Reflectance of Black Silicon with Sol-Gel ZnO Passivation Films: Optical Simulation and Experimental Correlation

The results of a study of the optical properties of a black silicon (BS) layer passivated with ZnO films obtained by the sol-gel technique are presented. The BS layer was formed by the reactive ion etching process using an SF6/O2 plasma. The reflectance spectra of the BS/ZnO structures were simulated using the finite difference time domain method. In this simulation, the structure is considered a thick silicon substrate with regular near-surface straight circular nanocones uniformly coated with a thin ZnO film. The reflectance of the experimental samples was measured using a spectrometer with an integrating sphere. The ZnO sol-gel film, in addition to surface passivation of the BS layer, noticeably improves the reflectance in the entire spectral range necessary for the operation of a solar cell. BS/ZnO structures exhibit a low reflectivity in the wavelength range of 400–800 nm and at radiation incidence angles up to 50°. Thicker films are most preferred. Studies have shown that the simulation results are in good agreement with experimental data in the case of thin films. For structures with thick ZnO films, it is necessary to take into account the differences in the morphology of the model and real surfaces.