Effect of Drive-In Temperature and N₂/O₂ Gas Flow on Boron Diffusion Profiles in p⁺ Emitters for n-Type PERT Silicon Solar Cells

The realization of high-efficiency passivated emitter and rear totally diffused (PERT) solar cells on n-type silicon substrates requires precise control of the boron-doped p⁺ emitter. In this work, we investigate the effect of drive-in temperature on the electrical and structural properties of boron emitters formed by a two-step diffusion process using a boron nitride (BN) solid source. Seven samples were processed at drive-in temperatures ranging from 890°C to 1000°C, and their carrier concentration depth profiles were characterized by electrochemical capacitance-voltage (ECV) measurements.

The results show a strong dependence of both junction depth and surface concentration on drive-in temperature. Increasing the temperature from 890°C to 1000°C leads to a progressive deepening of the p-n junction from approximately 0.5 µm to 0.88 µm, accompanied by a reduction in sheet resistance from 74 Ω/sq down to 23 Ω/sq. Surface boron concentrations span nearly two orders of magnitude across the sample set, ranging from ~2×10²⁰ to ~8×10²¹ atom/cm³. Samples processed at intermediate temperatures (975°C) exhibit a favourable combination of moderate surface concentration and sufficient junction depth, suggesting a reduced risk of Auger recombination while maintaining adequate lateral conductivity.

A systematic comparison across all samples highlights the sensitivity of the emitter profile to thermal budget and points to an optimal drive-in temperature window for balancing emitter saturation current density, sheet resistance, and junction depth in PERT cell fabrication. These findings contribute to the optimization of the boron diffusion process for high-efficiency n-type silicon solar cells.