JOINT APPLICATION OF THE BLACK SILICON LAYER AND THE ZnO FILM IN SOLAR CELLS

Abstract

In recent years, black silicon (b-Si) has become of great interest as frontal antireflective surfaces of solar cells. However, the low stability of structural and optical properties over time hinders the real application of b-Si in the production of solar cells. To solve the mentioned problem, it is proposed to use continuous stabilizing films of zinc oxide doped with aluminum (ZnO:Al). ZnO:Al thin films are obtained by sol-gel deposition at annealing temperatures 350…550 0C using different reagents as a starting material. The dependence of structural, morphological and optical properties of ZnO:Al films on the deposition conditions is investigated, using atomic-force microscopy and optical absorption measurements. The obtained ZnO:Al films have optical transmittance up to 95% in a wide spectral range. Black silicon layers are fabricated by the method of reactive ion etching in a gas mixture of SF₆/O₂ on monocrystalline Si substrate. The morphology of b-Si is studied by scanning electron microscopy, while the optical properties - by the spectrometer with an integrating sphere. The structure evolution and the dependence of final structure geometry on the gas composition and etching time are investigated. The reflection of b-Si layers was lower than 2% in the spectral range 400…1000 nm. The possibility of the joint application of the b-Si layers and the ZnO:Al films as frontal antireflective surfaces of solar cells is analyzed. By the finite difference time domain method, it is shown that ZnO:Al films can not only ensure the stability of b-Si layers over time, but also reduce the solar reflection leading to values less than 1 % in the whole spectral range for Si solar cell operation.