Edson Laureto

Photo-oxidation remains a challenge for achieving long-term stability in organic electronic devices. Rubrene (Rub), a small-molecule semiconductor known for its exceptional optoelectronic properties, illustrates this problem as its highly sensitive to light and oxygen. In addition, its limited processability, requiring the use of halogen solvents or thermal evaporation for its deposition, further restricts its practical use in large-area processing . This works shows how both problems can be addressed by a colloidal approach where Rub is encapsulated through a miniemulsion method, producing stable, water-dispersible nanoemulsions (NPs). Their emission and absorption properties in the liquid, and solid films, show that nanoencapsulation preserves the intrinsic vibronic fingerprint of Rub, while inducing spectral shifts and emission narrowing, enhancing molecular ordering and stronger intermolecular coupling, quantified by calculating the Huang–Rhys factor. Systematic investigation of photo-oxidation kinetics reveals a modulation effect: in dispersion, Rub NPs oxidize faster than molecular Rub in chloroform, due to enhanced oxygen access from their large surface area, while maintaining colloidal stability. In contrast, NP-based Rub films exhibits significantly improved photostability, preserving over twice the residual absorbance of annealed neat Rub films under 11 W/m2 irradiation. Atomic Force Microscopy and Fourier Transform Infrared Spectroscopy confirm the synergistic role of excess surfactant and nanoencapsulation in Rub oxidation, while thermal annealing fine-tunes film morphology, improving stability and reducing oxygen diffusion pathways. This work establishes nanoemulsion-based confinement as an effective strategy to modulate photo-oxidation in highly reactive organic semiconductors, offering new design rules for environmentally processed, photostable optoelectronic materials and oxygen-sensing platforms.

The use of solar panels for the purpose of converting solar energy into electrical energy has been increasingly common in the community, where the vast majority of these panels are produced from inorganic materials, especially silicon (Si). In recent decades, many researchers have been analyzing organic and hybrid materials in order to apply them to photovoltaic devices. The use of organic and hybrid materials in devices is advantageous due to some factors, such as: low production cost, variety of materials available, production of flexible devices. A fundamental analysis for any photovoltaic device is the external quantum efficiency measure (EQE). This technique correlates the number of incident photons with the number of electrons generated, making it possible to know in which region of the electromagnetic spectrum the photovoltaic device is more efficient. This work aims to apply the external quantum efficiency characterization technique for the evaluation of different types of photovoltaic devices in terms of their stability

Atualmente, fontes de luz polarizada encontram diversas aplicações em dispositivos optoeletrônicos, “displays”, em testes de tensões em peças mecânicas e até em estudos de mineralogia. Uma das principais necessidades é determinar o estado de polarização (linear, circular, elíptico, ou uma sobreposição destes) do feixe luminoso. Para este fim, aplicamos neste trabalho a técnica de Elipsometria de Emissão para investigar os estados de polarização de diferentes fontes de luz. Esta técnica está baseada na teoria de Stokes e os tipos de polarização estão correlacionados aos parâmetros de Stokes. Realizamos medidas em feixes de luz proveniente de um LASER polarizado, um LASER polarizado passando por um defasador quarto de onda a ± 45° (polarização circular), um LED despolarizado e, esse mesmo LED, com sua luz refletida sobre uma placa de vidro em diversos ângulos e inclusive no ângulo de Brewster. A montagem experimental é composta de um defasador quarto de onda, um polarizador linear e um detector de luz. Os resultados obtidos apresentaram um desvio de aproximadamente 1% em relação à polarização conhecida das fontes de luz. Desta maneira, foi possível constatar que a técnica de Elipsometria de Emissão pode ser aplicada para se determinar a polarização da luz proveniente de fontes luminosas em geral.

Recent advances in the production and development of two-dimensional transition metal dichalcogenides (2D TMDs) allow applications of these materials, with a structure similar to that of graphene, in a series of devices as promising technologies for optoelectronic applications. In this work, molybdenum disulfide (MoS₂) nanostructures were grown directly on paper substrates through a microwave-assisted hydrothermal synthesis. The synthesized samples were subjected to morphological, structural, and optical analysis, using techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman. The variation of synthesis parameters, as temperature and synthesis time, allowed the manipulation of these nanostructures during the growth process, with alteration of the metallic (1T) and semiconductor (2H) phases. By using this synthesis method, two-dimensional MoS₂ nanostructures were directly grown on paper substrates. The MoS₂ nanostructures were used as the active layer, to produce low-cost near-infrared photodetectors. The set of results indicates that the interdigital MoS₂ photodetector with the best characteristics (responsivity of 290 mA/W, detectivity of 1.8 × 10⁹ Jones and external quantum efficiency of 37%) was obtained using photoactive MoS2 nanosheets synthesized at 200 °C for 120 min.

Luminescence down-shifting (LDS) is used in several photovoltaic technologies aiming to improve the photon conversion efficiency (PCE) of the devices through the increase of the light harvesting in the regions of the electromagnetic spectrum where the EQE of the solar cells is poor. The aim of this work was to produce films of mixtures (blends) of two luminescent materials, dispersed in a poly-methyl methacrylate (PMMA) matrix, hoping to improve their properties both as LDS layer and as UV filter when applied on the clear, external surface of P3HT:PC ₆₁ BM photovoltaic devices. The best results led to an increment of 7.4% in the PCE of the devices, and a six fold enhancement in their half-life ( T _50% ). This study indicates that multidye LDS layers with optimized optical properties can lead to an effective improvement in the performance and operational stability of OPVs.