n-TOPCon solar cells have attracted attention due to their unique ultra-thin silicon dioxide (SiOx) layer and n+ polycrystalline silicon (poly-Si) layer, which helps achieve low recombination current density (J0) and reduced contact resistance (ρc).

The laser enhanced contact optimization (LECO) process is replacing the traditional high-temperature sintering process and becoming a mainstream technology. The effects of different parameters (sintering temperature, laser power, reverse voltage) in the LECO process on the metal contact recombination current density, contact resistivity and I-V characteristics were studied. A maximum efficiency of 25.97% was achieved using a sintering temperature of 790°C, a laser power of 18W and a reverse voltage of 16V.

Materials and Methods

Schematic diagram of n-TOPCon solar cell structure and LECO process

n-TOPCon solar cell structure: including p+ emitter, Al2O3 and SiNx passivation layers on the front surface, and SiOx and n+ poly-Si layers on the back surface.

LECO process flow:

Laser irradiation: Use infrared laser (wavelength 1064 nm, power 18-24 W) to scan the front surface in full width, and the laser energy is concentrated on the tip of the pyramid texture.

Reverse voltage application: Apply a reverse voltage of 10-20 V during laser action to guide the directional movement of photogenerated carriers (electrons and holes) and promote the mutual diffusion of silver (Ag) and silicon (Si).

Contact optimization mechanism: Direct silver-silicon contact: The local high temperature induced by the laser makes the silver in the silver paste form direct contact with silicon, reducing the interface resistance.

Nanosilver colloid in the glass layer: The laser and reverse voltage cause the silver to form a conductive network in the glass layer, transmitting current through the tunneling effect.