Eliminating light- and elevated temperature-induced degradation in P-type PERC solar cells by a two-step thermal process

• Published in: Solar energy materials and solar cells Vol. 209; p. 110470
• Main Authors: Sen, Chandany, Chan, Catherine, Hamer, Phillip, Wright, Matthew, Chong, CheeMun, Hallam, Brett, Abbott, Malcolm
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2020; Elsevier BV
• Subjects: Annealing; Belts; Carrier lifetime; Contact resistance; Degradation; Eliminating; Emitters; Heat resistance; High temperature; Light- and elevated temperature-induced degradation (LeTID); Multi-crystalline silicon (mc-Si); Photovoltaic cells; Silicon; Silicon substrates; Solar cells; Two-step thermal process; Two-step thermal process; Contact resistance; Eliminating; Multi-crystalline silicon (mc-Si); Light- and elevated temperature-induced degradation (LeTID)
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2020.110470

Light- and elevated temperature-induced degradation (LeTID) can have a severe impact on the carrier lifetime of silicon substrates used in solar cell production and thus remains a crucial challenge for manufacturers. In this work, we introduce a two-step annealing process to mitigate LeTID in multi-crystalline silicon (mc-Si) passivated emitter and rear cell (PERC) solar cells. We demonstrate that the first annealing step (450 °C) with a slow belt speed (0.5 m/min) plays a primary role in mitigating LeTID in the cells, but also results in an increase in contact resistance. The application of a second annealing step at a similar temperature (400–500 °C) with a faster belt speed (1.4 m/min) recovers the contact resistance whilst maintaining the stability of the cell. Applying this approach to the p-type mc-Si PERC solar cells resulted in a reduction of efficiency loss during light soaking from ~6%rel (control) to ~1%rel (treated sample). This finding is significant for p-type mc-Si solar cell manufacturers, as the process can be applied to finished cells using a standard belt firing furnace to stabilise cell efficiency for long term operation in the field. •1st-step annealing can mitigate LeTID in p-type mc-Si PERC solar cell.•However, 1st-step annealing causes Rc to degrade, resulting in a significant loss in ƞ and FF.•2nd-step annealing at low temperature recovers the degradation of Rc and maintain the stability of the cells.•2nd-step annealing at high temperature also recovers the degradation Rc.•However, 2nd-step annealing at high temperature may re-activate LeTID, mainly on the dislocation cluster sites.