Low-cost spray-deposited ZrO ₂ for antireflection in Si solar cells

Low-cost spray deposition is employed to investigate the possibility of using earth-abundant ZrO ₂ as the antireflection coating in Si solar cells. Structural, optical, and electrical properties of spray-deposited ZrO ₂ films are investigated. Spray-deposited ZrO ₂ is highly transparent with a refractive index of 2.0 at 600 nm. Reflection and transmission spectra of ZrO ₂ films reveal that the optical properties of spray-deposited ZrO ₂ are comparable to SiN _x deposited by plasma-enhanced chemical vapor deposition. Atomic force microscopy studies show that spray-deposited ZrO ₂ is crack/pore-free and its surface roughness has a root-mean-square value of 0.7 nm for a 75-nm film. Spray-deposited ZrO ₂ at 550 °C is polycrystalline with a cubic lattice but largely amorphous at 450 °C as determined by X-ray diffraction. Capacitance-voltage measurements indicate that spray-deposited ZrO ₂ has a negative charge density of 8.19 × 10 ¹¹ cm ⁻² for a 75-nm film. Post-deposition annealing results in a significant decrease in oxide capacitance which is attributed to the formation of SiO ₂ at the ZrO ₂ /Si interface. The resistivity of as-deposited ZrO ₂ is 3.69 × 10 ¹² Ω-cm and it improves to 2.46 × 10 ¹³ Ω-cm after post-deposition annealing in air at 600 °C for 1 h.