Effect of thermal oxide layers on the front surface field characteristics of n-type silicon solar cells

This study investigates the effect of oxygen flow variation during the annealing process of the n/n + junction used to form phosphorus-doped regions in monocrystalline silicon wafers, which involves studying the n + doped layer for the front surface field (FSF) in n-type PERT (Passivated Emitter Rear Totally Diffused) solar cells. Two structures, referred to as n-900 and n-850, were fabricated by phosphorus diffusion at temperatures of 900 °C and 850 °C, respectively, for 20 min, using phosphorus-doped paper sheets in a Tempress furnace. Thermal oxidation was conducted at 800 °C for 30 min with oxygen flow rates of 0.2, and 4 SLM (standard liters per minute) in a specialized quartz tube. Four-point probe (4PP) measurements revealed a significant reduction in sheet resistance, especially at 900 °C. Electrochemical capacitance-voltage (ECV) profiling showed active phosphorus surface concentrations of 6.0 × 10 20 and 3.0 × 10 20 atoms.cm −3 for the 850 °C and 900 °C conditions, with corresponding junction depths of 0.43 μm and 0.60 μm, respectively. Quasi-steady-state photoconductance (QSSPC) measurements indicated a substantial improvement in effective minority carrier lifetime, exceeding 180 μs at 850 °C. The results reveal a clear trade-off: increasing the oxygen flow during annealing lowers the active phosphorus surface concentration and increases junction depth, but this comes at the cost of a reduced effective carrier lifetime, whereas samples annealed at 850 °C consistently outperform those annealed at 900 °C in terms of passivation quality. Because silicon, phosphorus and oxygen are all main group elements, this work speaks directly to the doping and oxidation chemistry of main group semiconductor materials, providing quantitative insight of interest to the readership of Main Group Chemistry. These findings highlight the critical role of oxygen ambient during annealing in optimizing dopant activation and carrier lifetime in high-efficiency silicon solar cells.