Abstract
Copper nitride (Cu3N), a metastable semiconductor material, but with reasonably-high-stability at room temperature, is drawing a great deal of attention as a very promising next-generation, earth-abundant, thin-film solar absorber. Its non-toxicity, on the other hand, makes it a very attractive eco-friendly semiconducting material. In the present work, Cu3N thin films were grown by employing radio-frequency magnetron sputtering, at room temperature, with 50-W RF-power, and partial nitrogen pressures of 8.0 and 1.0, onto glass substrates. Thus, the influence of argon on the optical properties of the Cu3N thin films was studied, with the goal of being able to achieve a low-cost, light absorber material, with appropriate properties in order to substitute the more conventional silicon, in photovoltaic cells. Variable-angle spectroscopic ellipsometry measurements have been conducted at three angles, 50∘, 60∘, and 70∘, respectively, in order to obtain the two ellipsometric parameters psi, ψ, and delta, Δ, respectively. For the constructed optical model, the bulk planar Cu3N layer is described by a one-dimensional graded-index model, combine with the mixture of a Tauc-Lorentz oscillator and up to four Gaussian oscillators, whereas a BEMA model with 50%-air-void is adopted in order to account for the existing surface-roughness layer. In addition, the optical properties such as the energy-band gap, and refractive index and absorption coefficient, were determined in order to assess the actual capability of this material as a light absorber for solar cells. The direct and indirect band gap energies were accurately calculated, and they were found to be in the ranges of 2.14-2.21 eV and very clse to 1.50 eV, respectively.