The Use of Nanostructured Calcium Silicate in Solar Cells
Nanostructured calcium silicate (NCaSil) had previously been found to be photoactive and mildly semiconducting. Its use in solar cells was investigated in this project. Many different types of solar cells exist. Most common on the market are silicon-based cells, which generate charge separation through electric fields at p/n junctions. Over the last decade, dye-sensitised solar cells (DSSCs) have been heavily researched. DSSCs depend on effective electron/hole separation at the dye and efficient transfer to the electron- and hole-conducting materials. An older and little-researched form of cells is the photogalvanic cell, of which there are two forms. One contains a semiconducting material, whereas the other comprises of either one or two redox couples, in which at least one species is photoactive. An example of the latter form of cell is the odide/triiodide redox couple, which is commonly the electrolyte of choice in DSSCs and semiconductor-containing photogalvanic cells. This project predominantly investigated the use of NCaSil in conjunction with the iodide/triiodide redox couple and its use in solar cells. The project ascertained that, when used with the iodide/triiodide, the NCaSil did not act as a semiconducting material (either as in a DSSC or semiconductor photogalvanic cell). Rather iodide/triiodide's photogalvanic process dominated the cell, despite the presence of NCaSil. Furthermore, the addition of the stable NCaSils to the iodide/triiodide (with 5 wt% CaCl2) created "soggy sand electrolytes". These electrolytes showed increased conductivities, despite their higher viscosities, due to a synergistic effect. Soggy sand electrolytes show great promise in the development of more solid-like DSSCs. Furthermore, the project observed that the performance of NCaSil cells was maximized with a 70 wt% ethanol (30 wt% water) solvated electrolyte, with 1.5 wt% CaCl2 added to this electrolyte (or 5 wt % CaCl2 in the water content). When used long-term in conjunction with Reinforced NCaSil, a gel was formed, which showed promising activity. This activity was attributed to the interaction of surface-bound Ca2+ to iodine. Similar gels formed from vanadium- and cerium-treated NCaSil also showed great cell performance. Cell performance was further enhanced by backing the cell with a reflective or light scattering material, such as Teflon tape.