A Failure Mode Affecting the Reliability of LECO‐Treated High‐Efficiency TOPCon Solar Cells

Journal article

Laser‐enhanced contact optimization (LECO) has become an essential process in enabling the fabrication of >25% efficient tunnel oxide–passivated contact (TOPCon) solar cells, now in use in >100 GW of silicon solar module production. LECO improves the metal–semiconductor interface in silicon solar cells, thus resulting in an excellent trade‐off between contact resistance (ρc < 1 mΩ.cm2) and surface recombination (J0met < 160 fA/cm2). This work presents a new failure mode observed at the front p+‐Ag contact in LECO‐treated TOPCon solar cells, which is not observed in standard screen‐printed metallization. The bias and temperature stress severely degrade the dark contact resistance in LECO‐treated TOPCon, leading to an increase in series resistance of over 100 Ω in a 2 x 2 cm2 cell. Unlike standard TOPCon, where degradation has been ascribed to the n+‐Ag contact, the LECO cells show the most prominent degradation at the p‐type contact side. Luminescence measurements on stressed samples show reduced recombination, which could be attributed to improved passivation at the p+‐Ag interface and/or the enhancement of other recombination‐limiting factors such as AlO x passivation, but negatively impacting conductivity. The temperature and bias stress also deteriorate the light current–voltage characteristics for the samples that underwent the LECO process. These results reveal a potential degradation mode in LECO‐treated TOPCon solar cells, indicating the need for further investigation into its impact on efficiency gain, long‐term reliability, and bankability.

Authors: Xiong, Y; Fattah, TOA; Okamoto, K; Bonilla, RS

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Wiley
• Journal: Solar RRL
• Article number: 202500151
• Publication date: 2025-05-28
• Acceptance date: 2025-04-28
• DOI: 10.1002/solr.202500151
• EISSN: 2367-198X
• ISSN: 2367-198X
• Language: English
• Keywords: TOPCon solar cells; metalization; reliability; contact resistance; LECO