Spray-deposited Al₂O₃ for rear passivation and optical trapping in silicon solar cells

Low-cost spray deposition is employed to investigate the suitability of spray-deposited Al₂O₃ for rear passivation and optical trapping in passivated emitter rear contact (PERC) Si solar cells. Structural, optical, and electrical properties of spray-deposited Al₂O₃ films are investigated. Capacitance-voltage measurements indicate that spray-deposited Al₂O₃ has a negative charge density of 3.19 × 10¹² cm^-2 for an 80-nm film, suggesting that it can serve as the passivation layer. Optical properties of spray-deposited Al₂O₃ are identical to the Al₂O₃/SiN_x stack prepared by atomic layer deposition and plasma-enhanced chemical vapor deposition, indicating that it can also serve as the optical trapping layer. Atomic force microscopy studies show that spray-deposited Al₂O₃ is crack and pore free, and its surface roughness has a root-mean-square value of 0.52 nm for an 80-nm film. Spray-deposited Al₂O₃ is amorphous as determined by X-ray diffraction. X-ray photoelectron spectroscopy analysis suggests that spray-deposited Al₂O₃ is slightly Al-rich. The resistivity and breakdown field of an 80-nm Al₂O₃ film are 5.46 × 10¹⁴ Ω-cm and 3.28 MV/cm, respectively, which are stable after 800°C firing. These properties suggest that spray-deposited Al₂O₃ is a promising candidate to replace the Al₂O₃/SiN_x stack in Si PERC cells.