Improvement of multi-crystalline silicon wafer quality during solar cell fabrication process

The increased use of low quality multi-crystalline silicon (mc-Si) for photovoltaic applications requires an adaption of the solar cell fabrication processes to that material. In the present work, we demonstrate that slow cooling after a high temperature process can lead to a decrease of the dissolved impurity concentration within the wafer and thus, to an increase of the electron lifetime. A decrease of the interstitial iron concentration of more than 97% has been observed. Correspondingly, a lifetime enhancement of up to 120% in comparison to the initial electron lifetime has been found. Especially low lifetime areas on mc-Si wafers seem to be affected by these temperature treatments. This makes slow cooling a promising tool to engineer the wafer quality during the solar cell fabrication process, especially for very low quality materials.