Enhancing the reliability of TOPCon technology by laser-enhanced contact firing

Tunneling oxide passivated contact (TOPCon) solar cells have made a considerable impact on the global photovoltaic (PV) market. Yet, its relatively poorer reliability compared to Passivated Emitter and Rear Contact (PERC) solar cells puts costly limitations on the module bill of materials that can be used. The use of silver/aluminum (Ag/Al) paste for front-side metallization is identified as a key factor contributing to the relatively poor reliability of TOPCon modules, particularly at high temperatures and humidity. However, very recently, laser-assisted firing techniques such as laser-enhanced contact optimization (LECO) that combine conventional co-firing at relatively low temperatures with a subsequent laser treatment have emerged as an appealing alternative to standard one-step cofiring. The main driver for laser-assisted firing is enabling higher power conversion efficiencies (PCE). This technique permits the application of screen printing pastes with considerably reduced levels of aluminum (Al), or even the complete exclusion of Al. Consequently, the enhancement in PCE values may not only boost PCE, but may also offer benefits in terms of reliability. This study investigates the impact of Jolywood Special Injected Metallization (JSIM) method on the reliability of TOPCon solar cells. Cell level damp heat testing at 85 °C and 85% relative humidity (DH85) with selected impurities reveals a significant improvement for the JSIM solar cells versus the standard baseline TOPCon cells. Baseline cells experienced rapid degradation, with a substantial (∼92%rel) loss in PCE attributed to a significant (∼13,000%rel) increase in series resistance (Rs) when exposed to sodium chloride (NaCl). Conversely, JSIM cells showcased remarkable resilience, displaying only a modest drop in PCE (∼3.6%rel) under similar conditions. This work clearly shows that laser-assisted firing processes such as JSIM also significantly improve the reliability of TOPCon solar cells. This improvement is due to the compatibility of these processes with screen printing pastes that have low or zero Al concentration for the TOPCon front. Consequently, this approach enables using more cost-effective materials for TOPCon modules, thereby reducing the overall cost of solar electricity.