Unlocking the potential of boronsilicate glass passivation for industrial tunnel oxide passivated contact solar cells

• Published in: Progress in photovoltaics Vol. 30; no. 3; pp. 310 - 317
• Main Authors: Liao, Baochen, Ge, Jia, Wu, Xinyuan, Wang, Qiang, Yeo, Reuben J., Du, Zheren
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.03.2022
• Subjects: Aluminum oxide; Boron; BSG passivation; BSG‐TOPCon; Circuits; Emitters; front‐rear interlock; industrial firing activation; lower temperature paste; Mass production; Metallizing; Passivity; Photovoltaic cells; Silicon dioxide; Solar cells; Tunnels
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.3519

In this work, we present a breakthrough in boronsilicate glass (BSG) passivated industrial tunnel oxide passivated contact (i‐TOPCon) solar cells. We find that a high‐temperature firing process significantly improves the front side BSG passivation quality; however, the use of such high‐temperatures is undesirable for metallization as it could lead to more junction damage by the metal paste spikes. In this study, we present a simple and industrially viable method to resolve this dilemma. With a high‐temperature industrial firing activation step to maximize the potential of BSG passivation, a low emitter saturation current (J0e) of 34 fA/cm2 has been achieved, demonstrating excellent boron emitter passivation that is comparable to state‐of‐the‐art SiO2 and Al2O3‐based passivation methods on similar structures and boron emitters. Applying this solution to cell device, the open‐circuit voltage (Voc) is improved by about 6 mV, corresponding to an absolute cell efficiency improvement of about 0.2%. Furthermore, after activating the BSG passivation, a lower temperature paste could be used at the rear side which further improves the Voc by around 3 mV. Combined together, an overall improvement of Voc close to 10 mV is achieved, propelling the cell Voc into the 690‐mV era. The effectiveness of this solution was also verified in a mass production line, with average cell efficiencies of around 23.2% (0.5% more than the baseline) and a maximum cell efficiency and Voc of 23.4% and 693 mV, respectively. This work opens new routes for further improving conventional solar cell efficiencies, in particular for BSG‐passivated TOPCon solar cells. A simple and industrially viable method is presented to resolve the bottleneck faced by boronsilicate glass‐passivated TOPCon (BSG‐TOPCon) solar cells. With the two‐step method developed, the BSG layer demonstrated passivation performance comparable to other state‐of‐the‐art dielectric layers and improved the cell Voc by almost 10 mV. This work opens many new routes for the further improvement of BSG‐TOPCon solar cell efficiencies and gives us one good candidate for boron emitter passivation in device applications.