In situ phosphorus-doped polycrystalline silicon films by low pressure chemical vapor deposition for contact passivation of silicon solar cells

Abstract

In situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films by low pressure chemical vapor deposition (LPCVD) were studied in this work for the fabrication of poly-Si passivating contacts. In situ doping was targeted for enabling the full potential of the high-throughput LPCVD technique, as it could allow leaner fabrication of industrial solar cells featuring poly-Si passivating contacts than the more common ex situ doping routes. By careful optimization of the deposition temperature and the flows of the carrier gas (H-2) and the dopant precursor (PH3), high doping in the poly-Si layers was achieved with active P concentrations up to 1.3.10(20) cm(-3) . While reduction in the deposition rate (r(dep)) and thus in the throughput is a known problem when growing in situ P-doped films by LPCVD, this reduction could be limited, and the resulting r(dep) was equal to 0.078 nm/s. The developed poly-Si films were characterized both structurally and in terms of their passivation potential in poly-Si contacts. The latter yielded recombination current densities down to 1.5 fA/cm(2) in passivated (J(0, p)) and 25.6 fA/cm(2) in screen-printing metallized (J(0, m)) regions on saw-damage removed (SDR) Cz-Si surfaces, accompanied by a contact resistivity (rho(c,m)) of 4.9 m Omega.cm(2). On textured Cz-Si surfaces, the corresponding values were J(0, p) = 3.5 fA/cm(2), J(0,m )= 56.7 fA/cm(2), and rho(c,m) = 1.8 m Omega.cm(2). Optical impact of the developed poly-Si films was also assessed and a short circuit density loss of 0.41 mA/cm(2) is predicted per each 100 nm of poly-Si applied at the rear side of solar cells.