Pulsed Laser Annealed Ga Hyperdoped Poly-Si/SiOx Passivating Contacts for High-Efficiency Monocrystalline Si Solar Cells

Polycrystalline Si (poly-Si)-based passivating contacts are promising candidates for high-efficiency crystalline Si solar cells. We show that nanosecond-scale pulsed laser melting (PLM) is an industrially viable technique to fabricate such contacts with precisely controlled dopant concentration profiles that exceed the solid solubility limit. We demonstrate that conventionally doped, hole-selective poly-Si/SiO_x contacts that provide poor surface passivation of c-Si can be replaced with Ga- or B-doped contacts based on non-equilibrium doping. We overcome the solid solubility limit for both dopants in poly-Si by rapid cooling and recrystallization over a timescale of ∼25 ns. We show an active Ga dopant concentration of ∼3 × 10²⁰ cm⁻³ in poly-Si which is six times higher than its solubility limit in c-Si, and a B dopant concentration as high as ∼10²¹ cm⁻³. We measure an implied open-circuit voltage of 735 mV for Ga-doped poly-Si/SiO_x contacts on Czochralski Si with a low contact resistivity of 35.5 ± 2.4 mΩ cm². Scanning spreading resistance microscopy and Kelvin probe force microscopy show large diffusion and drift current in the p-n junction that contributes to the low contact resistivity. Our results suggest that PLM can be extended for hyperdoping of other semiconductors with low solubility atoms to enable high-efficiency devices.