Influence of laser induced sintering on contact performance of TOPCon solar cells

<sec>Laser induced sintering, also known as laser enhanced contact optimization (LECO), can significantly reduce the contact resistance between metal electrodes and silicon in TOPCon solar cells, thereby improving its efficiency. In this work, the effects of LECO process parameters such as reverse bias and laser intensity on the performance of TOPCon solar cells are investigated and their influencing mechanisms are analyzed in detail. In the LECO process, as the reverse bias voltage increases, the efficiency of the solar cell first increases and then decreases, while the contact resistivity first decreases and then increases. When the reverse bias voltage is high, the solar cell may experience reverse breakdown. Once the solar cell experiences reverse breakdown, both the illuminated and non-illuminated areas become conducting. Due to the current diversion effect, the local conducting current density in the illuminated area is much lower than the current density without reverse breakdown of the solar cell, Therefore, the Joule heating caused by this is also much smaller, and the contact resistance between the metal and silicon increases, resulting in a decrease in the efficiency of the solar cell.</sec><sec>Secondly, the influence of secondary high-temperature sintering and secondary LECO on the performance of TOPCon is studied. When the secondary sintering temperature increases from 280 ℃ to 680 ℃, the efficiency of TOPCon sharply decreases from 26.35% to 1.3%. However, by subjecting the solar cells that have undergone secondary high-temperature sintering to secondary LECO treatment, the efficiency can be restored to the level before the secondary high-temperature sintering. Thirdly, TOPCon solar cells prepared using improved pure silver paste does not form effective metal-semiconductor contact between the silver electrode and silicon before LECO treatment, resulting in an average efficiency of only 0.02%. However, after LECO treatment, the efficiency of solar cells using pure silver paste increases to 26.35%, which is 0.41% higher than the reference solar cells using traditional silver aluminum paste. Fourthly, a physical model of LECO induced silver-silicon contact formation is proposed, providing a reasonable explanation for how secondary high-temperature sintering and secondary LECO treatment affect the performance of TOPCon. This is of great significance for further understanding and optimizing the application of LECO technology in TOPCon solar cells.</sec>