MODELING THE REFLECTION OF THE BLACK SILICON LAYER PASSIVATED BY A ZINC OXIDE FILM
Keywords:
black silicon, zinc oxide, modeling, Finite Difference Time Domain method, reflection, solar cellAbstract
Black silicon (black silicon, b-Si) is a needle-like surface where needles have a height of more than 0.3 µm, and a diameter of less than 1.0 µm. The optical radiation incident on it is almost completely absorbed due to multi-reflections from the side surfaces of the needles, which makes b-Si attractive for use in silicon solar cells as frontal antireflection surfaces. However, the low stability of structural properties in the course of time complicates the practical application of b-Si in the production of solar cells. In addition, surface recombination losses significantly reduce the efficiency of b-Si-based solar cells. These problems can be solved by protection and passivation of the bSi surface, by using specific dielectric films.
In this work, the simulation of reflection of the b-Si layers passivated by zinc oxide (ZnO) films in order to determine the possibility of their combined use in solar cells is carried out.
The optical model of the b-Si/ZnO structure is considered as a thick substrate with conical diffusers located on it, which are coated with a continuous thin film. The numerical modeling has been carried out using the Finite Difference Time Domain (FDTD) method at normal and different angles of radiation incidence. It is shown that, irrespective of the film thickness, all model structures demonstrate a decrease in the reflection coefficient in comparison with the initial b-Si. An increase in the ZnO film thickness leads to a decrease in the calculated reflection coefficient in the visible range. It is also shown that the reflection coefficient grows with increasing the angle of optical radiation incidence on the surface of the structure. The characteristics of the Brewster effect manifestation (pseudo-Brewster angle) in the b-Si/ZnO structure are considered.
The results of modeling come to prove that the ZnO films not only easure the stability of structural properties and the efficient passivation of the b-Si layers, but also improve their antireflection characteristics in the spectral range of functioning of silicon solar cells.
