Porous silicon Bragg mirrors on single- and multi-crystalline silicon for solar cells

Porous silicon Bragg mirrors at back-side of single crystalline and multicrystalline silicon solar cell were numerically simulated by transfer matrix method. It allows to choose the optimal parameters of porous stack of bi-layers (indexes of refraction, number of bi-layers) when the increase of photon absorption in 900-1050 nm spectral region is achieved. Application of Bragg mirrors at back-side of single crystalline solar cell can improve the efficiency on more than 0.8% in absolute for 200 mu m both-side textured thickness wafer. The simulated results were compared with characteristics of Bragg mirrors fabricated by electrochemical etching of single- and multi-crystalline silicon. It is shown that despite the natural crystallites disorientation the efficient Bragg mirrors can be fabricated on multicrystalline silicon wafers in such way. Maximum measured reflectivity for Bragg mirrors on multicrystalline substrate achieves approximately 62%, whereas for single crystalline silicon the reflectivity in maximum is more than 90%. (C) 2013 Elsevier Ltd. All rights reserved.