In this effort, 10 mu m thick rear contact (RC) silicon-germanium (SiGe) based solar cell device has been discussed with SiC (20 nm)-based front surface passivation for the suppression of interface recombination as well as improvement of short circuit current density (J(SC)) and open-circuit voltage (V-OC). The design principles presented here balance the electronic and photonic effects together and is a significant step to design highly efficient thin solar cells. Photo reflectance is significantly reduced in the UV/visible spectral region due to the presence of SiC. This results in external quantum efficiency (EQE) >90% in the spectrum range of 400-650 nm wavelength. Also, at wavelengths equivalent to 300 nm, SiC passivated device shows record EQE of 85%. The presence of SiC as a surface passivating layer shows enhanced surface characteristics in terms of reduced surface recombination and higher photon absorption rate. This results in 15.4% power conversion efficiency (PCE) under standard air mass 1.5 illuminations. Further, the proposed device has also been analyzed for concentrator photovoltaics (CPV) applications, resulting in 18.4% and 19.3% efficiencies at 1 W/cm(2) (10 suns, 27 degrees C) and 2 W/cm(2) (20 suns, 27 degrees C) respectively. Till date, the proposed design proves to be highly efficient in the sub 10 gm regime. All the simulations have been done using DEVEDIT and ATLAS device simulator (C) 2016 Elsevier Ltd. All rights reserved.