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CIES2020 - XVII Congresso Ibérico e XIII Congresso Ibero-americano de Energia Solar RESUMO: Este trabalho descreve as principais linhas de investigação que estão em curso no âmbito do projeto LocalEnergy (http://localenergy.lneg.pt). LocalEnergy é um projeto multidisciplinar de Investigação, Desenvolvimento e Inovação (I&D&I), envolvendo atividades no domínio da ciência dos materiais, da geologia e das energias renováveis. Essas atividades estão orientadas para a indústria e assentam numa abordagem disruptiva visando o desenvolvimento de materiais termoelétricos, através da utilização de materiais à base de tetraedrites naturais e sintéticas, e o desenvolvimento de novos absorsores para células solares de filmes finos, usando materiais à base de tetraedrites sintéticas. Considerando que Portugal é um dos países europeus com maior nível de irradiação de energia solar e que a tetraedrite é um recurso mineral local, presente na Zona Sul Portuguesa da Faixa Piritosa Ibérica, o projeto LocalEnergy representa uma oportunidade para o desenvolvimento de sistemas energéticos sustentáveis baseados na maximização e exploração de dois importantes recursos endógenos (energia solar e recursos minerais). ABSTRACT: This work describes the main lines of investigation that are underway within LocalEnergy project (http://localenergy.lneg.pt). LocalEnergy is a multidisciplinary Research, Development and Innovation project, involving activities in the field of materials science, geology and renewable energies. These activities are oriented towards the industry and are based on a disruptive approach aimed at the development of thermoelectric materials, through the use of materials based on natural and synthetic tetrahedrites, and the development of new absorbers for thin film solar cells, using materials based on synthetic tetrahedrites. Considering that Portugal is one of the European countries with the highest level of irradiation of solar energy and that tetrahedrite is a local mineral resource, present in the Portuguese zone of the Iberian Pyrite Belt, LocalEnergy project represents an opportunity for the development of sustainable energy systems based on the maximization and exploration of two important endogenous resources (solar energy and mineral resources). info:eu-repo/semantics/publishedVersion

Physical review materials 2(7), 075404 (2018). doi:10.1103/PhysRevMaterials.2.075404, The copper zinc tin sulfide (CZTS) compound is a promising candidate as an alternative absorber materialfor thin-film solar cells. In this study, we investigate the direct formation of Cu1.92ZnSnx (Sb1−x )S4 compounds[CZT(A)S], with x = 1, 0.85, 0.70, and 0.50, via a mechanochemical synthesis (MCS) approach, starting frompowders of the corresponding metals, zinc sulfide, and sulfur. The thermal stability of theCZT(A)S compoundswasevaluated in detail by in situ synchrotron high-energy x-ray diffraction measurements up to 700 °C. The CZT(A)Scompounds prepared viaMCS revealed a sphalerite-type crystal structure with strong structural stability over thestudied temperature range. The contribution of the MCS to the formation of such a structure at room temperatureis analyzed in detail. Additionally, this study provides insights into the MCS of CZTS-based compounds: thepossibility of a large-scale substitution of Sn by Sb and the production of single phase CZT(A)S with a Cu-poor/Zn-poor composition. A slight increase in the band gap from 1.45 to 1.49–1.51 eV was observed with theincorporation of Sb, indicating that these novel compounds can be further explored for thin-film solar cells., Published by APS, College Park, MD

The copper zinc tin sulfide (CZTS) compound is a promising candidate as an alternative absorber material for thin-film solar cells. In this study, we investigate the direct formation of Cu1.92ZnSnx(Sb1-x)S-4 compounds [CZT(A)S], with x = 1, 0.85, 0.70, and 0.50, via a mechanochemical synthesis (MCS) approach, starting from powders of the corresponding metals, zinc sulfide, and sulfur. The thermal stability of the CZT(A)S compounds was evaluated in detail by in situ synchrotron high-energy x-ray diffraction measurements up to 700 degrees C. The CZT(A)S compounds prepared via MCS revealed a sphalerite-type crystal structure with strong structural stability over the studied temperature range. The contribution of the MCS to the formation of such a structure at room temperature is analyzed in detail. Additionally, this study provides insights into the MCS of CZTS-based compounds: the possibility of a large-scale substitution of Sn by Sb and the production of single phase CZT(A)S with a Cupoor/Zn-poor composition. A slight increase in the band gap from 1.45 to 1.49-1.51 eV was observed with the incorporation of Sb, indicating that these novel compounds can be further explored for thin-film solar cells. info:eu-repo/semantics/publishedVersion

The metal (Ni) contamination on crystallized silicon obtained by metal induced crystallizaion (MIC) was estimated by Spectroscopic Ellipsometry (SE) using a new simulation approach. The method employs the addition of Ni as reference for a Bruggeman Effektive Medium Approximation (BEMA) to simulate the optical response of the crystallized silicon. Samples with different initial metal/silicon ratios were annealed and crystallized. Besides determining thickness, surface roughness and crystalline fraction, this new approach using SE has shown to be sensible to changes on the initial metal thickness used on the crystallization process being able of determining in a quick and non destructive way the Ni concentration inside MIC poly-Si films. The effectiveness of the obtained results was confirmed by RBS. An accurate determination of the initial Ni thickness that is deposited onto the amorphous silicon prior to crystallization is not possible using a quartz oscillator due to the very low quantity of evaporated materials. A better relation between defferent metal amounts present inside the crystallized films can be obtained by integratingthe Ni distribution in the RBS spectra. The obtained values are proportional to the Ni volume fraction determined by SE ellipsometry proves to be sensible to a metal volume fraction as low as 0.24%, corresponding to an initial Ni average thickness of 0.05 nm.

SFRH/BD/131836/2017 SFRH/BD/122286/2016 PD/BD/105876/2014 The current trend for smart, self-sustainable, and multifunctional technology demands for the development of energy harvesters based on widely available and environmentally friendly materials. In this context, ZnSnO3 nanostructures show promising potential because of their high polarization, which can be explored in piezoelectric devices. Nevertheless, a pure phase of ZnSnO3 is hard to achieve because of its metastability, and obtaining it in the form of nanowires is even more challenging. Although some groups have already reported the mixing of ZnSnO3 nanostructures with polydimethylsiloxane (PDMS) to produce a nanogenerator, the resultant polymeric film is usually flat and does not take advantage of an enhanced piezoelectric contribution achieved through its microstructuration. Herein, a microstructured composite of nanowires synthesized by a seed-layer free hydrothermal route mixed with PDMS (ZnSnO3@PDMS) is proposed to produce nanogenerators. PFM measurements show a clear enhancement of d33 for single ZnSnO3 versus ZnO nanowires (23 ± 4 pm/V vs 9 ± 2 pm/V). The microstructuration introduced herein results in an enhancement of the piezoelectric effect of the ZnSnO3 nanowires, enabling nanogenerators with an output voltage, current, and instantaneous power density of 120 V, 13 μA, and 230 μW·cm-2, respectively. Even using an active area smaller than 1 cm2, the performance of this nanogenerator enables lighting up multiple LEDs and other small electronic devices, thus proving great potential for wearables and portable electronics. publishersversion published