovskite and garnet at lower temperatures and relatively short synthesis times. The feasibility of use in porous single-fired ceramic glazes has been studied, whose chromatic coordinates have been collected using an Ultraviolet-Visible Spectrophotometer based on the CIEL*a*b* system.

Because of the increasing demand for photovoltaic energy and the generation of end-of-life photovoltaic waste forecast, the feasibility to produce glass substrates for photovoltaic application by recycling photovoltaic glass waste (PVWG) material was analyzed. PVWG was recovered from photovoltaic house roof panels for developing windows glass substrates; PVWG was used as the main material mixed with other industrial waste materials (wSG). The glass was casted by air quenching, annealed, and polished to obtain transparent substrates samples. Fluorine-doped tin oxide (FTO) was deposited as back contact on the glass substrates by spray pyrolysis. The chemical composition of the glass materials was evaluated by X-ray fluorescence (XRF), the thermal stability was measured by differential thermal analysis (DTA) and the transmittance was determined by UV-VIS spectroscopy. The surface of the glass substrates and the deposited FTO were observed by scanning electron microscopy (SEM), the amorphous or crystalline state of the specimens were determined by X-ray diffraction (XRD) and the sheet resistance was evaluated by the four-point probe method. The sheet resistance of the deposited FTO on the wSG substrate was 7.84 ± 3.11 Ω/□, lower than that deposited on commercial soda-lime glass (8.48 ± 3.67 Ω/□), meaning that this material could present improved conduction of the produced electrons by the photovoltaic effect. This process may represent an alternative to produce glass substrates from waste materials that could be destined for photovoltaic applications, especially the production of ecological photovoltaic windows.

Solid solutions of ceramic pigments of red shade have been synthesized based on YAlO3 perovskite structure doped with chromium by means of conventional synthesis; that is, the “ceramic route”. To optimize this synthesis, an emphasis has been made on the study of stoichiometry, calcination conditions and mineralizer incorporation. Various studies have demonstrated the high stability of perovskite structures, which ensures stable coloration at high temperatures. This is a highly important factor in the ceramic sector, given the scarcity of red glazes functional at temperatures close to those required of porcelain stoneware and their environmental constraints. Such a limitation makes it impossible in the European community to manufacture using toxic materials such as Se and Cd (cadmium sulfoselenide) that offer interesting colors at low temperatures. Pigments have been synthesized within the Y_1−xCr_xAlO₃, YCr_xAl_1−xO₃ and Y_1−xAl_1−yCr_x+yO₃ chromium-doped systems in molar ratios between n = 0.01 molar and n = 0.10 molar. The pigments obtained have been characterized by X-ray diffraction to identify the crystalline phases responsible for the shade; that is, the formation of the perovskite crystalline structure YAlO₃ responsible for the red shade, together with lateral phases of garnet Y₃Al₅O₁₂ of lower intensity. Visible ultraviolet spectrophotometry shows absorption bands corresponding to Cr(III) in octahedral position and the appearance of Cr(IV) in both octahedral and tetrahedral positions. The morphology of the samples was studied using a scanning electron microscope, obtaining information from the secondary and back scattered electrons. The viability of its use in ceramic glazes was verified after applying them mixed at 4% by weight in a glaze to an industrial porous single-firing cycle, collecting the L*a*b* chromatic coordinates using a visible ultraviolet spectrophotometer based on the CIE L*a*b* system, giving rise to red colorations.

In this study, ZnO/Ag nanocomposites were synthesized using a facile chemical route involving metallic precursors of zinc acetate dehydrate and silver acetate, and dissolving the two metallic precursors in EtOH. The final concentration of the solution was 0.4 M. The different nanocomposites were synthesized using different atomic percentages of silver to compare the amount of silver nanoparticles with the bactericidal power of the nanocomposites. They were prepared at concentrations of 0, 1, 3, 5, 7, and 10 at%. The as-prepared nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) to study their structural and morphological properties. SEM showed that there is a clear effect of Ag on the size of the ZnO particles, since when silver percentages of 1 at% are included, the grain size obtained is much smaller than that of the ZnO synthesis. The effect is maintained for 3, 5, 7, and 10 at% silver. Transmission electron microscopy (TEM) compositional mapping confirms the presence of spherical nanoparticles in the synthesized samples. The size of the nanoparticles ranges from about 10 to about 30 nm. In addition, UV-Vis and Raman spectroscopy were performed to obtain structural details. The different samples show an increase in the absorption in the visible range due to the incorporation of the silver NPs. Measurement of the antimicrobial activity was tested against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) It is shown that zinc oxide has bactericidal power for these two groups of bacteria and also that when it is used together with silver NP, this effect improves, eliminating more than 90% of inoculated bacteria.

Doped ZnO are among the most attractive transparent conductive oxides for solar cells because they are relatively cheap, can be textured for light trapping, and readily produced for large-scale coatings. Here, we focus on the development of alternative Na and K-doped ZnO prepared by an easy low-cost spray pyrolysis method for conducting oxide application. To enhance the electrical properties of zinc oxide, alkali-doped Zn_1−x M_xO (x = 0.03) solid solutions were investigated. The resulting layers crystallize in a single hexagonal phase of wurtzite structure with preferred c-axis orientation along a (002) crystal plane. Dense, well attached to the substrate, homogeneous and highly transparent layers were obtained with great optical transmittance higher than 80%. The optical energy band gap of doped ZnO films increase from 3.27 to 3.29 eV by doping with Na and K, respectively. The electrical resistivity of the undoped ZnO could be decreased from 1.03 × 10⁻¹ Ω.cm to 5.64 × 10⁻² Ω.cm (K-doped) and 3.18 × 10⁻² (Na-doped), respectively. Lastly, the carrier concentrations increased from 5.17 × 10¹⁷ (undoped ZnO) to 1 × 10¹⁸ (doped ZnO).

ZnO thin films with oxygen vacancies and doped with Al, Ga, and In (Zn_1-xM_xO_1−y (x = 0.03)) have been successfully deposited on soda-lime glass substrates using a simple soft chemical method. The crystalline structure shows a single hexagonal phase of wurtzite with preferred crystal growth along the 002 plane. The surface morphology, characterized by SEM, revealed that the grain shape varies depending on the dopant agent used. Optical measurements displayed an increase in the bandgap values for doped films from 3.29 for ZnO to 3.35, 3.32, and 3.36 for Al, Ga, and In doped films, respectively, and an average transmittance superior to 90% in some cases (in the range between 400 and 800 nm). The electrical response of the films was evaluated with a four-point probe being 229.69, 385.71, and 146.94 Ω/sq for aluminium, gallium, and indium doped films, respectively.