Thin-film processing
Thin-film processing represents a natural extension of our expertise in wet-chemistry synthesis and colloidal materials. Functional compounds obtained through the different synthetic strategies developed within the group can be further processed into thin films, enabling their integration into architectures relevant for practical applications.
Alongside more established deposition approaches such as spin-coating and dip-coating, particular attention is devoted to spray-coating techniques, which allow the preparation of uniform coatings with controlled thickness and morphology over large areas and on different substrates (https://doi.org/10.1021/la4010246). The availability of dedicated instrumentation in our laboratory enables the controlled deposition of solution-processed materials into functional thin films, providing a versatile platform to translate chemically engineered materials into photoactive systems.
Figure 1. Ultrasonic spray-coating system (ND-SP Ultrasonic Spray Coater, Nadetech Innovations, Spain) used in our laboratory for the controlled deposition of solution-processed materials into uniform thin films suitable for device integration
The spray-coating setup available in our laboratory allows deposition under controlled environmental conditions, including regulation of relative humidity and nitrogen atmosphere, together with precise control of the substrate temperature through a heated stage (up to 250 °C). These capabilities provide a flexible platform for the development and optimization of thin films for different applications.
Within the group, these strategies are currently being developed in two main research directions: perovskite solar cells and photoelectrochemical and photocatalytic applications.
Perovskite solar cells
Metal halide perovskites represent one of the most promising classes of materials for next-generation photovoltaic technologies, thanks to their excellent optoelectronic properties and compatibility with solution-based processing (https://doi.org/10.1021/acsaem.3c01274https://doi.org/10.1002/aenm.202100698, https://doi.org/10.1063/5.0161023, https://doi.org/10.1002/cssc.202201590) . Within our group, thin films of a wide range of halide-based perovskites are prepared starting from solution-processed precursors through spray-coating approaches. The main perovskite compositions currently investigated include:
• Cs₃Sb₂I₉₋ₓClₓ
• Cs₃(Sb,Bi)₂I₉
• CsMAFA–Sb,Bi–ICl (MA = methylammonium chloride, FA = formamidinium iodide)
Through the optimization of deposition parameters — including solvent composition, precursor concentration, deposition temperature and stage movement — this approach enables the formation of perovskite layers exhibiting a preferential out-of-plane crystallographic orientation, which is particularly favorable for optoelectronic applications(https://doi.org/10.1021/jacs.8b13104).
Figure 2. Morphological and structural characterization of spray-coated halide perovskite thin films. SEM images reveal the surface morphology of the deposited layers (A-D), while X-ray diffraction (XRD) and grazing-incidence wide-angle X-ray scattering (GIWAXS) patterns (E-G) confirm the crystalline structure and preferential out-of-plane orientation of the perovskite films.
Photoelectrochemistry and photocatalysis
Photoelectrochemistry
Within our group, we focus on the development of thin-film photoelectrodes that integrate nanostructured and solution-processed semiconductors into functional architectures. By carefully controlling film morphology and interfacial properties, we aim to optimize charge transport and light-driven reactivity, which are essential for efficient and stable PEC devices.
Our expertise includes the preparation of semiconductor thin films from a range of materials, including Cu₂O, CuWO₄, and other metal oxide systems, using spray-coating techniques starting from colloidal or laser-ablated precursors. These materials have been explored for specific photoelectrochemical (PEC) roles, with Cu₂O serving as a photocathode for hydrogen evolution reaction (HER) and Fe-modified CuWO₄ as a photoanode for oxygen evolution reaction (OER). The approach enables deposition on both rigid and flexible substrates, such as PET–ITO, providing a versatile platform for the development of PEC devices for solar-to-chemical energy conversion and other photoactive applications.
Figure 3. Characterization of thin-film photoelectrodes produced via spray-coating techniques. (a-d) SEM cross-section of a Cu₂O film showing different layer composition (figure from: https://doi.org/10.1002/adsu.202200397). (e) Chopped chronoamperometry profile of a CuWO₄ photoelectrode, highlighting reproducible photocurrent generation under intermittent illumination (figure from: https://doi.org/10.1002/admi.202500610). (f-g) Spray-coated films on flexible PET–ITO substrates, demonstrating the compatibility of our deposition approach with flexible device platforms (figure from: small structures).
Thin‑film photoelectrodes produced through our controlled spray‑coating approaches can be characterized using a range of complementary techniques that provide insight into their photoelectrochemical behavior. SEM cross-sections (a–d) reveal uniform morphology and thickness of the deposited films, as well as the different composition of layers, while chopped chronoamperometry profiles (e) highlight stable photocurrent generation under intermittent illumination. Images of spray‑deposited films on flexible conductive substrates (f–g) demonstrate the compatibility of our approach with device-oriented processing. Some of these characterization measurements are carried out in collaboration with other groups within the department, leveraging complementary expertise and instrumentation to fully explore the structural and photoelectrochemical properties of our thin-film systems.
Photocatalysis
Photocatalysis provides a sustainable approach for the conversion of renewable or waste-derived feedstocks into value-added chemicals using light-driven redox processes. Within our group, we focus on the design and preparation of nanostructured photocatalysts that combine tailored composition, morphology, and surface properties to maximize light absorption and catalytic activity.
Current efforts involve the development of Fe@CuWO₄ nanoparticles as heterogeneous photocatalysts for the valorization of biomass-derived molecules such as glycerol. These nanomaterials are capable of generating reactive oxygen species (ROS) in solution upon illumination, driving selective oxidation reactions. By exploiting these properties, we aim to establish versatile photocatalytic platforms for the sustainable transformation of waste or low-value substrates into useful chemical products, illustrating the potential of combining advanced material design with light-driven chemistry in green and circular chemistry.
Figure 4. Photocatalytic degradation of methylene blue (MB) by Fe@CuWO₄ nanoparticles in suspension (a). (b) Representative EPR signal indicating the formation of reactive oxygen species (ROS) upon light excitation, which contribute to the photocatalytic degradation of MB. (c) Schematic representation of photogenerated chargecarrier pathways under illumination, illustrating the separation of electrons and holes that drive redox processes in solution.