Understanding and Mitigating the Contamination of Intrinsic poly-Si Gaps in Passivated IBC Solar Cells
Matthew B. Hartenstein1,2, William Nemeth2, Vincenzo LaSalvia2, Matthew Page2, David L. Young2, Paul Stradins2, Sumit Agarwal1
1Colorado School of Mines, Golden, CO, United States
/2National Renewable Energy Laboratory, Golden, CO, United States

Interdigitated back contact (IBC) monocrystalline silicon (c-Si) solar cells are the current record holders for silicon photovoltaic efficiencies based on various contacting structures. However, IBC solar cells have not yet been demonstrated using the tunneling oxide passivated contact (TOPCon) structure fully contacted with doped polycrystalline silicon (poly-Si) fingers separated by intrinsic poly-Si. We investigate factors that are critical for the performance of IBC solar cells based on poly-Si passivated contact. During patterning of doped lines using direct plasma deposition through a shadow mask, we show that the intrinsic poly-Si gap becomes contaminated with dopants, leading to shunting. Possible contamination mechanisms during high-temperature annealing ― gas-phase dopant transfer and solid-phase diffusion ― are tested, and gas-phase transfer is shown to most strongly affect the intrinsic gap conductivity. Strategies developed to mitigate the contamination, such as amorphous to poly-Si crystallization in oxygen and crystallization using a capping layer of amorphous silicon (a-Si) will lead to improved IBC fabrication methods. Better IBC manufacture techniques will reduce the cost of such high efficiency cells and modules, promoting the expanded use of solar energy.