| Description |
The demand for low-cost sources of alternative energies has spurred incredible research efforts in the field of thin film photovoltaics. This dissertation presents results pertaining especially to the composition and microstructure of solution-deposited cadmium telluride (CdTe) and Cu2SnZnS(e)4 (CZTS(e)) polycrystalline thin films. Thin film photovoltaic modules using CdTe absorber layers are commercially established, but opportunities still exist for further cost reduction. In this work, a novel method of aqueous solution deposition of CdTe1-xSx (x≤0.05) thin films is described. The evolution of composition, phases, and microstructure is investigated. The resulting film properties are promising for thin film PV devices as evidenced especially by photoluminescence, which is directly related to minority carrier lifetime. CZTS(e) and related alloys are of interest as sustainable materials for use in thin film photovoltaics since they share similar electronic and crystal structures to the established Cu(In,Ga)Se2, but are comprised of earth-abundant and industrially available elements. However, large open-circuit voltage deficits have limited device efficiency and are thought to be related to large band gap and electrostatic potential fluctuations due to both secondary phase formation as well as large-scale Cu-Zn antisite formation. Using transmission x-ray microscopy tomography, we directly image and quantify the length scales over which elemental fluctuations occur and show evidence of micron-scale Cu to Zn anticorrelations over a previously inaccessible combination of resolution and sample iv size that is consistent with the length scale of grains in this material. These results yield insights into the details of composition, phase, and microstructure, which are closely related to resulting electronic properties, in two important materials for thin film photovoltaics and thus contribute to their understanding. |
