Abstracts Category : Other

First-Principles Study of Inorganic Double Perovskites for the Application of Solar Cells and Fuel Cells :

by Shuai Zhao

Recently, perovskite materials have attracted much attention in the application of renewable energy. For instance, the hybrid of inorganic?organic lead halide perovskite has been regarded as the most promising light?harvesting material for next generation solar cells. On the other hand, the transition metal (TM) oxide perovskites have also been studied extensively as electrodes of fuel cells and lithium?air batteries. Several issues are needed to solve, such as the lead pollution of PSCs and the high working temperature of SOFCs to realize the commercialization of perovskite solar cells (PSCs) and solid oxide fuel cells (SOFCs). Therefore, this thesis focuses on the theoretical studies of a series of inorganic double perovskites as the PSCs absorbers and the SOFCs electrodes. In chapter 1, the structural and electronic properties of perovskite materials are briefly introduced. The working principles of PSCs and SOFCs are described. The previous theoretical studies are also reviewed. In the end of this chapter, the motivation of this thesis is presented. In chapter 2, the theoretical backgrounds and simulation approach are briefly summarized, including the density functional theory (DFT), on?site coulomb potential correction method, optical calculation method, and climbing?image nudged elastic band method. In chapter 3, the electronic and optical properties of the double halide perovskites Cs2NaBX6 (B = Sb, Bi; X = Cl, Br, I) are studied to evaluate the potential application of solar energy conversion. The calculated results revealed that the inorganic double iodide perovskites, Cs2NaSbI6 and Cs2NaBiI6, have suitable bandgaps of 1.65 eV and 1.68 eV, suggesting the potential application as the visible?light absorber of perovskite solar cells. In chapter 4, the electronic and optical properties of Mo?based double oxide perovskites Sr2BMoO6 (B = Mg, Ca, and Zn) are studied by first?principles calculations. The electronic band structures demonstrate that these double perovskites are semiconductor. The alkaline metals (Mg and Ca) doped double perovskites have direct bandgaps, while the Zn?doped double perovskite exhibits the indirect bandgap. B?site substation significantly influence the electronic and optical properties of perovskites, which can be a useful approach to design novel absorbers of perovskite solar cells. 3 In chapter 5, the Mo?based double oxide perovskites Sr2BMoO6 (B = Mg, Cr, Co and Ni) are studied with the primary focus on the mixed ionic and electronic conductivity. The effects of substituted elements on the vacancy formation and migration are analyzed from the calculated ground states energy. Co?substituted double perovskite is predicted to possess the best oxygen ionic conductivity among these Mo?based double perovskites. According to the calculated charge density, the substituted cations (e.g., Mg2+, Cr3+, Co2+, and Ni2+) accommodate the additional electrons released from oxygen vacancy, which plays an important role in the oxygen ionic conductivity in these double oxide perovskites. In chapter 6,Advisors/Committee Members: , .