How LECO process could push TOPCon solar cell efficiency beyond 26%

A new study by researchers from University of New South Wales (UNSW) and Chinese solar cell specialist Laplace suggests that laser-enhanced contact optimisation (LECO) could unlock further efficiency gains in industrial TOPCon solar cells, potentially pushing performance past 26% through improved contact engineering.

The LECO process consists of using a highly intense laser pulse on the front side of the solar cell at a constant reverse voltage of more than 10 V, with the resulting current flow of several amperes considerably reducing the contact resistivity between semiconductor and metal electrode.

The researchers combined numerical simulation and process modeling to better understand how LECO reduces recombination losses at the metal-emitter interface, which is considered a long-standing bottleneck for high-efficiency n-type TOPCon devices.

“Our work provides a detailed, physics-based understanding of how LECO improves contact passivation and reduces recombination losses in industrial TOPCon solar cells,” corresponding author Bram Hoex told pv magazine.

“It also provides a clear physical explanation for the performance gains observed with LECO in industrial applications.”

“It highlights that contact geometry, beyond just materials or firing conditions, is a critical lever for optimizing next-generation TOPCon cells. Furthermore, it offers practical guidance on how to balance recombination and resistive losses through coordinated process and design optimisation. Ultimately, it establishes a viable pathway for conventional TOPCon cells to narrow the performance gap with more advanced architectures.”

The researchers found that lowering the peak firing temperature during metallisation plays a key role in reducing recombination. Rather than altering the boron doping profile, which remains largely unchanged during firing, lower temperatures lead to non-uniform, partial metal contacts.

This partial contact formation reduces the effective recombination current density, as less of the emitter surface is in direct contact with metal.

“The suppression mechanism is not driven by dopant redistribution, but by changes in contact morphology,” the authors of the study explained.

While partial contacts help reduce recombination, they typically increase contact resistance, which is a trade-off that can hurt overall performance. This is where LECO comes in. The laser-based process locally improves poorly formed contacts, enabling low-resistance silver–silicon interfaces without requiring high-temperature firing.

According to the research team, LECO effectively “repairs” underfired regions while preserving the benefits of reduced recombination.

Using a simulated industrial TOPCon cell with a baseline efficiency of 25.5%, the team demonstrated that combining optimizsed firing conditions to reduce contact fraction and selective emitter doping to lower intrinsic recombination could increase efficiency to 26.07%.

A key parameter is the partial metal contact ratio, which is the fraction of a solar cell’s emitter surface that is actually in direct physical contact with the metal electrode, rather than being separated by a passivating layer. In the baseline device, this value was around 37%. The study suggests it could be reduced to nearly 1% with optimised processing, without significantly increasing contact resistivity.

The authors concluded that LECO-enabled optimisation provides “a viable path” to extend the lifetime of mainstream TOPCon technology in the rapidly evolving solar market and compete with heterojunction (HJT) and back-contact (BC) PV technologies.

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