Dunham, Scott TGehrke, Aaron2024-10-162024-10-162024-10-162024Gehrke_washington_0250E_27383.pdfhttps://hdl.handle.net/1773/52556Thesis (Ph.D.)--University of Washington, 2024To improve the performance of Cu(In,Ga)Se2 and Cd(Se,Te) thin-film photovoltaic devices, a robust understanding of the alloy species is needed. The presence of alloying introduces unique challenges, as multiple species are randomly dispersed on the same lattice sites in the material. To optimize device performance, it is necessary to understand and control the precise arrangement of these alloy species. First, it is necessary to understand the energetic interactions between the alloy species and the other species (and defects) in the system, as these interactions determine the types of ordering expected. Second, it is necessary to understand the diffusivity of the alloy species, as it is needed to predict the actual kinetically-limited structures that form under different processing conditions. Third, it is necessary to understand how the alloy arrangement affects the behavior of other critical defects in the material, as this can impact phenomena such as dopant activation. Multi-scale modeling, where results from ab initio calculations (such as those from density functional theory) are fed into higher-level models (such as kinetic lattice Monte Carlo and continuum simulations), is well-suited for exploring the behavior of alloys considered here. In this work, we predict the diffusion under varying conditions of In and Ga in Cu(In,Ga)Se2 and of the intrinsic defects in Cd(Se,Te). We develop a nearest-neighbor interaction model to predict In/Ga ordering in Cu(In,Ga)Se2 alloys, finding a positive correlation between the Ga concentration and the presence of vacancies on the Cu-sublattice. We use this model to predict the band gap fluctuations resulting from these composition variations under a range of different processing conditions, producing results that agree well with experiment. We demonstrate a mechanism to passivate detrimental CuIn defects in Cu(In,Ga)Se2. We conduct a detailed analysis of the effects of Se/Te ordering in Cd(Se,Te) on the formation of detrimental AX center compensating defects, and investigate possible mitigation methods. Lastly, we present work done in conjunction with the UW MEM-C program on (101 ̅0) surface reconstructions in ZnO.application/pdfen-USnoneMaterials ScienceComputational chemistryMaterials science and engineeringThesis