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

Abstract

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/SiOx 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/SiOx 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.

Laser Activation for Highly Boron-Doped Passivated Contacts

“…Maskless, defect-free patterning of the p ++ -poly Si layers, as performed here, would substantially simplify the fabrication process and could open the door for the low-cost, large-scale, industrial production of this passivated contact solar cell design. A laser process for dopant activation in hole-selective poly Si/SiO 2 passivation stacks has also recently been introduced by Chen et al [19]. Their main focus was the use of gallium as an alternative p-type dopant instead of boron to overcome the passivation loss arising from boron segregation at the interface between SiO 2 and c-Si.…”