EPFL and CSEM test co-annealing process for TOPCon PV cells

Researchers from the PV-lab at EPFL and the Sustainable Energy Center at CSEM has studied a single-step annealing process for TOPCon solar cells to replace the conventional two-step method. They used plasma-enhanced chemical vapor deposition (PECVD) to form both the boron emitter at the front and the poly-Si passivating contact at the rear in one thermal step. Boron emitter profiles were achieved with surface concentrations and depths ranging from 100 to 600 nm by adjusting deposition and annealing settings. The study found that p-type poly-Si layers were suitable for co-annealing when an N₂O plasma treatment was applied to tunnel oxide formed through UV-O₃ exposure. The process achieved implied open-circuit voltages up to 720 mV and low contact resistivity. A proof-of-concept solar cell fabricated using this method showed a power conversion efficiency of 21%.