The impact of rapid thermal processing (RTP) on crystalline silicon solar cell performance and light induced degradation (LID)

In this paper the impact of rapid thermal processing (RTP) on AL-BSF crystalline silicon solar cell performance is reported. The efficiency of both mono and multi crystalline cells are observed to depend on the belt speed. The fast ramp rates of ~100°C/s and over with the IR belt furnace has enabled the realization of the benefits of a uniform Al-BSF, which led to open circuit voltage (VOC) of ~643 mV for all the belt speeds. This indicates that, although the ramp up rate depends on belt speed, the absolute value is not critical to yielding good VOC provided it is ~100°C/s. However, the ramp down rate made a difference in the fill factor (FF) and led to the dependence of efficiency on the belt speed. The multi crystalline cells benefited from the short dwell time for optimum bulk hydrogenation and fast ramp down for good front contacts and therefore, the dependence of the minority carrier lifetime on belt speed. Also, LID is observed to depend on belt speed and contact firing. The higher the belt speed the lower the degradation due to LID and the higher the ideality factor, the more severe the degradation. Thus, cells fired at 250 IPM with n-factor of 1.06 showed lower LID after 30 minutes and 24 hours than the commercial cell that had 1.10 n-factor after contact firing.