INVESTIGATION INTO HIGH TEMPERATURE POST-ANNEALING OF ZNO:AL AS A PROSPECTIVE TRANSPARENT CONDUCTIVE OXIDE WINDOW LAYER FOR SUPERSTRATE SILICON NANOSTRUCTURE SOLAR CELLS

摘要

Aluminium doped zinc oxide (ZnO:Al) thin-films prepared by both radio frequency sputtering and sol-gel spin coating were annealed under temperatures up to 1100 °C. The study investigated the basic structural, electrical and optical properties of the transparent conducting oxide (TCO) ZnO:Al at various annealing temperatures and gases. This experiment revealed that RF sputtered ZnO:Al TCO films maintain their high optical transmission properties and high crystalline structure after post-annealing even at temperatures up to 1000 °C. However resistivity increases after annealing above 400 °C. The sol-gel ZnO:Al samples in this experiment on the other hand have the lowest resistivity when post-annealed to 1000 °C. The experimental tools used to characterize the material properties include: ellipsometry, X-ray diffraction, X-ray photoelectron spectroscopy, four point-probe, spectrophotometry for reflection and transmission, Hall measurements, scanning electron microscopy and atomic force microscopy. This particular material may potentially be used as a hetero-junction or TCO window layer for thin-film solar cells such as silicon nanostructure solar cells or polycrystalline solar cells as high temperatures are usually required in the crystallization of these types of solar cells.