Effect of heat treatment of spin-cast solar silicon sheet on crystalline defects

Silicon sheets were fabricated via spin-casting, which is a ribbon manufacturing method for photovoltaics. Although the advantages of spin-casting include rapid processing and mass production with no silicon loss, crystalline defects such as random grain boundaries (GBs), sub-GBs, or dislocations are generated from rapid solidification. These defects are an important factor in the decreased conversion efficiency of solar cells. Spin-cast sheets were annealed at 950 °C, 1200 °C, and 1350 °C for 2 h to eliminate defects and to increase the grain size. The effect of thermal processing on the sheets was analyzed by comparing them with as-cast sheets and investigated by electron backscattered diffraction, photoluminescence, and etch-pit density. It was confirmed that sub-GBs were almost completely assimilated with neighboring grains with the 1350 °C heat treatment. Suppression of dislocations was observed through the decrease in the D-band peak with low-temperature photoluminescence (PL, 10 K), and few dislocation clusters were observed from the Secco-etched sheet annealed at 1350 °C.