Efficiency increase of lossy solar cells by laser post-processing and detailed analysis of the current-voltage characteristics

The current-voltage (I-V) characteristics of processed industrial multicrystalline silicon (mc-Si) solar cells usually vary within a narrow range (e.g. +/-1 % abs. efficiency). Nevertheless, occasionally cells with very low efficiencies are produced with loss mechanisms such as local shunts or areas with unusually high recombination. In this paper we investigated industrial mc-Si solar cells with exceptionally low efficiencies in detail by dark and illuminated I-V measurements followed by an analysis based on the two-diode-model to determine the dominant electrical loss mechanisms. Subsequently spatially-resolved lock-in thermography (LIT) measurements were used to localise defect positions in these solar cells. These defects were electrically isolated with a laser. The solar cells were characterised again using the same analysis methods. For shunted cells an efficiency gain of up to 2.4 % absolute was obtained and the shunts disappeared. A detailed investigation of I-V data before and after laser isolation followed by a parameter study based on a two-diode-model is presented.