Cutting Back-Contact TOPCon Solar Cells to Minimize Recombination Losses

A research team from the University of New South Wales and DAS Solar has been studying the impact of laser cutting on back-contact TOPCon silicon solar cells. The team's goal was to identify the dominant loss mechanisms caused by cutting and determine practical design conditions that minimize efficiency degradation in cut-cell and module applications.

The scientists found that cutting full-size solar cells into half, third, or quarter segments minimizes resistive losses, which scale quadratically with cell length. However, laser scribing exposes raw, unpassivated edges and creates dangling bonds and process defects that significantly elevate carrier recombination and affect cell performance.

The researchers evaluated half-, third-, and quarter-cell configurations using Quokka3 device simulations, which model the electrical behavior of photovoltaic devices. They found that cutting in the gap between n-type and p-type contacts reduces the efficiency penalty by approximately 50% compared with cutting through the p-type contact region.

The team's analysis showed that the efficiency loss caused by cut-induced edge recombination increases linearly with the ratio of cut-edge length to active cell area. They also found that cutting in the gap between the emitter and back-surface-field (BSF) regions provides the most effective strategy for suppressing edge-recombination losses and preserving TBC cell efficiency.

The simulations also showed that cut cells exhibit larger efficiency losses under low irradiance due to increased resistive losses and recombination of diffusive hole transport. An optimal post-cut gap width of approximately 0.3 mm was identified for minimizing the total efficiency loss.

## Optimizing Cut-Cell Manufacturing

The research team's work establishes practical design guidelines for industrial TBC cut-cell manufacturing. They demonstrated that optimized gap-region cutting can substantially mitigate cut-induced recombination losses without additional edge-passivation processing.

## Reducing Efficiency Losses

The team's findings suggest that cutting in the gap between the emitter and BSF regions provides the most effective strategy for suppressing edge-recombination losses and preserving TBC cell efficiency. This approach can help minimize the total efficiency loss and reduce the impact of resistive losses and recombination of diffusive hole transport.

The research work was presented in "Simulation of gap-region cutting for suppressing edge recombination losses in tunnel oxide passivated back-contact solar cells," published in Solar Energy. The team's previous collaboration with DAS Solar resulted in the fabrication of a TBC cell with a power conversion efficiency of 27%. The cell is based on a zero-busbar (ZBB) design, which requires significantly lower silver (Ag) content for metallization.