Tailoring the Optical Properties of APCVD Titanium Oxide Films for All-Oxide Multilayer Antireflection Coatings

In this paper, the optical properties and microstructure of titanium oxide (TiO_x) thin films deposited by in-line atmospheric pressure chemical vapor deposition (APCVD) are tailored to act as effective antireflection coatings (ARCs) in crystalline silicon solar cells. The ability to control the crystalline phase, microstructure, and optical properties of these TiO_x films by varying the deposition conditions is demonstrated. Because the refractive index of TiO_x can be widely varied by changing the deposition temperature, these films can be applied as single- or double-layer ARCs (DLARCs) in crystalline silicon solar cells featuring a thin front-side passivation layer (e.g., thermal silicon oxide, aluminum oxide) or as a rear-side capping layer in rear passivated cells. Reflectance measurements on oxide-based DLARCs deposited on anisotropically textured monocrystalline Si wafers are presented for unencapsulated samples, along with the modeled performance of similar structures encapsulated in ethylene-vinyl acetate under varying angles of incidence. In the experiments on unencapsulated samples, two of the oxide-based DLARCs outperform a standard SiN_x ARC, and all four outperform the SiN_x ARC when encapsulated.