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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.