Various impacts of firing temperature on crystalline silicon

The firing step in the manufacturing process of a solar cell is decisive for various parameters. For example, hydrogen from the passivation layers is introduced to the interfaces and into the sample. This serves to passivate defects and thus leads to an increase in the lifetime of the charge carriers. Conversely, higher firing temperatures result in stronger light- and elevated temperature-induced degradation (LeTID) and can introduce more impurities. In addition, contact formation occurs during firing. Therefore, the ideal firing temperature is a difficult to find optimum with various dependencies. In this work, we varied firing peak set temperatures between 650 degrees C and 950 degrees C. In dependence of the firing temperature, we studied the initial lifetime and iron concentration in float zone (FZ) and Czochralski (Cz) grown silicon wafers with and without phosphorus gettering and with aluminum oxide (AlOx) and hydrogen-rich silicon nitride (SiNx:H) passivation. With atomic layer deposited (ALD) AlOx passivation the initial lifetime is decreasing with higher firing temperatures, and interstitial iron concentration ([Fe-i]) is rising to a saturation in the range of 10(11) cm(-3) at around 800 degrees C. In contrast, SiNx:H passivation results in highest lifetimes at around 800 degrees C. Regarding LeTID, the results for SiNx:H passivated samples are in good agreement to literature and an increase in maximum degradation is observed with higher firing temperatures. However, with low hydrogen-containing ALD AlOx it is more complicated. For Cz material with ALD AlOx no clear correlation between firing temperature and extent of degradation could be found. Therefore, finding an optimum firing temperature remains a challenge for each material and passivation-layer-stack.