Loading...
5 results
Search Results
Now showing 1 - 5 of 5
- Sub-Bandgap Sensitization of Perovskite Semiconductors via Colloidal Quantum Dots IncorporationPublication . Ribeiro, Guilherme; Ferreira, G.; Menda, U.D.; Alexandre, Miguel; Brites, Maria João; Barreiros, M. Alexandra; Jana, S.; Águas, Hugo; Martins, Rodrigo; Fernandes, P.A.; Salomé, P.M.P.; Mendes, M.J.ABSTRACT: By taking advantage of the outstanding intrinsic optoelectronic properties of perovskite-based photovoltaic materials, together with the strong near-infrared (NIR) absorption and electronic confinement in PbS quantum dots (QDs), sub-bandgap photocurrent generation is possible, opening the way for solar cell efficiencies surpassing the classical limits. The present study shows an effective methodology for the inclusion of high densities of colloidal PbS QDs in a MAPbI3 (methylammonium lead iodide) perovskite matrix as a means to enhance the spectral window of photon absorption of the perovskite host film and allow photocurrent production below its bandgap. The QDs were introduced in the perovskite matrix in different sizes and concentrations to study the formation of quantum-confined levels within the host bandgap and the potential formation of a delocalized intermediate mini-band (IB). Pronounced sub-bandgap (in NIR) absorption was optically confirmed with the introduction of QDs in the perovskite. The consequent photocurrent generation was demonstrated via photoconductivity measurements, which indicated IB establishment in the films. Despite verifying the reduced crystallinity of the MAPbI3 matrix with a higher concentration and size of the embedded QDs, the nanostructured films showed pronounced enhancement (above 10-fold) in NIR absorption and consequent photocurrent generation at photon energies below the perovskite bandgap.
- Copper-Arsenic-Sulfide Thin-Films from Local Raw Materials Deposited via RF Co-Sputtering for PhotovoltaicsPublication . Centeno, Pedro; Alexandre, Miguel; Neves, Filipe; Fortunato, Elvira; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel JoaoABSTRACT: he inexorable increase of energy demand and the efficiency bottleneck of monocrystalline silicon solar cell technology is promoting the research and development of alternative photovoltaic materials. Copper-arsenic-sulfide (CAS) compounds are still rather unexplored in the literature, yet they have been regarded as promising candidates for use as p-type absorber in solar cells, owing to their broad raw material availability, suitable bandgap and high absorption coefficient. Here, a comprehensive study is presented on the structural and optoelectronic properties of CAS thin-films deposited via radio-frequency magnetron co-sputtering, using a commercial Cu target together with a Cu-As-S target with material obtained from local resources, specifically from mines in the Portuguese region of the Iberian Pyrite Belt. Raman and X-ray diffraction analysis confirm that the use of two targets results in films with pronounced stoichiometry gradients, suggesting a transition from amorphous CAS compounds to crystalline djurleite (Cu31S16), with the increasing proximity to the Cu target. Resistivity values from 4.7 m ohm center dot cm to 17.4 ohm center dot cm are obtained, being the lowest resistive films, those with pronounced sub-bandgap free-carrier absorption. The bandgap values range from 2.20 to 2.65 eV, indicating promising application as wide-bandgap semiconductors in third-generation (e.g., multi-junction) photovoltaic devices.
- Mortars from the Palace of Knossos in Crete, Greece: A Multi-Analytical ApproachPublication . Carvalho, Fernanda; Sousa, Pedro; Leal, Nuno; Simão, J.; Kavoulaki, Elissavet; Lima, M.M.R.A.; Silva, Teresa; Águas, Hugo; Padeletti, GiuseppinaABSTRACT: The study of building materials constituting cultural heritage is fundamental to understand their characteristics and predict their behavior. When considering materials from archaeological sites, their characterization can provide not only relevant information for a broader understanding of the site and its importance and significance but can also increase knowledge about ancient materials and their performance. The Palace of Knossos is a very important archaeological site in the European history context, and its preservation benefits from the characterization of the constituent materials. Samples of mortars from this monument were collected under the scope of the H2020 HERACLES project, where a multi-analytical approach was chosen using established protocols for the different sample typologies. Instrumental techniques such as optical microscopy (OM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and simultaneous thermogravimetry and differential thermal analysis (TG-DTA) were used for the chemical, mineralogical, and morphological characterization of these mortar samples. The results indicate that the majority are lime mortars, both aerial and hydraulic, but gypsum-based mortars were also identified. Differences in the chemical composition of the samples in distinct areas of the monument allowed us to reflect on the variety of materials used in the construction of the Palace of Knossos.
- Bedding mortars from medieval ceramic flooring from the Alcobaça Monastery in PortugalPublication . Carvalho, Fernanda; Nunes, A.; Pagará, A.; Costeira, I.; Silva, Teresa; Leal, Nuno; Simão, J.; Galhano, Carlos; Águas, Hugo; Lima, M.M.R.A.; Veiga, JPABSTRACT: Bedding mortars are fundamental materials to ensure the stability of titles, especially in the case of flooring which withstand the impact of people circulation. In a church, the quality of mortars, tiles pieces and their maintenance over time can be decisive for pavement durability. Inside the church of Santa Maria de Alcobaça Monastery, stone slabs are currently the main and the most applied type of paving in terms of covered area.
- LocalEnergy: Local Resources for Multifunctional Tetrahedrite-based Energy: Harvesting ApplicationsPublication . Neves, Filipe; Correia, J.B.; Esperto, Luís; Mascarenhas, João; Figueira, Isabel; de Oliveira, Daniel Pipa Soares; Salgueiro, Rute; Silva, Teresa; Santos, Beatriz; Lopes, E.B.; Gonçalves, António Pereira; Centeno, Pedro; Fortunato, Elvira; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel Joao