Laser-Assisted Metallization Advances For TOPCon Solar Cells

Materials matter in metallization. This process of applying metallic contacts to the wafer surface relies on silver, a precious metal. Thus, in addition to its role in performance, metallization is the key driver of cell production costs. This is the step that transforms the solar cell – until now only a technical structure – into a practical and functional photovoltaic device. The metallization process involves depositing metallic contacts on both sides of the wafer and sintering them into the silicon, enabling them to collect the generated charge carriers. The step also lays the platform that enables a series connection of cells through busbars. Developments in metallization are a collective effort from 3 different streams – metallization pastes, screen printers, and screens.

Laser assisted metallization: A somewhat revolutionary improvement that played a significant role in the TOPCon’s unprecedented progress is laser-assisted contact optimization. At its core, the process uses laser power to form the front contacts of TOPCon solar cells. Traditionally, the p+ emitters of TOPCon cells have been challenging to establish contact using pure silver paste, requiring aluminum additives to lower contact resistivity. However, this also led to higher recombination and efficiency losses due to the formation of silver-aluminum spikes. The laser-assisted process changes this dynamic by enabling electron injection and laser-induced carrier support, allowing silver precipitation and silver-silicon colloids to form direct contacts efficiently, explained leading paste maker DKEM at TaiyangNews conference. In the TaiyangNews Cell & Module Technology Trends 2025 report published recently, we discuss the techno-commercial details of this laser-assisted metallization, often referred to as Laser Enhanced Contact Optimization, or LECO, a proprietary name of its inventor, Cell Engineering.

Front contacting pastes: Zinan Zhang, technical director at leading silver paste supplier Solamet, nicely summarized the evolution of TOPCon technology from a metallization perspective in his presentation "Innovative Metallization Solutions" at the TaiyangNews High-Efficiency Solar Technologies Conference. The TOPCon cell initially featured a homogeneous p+ emitter metallized with Ag-Al paste, with mass-scale efficiency ranging from 24.5% to 25%. By the end of Q3 2023, this had progressed to a more efficient TOPCon cell, achieving up to25.3% efficiency with the introduction of laser doping selective emitter (LDSE) technology. Furthermore, the adoption of the LECO process, combined with selective emitter technology, boosted mass-scale TOPCon cell efficiency to 26% by the end of Q12024. More recently, replacing SE technology with the LECO metallization process alone has pushed the cell efficiency close to 26% and beyond. However, the pastes are not just a drop-in replacement when adopting laser-assisted metallization (see Pushing The Efficiency Limit: Solamet’s Perspective).

At the TaiyangNews conference in May 2024, metallization segment leader DKEM discussed the topic of paste optimization with respect to laser-induced metallization. Fangqing Guo, DKEM’s new technology development director, emphasized in his presentation "Innovative Metallization Pastes Enabling the TOPCon Technology Upgrade" that one of the most significant improvements in pastes for laser-assisted metallization process is glass frit optimization. Previously, silver-aluminum pastes relied on aggressive etching to facilitate aluminum-assisted contact formation. With laser-assisted metallization technology, aluminum is no longer necessary, allowing for tuned glass frits with weaker etching capability, which reduces metal-induced recombination. Minimizing the etching depth and area helps preserve passivation integrity and achieve higher efficiency.

Another key aspect of LECO is that it enables the formation of insulated contacts, which enhance electron flow and reduce contact resistivity. The contacts can be further optimized by fine-tuning laser parameters such as voltage and power. However, challenges arise when increasing voltage, as edge darkening can occur. To mitigate this, glass frit tuning is employed to widen the process window, ensuring consistent and high efficiency across the LEF metallization process. DKEM also presented the reliability test results of the contacts formed with the help of lasers, which showed that these metallic patterns have better moisture and acid resistance.

The text is an edited excerpt from TaiyangNews’ latest Market Survey on Solar Cell Production Equipment 2025, which can be downloaded for free here.