The trichalcogenides Sb 2 S 3 , Sb 2 Se 3 , Bi 2 S 3 , and Bi 2 Se 3 share an orthorhombic crystal structure and have recently been pointed out as promising materials for application in solar energy harvesting, such as photovoltaic solar cells, because of their ultimate structural and electronic/optical properties. In this work, using a firstprinciples theoretical approach, we investigated the origin of the electrical conduction in bulk systems as well as the energy band alignment in different heterostructures composed of these compounds. In the first part, formation energy and thermodynamic transition energy of native point defects are evaluated. In the second part, surface properties such as free energy and electron affinity were obtained. In the third part, the energy alignments of some possible heterostructures were proposed. The excellent agreement between theoretical results and reported experimental values indicates that these trichalcogenides have their electrical properties ruled by native point defects, mainly antisites. The energy alignment between the trichalcogenides and usual photovoltaic substrates shows that these materials can be successfully applied to the construction of type-II staggered heterojunctions. A last analysis is done by considering only homo-and heterojunction of trichalcogenides, showing that these materials could lead to high-efficiency cells with broad spectral absorption and high conduction/valence band offsets.

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A metastable phase of Bi2Se3 with orthorhombic structure has been obtained by potentiostatic electrodeposition onto Si(100) substrate. The ideal stoichiometry and single orthorhombic phase could be obtained only within a restricted potential window, where mutual underpotential codeposition is assumed to occur. Optical and electrical characterization indicates a bandgap of 1.25 eV, close to the maximum efficiency in the Shockley-Queisser limit, and n-type semiconducting behavior with moderate electrical resistivity. Theoretical calculations using density functional theory were used to support the structural and optical results. Due to the favorable set of properties with respect to isomorphic compounds such as Bi2S3, Sb2S3 and Sb2Se3 this material could lead to efficient and low-cost new thin film-based photovoltaic devices.

The compound Prussian Blue (PB), and its reduced form Prussian White (PW) are nowadays considered, in applied and fundamental research groups, as potential materials for sustainable energy storage devices. In this work, these compounds were prepared by potentiostatic electrochemical synthesis, by using different deposition voltages and thicknesses. Thick, compact and uniform layers were characterized by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Results have shown a well-defined transition voltage for growing Prussian Blue phases and a strong dependence of the morphology/growing orientation of the samples as a function of applied potential and thickness. For the negative potential tested of −0.10 V vs. SCE, a mixture of cubic and rhombohedral phases was observed.

Self-assembled polyaniline (PANI) nanotubes were prepared in the presence of three different sulfonic acids as dopant, namely, p-toluenesulfonic acid, camphorsulfonic acid, and tetrakis(4-sulfonatophenyl)porphyrin, by oxidative polymerization using ammonium peroxydisulfate as the oxidant. The morphology of the PANI nanotubes was determined by SEM and TEM and the electrical conductivity was measured as a function of temperature. The PANI nanotubes were also characterized by FTIR, XRD, UV-Vis, and cyclic voltammetry. We have found that the dopants had a noteworthy effect on the electrical conductivity whithout significant changes in the morphology of the PANI nanotubes.

Bismuth selenide (Bi 2 Se 3 ) is a semiconductor presenting two distinct crystalline phases with distinct bandgap and interesting optical, thermoelectric and topological electronic properties. In this work, thin films were grown by electrodeposition under constant potential onto silicon (100) substrate. It is shown that under an optimum set of deposition parameters, very smooth and thick films can be obtained. Such smoothness of the samples is highly desirable for future devices applications. Structural characterization of the samples indicates a majority of a metastable orthorhombic phase, while successively traces of rhombohedral and amorphous phases were detected. On the other hand, morphological characterization evidences the formation of compact, uniform and smooth layers. A full recrystallization to the rhombohedral structure can be achieved by using short time and low temperature thermal treatments.

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Experimental and theoretical data support the easy reduction of Au3+ into self-stabilized nanoparticles by citrus flavonoids.