In this paper we report the development of fluorinated nanocrystalline SiO:F:H materials prepared by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique, the characteristics of which are better than previously developed material like ZnO, n-mu c-SiOx:H for application as back reflector for a-Si (single and multi-junction) solar cells. For a good Back Reflector the material should have low refractive index which increases reflectance of the layer. Earlier we have developed n-type microcrystalline hydrogenated silicon oxide (mu c-SiO:H) material by the RF-PECVD method (13.56 MHz) from source gas mixture of silane (SiH4), carbon dioxide (CO2), hydrogen (H-2) having the refractive index of 2.1. By adding fluorine to the gas mixture the refractive index is reduced to 1.70 which will make the material a better reflector for a-Si solar cells. The material has been characterized in detail by the following studies, viz: (1) structural studies by HRTEM, AFM, Raman and FTIR spectroscopy and (2) optoelectronic properties using temperature dependent conductivity measurements and (3) Ellipsometry and UV-VIS spectrum analysis etc. The optimized material shows superior properties than mu c-SiO:H thin film. The refractive index is 1.85, E-04 = 2.61 eV, lateral electrical conductivity is 10(-8) S cm(-1) and Raman crystallinity is X-c = 48.0%. These tailored properties make this material most suitable for use as Back Reflector Layer (BRL) in a-Si solar cells, and also as Internal Reflection Layer (IRL) in Micromorph solar cells. (C) 2015 Elsevier B.V. All rights reserved.