First-Principles Exploration of the Structural Motifs of Chalcogenides and Their Relationship to Electronic and Photovoltaic Properties

The bulk photovoltaic effect (BPVE) refers to the production of electric currents from the valence band promotion of electrons to the conduction band in a pure, undoped, and insulating material from the absorption of electromagnetic radiation. For a material to be able to create a current in response to non-polarized solar irradiation, it must be a polar compound with a band gap in the visible spectrum, 1.1 - 3.1 eV. The purpose of this work is to provide computational evidence that the pursuit of materials other than pure oxides for use as bulk photovoltaic materials is worthy. To convince the scientific community that compounds containing isoelectronic elements of O, the chalcogens S and Se, should be synthesized and, as importantly, are capable of being synthesized, three distinct subject areas will be presented. The first demonstrates that it is possible to alloy sulfur with an oxide perovskite, lead titanate (PTO), to create thermodynamically stable polar oxysulfides with band gaps in the visible spectrum. In the second, it will be shown that non-oxide non-perovskite materials can generate BPVE responses larger by an order of magnitude over the oxide perovskites listed in the literature to date. The third area does not address solar energy use directly. Instead, it alerts the scientist that creating ABS3 compounds by using temperature and time profiles used to synthesize ABO3 compounds has probably led to an incomplete characterization of these sulfides. As such, it provides first-principles based evidence that synthesis experimentation involving chalcogens does not and should not simply mirror that of pure oxide synthesis. The scientific community's knowledge of chalcogenides is far from complete, opening up exciting possibilities for new material discoveries.