Swiss researchers develop leaner co-annealing for TOPCon cells

A research team from Switzerland has demonstrated a leaner fabrication process for TOPCon solar cells using a single-step co-annealing method. The process forms boron emitters at the front and poly-Si passivating contacts at the rear in one thermal treatment. Both contacts are produced using PECVD-deposited layers, which reduces process complexity and eliminatesadditional steps. The team has tailored boron emitter profiles with surface concentrations ranging from 3 × 10¹⁹ to 1 × 10²⁰ cm⁻³ and depths between 100 and 600 nm. The study shows that UV-O₃ tunnel oxides treated with N₂O plasma enable effective co-annealing of n-type poly-Si layers. The approach achieved open-circuit voltages up to 720 mV, contact resistivity below 100 mΩ·cm² and demonstrated a proof-of-concept solar cell with 21% efficiency.