Investigation of light-induced degradation in N-Type silicon heterojunction solar cells during illuminated annealing at elevated temperatures

In this paper, we study a light-induced degradation (LID) mechanism observed in commercial n-type silicon heterojunction (SHJ) solar cells at elevated temperatures using dark- and illuminated annealing for a broad range of illumination intensities (1-40 kWm(-2)) at temperatures from 25 to 180 degrees C. Three key results are identified. Firstly, an increase in solar conversion efficiency (eta) of up to 0.3% absolute is observed after 3 min of dark annealing at 160 degrees C, attributed to improved surface passivation and a reduction in series resistance. Secondly, a temperature-dependent light-induced degradation behaviour is observed at temperatures as low as 85 degrees C under 1-sun equivalent illumination, with increasing degradation extent and rate for increasing temperatures. At 160 degrees C, an average eta loss of 0.5 + 0.3% absolute is observed after only 5 min and exceeding 0.8% in some cells. Thirdly, a subsequent light intensity-dependent recovery occurs with continued illumination exposure. Under 1-sun illumination at 160 degrees C, a reduction in net eta loss up to 0.05 +/- 0.1% absolute is observed after 2 h. Increasing the illumination intensity to 40 kWm(-2) accelerates the recovery and can result in a net eta improvement of 0.2% absolute at 150 degrees C within 100 s. The results suggest that attempts to improve the efficiency of SHJ solar cells using illuminated annealing could be detrimental to cell performance if not carefully optimised. Further investigation is required to identify the exact nature of the underlying defect mechanism(s) and develop appropriate mitigation strategies on commercially suitable timescales.